Regulation of Transforming Growth Factor-beta Type II Receptor Expression in Human Breast Cancer MCF-7 Cells by Vitamin D3 and Its Analogues*

Gengfei WuDagger §, Robert S. Fan§, Wenhui Lipar , Venkateswarlu Srinivaspar , and Michael G. Brattainpar **

From the Dagger  Department of Pharmacology, Dartmouth Medical School, Hanover, New Hampshire 03755, the  Department of Biochemistry and Molecular Biology, Medical College of Ohio, Toledo, Ohio 43699-0008, and the par  Department of Surgery, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78284-7840

    ABSTRACT
Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References

In view of the tumor suppressor role of the transforming growth factor-beta (TGFbeta ) type II receptor (RII), the identification and characterization of agents that can induce the expression of this receptor are of potential importance to the development of chemoprevention approaches as well as treatment of cancer. To date, the identification of exogenous agents that control RII expression has been rare. We demonstrated that proliferation of MCF-7 early passage cells (MCF-7 E), which express RII and are sensitive to TGFbeta growth inhibition activity, was significantly inhibited by vitamin D3 and its analogue EB1089. In contrast, proliferation of MCF-7 late passage cells (MCF-7 L), which have lost cell surface RII and are resistant to TGFbeta , was not affected by these two compounds. TGFbeta -neutralizing antibody was able to block the inhibitory effect on MCF-7 E cells by these compounds, indicating that treatment induced autocrine-negative TGFbeta activity. An RNase protection assay showed approximately a 3-fold induction of the RII mRNA, while a receptor cross-linking assay revealed a 3-4-fold induction of the RII protein. In contrast, there was no change in either RII mRNA or protein in the MCF-7 L cells.

    INTRODUCTION
Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References

Transforming growth factor-beta (TGFbeta )1 comprises a family of hormone-like polypeptides that affects cell growth, adhesion, and differentiation (1). They act as growth inhibitors for most epithelial cells and some cancer cells. Two pathways are primarily involved in mediating effects of TGFbeta on cell growth and differentiation. One pathway involves blockade of cell cycle transit, while the other involves alteration of the extracellular matrix environment.

TGFbeta s elicit their effects by binding to cell surface receptors. Three major types of receptors have been shown to be present in most TGFbeta -responsive cell lines. They are designated as type I (RI), type II (RII), and type III (RIII), respectively. RIII is a 280-330-kDa glycoprotein that has no functional signaling domain but rather serves as a ligand storage protein and presents TGFbeta to the signaling receptors (2). RI and RII, which are glycoproteins of ~55 and 85 kDa, respectively, form a heteromeric receptor complex. Both are serine/threonine kinases, and each appears to be indispensable for TGFbeta signaling (3-5). The direct involvement of both RI and RII in conferring TGFbeta effects indicates that loss of either of the functional receptors would contribute to loss of autocrine TGFbeta activity. Loss of negative autocrine TGFbeta activity results in a growth advantage caused by an imbalance in positive and negative regulators, possibly leading to tumor formation and progression (6, 7). Recent evidence has shown a loss of RII is often associated with the failure to respond to autocrine and exogenous TGFbeta . We have previously demonstrated that re-expression of this receptor in an RII-deficient breast cancer cell line (late passage MCF-7) leads to restoration of TGFbeta sensitivity and reduced malignancy in athymic nude mice (6). In addition, it has been shown that mutational inactivation of RII occurs frequently in a subset of colon tumors with microsatellite instability (7), and reconstitution of RII expression by stable transfection also leads to reversal of malignancy in these cells (8). Others have noted that loss of RII expression is important in other types of malignancies (9-15). These lines of evidence suggest that RII is a critical determinant for conferring TGFbeta tumor suppression as well as negative autocrine TGFbeta growth function. Consequently, agents that can induce RII expression would be valuable in the development of approaches for cancer treatment and prevention where receptor expression appears to be repressed, such as estrogen receptor-positive (ER+) breast cancer (16, 17). To date, no such agents have been carefully characterized for their ability to induce RII. Although Cohen et al. (55) showed increased RII mRNA in a human neuroblastoma cell line after retinoic acid (RA) treatment, they were not able to detect cell surface RII. In addition, they failed to test for increased autocrine activity and increased responsiveness/growth inhibition to TGFbeta after RA treatment. A study by Turley et al. (56) in RL human B lymphoma cells demonstrated increased RII protein levels following treatment with RA and vitamin E succinate. However, they did not investigate whether this correlated with increased levels of cell surface RII.

Development of effective therapeutic and preventive approaches for breast cancer remains an issue, since conventional treatment by antiestrogens such as tamoxifen often leads to resistance in estrogen receptor-positive tumors (18), and chemotherapy of estrogen receptor-negative tumors is even less effective (19). Since there is a high incidence of vitamin D receptors (VDRs) in human breast cancer tumors (21, 22), vitamin D3 is an appealing candidate as a new therapeutic agent. Like other steroid hormones, it mediates its effect through interaction of its nuclear receptor (VDR) with DNA-responsive elements in the target genes (20). Moreover, many breast cancer cell lines are responsive to vitamin D3 antiproliferative effects both in vitro and in athymic mice (23). However, a major drawback for its clinical application is that the doses effective for suppressing tumor growth often cause hypercalcemia. Consequently, analogues have been developed to reduce the calcemic effects while increasing the potency of inhibition of proliferation (23, 24). Two analogues, EB1089 and MC903, both of which are derived by modification of the C17 side chain of vitamin D3, have been shown to be effective against rat breast tumors in vivo (24) or as an antiproliferative agent when given topically for psoriasis as well as for cutaneous metastatic breast cancer (25). However, the mechanisms of vitamin D3-mediated growth inhibition and in particular its anti-tumor action remain largely unresolved.

