Different Molecular Motors Mediate Platelet-derived Growth Factor and Lysophosphatidic Acid-stimulated Floating Collagen Matrix Contraction

Fibroblast-collagen matrix contraction has been used as a model system to study how cells organize connective tissue. Previous work showed that lysophosphatidic acid (LPA)-stimulated floating collagen matrix contraction is independent of Rho kinase, whereas platelet-derived growth factor (PDGF)-stimulated contraction is Rho kinase-dependent. The current studies were carried out to learn more about the molecular motors responsible for LPA- and PDGF-stimulated contraction. We found that neither PDGF nor LPA-dependent contractile mechanisms require myosin II regulatory light chain kinase or increased phosphorylation of myosin II regulatory light chain (measured as diphosphorylation). Low concentrations of the specific myosin II inhibitor blebbistatin blocked PDGF-stimulated matrix contraction and LPA-stimulated retraction of fibroblast dendritic extensions but not LPA-stimulated matrix contraction. These data suggest that PDGF- and LPA-stimulated floating matrix contraction utilize myosin II-dependent and -independent mechanisms, respectively. LPA-dependent, Rho kinase-independent force generation also was detected during fibroblast spreading on collagen-coated coverslips. Fibroblast-collagen matrix contraction has been used as a model system to study how cells organize connective tissue. Previous work showed that lysophosphatidic acid (LPA)-stimulated floating collagen matrix contraction is independent of Rho kinase, whereas platelet-derived growth factor (PDGF)-stimulated contraction is Rho kinase-dependent. The current studies were carried out to learn more about the molecular motors responsible for LPA- and PDGF-stimulated contraction. We found that neither PDGF nor LPA-dependent contractile mechanisms require myosin II regulatory light chain kinase or increased phosphorylation of myosin II regulatory light chain (measured as diphosphorylation). Low concentrations of the specific myosin II inhibitor blebbistatin blocked PDGF-stimulated matrix contraction and LPA-stimulated retraction of fibroblast dendritic extensions but not LPA-stimulated matrix contraction. These data suggest that PDGF- and LPA-stimulated floating matrix contraction utilize myosin II-dependent and -independent mechanisms, respectively. LPA-dependent, Rho kinase-independent force generation also was detected during fibroblast spreading on collagen-coated coverslips. Form and function of multicellular organisms depend on tissue-specific programs of cell motility. Fibroblasts synthesize, organize, and maintain connective tissues during development and in response to injury and fibrotic disease. The motile mechanisms that fibroblasts use to remodel the extracellular matrix during these morphogenetic processes have been studied by using cells cultured in three-dimensional collagen matrices (1Tomasek J.J. Gabbiani G. Hinz B. Chaponnier C. Brown R.A. Nat. Rev. Mol. Cell. Biol. 2002; 3: 349-363Crossref PubMed Scopus (3189) Google Scholar, 2Grinnell F. Trends Cell Biol. 2003; 13: 264-269Abstract Full Text Full Text PDF PubMed Scopus (668) Google Scholar). As fibroblasts exert force on and move collagen fibrils of the matrix, collagen concentration around the cells increases, and the corresponding decrease in matrix volume (typically referred to as contraction) can be measured as a decrease in the diameter of free matrices or a decrease in height of restrained matrices. During contraction of restrained matrices, collagen fibrils become oriented in the same plane as restraint, and mechanical loading develops. In floating matrices, on the other hand, contraction occurs without collagen fibrils developing a particular orientation, and the matrix remains mechanically unloaded (1Tomasek J.J. Gabbiani G. Hinz B. Chaponnier C. Brown R.A. Nat. Rev. Mol. Cell. Biol. 2002; 3: 349-363Crossref PubMed Scopus (3189) Google Scholar, 2Grinnell F. Trends Cell Biol. 2003; 13: 264-269Abstract Full Text Full Text PDF PubMed Scopus (668) Google Scholar, 3Brown R.A. Prajapati R. McGrouther D.A. Yannas I.V. Eastwood M. J. Cell. Physiol. 