©1995 by The American Society for Biochemistry and Molecular Biology, Inc.
Transcriptional Activation of egr-1 by Granulocyte-Macrophage Colony-stimulating Factor but Not Interleukin 3 Requires Phosphorylation of cAMP Response Element-binding Protein (CREB) on Serine 133 (*)

Hu-Jung Julie Lee , Robert C. Mignacca (§) , Kathleen M. Sakamoto (¶)

From the (1)Division of Hematology/Oncology, Gwynne Hazen Cherry Memorial Laboratories, Department of Pediatrics, A2-312 UCLA School of Medicine and Jonsson Comprehensive Cancer Center, Los Angeles, California 90095-1752

ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS AND DISCUSSION
FOOTNOTES
ACKNOWLEDGEMENTS
REFERENCES

ABSTRACT

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 3 (IL-3) stimulate the proliferation and maturation of myeloid progenitor cells following interaction with heterodimeric receptors that share a common subunit required for signal transduction. Our previous studies have demonstrated that GM-CSF and IL-3 activate signaling pathways which converge upon a cAMP response element-binding protein (CREB)-binding site of the human immediate early response gene (early growth response gene-1, egr-1) promoter. Using electromobility supershift assays and antibodies directed against CREB phosphorylated on serine 133, we show that CREB is phosphorylated on serine 133 in response to GM-CSF or IL-3 stimulation. We demonstrate that phosphorylation of CREB on serine 133 substantially contributes to transcriptional activation of egr-1 in response to GM-CSF but not IL-3. These studies suggest that phosphorylation of CREB may play different roles during signal transduction, resulting in unique and overlapping biological functions in myeloid cells.


INTRODUCTION

Granulocyte-macrophage colony-stimulating factor (GM-CSF)()and interleukin 3 (IL-3) share many biological functions which may be mediated by a common receptor subunit critical for transmission of signals from the cell surface to the nucleus of myeloid cells(1, 2, 3, 4) . It has been shown that GM-CSF and IL-3 exhibit overlapping activities throughout myeloid cell development; however, the precise mechanisms leading to the biological activities elicited by these two growth factors are still unclear (1-3).

The receptors for GM-CSF and IL-3 are members of the hematopoietin receptor superfamily, which includes receptors for interleukins 4 through 9 and the prolactin and growth hormone receptors(4, 5, 6) . GM-CSF or IL-3 stimulation of target cells results in tyrosine phosphorylation of similar sets of proteins(7, 8) . These receptors do not contain consensus sequence motifs for tyrosine or serine-threonine kinases(6) . However, nonreceptor tyrosine kinases such as Jak2 form complexes with the GM-CSF and IL-3 receptors(4) . Both GM-CSF and IL-3 activate pathways, which result in the phosphorylation of Raf, Vav, Fes, Shc, and microtubule-associated protein kinase and induce phosphorylation of DNA-binding proteins that recognize the -interferon response region (4, 8-10). Recently, GM-CSF and IL-3 were demonstrated to induce phosphorylation of a novel STAT protein, STAT5, in the hematopoietic cell line OTT-1(11) . These findings suggest significant redundancy in the signaling pathways activated by GM-CSF and IL-3.

We demonstrated previously that signaling by GM-CSF or IL-3 results in rapid and transient induction of the immediate early response gene (early growth response gene-1, egr-1)(12) . egr-1 encodes a zinc finger DNA-binding protein which recognizes the sequence CGCCCCCGC(13, 14) . Like c-fos, this gene is induced by a variety of stimuli, including serum, tetradecanoylphorbol acetate (TPA) and other growth factors (e.g. nerve growth factor (NGF))(15, 16) . egr-1 has also been demonstrated to be necessary for macrophage but not granulocyte differentiation(17) . The immediate early genes are believed to be critical for GM-CSF and IL-3 action, as many of them, including egr-1 and c-fos, encode transcription factors which participate in the regulation of transcription of late response genes(18) . Many cytokine-induced late response genes encode myeloid-specific proteins that function as determinants of myeloid cell differentiation (18).