In this report, we show a correlation between RII expression and vitamin D3 inhibition in MCF-7 sublines that differ dramatically in their RII expression and hence their TGFbeta sensitivity as well. We hypothesized that vitamin D3's mechanism of inhibition might involve induction of TGFbeta autocrine activity through increased expression of RII. This hypothesis was confirmed by RNase protection assays showing approximately 3-fold induction of the RII mRNA and a 3-4-fold induction of cell surface RII protein. The increased inhibition by vitamin D3/analogues was blocked by TGFbeta -neutralizing antibodies, indicating an induction of negative autocrine TGFbeta activity.

The use of an essential dietary nutrient with antiproliferative and anti-tumor properties represents an attractive approach for chemoprevention and/or therapy. This is particularly true of vitamin D compounds, since the high stress western style diet associated with colon and breast cancer is also associated with low levels of vitamin D and calcium (26). Thus, increased autocrine negative TGFbeta activity mediated by vitamin D3 compounds in MCF-7 E cells may provide a novel mechanism for blocking malignant progression by chemopreventive approaches.

    MATERIALS AND METHODS
Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References

Cell Cultures-- MCF-7 E cells (passage number 150) were kindly provided by Drs. Robert J. Pauley and Herbert D. Soule from the Michigan Cancer Foundation. MCF-7 L cells were obtained from the ATCC and used at a passage number greater than 500. These cell lines were cultured in McCoy's 5A medium supplemented with 10% fetal bovine serum, pyruvate, vitamins, amino acids, and antibiotics. Working cultures were maintained at 37 °C in a humidified atmosphere of 5% CO2.

Vitamin D3 Compounds-- 1,25-(OH)2 vitamin D3 as well as its analogues EB1089 and MC903 were generous gifts from Dr. Lise Binderup of LEO Pharmaceutical Products (Ballerup, Denmark). Stock solutions were prepared in isopropyl alcohol at 4 mM. Serial dilutions were made in absolute ethanol and stored at -20 °C protected from light. These diluted solutions were added to the experimental culture media at a final ethanol concentration of 0.1%. Control cells received 0.1% ethanol vehicle, which had no effect on cell proliferation.

DNA Synthesis Assay-- [3H]thymidine incorporation into DNA was measured as described previously to determine TGFbeta and vitamin D3 sensitivity (6). Briefly, MCF-7 cells were seeded in 24-well tissue culture plates at a density of 1.5 × 104 cells/well in 1 ml of medium. Various concentrations of compounds (1,25-(OH)2 D3, EB1089, MC903, or TGFbeta ) were added after cell attachment (approximately 2 h). Following 4 days of incubation, cells received a 2-h pulse with [3H]thymidine (7 µCi, 46 Ci/mmol, Amersham Pharmacia Biotech). DNA was then precipitated with 10% ice-cold trichloroacetic acid, and the amount of [3H]thymidine incorporated was analyzed by liquid scintillation counting in a Beckman LS 7500 scintillation counter as described previously (6). To determine whether there is an increase in the inhibitory effects by TGFbeta 1 following EB1089 treatment, MCF-7 E cells, which are TGFbeta -responsive, were plated as described above. Various concentrations of EB1089 plus 0.1 ng/ml of TGFbeta 1 were added after attachment. Cells were incubated and [3H]thymidine incorporation was determined as described above.

TGFbeta -neutralizing Antibody Assay-- Cells were resuspended at a concentration of 1.5 × 104 cells/ml and plated into 24-well tissue culture plates (1 ml/well) either untreated or in the presence of 10 µg/ml TGFbeta 1 neutralizing antibody (R & D Systems) or control normal IgG. After 3 h of incubation, different concentrations of vitamin D3 compounds were added as indicated. Cells were allowed to grow for 72 h without changing the media, followed by determination of [3H]thymidine incorporation as described above.

RNA Analysis-- RNase protection assays were performed to determine RII RNA expression levels after vitamin D3 treatment. A 476-base pair fragment of the RII cDNA within the cytoplasmic region was obtained by polymerase chain reaction with the following primers: 5'-TGGACCCTACTCTGTCTGTG-3' and 5'-TGTTTAGGGAGCCGTCTTCA-3'. The fragment was subcloned into a pBSK (-) plasmid (Stratagene, La Jolla) for making the RII riboprobes. In vitro transcription using T3 RNA polymerase yields antisense riboprobes that protect a 476-base pair RII fragment. RNase protection assays were performed as described previously (27). Briefly, exponentially growing cells were treated with EB1089 at 1 × 10-8 M for the indicated time periods. Cells were solubilized in guanidine thiocyanate, and total RNA was obtained by cesium chloride gradient ultracentrifugation (28). 40 µg of total RNA was used for overnight hybridization with 32P-labeled antisense riboprobes. Following RNase A and T1 treatment, the protected double-stranded RNA fragments were heat-denatured at 95 °C and analyzed by urea-polyacrylamide gel electrophoresis, and the radioactive probes were visualized by autoradiography. Actin was used as an internal control for normalizing the amount of sample loading.

Receptor Cross-linking-- Simian recombinant TGFbeta 1 was purified as described (29) and iodinated by the chloramine T method (30). MCF-7 cells were seeded into 35-mm2 tissue culture wells at a density of 105 cells/well. In the kinetic studies, exponentially growing cells were treated with various concentrations of the compounds for 24 h or with a single concentration for the indicated time periods. Cell monolayers were then incubated with 200 pM 125I-labeled TGFbeta 1 at 4 °C for 4 h followed by chemical cross-linking with disuccinimidyl suberate for 15 min (31). Labeled cell monolayers were solubilized in 200 µl of 1% Triton X-100 with 1 mM phenylmethylsulfonyl fluoride. Equal amounts of cell lysate protein were separated by 4-10% gradient SDS-polyacrylamide gel electrophoresis under reducing conditions and exposed for autoradiography.