1998; 175: 323-332Crossref PubMed Scopus (337) Google Scholar, 4Tranquillo R.T. Biochem. Soc. Symp. 1999; 65: 27-42PubMed Google Scholar, 5Cukierman E. Pankov R. Yamada K.M. Curr. Opin. Cell Biol. 2002; 14: 633-639Crossref PubMed Scopus (779) Google Scholar). The signaling mechanisms used by fibroblasts to regulate collagen matrix contraction depend on whether the cells are mechanically loaded or unloaded at the time that contraction is initiated as well as on the growth factor used to initiate contraction. For instance, stimulation of fibroblasts by lysophosphatidic acid (LPA) 1The abbreviations used are: LPAlysophosphatidic acidPDGFplatelet-derived growth factorDMEMDulbecco's modified Eagle's mediumMLCmyosin II regulatory light chainFBSfetal bovine serumFITCfluorescein isothiocyanateBSAbovine serum albuminPIPES1,4-piperazinediethanesulfonic acidsiRNAsmall interfering RNA. but not by platelet-derived growth factor (PDGF) causes robust force generation in restrained matrices (6Kolodney M.S. Elson E.L. J. Biol. Chem. 1993; 268: 23850-23855Abstract Full Text PDF PubMed Google Scholar), whereas LPA and PDGF stimulate floating matrix contraction equally well (7Shreiber D.I. Enever P.A. Tranquillo R.T. Exp. Cell Res. 2001; 266: 155-166Crossref PubMed Scopus (64) Google Scholar, 8Grinnell F. Ho C.H. Lin Y.C. Skuta G. J. Biol. Chem. 1999; 274: 918-923Abstract Full Text Full Text PDF PubMed Scopus (159) Google Scholar). lysophosphatidic acid platelet-derived growth factor Dulbecco's modified Eagle's medium myosin II regulatory light chain fetal bovine serum fluorescein isothiocyanate bovine serum albumin 1,4-piperazinediethanesulfonic acid small interfering RNA. Floating matrix contraction has presented something of an enigma because LPA stimulation of fibroblasts in floating matrices causes activation of the small G protein Rho (GTP loading) (9Grinnell F. Ho C.H. Tamariz E. Lee D.J. Skuta G. Mol. Biol. Cell. 2003; 14: 384-395Crossref PubMed Scopus (177) Google Scholar), but blocking Rho kinase with the pharmacological reagent Y27632 does not inhibit contraction (10Lee D.J. Ho C.-H. Grinnell F. Exp. Cell Res. 2003; 289: 86-94Crossref PubMed Scopus (25) Google Scholar). Conversely, PDGF stimulation of cells in matrices causes activation of Rac not Rho (9Grinnell F. Ho C.H. Tamariz E. Lee D.J. Skuta G. Mol. Biol. Cell. 2003; 14: 384-395Crossref PubMed Scopus (177) Google Scholar), but blocking Rho kinase inhibits PDGF-stimulated contraction (10Lee D.J. Ho C.-H. Grinnell F. Exp. Cell Res. 2003; 289: 86-94Crossref PubMed Scopus (25) Google Scholar). For fibroblasts migrating on two-dimensional substrata, the ability of cells to exert tractional force on the substratum depends on activation of Rho and Rho kinase (11Beningo K.A. Wang Y.L. Trends Cell Biol. 2002; 12: 79-84Abstract Full Text Full Text PDF PubMed Scopus (219) Google Scholar, 12Geiger B. Bershadsky A. Curr. Opin. Cell Biol. 2001; 13: 584-592Crossref PubMed Scopus (485) Google Scholar), which is believed to increase cell contraction through increased phosphorylation of myosin II regulatory light chain (MLC) (13Fukata Y. Amano M. Kaibuchi K. Trends Pharmacol. Sci. 2001; 22: 32-39Abstract Full Text Full Text PDF PubMed Scopus (667) Google Scholar, 14Schoenwaelder S.M. Burridge K. Curr. Opin. Cell Biol. 1999; 11: 274-286Crossref PubMed Scopus (650) Google Scholar). In addition to Rho kinase, the spatial and temporal pattern of MLC phosphorylation in fibroblasts is controlled by MLC kinase (15Katoh K. Kano Y. Amano M. Kaibuchi K. Fujiwara K. Am. J. Physiol. 2001; 280: C1669-C1679Crossref PubMed Google Scholar, 16Katoh K. Kano Y. Amano M. Onishi H. Kaibuchi K. Fujiwara K. J. Cell Biol. 2001; 153: 569-584Crossref PubMed Scopus (271) Google Scholar, 17Totsukawa G. Yamakita Y. Yamashiro S. Hartshorne D.J. Sasaki Y. Matsumura F. J. Cell Biol. 2000; 150: 797-806Crossref PubMed Scopus (541) Google Scholar). Other mechanisms of force generation independent of MLC phosphorylation also have been described (18Nobe H. Nobe K. Fazal F. De Lanerolle P. Paul R.J. Am. J. Physiol. 