Altered surface expression and increased turnover of the
6ß4 integrin in an undifferentiated carcinoma
Colette M. Witkowski2,
G.Tim Bowden,
Ray B. Nagle1 and
Anne E. Cress3
Department of Radiation Oncology and
1 Department of Pathology, The University of Arizona Cancer Center, 1515 North Campbell Avenue, Tucson, AZ 85724-5024, USA
2 Present address: Biomedical Sciences Department, Southwest Missouri State University, 901 South National Avenue, Springfield, MO 65804-0094, USA
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Abstract
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The integrin
6ß4, predominantly expressed on tissues of epithelial origin, is known to be variably expressed on carcinomas. The biochemical changes resulting in altered expression during tumor progression are unknown. We have analyzed the expression of
6ß4 in a multi-step mouse model of skin carcinogenesis representing normal keratinocyte, benign papilloma and malignant undifferentiated carcinoma. All cell lines expressed the
6 integrin exclusively as the
6ß4 integrin heterodimer. Analysis of this integrin by flow cytometry and immunoprecipitation of surface labeled proteins revealed that the undifferentiated carcinoma cells have an ~75% reduction in surface expression of the integrin as compared with the keratinocyte and papilloma cell lines. The
6ß4 integrin which remains expressed on the carcinoma cells is diffusely distributed in the membrane and has an ~2.5-fold increased biological turnover as compared with normal keratinocytes. The decreased biological half-life and the loss of polarized expression of
6ß4 on the carcinoma cells suggests an altered functional role for the
6ß4 integrin on carcinoma cells during tumor progression. These factors may contribute to the known supression of hemidesmosome structures and the increased migration phenotype associated with some epithelial carcinomas.
Abbreviations: DPBS, Dulbecco's phosphate-buffered saline; ECM, extracellular matrix.
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Introduction
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The
6ß4 integrin is primarily expressed on epithelial tissues (14) and a subset of endothelial cells. The
6ß4 integrin plays a pivotal role in assembly of the hemidesmosome, or stable anchoring contact (58). The hemidesmosome is a complex structure comprised of several proteins that collectively assemble providing an attachment site for the intermediate filament network in epithelial cells (9). The unique cytoplasmic domain of the ß4 subunit (~100 kDa) and tissue-specific splice variants of ß4 suggest a specialized function(s) (1012). Recent studies suggest that the
6ß4 integrin is able to transduce signals from the extracellular matrix to the interior of the cell, critically modulating the organization of the cytoskeleton, cell proliferation, apoptosis and differentiation (13). Other studies indicate that the
6ß4 integrin can function in migration through its ability to promote the formation and stabilization of actin-containing motility structures (14).
Epithelial malignancies such as invasive human prostate, bladder and basal cell cancers have lost expression of the
6ß4 integrin (1518) while in other malignancies, such as human colon cancer, expression persists and in human breast cancer expression is variable (1922). Recently we have shown that alteration in cellular adhesion events in human prostate cancer are manifested by alterations in both the extracellular matrix (ECM) and the integrins involved in cellECM attachment. In contrast to normal prostate glands, neoplastic glands do not contain fibronectin, collagen VII or the
2 and ß3 chains of laminin 5 (23,24). Accompanying this loss of ECM molecules is loss of expression of several integrins (i.e.
25,
vß3 and
6ß4) and the hemidesmosome structures (16,25). The loss of both hemidesmosome-associated structures and basal cell differentiation has been associated with early stromal invasion in prostate cancer (26). The integrins which are expressed in the neoplastic glands include the other partner for
6,
6ß1, and another laminin receptor, the
3ß1 integrin (16).
In this study we have further investigated the fate of the
6ß4 integrin during tumor progression in an established in vitro model of multi-step mouse skin carcinogenesis previously described in detail (2729). This model was used to determine if an alteration in
6ß4 expression accompanies malignant progression and whether this alteration is associated with benign or invasive cancer. This model represents the three main stages of carcinogenesis; a normal keratinocyte, benign papilloma and carcinoma (30). The model consists of a normal keratinocyte cell line (291) isolated from a Balb/c Ras mouse, a benign papilloma cell line (291.09) and an undifferentiated squamous cell carcinoma (291.03) cell line. The uniqueness of this model is that the cell lines result from a common lineage. Both tumor cell lines were derived from the established keratinocyte cell line. In addition, all cell lines express the
6 integrin exclusively as the
6ß4 heterodimer, whereas in human carcinomas both the
6ß4 and the
6ß1 heterodimers co-exist (16,31,32). This model allowed investigation of the fate of the
6ß4 integrin exclusively during multi-step tumor progression.