Mink Lung Epithelial Cell Growth Inhibition Assay-- MCF-7 E cells were plated into 100-mm2 tissue culture dishes and allowed to reach 70-80% confluency. The medium was then removed and replaced with 5 ml of fresh McCoy's 5A medium supplemented with pyruvate, vitamins, amino acids, and antibiotics (SM). The cells were then treated with EB1089 (1 × 10-8 M) or with vehicle only for 24 h. Following treatment, the conditioned medium was collected, and the indicated volumes were used to treat mink lung epithelial cells plated in 96-well tissue culture plates at a density of 1500 cells/well. In addition, a standard TGFbeta growth inhibition curve was generated by treating the cells with various concentrations of TGFbeta 1. The mink lung epithelial cells were allowed to incubate for 3 days at which time the medium was removed and replaced by 100 µl of fresh SM. Colonies were immediately visualized by staining with 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (Sigma) for 2 h. The stained cells were solubilized with Me2SO (dimethyl sulfoxide) (Mallinckrodt) and the relative cell numbers were then determined by the resultant absorbance at 595 nm.

Luciferase Assay-- The TGFbeta -responsive cyclin A promoter in tandem with a luciferase reporter construct (-133/-2) was used as described previously (32). The reporter construct (-133/-2) contains only the activating transcription factor site, which has been shown to be the site required to mediate down-regulation of cyclin A promoter activity by TGFbeta 1 in mink lung epithelial cells (32). MCF-7 E cells were transiently transfected with 30 µg of luciferase reporter construct and 7 µg of beta -galactosidase plasmid by electroporation with a Bio-Rad gene pulser at 250 mV and 960 microfarads. Cells were plated into a six-well tissue culture plate and treated with TGFbeta -neutralizing antibody (10 µg/ml) or control normal IgG and allowed to attach for 3 h. Following attachment, cells were treated with EB1089 (1 × 10-8 M), while control cells were treated with vehicle only. At 51 h post-transfection, cells were harvested with 100 µl of lysis buffer (Luciferase assay system, Promega). Luciferase activity was determined according to the manufacturer's instruction using a luminometer (Berthold Lumat LB 0501) and expressed as relative units after normalization to beta -galactosidase.

    RESULTS
Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References

TGFbeta Sensitivity of MCF-7 Cells-- Inconsistent response of MCF-7 cells to TGFbeta has been observed in several laboratories (34, 35), probably due to growth selection during long term passage of cultures. Having obtained both early (150) and late (>500) passage MCF-7 cells, we decided to first test whether they responded differently to TGFbeta (Fig. 1). MCF-7 E cells showed a significant dose-dependent inhibition by TGFbeta with an IC50 of 0.2 ng/ml. In contrast, MCF-7 L cells demonstrated complete resistance to TGFbeta up to 25 ng/ml (Fig. 1). As described below, MCF-7 E cells expressed RII mRNA and protein in contrast to MCF-7 L cells, which had 5-fold less mRNA and no detectable cell surface protein.


View larger version (9K):
[in this window]
[in a new window]
 
Fig. 1.   Effect of TGFbeta on DNA synthesis in MCF-7 cells. MCF-7 E (open circle ) and MCF-7 L cells (bullet ) were plated at a density of 1.5 × 104 cells/well in 24-well tissue culture plates. Various concentrations of TGFbeta (0.2-25 ng/ml) were added after cell attachment. After 4 days of incubation, [3H]thymidine incorporation into DNA was measured following a 2-h pulse and expressed as a percentage of control in the absence of TGFbeta . Each point is the mean ± S.E. of four replicates.

Vitamin D3 Sensitivity-- Effects of 1,25-(OH)2 D3 and its analogues on cell proliferation of MCF-7 cells were investigated by assessing [3H]thymidine incorporation following treatment by these compounds as described under "Materials and Methods." MCF-7 E cells showed a dose-dependent inhibition by vitamin D3 with an IC50 of 5 × 10-8 M. In contrast, MCF-7 L cells were not affected by vitamin D3 (Fig. 2A). Vitamin D3 analogues EB1089 and MC903 demonstrate similar growth-inhibitory patterns (Fig. 2, B and C). The overall potency of growth inhibition by EB1089 was approximately 2 orders of magnitude higher than vitamin D3. MCF-7 E cells showed an IC50 of 2.5 × 10-10 M, and MCF-7 L cells did not respond to EB1089 treatment up to 1 × 10-7 M.


View larger version (11K):
[in this window]
[in a new window]
 
Fig. 2.   Effect of 1,25-(OH)2 D3 and EB1089 on DNA synthesis in MCF-7 cells. Cells were plated into 24-well plates at a density of 1.5 × 104 cells/well. Different concentrations of vitamin D3 (A), EB1089 (B), or MC903 (C) were added to tissue culture media after cell attachment. DNA synthesis was evaluated by measuring [3H]thymidine incorporation into DNA after a 2-h pulse. Results were presented as the percentage of incorporation of control with carrier ethanol alone. Each point is the mean ± S.E. of four replicates. bullet , MCF-7 E; open circle , MCF-7 L.

TGFbeta Autocrine Activity-- The correlation between TGFbeta and vitamin D3 sensitivity suggested that vitamin D3 may function through increasing TGFbeta autocrine-negative activity in MCF-7 E cells. To test this hypothesis, TGFbeta -neutralizing antibodies were used to determine whether they were capable of blocking the growth inhibition induced by these compounds (Fig. 3). At 10 µg/ml, TGFbeta 1-neutralizing antibody reversed the inhibitory effect of vitamin D3 and its analogues, generating an approximately 60% increase in DNA synthesis as compared with the normal chicken IgG treatment. In contrast, MCF-7 L cells did not respond to TGFbeta 1-neutralizing antibody, indicating a lack of induction of autocrine TGFbeta activity. These results indicate that the growth-inhibitory mechanism of vitamin D3 involves induction of TGFbeta autocrine-negative activity in MCF-7 E cells.