2003; 284: C599-C606Crossref PubMed Scopus (30) Google Scholar, 19Obara K. Nikcevic G. Pestic L. Nowak G. Lorimer D.D. Guerriero Jr., V. Elson E.L. Paul R.J. de Lanerolle P. J. Biol. Chem. 1995; 270: 18734-18737Abstract Full Text Full Text PDF PubMed Scopus (27) Google Scholar), even in smooth muscle cells (20Ye L.H. Kishi H. Nakamura A. Okagaki T. Tanaka T. Oiwa K. Kohama K. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 6666-6671Crossref PubMed Scopus (26) Google Scholar, 21Ai S. Kuzuya M. Koike T. Asai T. Kanda S. Maeda K. Shibata T. Iguchi A. Atherosclerosis. 2001; 155: 321-327Abstract Full Text Full Text PDF PubMed Scopus (81) Google Scholar) where MLC phosphorylation generally is thought to be the key regulator of contractile activity (22Kamm K.E. Stull J.T. J. Biol. Chem. 2001; 276: 4527-4530Abstract Full Text Full Text PDF PubMed Scopus (472) Google Scholar). The current studies were carried out to learn more about the molecular motors responsible for LPA- and PDGF-stimulated fibroblast-collagen matrix contraction. We found that neither PDGF- nor LPA-dependent contractile mechanisms require MLC kinase or increased phosphorylation of MLC (measured as diphosphorylation). Low concentrations of the specific myosin II inhibitor blebbistatin blocked PDGF-stimulated matrix contraction and LPA-stimulated retraction of fibroblast dendritic extensions but not LPA-stimulated matrix contraction. These data suggest that PDGF- and LPA-stimulated floating matrix contraction utilize myosin II-dependent and -independent mechanisms, respectively. LPA-dependent and Rho kinase-independent force generation also was detected during fibroblast spreading on collagen-coated coverslips. Materials—Dulbecco's modified Eagle's medium (DMEM) and trypsin/EDTA solution were obtained from Invitrogen. Bovine serum albumin (BSA; fatty acid-free), l-ascorbic acid, and lysophosphatidic acid (LPA) were obtained from Sigma. Fetal bovine serum (FBS) was obtained from Atlanta Biologicals (Norcross, GA). Goat serum was obtained from Zymed Laboratories Inc. Vitrogen “100” collagen was obtained from Cohesion (Palo Alto, CA). Platelet-derived growth factor (PDGF) (BB isotype) was obtained from Upstate Biotechnology, Inc. (Lake Placid, NY). Y27632 was obtained from Calbiochem-Novabiochem. Blebbistatin was obtained from Toronto Research Chemicals Inc. (Ontario, Canada). Mouse anti-vinculin, mouse anti-actin, mouse anti-myosin regulatory light chain (20,000), and mouse anti-MLC kinase were from Sigma. Rabbit anti-diphospho-MLC (Thr-18/Ser-19) was obtained from Santa Cruz Biotechnology (Santa Cruz, CA). Rhodamine-conjugated phalloidin and FITC-conjugated goat anti-mouse IgG H+L were obtained from Molecular Probes, Inc. (Eugene, OR). Horseradish peroxidase-conjugated goat anti-mouse IgG H+L and goat anti-rabbit IgG H+L were obtained from ICN Biomedicals, Inc. (Aurora, OH). Polyvinylidene difluoride membranes were obtained from Millipore Corp. (Bedford, MA). β-Nicotinamide adenine dinucleotide (reduced form) was obtained from Sigma. Enhanced chemiluminescence (ECL) Western blotting reagent was obtained from Amersham Biosciences. OligofectAMINE and Opti-MEM I were obtained from Invitrogen. Fluoromount G was obtained from Southern Biotechnology Associates (Birmingham, AL). Monolayer and Collagen Matrix Culture—Fibroblasts were from human foreskin specimens and cultured up to 10 passages in Falcon 75-cm2 tissue culture flasks in DMEM supplemented with 10% FBS (DMEM, 10% FBS) at 37 °C in a 5% CO2 humidified incubator. The culture medium was changed every 3–4 days. Cells were harvested by 0.25% trypsin/EDTA for 3 min at 37 °C followed by DMEM, 10% FBS. For monolayer culture experiments, harvested cells were seeded at a density of 4 × 104 cells on 22-mm square glass coverslips (Fisher) that previously had been collagen-coated (50 μg/ml for 30 min) and then cultured in DMEM containing growth and as Collagen matrix were using Vitrogen collagen as described previously F. Ho C.H. Lin Y.C. Skuta G. J. Biol. Chem. 1999; 274: 918-923Abstract Full Text Full Text PDF PubMed Scopus (159) Google Scholar, G. Ho C.H. Grinnell F. J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus (26) Google Scholar). collagen solution containing harvested cells was to 37 °C for 4 and then were on an by a a well of culture and to for min at 37 °C in 5% incubator. initiate floating