The ability of the
6ß4 integrin to polarize/cluster on the normal keratinocyte, the papilloma cell line and the carcinoma cell line was investigated using indirect immunofluorescence microscopy. The cell lines were routinely maintained in low calcium (0.020.04 mM) Eagle's medium, 5% fetal bovine serum, 5% conditioned medium from freshly isolated Balb/C newborn dermal fibroblasts and 10 ng/ml epidermal growth factor (27). The cells were grown on coverslips, washed with Dulbecco's phosphate-buffered saline (DPBS) and permeabilized with 0.1% Saponin. Antibody incubations were carried out at room temperature using a rat monoclonal antibody to the
6 subunit (GoH3), generously provided by Dr A. Sonnenberg (33) or purchased from Accurate Chemical and Scientific Corp. (Westbury, NY), and a rat monoclonal antibody to the mouse ß4 subunit (346-11A), generously provided by Dr S.J.Kennel (34). Secondary antibodies used were either FITC-conjugated goat anti-rat (Tago) or FITC-conjugated goat anti-rabbit (Cappel). Cells were fixed with 3% formaldehyde and mounted with 90% glycerol containing the quenching agent p-phenylenediamine.
Indirect immunofluorescence staining of the three cell lines with antibodies to
6 and ß4 under conditions of low (0.020.04 mM) and high (1.4 mM) calcium revealed a dramatic redistribution of the
6 and ß4 subunits. Figure 1
shows staining with antibodies to
6 and ß4 under conditions of high calcium. The keratinocyte and the papilloma lines demonstrated a streaked pattern that indicated polarization and clustering of this integrin. In contrast, the carcinoma cells could not be induced to polarize the
6ß4 integrin and displayed diffuse and peripheral staining of the subunits. Under conditions of low calcium, the pattern of
6 and ß4 staining on the three cell lines was diffuse and generally non-polarized (data not shown), similar to staining on the carcinoma cells in Figure 1
.
The
6ß4 integrin is polarized on the basal lateral membrane in normal epithelial cells (7,35). Loss of this compartmentalized expression is seen on carcinomas in situ and is a consistent alteration involving
6ß4 integrin on carcinomas in general (36,37). We observed this same phenomenon on the carcinoma cells in this model. The
6ß4 integrin on the carcinoma cells does not distribute or polarize as does the integrin on the keratinocyte and papilloma cells (Figure 1
). The mechanism(s) resulting in loss of polarization is unknown but could include alteration of the ß4 integrin, loss of cytoplasmic hemidesmosome-associated components or loss of laminin 5. The carcinoma cells in this model have been previously shown not to express at least two of the known proteins that associate with the hemidesmosome, the cytokeratin pair 5/14 (29). Loss of protein interactions with the cytoplasmic portion of ß4, different splice variants of ß4 or proteolytic processing of the ß4 integrin in the carcinoma cells may be involved in the loss of polarized expression of
6ß4.
Surface expression of
6ß4 on the carcinoma cells compared with the keratinocyte and papilloma cell lines was analyzed by flow cytometry. The cell lines were analyzed using antibodies to
6,
5ß1 and mouse ß4. The results are presented in Figure 2a
. Cells were trypsinized and washed in Hank's balanced salt solution containing 0.5 mg/ml soybean trypsin inhibitor (Sigma). Cell numbers were adjusted to 1.5x106 cells/ml. Antibody reactions were incubated on ice for 30 min. Cells were analyzed with a Becton/Dickinson FACStar Plus with ~10 000 events analyzed for each cell line/antibody combination. The keratinocyte and papilloma cells expressed similar amounts of
6 and ß4 on their surfaces. In contrast, the carcinoma cells showed decreased surface expression of both
6 and ß4 compared with the other two cell lines.
