β1 Integrin Regulates Fibroblast Viability during Collagen Matrix Contraction through a Phosphatidylinositol 3-Kinase/Akt/Protein Kinase B Signaling Pathway

Integrins regulate cell viability through their interaction with the extracellular matrix. Integrins can sense mechanical forces arising from the matrix and convert these stimuli to chemical signals capable of modulating intracellular signal transduction. The phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway is a major regulator of cell survival. It is not known, however, whether integrins, acting as mechanoreceptors, regulate cell survival via the PI3K/Akt pathway. Here, we show that in response to a matrix-derived mechanical stimulus, β1integrin regulated cell viability by regulating Akt activity in a PI3K-dependent fashion. To accomplish this, we employed fibroblasts cultured in collagen gels. During contraction of collagen matrices, fibroblasts underwent apoptosis. We demonstrate that ligation of β1 integrin with anti-β1 integrin antibodies protected fibroblasts from apoptosis. The nature of the survival signal activated by β1 integrin engagement with antibody was mediated by PI3K acting through Akt/protein kinase B. We show that Akt phosphorylation decreased during collagen contraction and that this decrease correlated precisely with the onset of fibroblast apoptosis. Fibroblasts transfected with constitutively active PI3K displayed increased Akt phosphorylation and were protected from anoikis and collagen gel contraction-induced apoptosis. Our data identify a novel role for β1 integrin in regulating fibroblast viability through a PI3K/Akt/protein kinase B signaling pathway in response to a matrix-derived mechanical stimulus. Integrins regulate cell viability through their interaction with the extracellular matrix. Integrins can sense mechanical forces arising from the matrix and convert these stimuli to chemical signals capable of modulating intracellular signal transduction. The phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway is a major regulator of cell survival. It is not known, however, whether integrins, acting as mechanoreceptors, regulate cell survival via the PI3K/Akt pathway. Here, we show that in response to a matrix-derived mechanical stimulus, β1integrin regulated cell viability by regulating Akt activity in a PI3K-dependent fashion. To accomplish this, we employed fibroblasts cultured in collagen gels. During contraction of collagen matrices, fibroblasts underwent apoptosis. We demonstrate that ligation of β1 integrin with anti-β1 integrin antibodies protected fibroblasts from apoptosis. The nature of the survival signal activated by β1 integrin engagement with antibody was mediated by PI3K acting through Akt/protein kinase B. We show that Akt phosphorylation decreased during collagen contraction and that this decrease correlated precisely with the onset of fibroblast apoptosis. Fibroblasts transfected with constitutively active PI3K displayed increased Akt phosphorylation and were protected from anoikis and collagen gel contraction-induced apoptosis. Our data identify a novel role for β1 integrin in regulating fibroblast viability through a PI3K/Akt/protein kinase B signaling pathway in response to a matrix-derived mechanical stimulus. extracellular matrix phosphatidylinositol 3-kinase protein kinase B monoclonal antibody terminal deoxynucleotidyltransferase-mediated biotinylated UTP nick end labeling constitutively active p110 subunit of PI3K internal ribosome entry site green fluorescent protein fluorescence-activated cell sorter Integrins are a family of αβ-heterodimeric cell-surface receptors that mediate attachment to the extracellular matrix (ECM)1 (1Ruoslahti E. Tumor Biol. 1996; 17: 117-124Crossref PubMed Scopus (124) Google Scholar). Integrins associate with signaling molecules in the focal adhesion complex, which serves as a signaling device and provides a direct link to the cytoskeleton (1Ruoslahti E. Tumor Biol. 1996; 17: 117-124Crossref PubMed Scopus (124) Google Scholar, 2Giancotti F.G. Ruoslahti E. Science. 