View larger version (13K):
[in this window]
[in a new window]
 
Fig. 3.   Effect of TGFbeta -neutralizing antibody on DNA synthesis of vitamin D3- or EB1089-treated MCF-7 cells. MCF-7 E (black-square) and MCF-7 L cells () were plated at a density of 1.5 × 104 cells/well. The addition of TGFbeta -neutralizing antibodies and vitamin D3 compounds was performed as described under "Materials and Methods." The results were expressed as the percentage increase in DNA synthesis relative to their respective control antibody-treated cells. Each point represents the mean ± S.E. of triplicate determinations.

Alteration of RII Expression-- Increased autocrine TGFbeta activity could result from enhanced expression of TGFbeta isoforms and/or their receptors. To test these possibilities, RNase protection assays were initially carried out on MCF-7 E cells to determine whether there were alterations of TGFbeta isoform expression upon treatment with vitamin D3 compounds. MCF-7 E cells expressed high levels of TGFbeta 1 mRNA and low levels of TGFbeta 2 and TGFbeta 3 mRNA. Treatment with EB1089 did not generate altered mRNA expression for any of the three TGFbeta isoforms (data not shown). In addition, enzyme-linked immunosorbent assay analysis of the conditioned medium showed no significant increase in the levels of activated TGFbeta 1 protein (data not shown). Since the levels of activated TGFbeta cannot be determined by enzyme-linked immunosorbent assay analysis, a growth inhibition bioassay on mink lung epithelial cells was performed. The condition medium from EB1089-treated and -untreated MCF-7 E cells was added to mink lung epithelial cells as described under "Materials and Methods." After exposure to either treated or untreated conditioned medium, no significant difference in growth inhibition was observed in the mink lung epithelial cells (Fig. 4). These results indicate that EB1089 treatment did not alter the activation of secreted growth and/or inhibitory peptides from MCF-7 E cells, one of which is likely to be TGFbeta 1, as demonstrated by enzyme-linked immunosorbent assay analysis. Taken together, these results suggest that the enhanced TGFbeta autocrine activity by vitamin D3 did not result from modulation of ligand expression or activation.


View larger version (25K):
[in this window]
[in a new window]
 
Fig. 4.   Determination of the levels of active TGFbeta in the condition media of EB1089-treated and -untreated MCF-7 E cells. Exponentially growing MCF-7 E cells were treated with EB1089 (10-8 M) or vehicle only for 24 h. Conditioned media were collected, and the volumes indicated were added to mink lung epithelial cells to assay for growth inhibition. A, standard TGFbeta 1 growth inhibition curve for mink lung epithelial cells. Results were expressed as the percentage of growth inhibition. box-dot , CCL-64. B, the percentage of growth inhibition caused by the indicated volume of condition medium. Each point represents the mean ± S.E. of four determinations. black-square, MCF-7 E (EtoH); , MCF-7 E (EB1089).

The other possibility for increased autocrine TGFbeta activity upon treatment with vitamin D3 compounds was induction of receptor expression; therefore, we determined whether vitamin D3 analogue treatment modulated expression of RII mRNA. EB1089 (10-8 M) was utilized to determine the kinetic effects on RII expression. MCF-7 E cells expressed 5-fold higher RII mRNA than MCF-7 L cells. After exposure to EB1089, a 3-fold increase in the RII mRNA levels of MCF-7 E cells was observed. In contrast, no significant modulation was noted for the MCF-7 L cells after exposure to EB1089 (Fig. 5). EB1089 treatment did not effect the levels of RI or RIII mRNA (data not shown).


View larger version (39K):
[in this window]
[in a new window]
 
Fig. 5.   Regulation of TGFbeta RII mRNA expression by EB1089. Exponentially growing MCF-7 E and MCF-7 L cells were treated with EB1089 (10-8 M) for 8, 16, and 24 h. Total RNA was collected, and RII mRNA expression levels were compared using RNase protection assays. Actin was used to normalize sample loading.

The increase in MCF-7 E RII mRNA expression led us to examine whether this corresponded to an increase in cell surface RII protein. This was tested by receptor cross-linking with 125I-labeled TGFbeta (Fig. 6A). The GEO cell line, which expresses all three types of TGFbeta receptors, was used as a positive control (lane 1). The specificity of cross-linking was demonstrated by competing with 100-fold cold TGFbeta 1 (lane 2). MCF-7 E cells expressed all three types of receptors (lane 3). Treatment of these cells with the indicated concentrations of vitamin D3 or EB1089 resulted in a 3-4-fold induction of RII, while expression levels of RI remained relatively unchanged (Fig. 6A). Compared with the MCF-7 E cells, no cell surface RII protein was detected in MCF-7 L cells. Treatment with the vitamin D3 compounds did not result in any change in receptor expression of these cells (Fig. 6B). To determine if the induction of RII protein in MCF-7 E cells was also time-dependent, a kinetic study was performed. Receptor cross-linking assays revealed a time-dependent increase of cell surface RII protein (Fig. 7A). Induction was detected as early as 8 h with a 3-4-fold increase after 24 h of treatment.