The shifts in peak fluorescence were calculated (secondary-only histogram mean subtracted from the antibody-produced histogram) and are presented in Figure 2b
. The mean peak of fluorescence generated by the
6 and ß4 antibodyantigen complexes were of lesser intensity on the carcinoma cells. Cross-calibration between log and linear scales indicated that 75 channels are equal to a doubling in fluorescence intensity. Using this parameter, surface expression of
6 and ß4 on the carcinoma cells was decreased to ~24% of the expression level on the keratinocyte and papilloma cell lines. All cell lines expressed the
5ß1 integrin at similar levels (Figure 2a and b
).
Both decreased and increased expression of the
6ß4 integrin have been observed on epithelial tumors in association with malignant conversion and progression (1518,22,31,32,3640). The decrease in the
6ß4 integrin observed on the carcinoma cells is not a general decrease in integrin surface expression overall (Figure 2a
), but specific for this integrin. Further, the decrease in surface
6ß4 on the carcinoma cells was not due to an altered
6 integrin subunit composition. A switch in or inappropriate expression of the ß1 integrins has been noted on cancer cells and, specifically,
6ß1 has been implicated in invasion and migration (4145). Since the
6 subunit forms a heterodimer with both the ß4 and ß1 subunits, it was formally possible that these carcinoma cells were expressing
6ß1 as well as
6ß4 on the cell surface. Western blot analysis (data not shown) ruled out an alternative
6ß1 subunit composition. The carcinoma cells retained the preferential association of the
6 subunit with the ß4 subunit.
To further evaluate the decreased surface expression on the carcinoma cells, surface proteins were labeled with biotin and immunoprecipitated with antibodies to the
6 and ß4 subunits. Cells were trypsinized and washed in DPBS containing soybean trypsin inhibitor. The surface-exposed proteins were labeled with NHS-LC biotin (Pierce, Rockford, IL) (46). Cell concentrations were adjusted to 5x106 cells/ml and equal cell numbers were immunoprecipitated. Cells were lysed in 50 mM TrisHCl, 150 mM NaCl, 10 mM EDTA, 1% NP-40, 1 mM phenylmethylsulfonyl fluoride, 17 mg/ml Calpain I inhibitor, 0.3 mM aprotinin and 1 mM leupeptin. Insoluble proteins were removed by centrifugation at 12 000 r.p.m. for 15 min. Supernatants were incubated with integrin antibodies for 2 h at 4°C with constant mixing. Antigenantibody complexes were precipitated with protein GSepharose or protein ASepharose (Pharmacia) with constant mixing at 4°C for 1 h and washed in 50 mM TrisHCl, pH 7.5, 0.5 M NaCl, 1 mM MgCl2, 0.1% Tween-20. Washed Sepharose beads were resuspended in SDS sample buffer (8% SDS, 0.2 M TrisHCl, pH 7.0, 12% sucrose), boiled and analyzed by polyacrylamide electrophoresis. The results are shown in Figure 3
. The
6 specific band is indicated at 143 kDa. The two bands above the
6 band are the ß4 specific bands (47). These results are consistent with the FACS data (Figure 2
) and confirm a decreased surface expression of this integrin heterodimer on the carcinoma cells.
There appears to be cleavage or processing of ß4 in all three lines (Figure 3
). Since the ß4 integrin was surface biotinylated, the processed forms of ß4 occur on the cell surface. Both the 200 and 185 kDa processed forms which have been previously reported (47,48) are present. Other immunoprecipitation experiments with an
5ß1 specific antibody demonstrate that although all the cell lines express the ß1 subunit, no ß1 co-precipitated with the
6 subunit from either the keratinocytes or carcinoma cells (data not shown).