The transcriptional activation of egr-1 in response to GM-CSF, IL-3, or serum stimulation in the factor-dependent human myeloid leukemic cell line, TF-1, requires the presence of the cAMP response element (CRE) contained within the -116 nucleotide region of the egr-1 promoter(12) . We found that the signaling pathways activated by GM-CSF and IL-3 converge upon the CRE-binding protein, CREB, which specifically binds the CRE in the -116-nt region of the egr-1 promoter(12) . Many growth factors, including GM-CSF, stimulate the transcription of specific genes by increasing intracellular cAMP, which results in the activation of protein kinase A and phosphorylation of several proteins(19, 20, 21) . The 43-kilodalton (kDa) cAMP response element-binding protein, CREB, is one of these factors phosphorylated by a protein kinase A-dependent pathway(21, 22) . Phosphorylation of serine 133 is critical for the activation of CREB and is required for the induction of specific genes (e.g. c-fos) by growth factors such as NGF(16, 21) . NGF stimulation of PC12 cells results in Ras-dependent phosphorylation of CREB, leading to the induction of c-fos by a protein kinase A-independent pathway(16) .

To characterize the post-translational modification of CREB in response to signaling pathways activated by GM-CSF and IL-3, we examined the phosphorylation of CREB in response to growth factor stimulation in TF-1 cells. We report here that GM-CSF and IL-3 induce phosphorylation of CREB on serine 133 in TF-1 cells. Moreover, we determined that phosphorylation of CREB on serine 133 substantially contributes to the the transcriptional activation of the -116 nucleotide region of the human egr-1 promoter in response to GM-CSF but not IL-3. Our findings also suggest that transcriptional events downstream may determine specificity for growth factors with overlapping activities through phosphorylation of specific nuclear proteins.


MATERIALS AND METHODS

Reagents and Cytokines

Antibodies for CREB (polyclonal antibodies) were purchased from Upstate Biotechnology, Inc. (Lake Placid, NY). Anti-phosphorylated CREB, raised against a CREB peptide containing phosphoserine 133, was generously provided by Dr. David Ginty(16) . Anti-rabbit IgG was purchased from Sigma. The enhanced chemiluminescence (ECL) detection kit was obtained from Amersham Corp. Recombinant human GM-CSF (rhGM-CSF) was provided by Amgen (Thousand Oaks, CA), and human IL-3 was provided by Immunex (Seattle, WA). The CREB and mutant CREB (serine 133 mutated to alanine) constructs were gifts from Dr. M. Montminy(22) . We subcloned the wild-type and mutant CREBs into the BC12 vector, which contains the cytomegalovirus (CMV) promoter for transient co-transfection assays(23) .

Cell Culture and Transfections

TF-1 cells were cultured in RPMI with 10% fetal calf serum, L-glutamine (2 mM), and penicillin (100 units/ml streptomycin, 100 µg/ml) at a ratio of 1 unit/ml to 1 µg/ml and either rhGM-CSF (500 pM) or rhIL-3 (500 pM) in nonadherent tissue culture plates. For transient transfection experiments, cells were factor- and serum-starved for 24 h and placed in RPMI, 0.5% bovine serum albumin (BSA) (Sigma). A total of 5 10 cells/sample were transfected by electroporation at 200 mV with 45 µg of total DNA (20 µg of egr-1 promoter construct -116cat, 22 µg of wild-type or mutant CREB, and 3 µg of CMV -galactosidase-containing plasmid). Cells grown in GM-CSF or IL-3 were resuspended in RPMI, 0.5% BSA and stimulated with 500 pM of rhGM-CSF, rhIL-3, or diluent control (phosphate-buffered saline (PBS), 0.02% BSA) for 4 h, at which time stimulation of the recombinant construct is maximal (data not shown). Cells were harvested and assayed for chloramphenicol acetyltransferase or -galactosidase activity as described previously(12) . The amount of acetylated and unacetylated [C]chloramphenicol was determined by liquid scintillation counting, and -fold stimulation by GM-CSF or IL-3 was corrected for transfection efficiency with the luciferase or -galactosidase assay (Promega). Statistical analysis (Student's t test) was performed using the STATWORKS program.