View larger version (41K):
[in this window]
[in a new window]
 
Fig. 6.   Effect of 1,25-(OH)2 D3 and EB1089 on expression of cell surface TGFbeta receptors. Receptor cross-linking assays were performed to determine modulation of cell surface TGFbeta receptor expression by the vitamin D3 compounds on MCF-7 E (A) and MCF-7 L cells (B). Cells were plated and allowed to grow to 70-80% confluency in 35-mm2 tissue culture dishes and then subjected to treatment with the indicated concentrations of vitamin D3 or EB1089 for 24 h. Monolayer of GEO cells (used as a positive control) and MCF-7 cells were incubated with 200 pM 125I-labeled TGFbeta 1 alone or in the presence of 20 nM cold TGFbeta 1 at 4 °C for 4 h, followed by chemical cross-linking with disuccinimidyl suberate. 150 µg of total cell lysate protein was separated by electrophoresis using 4-10% gradient SDS-polyacrylamide gel electrophoresis gels. The autoradiographs are representative of three similar experiments.


View larger version (22K):
[in this window]
[in a new window]
 
Fig. 7.   Kinetics of induction of cell surface TGFbeta RII. Exponentially growing MCF-7 E cells were treated with EB1089 (10-8 M) for the indicated time periods. A, receptor cross-linking was performed as described under "Materials and Methods." RI, RII, and RIII were visualized by autoradiography. B, the RII bands were quantified densitometrically with an Ambis scanning system and presented as -fold increase compared with the control at 0 h. The autoradiograph is representative of two separate experiments.

Responsiveness to Autocrine TGFbeta -- To evaluate whether RII induction by treatment with EB1089 enhanced autocrine TGFbeta sensitivity, TGFbeta -dependent promoter activity was analyzed using the TGFbeta -responsive cyclin A luciferase reporter construct (32). TGFbeta induces down-regulation of cyclin A promoter activity but requires a functional TGFbeta type I and II receptor complex (32, 33). Thus, an increase in functional receptor levels would result in enhanced down-regulation of cyclin A promoter activity. The cyclin A reporter construct (-133/-2) contains only the activating transcription factor site, which has been shown to mediate down-regulation of cyclin A promoter activity by TGFbeta 1 in mink lung epithelial cells (32). This reporter construct was transiently transfected into MCF-7 E cells, which are sensitive to TGFbeta , followed by treatment with TGFbeta -neutralizing antibody and EB1089 as described under "Materials and Methods." As expected, a decrease in luciferase activity was induced in MCF-7 E cells following treatment with EB1089. TGFbeta -neutralizing antibody reversed the decrease in cyclin A luciferase activity by EB1089, increasing it by approximately 70%. TGFbeta -neutralizing antibody alone had no significant affect on cyclin A luciferase activity (Fig. 8) The fact that EB1089 did not increase expression or activation of any of the three TGFbeta isoforms indicates that enhanced responsiveness to autocrine TGFbeta after EB1089 treatment is due to the increased expression of RII.


View larger version (9K):
[in this window]
[in a new window]
 
Fig. 8.   Effect of EB1089 on response to autocrine TGFbeta . MCF-7 E cells were transiently transfected with a TGFbeta -responsive cyclin A luciferase promoter construct (-133/-2) followed by treatment with either TGFbeta -neutralizing antibody or normal IgG. Following attachment (3 h), cells were treated with EB1089 (10-8 M) or vehicle only. At 51 h post-transfection, cells were harvested, and luciferase activity was measured and normalized to beta -galactosidase. Each point represents the mean ± S.E. of triplicate determinations.

    DISCUSSION
Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References

TGFbeta signaling requires a heteromeric assembly of its two Ser-Thr kinase receptors, designated RI and RII, respectively (36). A recent model illustrating the physical and functional interactions between the two receptors proposes that upon ligand binding, the constitutively active RII recruits RI and transphosphorylates the RI, which subsequently initiates downstream cytoplasmic events (37). Defects in expression of either receptor would contribute to loss of response to exogenous as well as endogenous TGFbeta . In particular, loss and/or lack of autocrine TGFbeta response plays a major role in enhancing tumor progression. As was demonstrated previously, antisense TGFbeta transfection in two early malignant colon carcinoma cell lines eliminated autocrine negative TGFbeta activity but did not block response to exogenous TGFbeta (27, 38). The TGFbeta antisense-transfected cells showed increased tumor growth and incidence in athymic nude mice, indicating that autocrine TGFbeta plays a key role in blocking tumor progression. Reestablishment of autocrine TGFbeta responsiveness leading to decreased tumorigenicity in cells with deficient TGFbeta receptor function was achieved by stable transfection of RII in breast cancer MCF-7 L cells (6) and in the human colon carcinoma cell line HCT116 (8). Based on these studies, agents that can control the expression of TGFbeta receptors may have therapeutic implications. In particular, agents that can enhance the expression level of RII in cells where it appears to be repressed may be an effective chemopreventive approach. To date, no such agents have been carefully and fully characterized for their ability to induce RII and subsequently enhance autocrine-negative TGFbeta activity. Characterization of these agents should lead to a better understanding of TGFbeta -mediated growth inhibition and its anti-tumor effects.

In the present study, we demonstrated for the first time that an increase in autocrine TGFbeta function by the active metabolite of vitamin D3 is solely due to an increase in RII expression. However, the effective dose of active vitamin D3, which induces negative autocrine TGFbeta activity would also cause hypercalcemia, leading to unwanted side effects. To overcome this problem, analogues such as EB1089 have been developed that have increased potency and reduced hypercalcemic effects (39). We have shown here that the analogue EB1089 has similar effects to the parental compound at lower concentrations, which make it an attractive and potential chemopreventive agent. Thus, vitamin D3 and its analogues can inhibit malignant cell growth through a novel mechanism of induction of negative autocrine TGFbeta activity.