The decreased expression of the surface labeled ß4 integrin on the carcinoma cells was investigated by analyzing the biological turnover rate of
6ß4. Pulsechase type experiments were used to assess the relative protein turnover rates of
6 and ß4 in the keratinocyte and carcinoma lines. Cells were grown to ~70% confluency and washed in medium without serum and methionine for 10 min. The methionine-deficient medium was exchanged for fresh medium containing 100 µCi/ml [35S]methionine (New England Nuclear Express Labeling Mix) for 3 h (pulse), washed with complete medium containing 10 mM methionine and incubated (chased) for 0, 8, 12, 18, 21 and 24 h. Whole cell lysates were subjected to immunoprecipitation with the antibody to
6 (1.6 µg GoH3/100 µg lysate). Samples were electrophoresed and gels were fixed, dried and exposed directly to Kodak XAR-5 film for 5 days at room temperature or exposed to a phosphorimaging screen (Molecular Dynamics) for 2 days and scanned on a Molecular Dynamics phosphorimager. The band intensity in pixels was analyzed using ImageQuant software (Molecular Dynamics). The pixel values are proportional to the strength of the radioactive signal. The intensity (integrated volume in arbitrary units of density) of each band was estimated, averaged (duplicate samples) and the data are graphed as percent control using the keratinocyte 0 chase for
6 (9.7x104) and ß4 (2.8x104) as the control (100%). Both the keratinocyte and carcinoma cells showed the same level of [35S]methionine incorporation into total protein at each time point as determined by trichloroacetic acid precipitation (data not shown). The incorporation of [35S]methionine into total protein was assayed by trichloroacetic acid precipitation of the cell lysate. The biological half-life, the time at which the [35S]methionine activity in the protein bands was decreased by 50%, was determined from these data using a best fit analysis.
The turnover rates of
6 and ß4 in the normal keratinocyte cells are very similar (Figure 4
). The abundance of these two subunits remains steady until 24 h, at which time
6 is decreased to 68% and ß4 to 61% of control. The estimated biological half-lives of the
6 and ß4 subunits are 42 and 45 h, respectively.
The rates of turnover of the
6 and ß4 proteins in the carcinoma cells are also similar to one another. The density values for
6 (9.8x104) and ß4 (2.7x104) at 0 h are similar to the keratinocyte values. The
6 and ß4 subunits immunoprecipitated from the carcinoma cells show an immediate decrease. By 8 h,
6 and ß4 levels are 67 and 78% of control, respectively. Levels of these two proteins show a steady decrease over the 24 h time course. By 24 h
6 and ß4 have decreased to 30 and 33% of control, respectively. The biological half-lives of the
6 and ß4 subunits on the carcinoma were estimated at 14 and 18 h, respectively.
These experiments indicate significantly different relative rates of protein turnover in the keratinocyte and carcinoma cells. The carcinoma cells have an ~2.5-fold increased rate of turnover of the
6 and ß4 subunits. The altered turnover rate suggests that post-translational mechanisms are potentially responsible for the decrease in
6ß4 integrin expressed on the surface of these carcinoma cells.
The results presented here suggest that tumor progression in this model system is accompanied by increased turnover of the
6ß4 integrin and loss of its polarization. These alterations may contribute to the apparent change in the function of the
6ß4 integrin from participation in the hemidesmosome to participation in cell migration events. The cell migration events may play a role in the invasive phenotype of the carcinoma cells since this change of function of the
6ß4 integrin was not observed in non-invasive benign papilloma producing cells.
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Acknowledgments
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The authors are grateful to Dr A.Sonnenberg (University of Amsterdam, The Netherlands) for providing the
6 antibody GoH3, Dr S.J.Kennel (Oak Ridge National Laboratory, TN) for providing the antibody 346.11A to mouse ß4 and to Dr Molly Kulesz-Martin for providing the mouse keratinocyte cell lines and for reading earlier drafts of this manuscript. This work was supported in part by grants ADCRC 1-023, Cancer Center Core Grant CA 23074, a Program Project Grant CA56666, CA40584 and the Schick Memorial Fund.