Electromobility Shift Assays and Supershift Experiments

TF-1 cells (5 10) cultured in either GM-CSF or IL-3 were factor- and serum-starved for 24 h and stimulated for 5 min. Cells were lysed by sonication in buffer with protease and phosphatase inhibitors, as described previously(24) . Two microliters of cell lysate were added to the gel shift reaction. The probe (0.1 ng) CRE from the human egr-1 promoter between nucleotides -57 and -76 was used. A complementary single-stranded oligonucleotide probe to CRE was synthesized with an Applied Biosystems synthesizer. The probe was prepared as described previously (12) and incubated with 2 µl of extract from unstimulated cells or IL-3- or GM-CSF-stimulated cells. One microgram of poly(di-dc) was added per reaction.

Western and Immunoblotting

TF-1 cells (4 10) were factor- and serum-starved for 24 h prior to stimulation. Cells in RPMI and BSA 0.5% were then stimulated for 10 min with diluent (PBS + BSA, 0.5%), rhGM-CSF (1 nM), rhIL-3 (1 nM), or TPA (50 ng/ml). Cells were lysed in boiling SDS buffer and boiled again for 5 min, as described previously(16) . The total cell lysate after centrifugation was loaded on a 10% SDS-polyacrylamide gel and blotted to nitrocellulose (Hybond-ECL). The blot was probed with antibody against phosphorylated CREB (0.14 µg/ml). For time course experiments, 4 10 cells were washed three times with PBS and factor- and serum-starved for 24 h prior to stimulation. Cells were stimulated with rhIL-3 (1 nM) or rhGM-CSF (1 nM) for 0, 2, 5, 10, or 15 min or with TPA (50 ng/ml) for 10 min. Cells were lysed with boiling SDS and boiled again for 5 min(16) . Total cell lysate was loaded onto a 10% SDS-PAGE and blotted to nitrocellulose in duplicate. The blot was probed with rat polyclonal anti-CREB antibody (1:7500) or anti-phosphorylated CREB antibody (0.14 µg/ml).


RESULTS AND DISCUSSION

IL-3 and GM-CSF Activation of Signaling Pathways Induce Phosphorylation of CREB on Serine 133 in TF-1 Cells

GM-CSF and IL-3 stimulation of TF-1 cells leads to rapid and transient induction of egr-1. In transfection assays, deletion of the CRE between nucleotides -57 and 76 in the context of the surrounding 116 nucleotides results in the abolition of GM-CSF- or IL-3-induced egr-1 expression(12) . The CRE is therefore required for transcriptional activation of egr-1. CREB binds the CRE of the egr-1 promoter in TF-1 nuclear extracts from both unstimulated and GM-CSF- or IL-3-stimulated cells.

CREB has been demonstrated to be phosphorylated on serine 133 in response to other growth factors. We performed electromobility shift assays with antibody directed against a CREB peptide phosphorylated on serine 133, using extracts from cells treated with GM-CSF or IL-3 for 10 min. In electromobility shift assays using anti-CREB antibody, an additional ``super'' shifted band was observed in nuclear extracts prepared from both unstimulated and GM-CSF-stimulated TF-1 cells (see Fig. 1A). In the presence of antibody directed against CREB phosphorylated on serine 133, a supershift complex was observed only with GM-CSF-stimulated nuclear extracts and not with unstimulated extracts (Fig. 1A). Similar results were seen using extracts from TF-1 cells stimulated with IL-3, except that a weaker supershift was observed with anti-phosphorylated CREB antibody (Fig. 1B). We demonstrated previously that CREB constitutively binds the CRE in the egr-1 promoter (12). CREB associates with the CRE from a number of heterologous promoters. Our data confirm these findings (Fig. 1, A and B, Complex III) and suggest that GM-CSF or IL-3 induces phosphorylation of CREB on serine 133 within 10 min of stimulation of cells.