A number of studies have reported that expression of RI and RII protein can be regulated by factors such as cell density (40, 41); exposure to parathyroid, adrenal, or androgenic hormones (42-44); and TGFbeta (45). However, these agents do not readily lend themselves to chemopreventive approaches. Moreover, these studies were restricted to cell surface analysis utilizing 125I-TGFbeta in receptor cross-linking and did not determine biological effects with respect to potential autocrine activity changes. In this study, we demonstrated a 3-fold increase in steady state RII mRNA levels (Fig. 4) by vitamin D3 treatment, which correlated with a 3-4-fold increase in cell surface RII protein (Figs. 5 and 6). This suggests that translational modifications were unlikely to be responsible for up-regulation of the RII protein. Induction of RII mRNA by vitamin D3 may involve transcriptional and post-transcriptional mechanisms. Vitamin D3 association with VDR can either increase the affinity of VDR binding to its target DNA sequence or cause conformational changes in the receptor leading to alterations in gene activation (46). VDR proteins were detected by Western analysis in both MCF-7 E and MCF-7 L cells (data not shown). The VD-VDR complex in combination with other steroid receptors could be directly involved in stimulation of the RII promoter activity or act indirectly by increasing the quantity or activity of related transcriptional activators. Examination of the recently characterized RII promoter region (47) did not reveal sequences analogous to the well established vitamin D3-responsive elements, indicating that induction of RII mRNA in MCF-7 E cells by vitamin D3 was unlikely to be a direct effect. The lack of RII induction in MCF-7 L cells suggests that the RII gene might be suppressed by factors or mechanisms that were not present in MCF-7 E cells and that certain transcriptional factors that were essential to activation of the VDR signaling pathway might be deficient in MCF-7 L cells. Unraveling these mechanisms may lead to novel approaches for reactivation of the RII tumor suppressor gene.

Modulation of TGFbeta expression or secretion by vitamin D3 has been shown in keratinocytes, chondrocytes, rat prostatic epithelial cells, and one human breast cancer cell line BT-20 (48-51). Danielpour (51) was able to demonstrate in a nontumorigenic rat prostate epithelial cell line that induction of TGFbeta autocrine activity by vitamin D3 was mediated by increases in all three isoforms of TGFbeta . In addition, other steroid hormones have been shown to increase activation of latent TGFbeta while not affecting total levels (52, 53). Interestingly, modulation of TGFbeta levels or its activation by vitamin D3 compounds was not observed in this study of this strain of human breast cancer cell line (MCF-7 E). A potential difficulty with chemopreventive approaches involving TGFbeta ligand induction rather than receptor induction resides in the tumor-enhancing effects associated with TGFbeta overexpression, such as angiogenesis and immunosuppression (54). However, EB1089 may offer an advantage in that induction of autocrine-negative TGFbeta activity occurs through RII and not its TGFbeta ligand. Enhancement of autocrine-negative TGFbeta activity, without the increase in TGFbeta ligand and the potential tumor-enhancing effects associated with it, makes the use of these compounds an attractive approach by offering a potential novel mechanism for cancer prevention and/or therapy.

In addition to vitamin D3, other related members of the steroid hormone family have been shown to modulate TGFbeta receptor expression. In human neuroblastoma cells, RA increased RII mRNA levels and RI protein as well as increasing expression and secretion of TGFbeta 1 (55). However, cell surface RII was undetectable by receptor cross-linking in this study. The up-regulation of TGFbeta 1 and the TGFbeta receptors occurred only in the neuroblastoma cell line that was responsive to RA-induced growth arrest. RA treatment of RL human B lymphoma cells induced a 2-fold increase in total RII protein. However, the study failed to examine whether that correlated to increased cell surface RII (54). In addition to RA, vitamin E succinate, which demonstrated potent growth inhibition, induced RI, RII, and TGFbeta proteins but did not affect their mRNA levels in RL human B lymphoma cells (56). Treatment of the lymphoma cells with TGFbeta 1-neutralizing antibodies could partially block the growth inhibitory functions of vitamin E succinate and RA, indicating that treatment induced a TGFbeta autocrine-negative loop. However, this study did not examine cell surface receptor levels; thus, the increase in negative TGFbeta autocrine activity could be due to increased ligand levels. Both of these studies demonstrated the ability of other agents to induce RII mRNA or protein levels but failed to either detect or investigate RII cell surface levels. In addition, these compounds also enhance ligand expression, which may have adverse effects on surrounding tissue. The observation that vitamin D3 induced autocrine negative TGFbeta activity through increased cell surface RII and not TGFbeta ligand may prove to be of significance in breast cancer therapy and/or prevention.

    ACKNOWLEDGEMENT

We thank Mu-En Lee for kindly providing the cyclin A luciferase reporter construct.

    FOOTNOTES

* This work was supported by National Institutes of Health Grants CA38173, CA50457, and CA72001 (to M. G. B.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

§ These authors contributed equally to the work.

** To whom correspondence should be addressed. Tel.: 210-567-4524; Fax: 210-567-3447.

1 The abbreviations used are: TGFbeta , transforming growth factor-beta ; RA, retinoic acid; VDR, vitamin D receptor; RI, RII, and RIII, TGFbeta receptor type I, II, and III, respectively.