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Notes
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3 To whom correspondence should be addressed Email: cress{at}azcc.arizona.edu

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References
|
---|
-
Hynes,R.O. (1992) Integrins: versatility, modulation and signaling in cell adhesion. Cell, 69, 1125.[ISI][Medline]
-
Kajiji,S., Tamura,R.N. and Quaranta,V. (1989) A novel integrin (alpha E beta 4) from human epithelial cells suggests a fourth family of integrin adhesion receptors. EMBO J., 8, 673680.[Abstract]
-
Sonnenberg,A., Linders,C.J., Daams,J.H. and Kennel,S.J. (1990) The alpha 6 beta 1 (VLA-6) and alpha 6 beta 4 protein complexes: tissue distribution and biochemical properties. J. Cell Sci., 96, 207217.[Abstract]
-
Kennel,S.J., Godfrey,V., Ch'ang,L.Y., Lankford,T.K., Foote,L.J. and Makkinje,A. (1992) The beta 4 subunit of the integrin family is displayed on a restricted subset of endothelium in mice. J. Cell Sci., 101, 145150.[Abstract]
-
Stepp,M.A., Spurr-Michaud,S., Tisdale,A., Elwell,J. and Gipson,I.K. (1990) Alpha 6 beta 4 integrin heterodimer is a component of hemidesmosomes. Proc. Natl Acad. Sci. USA, 87, 89708974.[Abstract]
-
Jones,J.C., Kurpakus,M.A., Cooper,H.M. and Quaranta,V. (1991) A function for the integrin alpha 6 beta 4 in the hemidesmosome. Cell Regul., 2, 427438.[ISI][Medline]
-
Sonnenberg,A., Calafat,J., Janssen,H., Daams,H., van der Raaij-Helmer,L.M., Falcioni,R., Kennel,S.J., Aplin,J.D., Baker,J., Loizidou,M. et al. (1991) Integrin alpha 6/beta 4 complex is located in hemidesmosomes, suggesting a major role in epidermal cell-basement membrane adhesion. J. Cell Biol., 113, 907917.[Abstract]
-
Carter,W.G., Kaur,P., Gil,S.G., Gahr,P.J. and Wayner,E.A. (1990) Distinct functions for integrins alpha 3 beta 1 in focal adhesions and alpha 6 beta 4/bullous pemphigoid antigen in a new stable anchoring contact (SAC) of keratinocytes: relation to hemidesmosomes. J. Cell Biol., 111, 31413154.[Abstract]
-
Jones,J.C., Asmuth,J., Baker,S.E., Langhofer,M., Roth,S.I. and Hopkinson, S.B. (1994) Hemidesmosomes: extracellular matrix/intermediate filament connectors. Exp. Cell Res., 213, 111.[ISI][Medline]
-
Hogervorst,F., Kuikman,I., von dem Borne,A.E. and Sonnenberg,A. (1990) Cloning and sequence analysis of beta-4 cDNA: an integrin subunit that contains a unique 118 kd cytoplasmic domain. EMBO J., 9, 765770.[Abstract]
-
Suzuki,S. and Naitoh,Y. (1990) Amino acid sequence of a novel integrin beta 4 subunit and primary expression of the mRNA in epithelial cells. EMBO J., 9, 757763.[Abstract]
-
Tamura,R.N., Rozzo,C., Starr,L., Chambers,J., Reichardt,L.F., Cooper,H.M. and Quaranta,V. (1990) Epithelial integrin alpha 6 beta 4: complete primary structure of alpha 6 and variant forms of beta 4. J. Cell Biol., 111, 15931604.[Abstract]
-
Borradori,L. and Sonnenberg,A. (1999) Structure and function of hemidesmosomes: more than simple adhesion complexes. J. Invest. Dermatol., 112, 411418.[Abstract/Free Full Text]
-
Rabinovitz,I. and Mercurio,A.M. (1997) The integrin alpha6beta4 functions in carcinoma cell migration on laminin-1 by mediating the formation and stabilization of actin-containing motility structures. J. Cell Biol., 139, 18731884.[Abstract/Free Full Text]
-
Allen,M.V., Smith,G.J., Juliano,R., Maygarden,S.J. and Mohler,J.L. (1998) Downregulation of the beta4 integrin subunit in prostatic carcinoma and prostatic intraepithelial neoplasia. Hum. Pathol., 29, 311318.[ISI][Medline]