1999; 285: 1028-1032Crossref PubMed Scopus (3821) Google Scholar). The continuous link between the ECM, integrins, signaling molecules, and the cytoskeleton has led to the discovery that integrins are capable of serving as mechanoreceptors (3Davies P.F. Physiol. Rev. 1995; 75: 519-560Crossref PubMed Scopus (2343) Google Scholar, 4Wilson E. Sudhir K. Ives H.E. J. Clin. Invest. 1995; 96: 2364-2372Crossref PubMed Scopus (268) Google Scholar, 5Ishida T. Peterson T.E. Kovach N.L. Berk B.C. Circ. Res. 1996; 79: 310-316Crossref PubMed Scopus (211) Google Scholar, 6MacKenna D.A. Dolfi F. Vuori K. Ruoslahti E. J. Clin. Invest. 1998; 101: 301-310Crossref PubMed Scopus (273) Google Scholar). As mechanoreceptors, integrins detect matrix-derived mechanical stimuli and convert these to chemical signals capable of modulating signal transduction. Integrin-ECM interaction activates signal transduction pathways that regulate a variety of cellular functions, including cell viability (7Meredith J.E., Jr. Fazeli B. Schwartz M.A. Mol. Biol. Cell. 1993; 4: 953-961Crossref PubMed Scopus (1398) Google Scholar, 8Frisch S.M. Francis H. J. Cell Biol. 1994; 124: 619-626Crossref PubMed Scopus (2775) Google Scholar, 9Brooks P.C. Montgomery A.M.P. Rosenfeld M. Reisfeld R.A., Hu, T. Klier G. Cheresh D.A. Cell. 1994; 79: 1157-1164Abstract Full Text PDF PubMed Scopus (2182) Google Scholar, 10Zhang Z. Vuori K. Reed J. Ruoslahti E. Proc. Natl. Acad. Sci. U. S. A. 1995; 92: 6161-6165Crossref PubMed Scopus (574) Google Scholar, 11Frisch S.M. Vuori K. Kelaita D. Sicks S. J. Cell Biol. 1996; 135: 1377-1382Crossref PubMed Scopus (227) Google Scholar, 12Stromblad S. Becker J.C. Yebra M. Brooks P.C. Cheresh D.A. J. Clin. Invest. 1996; 98: 426-433Crossref PubMed Scopus (349) Google Scholar). Not all integrins appear to be capable of regulating cell viability. However, β1 integrin, which mediates attachment to type I collagen, can regulate cell survival (7Meredith J.E., Jr. Fazeli B. Schwartz M.A. Mol. Biol. Cell. 1993; 4: 953-961Crossref PubMed Scopus (1398) Google Scholar). The biological effects of integrin-ECM binding are mediated through the interaction of the cytoplasmic domain of integrins with associated lipid and protein kinases. Specific lipid and protein kinase molecules known thus far to promote cell survival include pp125FAK(13Crouch D.H. Fincham V.J. Frame M.C. Oncogene. 1996; 12: 2689-2696PubMed Google Scholar, 14Frisch S.M. Vuori K. Ruoslahti E. Chan-Hui P.Y. J. Cell Biol. 1996; 134: 793-799Crossref PubMed Scopus (998) Google Scholar, 15Hungerford J.E. Compton M.T. Matter M.L. Hoffstrom B.G. Otey C.A. J. 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Wennstrom S. Warne P.H. Downward J. EMBO J. 1997; 16: 2783-2793Crossref PubMed Scopus (939) Google Scholar, 23Lee J.W. Juliano R.J. Mol. Biol. Cell. 2000; 11: 1973-1987Crossref PubMed Scopus (143) Google Scholar, 24Kauffmann-Zeh A. Rodriguez-Viciana P. Ulrich E. Gilbert C. Coffer P. Downward J. Evan G. Nature. 1997; 385: 544-548Crossref PubMed Scopus (1074) Google Scholar, 25Dudek H. Datta S.R. Franke T.F. Birbaum M.J. Yao R. Cooper G.M. Segal R.A. Kaplan D.R. Greenberg M.E. Science. 1997; 275: 661-668Crossref PubMed Scopus (2218) Google Scholar). Evidence has emerged demonstrating the important role of an integrin/PI3K/Akt/PKB signaling pathway in regulating epithelial cell survival (22Khwaja A. Rodriguez-Viciana P. Wennstrom S. Warne P.H. Downward J. EMBO J. 1997; 16: 2783-2793Crossref PubMed Scopus (939) Google Scholar, 23Lee J.W. Juliano R.J. Mol. Biol. Cell. 2000; 11: 1973-1987Crossref PubMed Scopus (143) Google Scholar). Attachment of these cells to the underlying basement membrane via integrins activates the PI3K/Akt/PKB survival signal. However, upon detachment, epithelial cells undergo anoikis. Unlike