    REFERENCES
Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References

  1. Roberts, A. B., and Sporn, M. B. (1990) Peptide Growth Factors 95, 419-472
  2. Lopez-Casillas, F., Wrana, J. L., and Massague, J. (1993) Cell 73, 1435-1444[Medline] [Order article via Infotrieve]
  3. Lin, H. Y., Wang, X-F., Ng-Eaton, E., Weinberg, R. A., Lodish, H. F. (1992) Cell 68, 775-785[Medline] [Order article via Infotrieve]
  4. Franzen, P., Ten Dijke, P., Ichijo, H., Yamashita, H., Schultz, P., Heldin, C-H., and Miyazono, K. (1993) Cell 75, 681-692[Medline] [Order article via Infotrieve]
  5. Bassing, C. H., Yingling, J. M., Howe, D. J., Wang, T., He, W. W., Gustafson, M. L., Shah, P., Donahoe, K., Wang, X-F. (1994) Science 263, 87-89[Medline] [Order article via Infotrieve]
  6. Sun, L., Wu, G., Willson, J. K. V., Zborowska, E., Yang, J., Rajkarunanayake, I., Wang, J., Gentry, L. E., Wang, X-F., Brattain, M. G. (1994) J. Biol. Chem. 269, 26449-26455[Abstract/Free Full Text]
  7. Markowitz, S., Wang, J., Myeroff, L., Parsons, R., Sun, L-Z., Lutterbaugh, J., Fan, R. S., Zborowska, E., Kinzler, K. W., Vogelstein, B., Brattain, M., Willson, J. K. V. (1995) Science 268, 1336-1338[Medline] [Order article via Infotrieve]
  8. Wang, J., Sun, L., Myerloff, L., Wang, X., Gentry, L. E., Yang, J., Liang, J., Zborowska, E., Markowitz, S., Willson, J. K. V., Brattain, M. G. (1995) J. Biol. Chem. 270, 22044-22049[Abstract/Free Full Text]
  9. Garrigue-Antar, L., Muñoz-Antonia, T., Antonia, S. J., Gesmonde, J., Vellucci, V. F., Reiss, M. (1995) Cancer Res. 55, 3982-3987[Abstract]
  10. Myeroff, L. L., Parsons, R., Kim, S.-J., Hedrick, L., Cho, K. R., Orth, K., Mathis, M., Kinzler, K. W., Lutterbaugh, J., Park, K., Bang, Y.-J., Lee, H. Y., Park, J.-G., Lynch, H. T., Roberts, A. B., Vogelstein, B., Markowitz, S. D. (1995) Cancer Res. 55, 5545-5547[Abstract]
  11. Kadin, M. E., Cavaille-Coll, M. W., Gertz, R., Massague, J., Cheifetz, S., George, D. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 6002-6006[Abstract]
  12. Park, K., Kim, S. J., Bang, Y. J., Park, J. G., Kim, N. Y., Roberts, A. B., Sporn, M. B. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 8772-8776[Abstract]
  13. Okamoto, A., Jiang, W., Kim, S. J., Spillare, E. A., Stoner, G. O., Weistein, B. I., Harris, C. L. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 11576-11580[Abstract/Free Full Text]
  14. Geiser, A. G., Burmester, J. K., Webbink, R., Roberts, A. B., Sporn, M. B. (1992) J. Biol. Chem. 267, 2588-2593[Abstract/Free Full Text]
  15. Inagaki, M., Moustakas, A., Lin, H. Y., Lodish, H. F., Carr, B. I. (1993) Proc. Natl. Acad. Sci. U. S. A. 90, 5359-5363[Abstract]
  16. Brattain, M. G., Ko, Y., Banerji, S. S., Wu, G., Willson, J. K. V. (1996) J. Mammary Gland Biol. Neoplasia 1, 365-372 [Medline] [Order article via Infotrieve]
  17. Kalkhoven, E., Roelen, B. A., de Winter, J. P., Mummery, C. L., van den Eijnden-van Raaij, A. J., van der Saag, P. T., van der Burg, B. (1995) Cell Growth Differ. 6, 1151-1161[Abstract]
  18. Jordan, V. C., Robinson, S. P., and Welshons, W. V. (1989) in Resistance to Antineoplastic Drugs (Kessel, D., ed), pp. 403-427, CRC Press, Boca Raton, FL
  19. Pasqualini, J. R., Sumida, C., and Giambiagi, N. (1988) J. Steroid Biochem. 31, 613-43[CrossRef][Medline] [Order article via Infotrieve]
  20. Haussler, M. R., Mangelsdorf, D. J., Komm, B. S., Terpening, C. M., Yamaoka, K., Allegretto, E. A., Baker, A. R., Shine, J., McDonnell, D. P., Hughes, M., Weigel, N. L., O'Malley, B. W., Pike, J. W. (1988) Recent Prog. Horm. Res. 44, 263-305[Medline] [Order article via Infotrieve]
  21. Eisman, J. A., Suva, L. J., Sher, E., Pearce, P. J., Funder, J. W., Martin, T. J. (1981) Cancer Res. 41, 5121-5124[Abstract]
  22. Berger, U., Wilson, P., McClelland, R. A., Colston, K., Haussler, M. R., Pike, J. W., Coombes, R. C. (1987) Cancer Res. 47, 6793-6799[Abstract]
  23. Abe-Hashimoto, J., Kikuchi, T., Matsumoto, T., Nishii, Y., Ogata, E., and Ikeda, K. (1993) Cancer Res. 53, 2534-2537[Abstract]
  24. Colston, K. W., Mackay, A. G., James, S. Y., Binderup, L., Chander, S., Coombes, R. C. (1992) Biochem. Pharmacol. 44, 2273-2280[CrossRef][Medline] [Order article via Infotrieve]
  25. Colston, K. W., Chander, S. K., Mackay, A. G., Coombes, R. C. (1992) Biochem. Pharmacol. 44, 693-702[CrossRef][Medline] [Order article via Infotrieve]