-
Cress,A.E., Rabinovitz,I., Zhu,W. and Nagle,R.B. (1995) The alpha 6 beta 1 and alpha 6 beta 4 integrins in human prostate cancer progression [Review]. Cancer Metastasis Rev., 14, 219228.[ISI][Medline]
-
Liebert,M. and Seigne,J. (1996) Characteristics of invasive bladder cancers: histological and molecular markers. Semin. Urol. Oncol., 14, 6272.[Medline]
-
Schofield,O., Kist,D., Lucas,A., Wayner,E., Carter,W. and Zachary,C. (1998) Abnormal expression of epiligrin and alpha 6 beta 4 integrin in basal cell carcinoma. Dermatol. Surg., 24, 555559.[ISI][Medline]
-
Hanby,A.M., Gillett,C.E., Pignatelli,M. and Stamp,G.W. (1993) Beta 1 and beta 4 integrin expression in methacarn and formalin-fixed material from in situ ductal carcinoma of the breast. J. Pathol., 171, 257262.[ISI][Medline]
-
Natali,P.G., Nicotra,M.R., Botti,C., Mottolese,M., Bigotti,A. and Segatto,O. (1992) Changes in expression of alpha 6/beta 4 integrin heterodimer in primary and metastatic breast cancer. Br. J. Cancer, 66, 318322.[ISI][Medline]
-
Gui,G.P., Wells,C.A., Browne,P.D., Yeomans,P., Jordan,S., Puddefoot,J.R., Vinson,G.P. and Carpenter,R. (1995) Integrin expression in primary breast cancer and its relation to axillary nodal status. Surgery, 117, 102108.[ISI][Medline]
-
Rabinovitz,I. and Mercurio,A.M. (1996) The integrin alpha 6 beta 4 and the biology of carcinoma. Biochem. Cell Biol., 74, 811821.[ISI][Medline]
-
Knox,J.D., Cress,A.E., Clark,V., Manriquez,L., Affinito,K.S., Dalkin,B.L. and Nagle,R.B. (1994) Differential expression of extracellular matrix molecules and the alpha 6-integrins in the normal and neoplastic prostate. Am. J. Pathol., 145, 167174.[Abstract]
-
Hao,J., Yang,Y., McDaniel,K.M., Dalkin,B.L., Cress,A.E. and Nagle,R.B. (1996) Differential expression of laminin 5 (alpha 3 beta 3 gamma 2) by human malignant and normal prostate. Am. J. Pathol., 149, 13411349.[Abstract]
-
Nagle,R.B., Hao,J., Knox,J.D., Dalkin,B.L., Clark,V. and Cress,A.E. (1995) Expression of hemidesmosomal and extracellular matrix proteins by normal and malignant human prostate tissue. Am. J. Pathol., 146, 14981507.[Abstract]
-
Bonkhoff,H. (1998) Analytical molecular pathology of epithelialstromal interactions in the normal and neoplastic prostate. Anal. Quant. Cytol. Histol., 20, 437442.[ISI][Medline]
-
Kulesz-Martin,M., Yoshida,M.A., Prestine,L., Yuspa,S.H. and Bertram,J.S. (1985) Mouse cell clones for improved quantitation of carcinogen-induced altered differentiation. Carcinogenesis, 6, 12451254.[Abstract]
-
Kulesz-Martin,M.F., Penetrante,R. and East,C.J. (1988) Benign and malignant tumor stages in a mouse keratinocyte line treated with 7,12-dimethylbenz[a]anthracene in vitro. Carcinogenesis, 9, 171174.[Abstract]
-
Schneider,B.L., Bowden,G.T., Sutter,C., Schweizer,J., Han,K.A. and Kulesz-Martin,M.F. (1993) 7,12-Dimethylbenz[a]anthracene-induced mouse keratinocyte malignant transformation independent of Harvey ras activation. J. Invest. Dermatol., 101, 595599.[Abstract]
-
Yuspa,S.H., Hennings,H., Roop,D., Strickland,J. and Greenhalgh,D.A. (1990) The malignant conversion step of mouse skin carcinogenesis. Environ. Health Perspect., 88, 193195.[ISI][Medline]
-
Tennenbaum,T., Yuspa,S.H., Grover,A., Castronovo,V., Sobel,M.E., Yamada,Y. and De Luca,L.M. (1992) Extracellular matrix receptors and mouse skin carcinogenesis: altered expression linked to appearance of early markers of tumor progression. Cancer Res., 52, 29662976.[Abstract]
-