Figure 1: Electromobility shift assays with CRE probe and TF-1 cells stimulated with GM-CSF or IL-3. A labeled oligonucleotide probe (0.1 ng) containing the CRE and sequences between nucleotides -57 to -76 of the egr-1 promoter was incubated with extracts from TF-1 cells stimulated for 10 min with diluent control (.02% BSA and PBS) (A and B), 1 nM rhGM-CSF (A), or 1 nM rhIL-3 (B). Total cell lysates from 5 10 cells/sample were prepared by a sonication method. Extracts were incubated with no competitor (lanes 1 and 6), 500-fold excess specific cold competitor (lanes 2 and 7), no antibody (lanes 3 and 8), anti-CREB antibody (lanes 4 and 9), and anti-phosphorylated CREB (lanes 5 and 10). Complex I represents a supershift complex with anti-CREB antibody, Complex II is with anti-phosphorylated CREB antibody, and Complex III is a specific complex. Results were confirmed in three independent experiments.



We performed Western analysis with TF-1 cell extracts at 10 min post-stimulation with GM-CSF, IL-3, or TPA. A 43-kDa protein was seen with anti-phosphorylated CREB antibody in response to GM-CSF and IL-3 (see Fig. 2), and the strongest signal was observed with TPA. TPA has been previously demonstrated to activate CREB by a protein kinase C-dependent pathway(15) . We found that the signal in response to IL-3 stimulation was weaker than that to GM-CSF or TPA stimulation. These results are consistent with the electromobility shift assay in which IL-3-stimulated nuclear extracts demonstrated a weaker supershift complex compared with extracts from GM-CSF-stimulated cells (Fig. 1B). A lower molecular weight protein also appears to be phosphorylated in response to GM-CSF, IL-3, or TPA. This 38-kDa band was observed in several experiments and could represent a short half-life of CREB during IL-3 stimulation or cross-reactivity with another member of the CREB/ATF family of transcription factors. The antibody directed against a phosphorylated CREB peptide also recognizes ATF-1.()This observation has been previously described by Ginty et al.(24) and Hummler et al.(25) . These data suggest that several independent pathways (i.e. protein kinase A-dependent or -independent and PKC-dependent pathways) could potentially activate CREB through phosphorylation on serine 133.


Figure 2: Western blot with phosphorylation of CREB on serine 133 induced by GM-CSF, IL-3, or TPA in TF-1 cells. TF-1 cells (4 10 cells/sample) were starved for 24 h and stimulated with GM-CSF or IL-3 (1 nM) or stimulated with TPA (50 ng/ml) for 10 min. Total cell lysates were prepared by the boiling SDS method, separated on a 10% SDS-PAGE, transferred to nitrocellulose membranes, and immunoblotted with anti-phosphorylated CREB antibody. The arrow represents the 43-kDa phosphorylated CREB. Experiments were repeated and confirmed three times.



To examine the kinetics of CREB phosphorylation, we performed a Western analysis at different time points following GM-CSF or IL-3 stimulation of TF-1 cells. Although the levels of CREB are constant (see Fig. 3A), phosphorylation of CREB is seen at 2 min following GM-CSF but not IL-3 stimulation. In contrast, CREB phosphorylation occurs 5-10 min following IL-3 stimulation. The CREB protein may be less stable in the presence of IL-3 compared with GM-CSF. The subtle difference in the time course of CREB phosphorylation suggests that GM-CSF and IL-3 signaling pathways possibly exhibit different kinetic properties which may contribute to the specificity of their biological activities. Other proteins with molecular masses of 70, 65, and 35 kDa that appear in Western blots (Fig. 3, A and B) most likely represent other cross-reacting proteins or members of the CREB/ATF family of transcription factors(26, 27, 28) .