  26. Khan, N., Yang, K., Newmark, H., Wong, G., Telang, N., Rivlin, R., and Lipkin, M. (1994) Carcinogenesis 15, 2645-2648[Abstract]
  27. Wu, S. P., Sun, L-Z., Willson, J. K. V., Humphrey, L . E., Kerbel, R., Brattain, M. G. (1993) Cell Growth Differ. 4, 115-123[Abstract]
  28. Chirgwin, J. M., Przybyla, A. E., MacDonald, R. J., Rutter, W. J. (1979) Biochemistry 18, 5294-5299[Medline] [Order article via Infotrieve]
  29. Gentry, L. E., Lioubin, M. N., Purchio, A. F., Marquardt, H. (1988) Mol. Cell. Biol. 8, 4162-4168[Medline] [Order article via Infotrieve]
  30. Ruff, E., and Rizzino, A. (1986) Biochem. Biophys. Res. Commun. 138, 714-719[Medline] [Order article via Infotrieve]
  31. Segarini, P. R., Roberts, A. B., Rosen, D. M., Seyedin, S. M. (1987) J. Biol. Chem. 262, 14655-14662[Abstract/Free Full Text]
  32. Yoshizumi, M., Wang, H., Hsieh, C-M., Sibinga, N. E. S., Perrella, M. A., Lee, M-E. (1997) J. Biol. Chem. 272, 22259-22264[Abstract/Free Full Text]
  33. Feng, X.-H., Filvaroff, E. H., and Derynck, R. (1995) J. Biol. Chem. 270, 24237-24245[Abstract/Free Full Text]
  34. Zugmaier, G., Ennis, B. W., Deschauer, B., Katz, D., Knabbe, C., Wilding, G., Daly, P., Lippman, M. E., Dickson, R. B. (1989) J. Cell. Physiol. 141, 353-361[Medline] [Order article via Infotrieve]
  35. Jeng, M. H., Dijke, P. T., Iwata, K. K., Jordan, V. C. (1993) Mol. Cell. Endocrinol. 97, 115-123[CrossRef][Medline] [Order article via Infotrieve]
  36. Wrana, J. L., Attisano, L., Carcamo, J., Zentella, A., Doody, J., Laiho, M., Wang, X-F., and Massague, J. (1992) Cell 71, 1003-1014[Medline] [Order article via Infotrieve]
  37. Wrana, J. L., Attisano, L., Wieser, R., Ventura, F., and Massague, J. (1994) Nature 370, 341-347[CrossRef][Medline] [Order article via Infotrieve]
  38. Wu, S. P., Theodorescu, D., Kerbel, R. S., Willson, J. K., Mulder, K. M., Humphrey, L. E., Brattain, M. G. (1992) J. Cell Biol. 116, 187-196[Abstract]
  39. Skowronski, R. J., Peehl, D. M., and Feldman, D. (1995) Endocrinology 136, 20-26[Abstract]
  40. Rizzino, A., Kazakoff, P., Ruff, E., Kuszynski, C., and Nebelsick, J. (1988) Cancer Res. 48, 4266-4271[Abstract]
  41. Muller, G. A., Behrens, J., Nussbaumer, U., Bohlen, P., and Birchmeier, W. (1987) Proc. Natl. Acad. Sci. U. S. A. 84, 5600-5604[Abstract]
  42. Centrella, M., McCarthy, T. L., and Canalis, E. (1988) Proc. Natl. Acad. Sci. U. S. A. 85, 5889-5893[Abstract]
  43. Cochet, C., Feige, J. J., and Chambaz, E. M. (1988) J. Biol. Chem. 263, 5707-5713[Abstract/Free Full Text]
  44. Kyprianou, N., and Isaacs, J. T. (1988) Endocrinology 123, 2124-2131[Abstract]
  45. Wakefield, L. M., Smith, D. M., Masui, T., Harris, C. C., Sporn, M. B. (1987) J. Cell Biol. 105, 965-975[Abstract]
  46. Ross, T. K., Darwish, H. M., Moss, V. E., Deluca, H. F. (1993) Proc. Natl. Acad. Sci. U. S. A. 90, 9257-9260[Abstract]
  47. Bae, H. W., Geiser, A. G., Kim, D. H., Chung, M. T., Burmester, J. K., Sporn, M. B., Roberts, A. B., Kim, S-J. (1995) J. Biol. Chem. 270, 29460-29468[Abstract/Free Full Text]
  48. Kim, H. J., Abdelkader, N., Katz, M., and Mclane, J. A. (1992) J. Cell. Physiol. 151, 579-587[Medline] [Order article via Infotrieve]
  49. Koli, K., and Keski-Oja, J. (1995) Cancer Res. 55, 1540-1546[Abstract]
  50. Boyan, B. D., Schwartz, Z., Park-Snyder, S., Dean, D. D., Yang, F., Twardzik, D., Bonewald, L. F. (1994) J. Biol. Chem. 269, 28374-28381[Abstract/Free Full Text]
  51. Danielpour, D. (1995) J. Cell. Physiol. 166, 231-239[CrossRef]
  52. Wakefield, L., Kim, S. J., Glick, A., Winokur, T., Colletta, A., and Sporn, M. (1990) J. Cell Sci. 13, 139-148[Medline] [Order article via Infotrieve]
  53. Roberts, A. B., and Sporn, M. (1992) Cancer Surv. 14, 205-220[Medline] [Order article via Infotrieve]
  54. Torre-Amione, G., Beauchamp, R. D., Koeppen, H., Park, B. H., Schreiber, H., Moses, H. L., Rowley, D. A. (1990) Proc. Natl. Acad. Sci. U. S. A. 87, 1486-1490[Abstract]
  55. Cohen, P. S., Letterio, J. J., Gaetano, C., Chan, J., Matsumoto, K., Sporn, M. B., Thiele, C. J. (1995) Cancer Res. 55, 2380-2386[Abstract]
  56. Turley, J. M., Funakoshi, S., Ruscetti, F. W., Kasper, J., Murphy, W. J., Longo, D. L., Birchenall-Roberts, M. C. (1995) Cell Growth Differ. 6, 655-663[Abstract]


Copyright © 1998 by The American Society for Biochemistry and Molecular Biology, Inc.