Tennenbaum,T., Weiner,A.K., Belanger,A.J., Glick,A.B., Hennings,H. and Yuspa,S.H. (1993) The suprabasal expression of alpha 6 beta 4 integrin is associated with a high risk for malignant progression in mouse skin carcinogenesis. Cancer Res., 53, 48034810.[Abstract]
-
Sonnenberg,A., Janssen,H., Hogervorst,F., Calafat,J. and Hilgers,J. (1987) A complex of platelet glycoproteins Ic and IIa identified by a rat monoclonal antibody. J. Biol. Chem., 262, 1037610383.[Abstract/Free Full Text]
-
Kennel,S.J., Foote,L.J., Falcioni,R., Sonnenberg,A., Stringer,C.D., Crouse,C. and Hemler,M.E. (1989) Analysis of the tumor-associated antigen TSP-180. Identity with alpha 6-beta 4 in the integrin superfamily. J. Biol. Chem., 264, 1551515521.[Abstract/Free Full Text]
-
Quaranta,V. (1990) Epithelial integrins. Cell Differ. Dev., 32, 361365.[ISI][Medline]
-
Carico,E., French,D., Bucci,B., Falcioni,R., Vecchione,A. and Mariani-Costantini,R. (1993) Integrin beta 4 expression in the neoplastic progression of cervical epithelium. Gynecol. Oncol., 49, 6166.[ISI][Medline]
-
Juliano,R.L. and Varner,J.A. (1993) Adhesion molecules in cancer: the role of integrins. Curr. Opin. Cell Biol., 5, 812818.[Medline]
-
Gomez,M., Navarro,P., Quintanilla,M. and Cano,A. (1992) Expression of alpha 6 beta 4 integrin increases during malignant conversion of mouse epidermal keratinocytes: association of beta 4 subunit to the cytokeratin fraction. Exp. Cell Res., 201, 250261.[ISI][Medline]
-
Gomez,M. and Cano,A. (1995) Expression of beta 1 integrin receptors in transformed mouse epidermal keratinocytes: upregulation of alpha 5 beta 1 in spindle carcinoma cells. Mol. Carcinog., 12, 153165.[ISI][Medline]
-
Downer,C.S., Watt,F.M. and Speight,P.M. (1993) Loss of alpha 6 and beta 4 integrin subunits coincides with loss of basement membrane components in oral squamous cell carcinomas. J. Pathol., 171, 183190.[ISI][Medline]
-
Dedhar,S., Saulnier,R., Nagle,R. and Overall,C.M. (1993) Specific alterations in the expression of alpha 3 beta 1 and alpha 6 beta 4 integrins in highly invasive and metastatic variants of human prostate carcinoma cells selected by in vitro invasion through reconstituted basement membrane. Clin. Exp. Metastasis, 11, 391400.[ISI][Medline]
-
Dedhar,S. and Saulnier,R. (1990) Alterations in integrin receptor expression on chemically transformed human cells: specific enhancement of laminin and collagen receptor complexes. J. Cell Biol., 110, 481489.[Abstract]
-
Chammas,R. and Brentani,R. (1991) Integrins and metastases: an overview. Tumour Biol., 12, 309320.[ISI][Medline]
-
Albelda,S.M. (1993) Role of integrins and other cell adhesion molecules in tumor progression and metastasis. Lab. Invest., 68, 417.[ISI][Medline]
-
Rabinovitz,I., Nagle,R.B. and Cress,A.E. (1995) Integrin alpha 6 expression in human prostate carcinoma cells is associated with a migratory and invasive phenotype in vitro and in vivo. Clin. Exp. Metastasis, 13, 481491.[ISI][Medline]
-
Isberg,R.R. and Leong,J.M. (1990) Multiple beta 1 chain integrins are receptors for invasin, a protein that promotes bacterial penetration into mammalian cells. Cell, 60, 861871.[ISI][Medline]
-
Giancotti,F.G., Stepp,M.A., Suzuki,S., Engvall,E. and Ruoslahti,E. (1992) Proteolytic processing of endogenous and recombinant beta 4 integrin subunit. J. Cell Biol., 118, 951959.[Abstract]
-
Potts,A.J., Croall,D.E. and Hemler,M.E. (1994) Proteolytic cleavage of the integrin beta 4 subunit. Exp. Cell Res., 212, 29.[ISI][Medline]
Received August 13, 1999;
accepted October 14, 1999.