matrix matrices were from the culture with a of DMEM containing and growth and were as For restrained matrix matrices were cultured in of DMEM, 10% FBS containing μg/ml acid Matrix contraction was carried out for the in the which the were for 10 min at with in 3 matrices were and on a and diameter was data are presented as the in diameter in were carried out in and every was or more and in the and are not the data and and were as described previously F. Ho C.H. Lin Y.C. Skuta G. J. Biol. Chem. 1999; 274: 918-923Abstract Full Text Full Text PDF PubMed Scopus (159) Google Scholar, G. Ho C.H. Grinnell F. J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus (26) Google Scholar). cells were in 4 μg/ml μg/ml and matrix and by using with a were by at for 10 min at 4 and the were in and for of by were to using to difluoride membranes was carried out at for The membranes were blocked with 5% in and then with anti-MLC kinase anti-MLC or anti-diphospho-MLC in blocking solution at 4 °C for with membranes were with peroxidase-conjugated goat anti-mouse IgG in 5% in or in in anti-MLC kinase and anti-MLC or peroxidase-conjugated goat anti-rabbit IgG in in for with membranes were by the of the and MLC was by using in matrices or on coverslips were for 10 min with in at blocked with in 3 for 30 and then for min with in the were with and for 10 min with in was in in and to cells for at 37 with were for 10 min with in and then FITC-conjugated goat anti-mouse IgG in in was to the cells for 30 min at 37 with were for 10 min with in and then were with phalloidin in in for 30 min at 37 were on glass with Fluoromount G. were and with a with a and work for of MLC kinase were with 10 at 37 for 10 min with in at 37 and then with at 37 the were for min with in were blocked with goat serum in for at 37 °C and then with mouse anti-MLC kinase in goat serum in for at 37 with were with FITC-conjugated goat anti-mouse IgG in goat serum in for at 37 were on glass with Fluoromount and were as light chain kinase was using and were obtained from the of For of was in 30 for min at followed by at 37 fibroblast were with DMEM and then with for min to cell but not 10% was to the cells were with DMEM, were with Opti-MEM I containing and OligofectAMINE with medium was and with 10% containing for an at which time cells were Rho and Collagen Matrix of the of collagen matrix contraction on Rho kinase with studies (10Lee D.J. Ho C.-H. Grinnell F. Exp. Cell Res. 2003; 289: 86-94Crossref PubMed Scopus (25) Google Scholar), addition of the Rho kinase inhibitor Y27632 had on LPA-stimulated contraction of floating matrices PDGF-stimulated contraction was matrices were restrained and to mechanical loading then LPA-stimulated contraction Rho (10Lee D.J. Ho C.-H. Grinnell F. Exp. Cell Res. 2003; 289: 86-94Crossref PubMed Scopus (25) Google Scholar, M. J.J. Exp. Cell Res. 2000; PubMed Scopus Google Scholar, M. H. A. H. E. T. M. T. Shibata M. M. Fujiwara K. M. Biochem. Res. 2000; PubMed Scopus Google Scholar). MLC and Collagen Matrix that LPA-stimulated floating matrix contraction was Rho In addition to Rho kinase, MLC kinase has been to a in fibroblast-collagen matrix contraction M. J.J. Exp. Cell Res. 2000; PubMed Scopus Google Scholar, Y. K. 2001; PubMed Scopus Google Scholar, J. Cell. Physiol. PubMed Scopus Google Scholar). whether MLC kinase was for LPA-stimulated collagen matrix were carried out using fibroblasts in which MLC kinase were using the by with anti-MLC kinase that cell with MLC but not the of the MLC kinase in human was used as a loading In corresponding by that the of MLC kinase was in MLC of the cell was in specific and as well as Fibroblasts in which MLC kinase was as to be were used to matrix contraction in the of LPA or PDGF with or without the Rho kinase inhibitor 3 from a The of contraction of MLC cells was not from LPA-stimulated floating matrix contraction in MLC cells even Rho kinase also was MLC and Collagen Matrix Other were carried out to the of LPA and PDGF on MLC phosphorylation with and without Rho kinase showed by using the that LPA but not PDGF and of fibroblasts on collagen-coated but for the not be used for fibroblasts in collagen matrices G. Ho C.H. Grinnell F. J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus (26) Google Scholar). MLC phosphorylation in fibroblasts in collagen matrices was using specific to MLC with MLC as a loading MLC as well as the has been in cell M. PubMed Scopus Google Scholar, J. Cell Biol. 1995; PubMed Scopus Google Scholar). 