epithelial cells, which are polarized and attach to the underlying basement membrane at their basal surface, mesenchymal cells are frequently surrounded by the ECM. Because mesenchymal cells are surrounded by the matrix, it is unlikely that unnecessary mesenchymal cells are eliminated by detachment and anoikis. However, recent studies indicate that matrix-derived mechanical signals can regulate cell survival (26Dimmeler S. Assmus B. Hermann C. Haendeler J. Zeiher A.M. Circ. Res. 1998; 83: 334-341Crossref PubMed Scopus (369) Google Scholar, 27Chen K.D., Li, Y.S. Kim M., Li, S. Yuan S. Chien S. Shyy J.Y. J. Biol. Chem. 1999; 274: 18393-18400Abstract Full Text Full Text PDF PubMed Scopus (494) Google Scholar). Currently, it is not known whether integrins, acting as mechanoreceptors, can regulate cell survival via the PI3K pathway in response to a matrix-derived mechanical stimulus. To begin to examine this issue, we employed three-dimensional type I collagen gels. We three-dimensional collagen for studies it has that three-dimensional matrix in and from and three-dimensional be E. R. D.R. Science. PubMed Scopus Google Scholar). is in the of of mesenchymal cells as which by the matrix. it has that during collagen gel fibroblasts undergo in response to in mechanical in the collagen matrix F. 1999; PubMed Scopus Google Scholar, F. Cell Biol. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar, J. C. A. S. T. S. J. Invest. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, F. M. M.A. Exp. Cell Res. 1999; PubMed Scopus Google Scholar). it is known that integrin mediates collagen gel contraction and that β1 integrin can as a and can regulate cell viability. we whether β1 integrin in response to a mechanical by collagen contraction can regulate fibroblast apoptosis. anti-β1 integrin we show that ligation of β1 integrin protected fibroblasts from in response to collagen gel The nature of the survival signal activated by β1 integrin engagement with anti-β1 integrin antibody was mediated by PI3K acting through We demonstrate that Akt activity during collagen matrix contraction and that this decrease correlated precisely with the onset of collagen matrix contraction-induced fibroblast apoptosis. of PI3K activity fibroblasts transfected with the active p110 subunit of PI3K protected fibroblasts from anoikis in and in response to collagen gel studies identify a novel role for β1integrin in regulating fibroblast viability via of a PI3K/Akt signaling pathway in response to contraction of type I collagen fibroblasts were cultured in and between and were as by J. C. A. S. T. S. J. Invest. 1998; Full Text Full Text PDF PubMed Scopus Google with fibroblasts were in of was to the cell to a of The was in a for at and a cell at and the in monoclonal antibody the β1 integrin was by of antibody the β1 integrin was a from of antibodies and the β1 integrin the integrin the of and antibody were from antibody which the integrin was from Akt antibody was from and Akt antibody was was to the of J. Cell Biol. PubMed Scopus Google with cells in gel were an in cell terminal to the fibroblasts from anoikis and type I collagen were for an in to the cells were with in for at and with for at The cells were in for at and by Fibroblasts in collagen were by gel for at of The was with and the cell was at for the of cells was in in and cells were Fibroblasts were and collagen for of were to and was the for The were at for at and were for at with protein and for at with were for of fibroblasts was as C.A. U. J. Clin. Invest. 