Figure 3: Time course of CREB phosphorylation in TF-1 cells stimulated with GM-CSF (A) or IL-3 (B). TF-1 cells (4 10 cells/sample) were starved and stimulated with GM-CSF (A) or IL-3 (B) for 0, 2, 5, 10, or 15 min or with TPA for 10 min. Cells were harvested and lysed with boiling SDS, and lysates were separated by 10% SDS-PAGE, transferred to nitrocellulose membranes, and immunoblotted with anti-CREB antibody (left) or anti-phosphorylated CREB antibody (right). The arrow represents the 43-kDa CREB or phosphorylated CREB. Results were confirmed in three separate experiments.



In myeloid cells, other examples of differences in the kinetics of protein phosphorylation following GM-CSF or IL-3 stimulation have been described. Phosphorylation of the STAT protein, pp93, occurs within minutes in response to GM-CSF stimulation, whereas phosphorylation in response to IL-3 was slightly delayed(29) . In addition, GM-CSF-induced activation of at least one other protein of similar mobility that was recognized by the phosphorylated STAT91 antibody was not detected following IL-3 stimulation(29) . Our data are consistent with these findings and demonstrate that phosphorylation of CREB, such as with pp93, may represent a delayed response downstream of the IL-3 signaling pathway. An alternative explanation is that there is delayed assembly of a functional receptor complex in target cells stimulated with IL-3 in comparison with cells stimulated with GM-CSF(30) .

Phosphorylation of CREB on Serine 133 Is Required for Transcriptional Activation of egr-1 in Response to GM-CSF but Not IL-3

We examined whether rapid phosphorylation of CREB in TF-1 cells was necessary for transcriptional activation by GM-CSF or IL-3 by performing co-transfection assays with the -116cat construct and wild-type or mutant CREB (serine 133 mutated to alanine). When wild-type CREB or vector is transfected with the -116cat construct, 3-4-fold stimulation was observed (p < 0.05; see Fig. 4). The -fold induction represents the percent acetylation of chloramphenicol acetyltransferase using extracts from GM-CSF- or IL-3-stimulated cells divided by diluent control. Since the mutation of serine 133 to alanine abrogates egr-1 induction by GM-CSF, we conclude that CREB phosphorylation on serine 133 plays a significant role in GM-CSF-induced egr-1 expression. The -fold stimulation with wild-type CREB was slightly less than vector in every experiment, which may be due to a squelching effect from the presence of both endogenous and exogenous CREB, an observation that has been made by others(31) . When the mutant CREB was co-transfected with -116cat, there was a statistically significant decrease in the -fold induction by GM-CSF (p < 0.05; see Fig. 4), but not IL-3 (p = 0.226; see Fig. 4). These data suggest that phosphorylation of CREB on serine 133 contributes to IL-3-induced transcriptional activation of egr-1 but is not critical. All experiments (n = 3-5) were performed in triplicate, and the CMV -galactosidase plasmid was transfected into TF-1 cells as the internal control. Although not statistically significant, the percent acetylation of diluent control from TF-1 cells cultured in IL-3 was 2-3-fold of the percent acetylation of diluent control in GM-CSF-cultured cells (data not shown).


Figure 4: Phosphorylation of serine 133 on CREB is required for GM-CSF- but not IL-3-induced transcriptional activation of egr-1. TF-1 cells (10) were factor- and serum-starved for 24 h and placed in serum-free media. Twenty micrograms of reporter construct -116cat and 22 µg of wild-type or mutant CREB were electroporated into TF-1 cells and stimulated with diluent control (.02% BSA in PBS), GM-CSF (1 nM), or IL-3 (1 nM) for 4 h. Three micrograms of CMV -galactosidase plasmid was co-transfected as the internal control for transfection efficiency. Chloramphenicol acetyltransferase or -galactosidase assays were performed. -Fold induction by GM-CSF (A) or IL-3 (B) represents percent acetylation of constructs stimulated with GM-CSF or IL-3, divided by percent acetylation of constructs stimulated with diluent control. p values were determined by paired t test analysis. Data represent three to five experiments, with each transfection performed in triplicate.