1996; PubMed Scopus Google Scholar). of protein from the cell were to and to were with and with the and with The were the The constitutively active p110 subunit of PI3K was by was the site of the the The cell was with this and the the and the was to fibroblasts of cells was by cell were as by and Francis S.M. Francis H. J. Cell Biol. 1994; 124: 619-626Crossref PubMed Scopus (2775) Google Scholar). were with in and with Fibroblasts in were the the the cells in were and by data are as were of the of cells collagen the of at was were for and and was by was at It has that fibroblasts undergo during contraction of collagen gels. We whether this was the for were collagen in in Fibroblasts collagen in the collagen from at to at collagen gel contraction the The of collagen gel contraction was to the of the collagen collagen from at to at and at collagen from to at The decrease in cell was to the of collagen gel contraction of cells underwent in the collagen as to the collagen gels. The cell in the collagen from cells the at to at the cell in the collagen to and by the cell was at the cell in collagen from to However, at the cell increased to The of fibroblasts collagen of of collagen and not the cell in increased from at to at with J. C. A. S. T. S. J. Invest. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, F. M. M.A. Exp. Cell Res. 1999; PubMed Scopus Google Scholar), we that the in fibroblast during collagen gel contraction in was to apoptosis. of by that at cells the collagen were and fibroblasts the collagen were and the were by The in cell by of fibroblasts in collagen were by to collagen gel fibroblasts the collagen matrix were and a with of the collagen matrix During contraction of the collagen matrix, fibroblasts in and their that were to the matrix. As their the fibroblasts in collagen that a of collagen be the cells membrane was in cells of gel that these cells were and integrin mediates contraction of type I collagen and the β1 integrin subunit can as a and cell viability. It has that of cell adhesion to the underlying matrix by with integrin cells to undergo a of known as anoikis. However, whether β1 integrin can regulate cell viability in response to a mechanical by contraction of a collagen matrix is not We whether β1 integrin fibroblast viability during collagen gel It has that anti-β1 integrin monoclonal antibody collagen gel anti-β1 integrin monoclonal antibody has collagen gel contraction J.L. B. Exp. Cell Res. 1994; PubMed Scopus Google Scholar). antibodies to signal transduction in collagen and the domain the β1integrin J.L. B. Exp. Cell Res. 1994; PubMed Scopus Google Scholar, J. Biol. Chem. 1993; Full Text PDF PubMed Google Scholar). It is important to that these antibodies in that can cell this not from capable of modulating cell The binding of these antibodies to fibroblasts has to regulate intracellular signaling pathways J.L. B. Exp. Cell Res. 1994; PubMed Scopus Google Scholar). in a to the of β1 integrin signaling from gel contraction fibroblasts were with of of the monoclonal antibodies and collagen with J.L. B. Exp. Cell Res. 1994; PubMed Scopus Google Scholar), we that the antibody to the β1 integrin collagen gel contraction in a the antibody to β1 integrin gel contraction the and monoclonal antibodies protected fibroblasts from apoptosis. We that the monoclonal antibody from by of to The antibody protected fibroblasts from in a Cell at were and the monoclonal antibody collagen gel the it of fibroblast in a cell at were and data indicate that direct engagement of β1 integrin with anti-β1 integrin antibody is capable of regulating fibroblast viability during collagen gel We whether antibodies to the subunit collagen gel contraction the of apoptosis. The monoclonal antibody the integrin as as the the integrin not collagen gel contraction and not not monoclonal antibodies the integrin the integrin and not contraction cell viability. we the of collagen gel contraction and of apoptosis. of fibroblasts with not collagen gel contraction and not not Our data indicate that the β1 integrin subunit not the fibroblast viability during collagen gel viability signal transduction pathways to be epithelial and cells, the PI3K/Akt/PKB survival pathway can be activated by and integrin binding H.C. Guan J.L. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 10148-10152Crossref PubMed Scopus (477) Google Scholar, 18Ilic D. Almeida E.A.C. Schlaepfer D.D. Dazin P. Aizawa S. Damsky C.H. J. Cell Biol. 1998; 143: 547-560Crossref PubMed Scopus (436) Google Scholar, A. Rodriguez-Viciana P. Wennstrom S. Warne P.H. Downward J. EMBO J. 1997; 16: 2783-2793Crossref PubMed Scopus (939) Google J.W. Juliano R.J. Mol. Biol. Cell. 2000; 11: 1973-1987Crossref PubMed Scopus (143) Google Scholar). We whether engagement of β1 integrin fibroblasts with antibody was capable of We the phosphorylation of by a of of Akt of the kinase Rev. 1999; PubMed Scopus Google Scholar). To these fibroblasts were and to of anti-β1 integrin It is important to that during these the of the antibody to fibroblasts to not their However, as a to and antibody of fibroblasts with antibody their to to not we that ligation of β1 integrin with the antibody increased the phosphorylation of and to decrease by However, anti-β1 integrin antibody and the antibody Akt phosphorylation We to whether ligation of β1 integrin by the antibody of cell adhesion Akt/PKB fibroblasts in were with anti-β1 integrin to Akt was at in fibroblasts by ligation of β1 integrin in a To whether of Akt/PKB was the fibroblasts were with and to anti-β1 integrin the in Akt/PKB phosphorylation mediated by ligation of β1 integrin with antibody data indicate that the with cells to has in that it However, data show that the antibody to β1 integrin cells that are are in it in an by the Akt survival signaling pathway via a PI3K-dependent Our data that fibroblast by ligation of β1 integrin with the antibody during collagen gel contraction be mediated via a survival signaling pathway. Our data that a survival pathway can regulate fibroblast viability during collagen matrix However, whether the PI3K/Akt survival signal in response to contraction of type I collagen matrices, fibroblast We the of Akt activity in fibroblasts as a of in and collagen gels. The of Akt phosphorylation decreased during type I collagen matrix and the onset of the decrease in Akt phosphorylation with the of gel contraction the for the decrease in Akt phosphorylation correlated precisely with the in which fibroblast during gel Akt activity was decreased at and by which was precisely fibroblast decrease in the of Akt phosphorylation in fibroblasts collagen is with the that fibroblasts not undergo in gels. data demonstrate that contraction of type I collagen is associated with a decrease in the PI3K/Akt survival signal. We that contraction of type I collagen is associated with a decrease in Akt activity and that this decrease in Akt activity with the onset of fibroblast apoptosis. We that ligation of β1 integrin with anti-β1 integrin antibody fibroblasts from collagen matrix contraction-induced apoptosis. Our in data fibroblasts to indicate that binding of β1integrin with antibody the activity of the Akt/PKB survival signal in a PI3K-dependent To whether fibroblast viability collagen can be regulated through a PI3K/Akt signaling we PI3K activity constitutively active a fibroblasts were transfected with a of to Fibroblasts were by to a of fluorescent of cells is in A. an antibody that of Akt was to that of PI3K activity in increased of fibroblasts displayed a in Akt/PKB phosphorylation at with fibroblasts We to whether fibroblasts were protected anoikis as by and Francis S.M. Francis H. J. Cell Biol. 1994; 124: 619-626Crossref PubMed Scopus (2775) Google Scholar). fibroblasts were to the cells the the cells were for anoikis a fluorescent in are fluorescent and of fibroblasts anoikis. in the of fibroblasts were fibroblasts were protected anoikis. in fluorescent and of fibroblasts that the of cells were in of fibroblasts were To whether of PI3K/Akt activity can fibroblasts from collagen gel contraction-induced fibroblasts were collagen and by a fluorescent at and for apoptosis. the the were with and the cells were by in collagen of