These results demonstrate that phosphorylation of CREB on serine 133 substantially contributes to the transcriptional activation of egr-1 by GM-CSF, but not by IL-3, supporting the hypothesis that phosphorylation events of previously existing transcription factors such as CREB mediate signaling pathways of GM-CSF and IL-3 in myeloid cells. Although CREB constitutively binds the CRE in the egr-1 promoter, phosphorylation of serine 133 on CREB most likely results in a conformational change leading to its association with the transcriptional machinery and induction of egr-1. As other phosphorylation sites may be modified in response to IL-3, this would explain the difference between GM-CSF and IL-3 in their requirements for CREB phosphorylation on serine 133. One possibility may be that GM-CSF and IL-3 might quantitatively differ in their abilities to phosphorylate this site. Alternatively, the CREB protein may be less stable in IL-3-cultured cells. Furthermore, the stoichiometries of CREB may be different in cells grown in IL-3 than those in GM-CSF. This would be consistent with the weaker supershift band with anti-phosphorylated CREB antibody seen in IL-3-stimulated cells (Fig. 1B). Similarly, in the Western analysis (Fig. 2), the 43-kDa band representing phosphorylated CREB is weaker following IL-3 stimulation than after GM-CSF stimulation.

GM-CSF- and IL-3-activated pathways may also diverge in the phosphorylation of specific downstream kinases that can then phosphorylate CREB at different sites. Previous studies have demonstrated that CA/calmodulin-dependent protein kinase, type 2 stoichiometrically phosphorylates CREB on serine 133 in addition to a second site in CREB(32) . More recently, differential activation of CREB by Ca/calmodulin-dependent protein kinases types II and IV has been shown to result in the phosphorylation of a site that negatively regulates CREB activity(33) . A similar difference in the activation of CREB may result from GM-CSF and IL-3 stimulation of myeloid cells. Alternately, other proteins binding to upstream egr-1 promoter elements may be required in addition to CREB to maximally activate egr-1 induction in response to IL-3.

In addition to neuropeptides, peptide growth factors such as fibroblast growth factor that activate receptor tyrosine kinases also mediate activation of CREB by a Ras-dependent pathway(16, 34) . Ginty et al.(16) demonstrated that NGF stimulation of PC12 cells resulted in phosphorylation of CREB on serine 133 by a novel CREB kinase. There is further evidence that kinases other than protein kinase A are capable of activating CREB. The serine/threonine kinase, p90, was shown to phosphorylate CREB on serine 133 in melanocytes stimulated with various growth factors(35) . Although NGF and other growth factors have been recently found to mediate phosphorylation of CREB on serine 133 by a protein kinase A-independent pathway, the kinases responsible for CREB phosphorylation by GM-CSF or IL-3 have not been identified. It is possible that GM-CSF or IL-3 may activate CREB through kinases such as p90 or a novel CREB kinase.

The unique role of CREB phosphorylation in transcriptional activation of target genes by GM-CSF and IL-3 adds a new perspective to the overlapping but distinct biological functions of these two cytokines. There may be subtle differences in the interactions between the GM-CSF and the IL-3 signaling pathways, since both ligands interact with a common receptor subunit. The specificity of pathways might be initially triggered by the unique GM-CSF or IL-3 subunits that bind ligand. Consequently, the kinases or phosphatases which associate with the subunits may be responsible for the regulation of CREB activation, thus conferring specificity in the induction of other target genes containing a critical cAMP response element. The present studies suggest that GM-CSF and IL-3 modify transcription factors by potentially distinct mechanisms, indicating that identification of kinases responsible for CREB activation will be critical in understanding signaling pathways regulating myeloid cell proliferation and differentiation.


FOOTNOTES

*
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked ``advertisement'' in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

§
Postdoctoral fellow supported by National Institutes of Health Training Grant 5TC CA09056 from the National Cancer Institute.