fibroblasts were of cells were at in collagen of fibroblasts were and at of cells were indicate that of PI3K/Akt activity can fibroblasts from collagen gel contraction-induced apoptosis. To that an in Akt activity was for of fibroblasts in collagen we fibroblasts and collagen and the of Akt Unlike in which the of Akt phosphorylation during collagen gel the of Akt phosphorylation in fibroblasts not decrease during collagen gel contraction is with that fibroblasts are protected collagen gel contraction-induced apoptosis. the of Akt phosphorylation in fibroblasts in increased the the of Akt phosphorylation in cells decreased in a during collagen gel to fibroblasts Attachment of epithelial cells to the underlying basement membrane via integrins activates the survival signaling protein Akt/PKB in a PI3K-dependent of epithelial cells is associated with a of the Akt/PKB survival signal and anoikis. Unlike polarized epithelial cells, which attach to the matrix at their basal surface, mesenchymal cells as fibroblasts are surrounded by the ECM. unnecessary mesenchymal cells are it is unlikely that from the matrix and undergo anoikis. However, the regulating mesenchymal cell viability to be Here, we show that in response to a matrix-derived mechanical stimulus, β1 integrin mesenchymal cell viability by regulating Akt activity in a PI3K-dependent fashion. Our data that β1 integrin is capable of acting as a and that in response to a mechanical by contraction of the type I collagen matrix, it fibroblast viability through a PI3K/Akt/PKB signaling pathway. During the of and unnecessary mesenchymal cells to be eliminated for to G. Invest. Google Scholar, B. C. D. C. D. J. Clin. Invest. 1993; 92: PubMed Scopus Google Scholar, A. M. G. J. 1995; Google Scholar, S. P. F. J. Invest. Full Text PDF PubMed Google Scholar, J. J. Cell Biol. 1998; PubMed Scopus Google Scholar). However, the signal that of cells surrounded by the matrix F. M. M.A. Exp. Cell Res. 1999; PubMed Scopus Google that a decrease in mechanical in collagen during gel contraction fibroblast apoptosis. with this we show that the of collagen contraction is upon the of collagen to the gels. we demonstrate that the of fibroblast is to the of gel The of gel contraction to be the for and not the of Fibroblasts in collagen of of collagen to in not undergo apoptosis. these data that in mechanical in the as the for of fibroblast and that the of collagen contraction is an important in the of the β1 integrin mediates attachment to collagen and contraction of collagen and can regulate cell survival. However, whether β1 integrin is capable of regulating fibroblast viability during collagen gel contraction is not this we show that β1 integrin fibroblast viability during collagen gel We demonstrate that direct engagement of β1 integrin with anti-β1 integrin antibodies fibroblasts from contraction-induced apoptosis. We anti-β1 integrin monoclonal antibodies that the domain of β1 integrin J.L. B. Exp. Cell Res. 1994; PubMed Scopus Google Scholar, J. Biol. Chem. 1993; Full Text PDF PubMed Google Scholar). antibodies to β1 signal transduction in collagen with a J.L. B. Exp. Cell Res. 1994; PubMed Scopus Google Scholar), we that anti-β1 integrin antibody collagen gel the antibody collagen gel this, we that antibodies were capable of fibroblasts from collagen gel contraction-induced apoptosis. We that collagen with the antibody decreased apoptosis. is the antibody gel the for of apoptosis. The was that the antibody protected contraction-induced apoptosis. Because the antibody gel this that the antibody by a pathway by a survival signal. the with the antibody that the effects we were to β1 integrin signaling and not from the contraction of the gel Attachment of epithelial cells to the via integrins provides a survival signal. from the matrix anoikis (7Meredith J.E., Jr. Fazeli B. Schwartz M.A. Mol. Biol. Cell. 1993; 4: 953-961Crossref PubMed Scopus (1398) Google S.M. Francis H. J. Cell Biol. 1994; 124: 619-626Crossref PubMed Scopus (2775) Google Scholar). Fibroblasts are epithelial cells to the of anoikis C.A. J. Med. 2000; PubMed Scopus Google Scholar). However, of matrix for fibroblasts undergo anoikis C.A. J. Med. 2000; PubMed Scopus Google Scholar, C.A. P. U. V. J. 1996; Google Scholar). in fibroblasts were in three-dimensional collagen of attachment to the is unlikely to be the by which fibroblasts undergo apoptosis. this we show that to gel fibroblasts are During collagen gel the cells in Because cell and to survival M. S. G.M. Science. 1997; PubMed Scopus Google Scholar), it is that in cell be for of fibroblasts during collagen gel recent that chemical signaling by integrin interaction with the can be by in the cytoskeleton in response to in the G.E. K. Mol. Biol. Cell. 1995; PubMed Scopus Google Scholar, M.E. Cell Biol. 1998; PubMed Scopus Google Scholar). in three-dimensional fibroblast not appear to be by cell detachment from the ECM. fibroblast in response to collagen matrix contraction to of a survival signal as a of integrin-ECM in the cytoskeleton and associated signal transduction of β1 integrin as a is to convert mechanical stimuli chemical β1integrin to regulate fibroblast viability during collagen gel it be capable of modulating survival signal transduction It has that integrins can promote epithelial cell survival through the PI3K/Akt pathway (22Khwaja A. Rodriguez-Viciana P. Wennstrom S. Warne P.H. Downward J. EMBO J. 1997; 16: 2783-2793Crossref PubMed Scopus (939) Google Scholar, 23Lee J.W. Juliano R.J. Mol. Biol. Cell. 2000; 11: 1973-1987Crossref PubMed Scopus (143) Google Scholar). Our data demonstrate that ligation of β1 integrin with anti-β1 integrin antibody in and fibroblasts in of Akt/PKB in a PI3K-dependent a of PI3K we that phosphorylation of Akt/PKB in response to ligation of β1 integrin by antibody is data indicate that direct engagement of β1 integrin with the antibody is capable of the activity of the Akt/PKB survival signal. It is important to that the with cells to their can adhesion and has these However, the that the antibody can Akt activity upon binding cells in that these the antibody in an fashion. It that the by which the antibody fibroblasts from is by β1 of a PI3K/Akt survival signal transduction pathway. The antibody contraction-induced apoptosis. However, the by which it was not by the Akt survival signal Akt activity was not increased ligation of β1 integrin with the antibody by the for gel To whether the PI3K/Akt survival signal fibroblast viability during contraction of type I collagen matrices, we Akt activity during matrix Akt phosphorylation during collagen gel and the decrease in Akt activity precisely the of fibroblast in response to gel led to examine whether of PI3K activity regulate fibroblast viability in collagen gels. To this issue, we PI3K activity by fibroblasts with the constitutively active p110 subunit of We that constitutively active PI3K was capable of the activity of Akt/PKB and that it protected fibroblasts from anoikis as as collagen gel contraction-induced apoptosis. we that of Akt activity during collagen matrix the of Akt activity in fibroblasts during matrix data that a by collagen gel contraction is by β1 integrin, which in the PI3K/Akt survival fibroblast apoptosis. of PI3K/Akt activity by of β1 integrin by antibody binding by of constitutively active PI3K fibroblasts contraction-induced apoptosis. the data the that β1 integrin can as a that is capable of a mechanical by collagen matrix Our data indicate that of during collagen gel contraction is by β1 integrin, which is capable of modulating the activity of the PI3K/Akt survival signal. the of fibroblast viability in collagen provides the of mesenchymal cell during and We Downward for the constitutively active PI3K for anti-β1 integrin antibody and for anti-β1 integrin antibody We for and of the