Recipient of Clinical Investigation Award CA59463-02 from the National Cancer Institute, a Leukemia Society of America Special Fellowship, a CONCERN Foundation Award, and a STOP CANCER Career Development Award. To whom correspondence should be addressed. Tel.: 310-206-5626; Fax: 310-206-8089.

The abbreviations used are: GM-CSF, granulocyte-macrophage colony-stimulating factor; IL-3, interleukin 3; rh, recombinant human; TPA, tetradecanoylphorbol acid; NGF, nerve growth factor; CRE, cAMP response element; CREB, cAMP response element-binding protein; CMV, cytomegalovirus; BSA, bovine serum albumin; PBS, phosphate-buffered saline; PAGE, polyacrylamide gel electrophoresis; ATF, activating transcription factor.

D. Ginty, personal communication.


ACKNOWLEDGEMENTS

We thank Gayle Baldwin, Judith Gasson, and Karen Yates for helpful suggestions and critical reading of the manuscript; Anne O'Shea-Greenfield for technical assistance and Wendy Aft for preparation of the manuscript. We appreciate the generosity of David Ginty, who provided the anti-phosphorylated CREB antibody and offered many helpful suggestions. We are grateful to Larry Souza (Amgen), who provided rhGM-CSF, and Steve Gillis (Immunex), who provided IL-3.


REFERENCES
  1. Gasson, J. C. (1991) Blood77, 1131-1145 [Medline] [Order article via Infotrieve]
  2. Sakamoto, K. M., and Gasson, J. C. (1991) Int. J. Cell Cloning9, 531-541 [Abstract]
  3. Sakamoto, K. M., Mignacca, R. C., and Gasson, J. C. (1994) Receptor & Channels2, 175-181
  4. Miyajima, A., Mui, A. L.-F., Ogorochi, T., and Sakamaki, K. (1993) Blood82, 1960-1974 [Medline] [Order article via Infotrieve]
  5. Bazan, J. F. (1990) Proc. Natl. Acad. Sci. U. S. A.87, 6934-6938 [Abstract]
  6. Cosman, D., Lyman, S. D., Idzerda, R. L., Beckmann, M. P., Park, L. S., Goodwin, R. G., and March, C. J. (1990) Trends Biochem. Sci.15, 265-270 [CrossRef][Medline] [Order article via Infotrieve]
  7. Carroll, M. P., Clark-Lewis, I., Rapp, U. R., and May, W. S. (1990) J. Biol. Chem.265, 19812-19817 [Abstract/Free Full Text]
  8. Duronio, V., Clark-Lewis, I., Federsppiel, B., Wieler, J. S., and Schrader, J. W. (1992) J. Biol. Chem.267, 21856-21863 [Abstract/Free Full Text]
  9. Hanazono, Y., Chiba, S., Sasaki, K., Mano, H., Miyajima, A., Arai, K., Yazaki, Y., and Hirai, H. (1993) EMBO J.12, 1641-1646 [Abstract]
  10. Larner, A. C., David, M., Feldman, G. M., Igarashi, K.-I., Hackett, R. H., Webb, D. S. A., Sweitzer, S. M., Petricoin, E. F., III, and Finbloom, D. S. (1993) Science261, 1730-1733 [Medline] [Order article via Infotrieve]
  11. Mui, A. L.-F., Wakao, H., O'Farrell, A.-M., Harada, N., and Miyajima, A. (1995) EMBO J.14, 1166-1185 [Abstract]
  12. Sakamoto, K. M., Fraser, J. K., Lee, H.-J. J., Lehman, E., and Gasson, J. C. (1994) Mol. Cell. Biol.14, 5975-5985 [Abstract]
  13. Cao, X., Mahendran, R., Guy, G. R., and Tan, Y. H. (1993) J. Biol. Chem.268, 16949-16957 [Abstract/Free Full Text]
  14. Christy, B., and Nathans, D. (1989) Proc. Natl. Acad. Sci. U. S. A.86, 8737-8741 [Abstract]
  15. Herschman, H. R. (1991) Annu. Rev. Biochem.60, 281-319 [CrossRef][Medline] [Order article via Infotrieve]
  16. Ginty, D. D., Bonni, A., and Greenberg, M. E. (1994) Cell77, 713-725 [Medline] [Order article via Infotrieve]
  17. Nguyen, H. Q., Hoffman-Liebermann, B., and Liebermann, D. A. (1993) Cell72, 197-209 [Medline] [Order article via Infotrieve]
  18. Liebermann, D. A., and Hoffman-Liebermann, B. (1994) Curr. Opin. Hematol.1, 24-32 [Medline] [Order article via Infotrieve]
  19. Coleman, D. L., Liu, J., and Bartiss, A. H. (1989) J. Immunol.143, 4134-4140 [Abstract/Free Full Text]
  20. Young, M. R. I., Lozano, Y., Djordjevic, A., Devata, S., Matthews, J., Young, M. E., and Wright, M. A. (1993) Int. J. Cancer53, 667-671 [Medline] [Order article via Infotrieve]
  21. Lalli, E., and Sassone-Corsi, P. (1994) J. Biol. Chem.269, 17359-17362 [Free Full Text]
  22. Gonzalez, G. A., and Montminy, M. R. (1989) Cell59, 675-680 [Medline] [Order article via Infotrieve]
  23. Sakamoto, K. M., Nimer, S. D., Rosenblatt, J. D., and Gasson, J. C. (1992) Oncogene7, 2125-2130 [Medline] [Order article via Infotrieve]
  24. Ginty, D. D., Kornhauser, J. M., Thompson, M. A., Bading, H., Mayo, K. E., Takahashi, J. S., and Greenberg, M. E. (1993) Science260, 238-241 [Medline] [Order article via Infotrieve]
  25. Hummler, E., Cole, T. J., Blendy, J. A., Ganss, R., Aguzzi, A., Schmid, W., Beermann, F., and Shutz, G. (1994) Proc. Natl. Acad. Sci. U. S. A.91, 5647-5651 [Abstract]
  26. Borrelli, E., Montmayeur, J.-P., Foulkes, N. S., and Sassone-Corsi, P. (1992) Crit. Rev. Oncogenesis3, 321-338 [Medline] [Order article via Infotrieve]
  27. Lee, K. A. W., and Masson, N. (1993) Biochim. Biophys. Acta1174, 221-233 [Medline] [Order article via Infotrieve]
  28. Meyer, T. E., and Habener, J. F. (1993) Endocr. Rev.14, 269-290 [Medline] [Order article via Infotrieve]
  29. Frank, D., Salgia, R., Griffin, J. D., and Greenberg, M. (1994) Blood84, 224a
  30. Ronco, L. V., Silverman, S. L., Wong, S. G., Slamon, D. J., Park, L. S., and Gasson, J. C. (1994) J. Biol. Chem.269, 277-283 [Abstract/Free Full Text]
  31. Quinn, P. G. (1993) J. Biol. Chem.268, 16999-17009 [Abstract/Free Full Text]
  32. Dash, P. K., Karl, K. A., Colicos, M. A., Prywes, R., and Kandel, E. R. (1991) Proc. Natl. Acad. Sci. U. S. A.88, 5061-5065 [Abstract]
  33. Sun, P., Enslen, H., Myung, P. S., and Maurer, R. A. (1994) Genes & Dev.8, 2527-2539
  34. Ginty, D. D., Glowacka, D., DeFranco, C., and Wagner, J. A. (1991) J. Biol. Chem.266, 15325-15333 [Abstract/Free Full Text]
  35. Bohm, M., Moellmann, G., Cheng, E., Alvarez-Franco, M., Wagner, S., Sassone-Corsi, P., and Halaban, R. (1995) Cell Growth & Differ.6, 291-302

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