4 a and of from min of growth factor of MLC were in cells in medium and in addition of Rho kinase inhibitor phosphorylation in every These that stimulation of floating collagen matrix contraction not require growth factor stimulation of MLC phosphorylation (measured as diphosphorylation). II and Collagen Matrix that neither MLC kinase nor stimulation of MLC phosphorylation was for collagen matrix contraction. We not the that MLC kinase or of MLC phosphorylation were for contraction to were carried out to more the of myosin II in contraction using the specific myosin II inhibitor blebbistatin A. J. 2003; PubMed Scopus Google Scholar). a for the of blebbistatin on floating matrix contraction. of the in the which is the same concentration that myosin II activity A. J. 2003; PubMed Scopus Google Scholar). In LPA-dependent contraction was by blebbistatin at We also the of blebbistatin on LPA-stimulated retraction of fibroblast dendritic As described fibroblasts in collagen matrices and a dendritic of PDGF the and of whereas LPA retraction in a Rho (9Grinnell F. Ho C.H. Tamariz E. Lee D.J. Skuta G. Mol. Biol. Cell. 2003; 14: 384-395Crossref PubMed Scopus (177) Google Scholar). occurs of and is not for matrix contraction (10Lee D.J. Ho C.-H. Grinnell F. Exp. Cell Res. 2003; 289: 86-94Crossref PubMed Scopus (25) Google Scholar). the of fibroblasts with (LPA) and (PDGF) As described addition of the Rho kinase inhibitor Y27632 blocked retraction by LPA with blebbistatin at or also blocked LPA-stimulated retraction but had on the extensions in the of PDGF These that LPA-dependent retraction of fibroblast dendritic extensions myosin the that PDGF and LPA floating collagen matrix contraction through molecular motors and that LPA was to exert force by a Rho myosin Rho and Cell on were carried out to learn the Rho kinase-independent of force generation also be during cell spreading on collagen-coated coverslips. that in fibroblasts with and In the of the Rho kinase inhibitor and were of cells had dendritic fibroblasts on collagen-coated in medium Rho kinase to tractional force for and of and Fibroblasts on collagen-coated coverslips in medium also and but to be cells in Fibroblasts in medium containing LPA and Rho kinase inhibitor more cells in PDGF of as well as and These that was a Rho kinase-independent of force for was obtained LPA was to fibroblasts previously in medium with PDGF Rho kinase inhibitor in which the dendritic extensions more and and even in the of the Rho kinase Conversely, addition of LPA to cells previously with PDGF in of blebbistatin to the in of Rho kinase inhibitor also fibroblasts in medium to the dendritic whereas cells in medium of as well as and were carried out to MLC in cells on collagen-coated that MLC was in cells in medium but in the of the Rho kinase The current studies were carried out to learn more about the molecular motors responsible for LPA- and PDGF-stimulated fibroblast-collagen matrix contraction. suggest that PDGF- and LPA-stimulated floating matrix utilize myosin II-dependent and -independent mechanisms, respectively. Previous studies (10Lee D.J. Ho C.-H. Grinnell F. Exp. Cell Res. 2003; 289: 86-94Crossref PubMed Scopus (25) Google Scholar) that LPA-stimulated force generation by fibroblasts in floating collagen matrices does not require Rho kinase In the current found that fibroblasts the matrices even MLC kinase was using and Rho kinase was in the of Rho kinase MLC was these that contraction was independent of MLC not the that MLC kinase or of MLC phosphorylation were for contraction to MLC have been M. PubMed Scopus Google Scholar, J. Cell Biol. 1995; PubMed Scopus Google Scholar). were carried using the specific myosin II inhibitor concentrations to inhibit myosin II activity A. J. 2003; PubMed Scopus Google Scholar), blebbistatin blocked not floating matrix contraction but also LPA-dependent retraction of the dendritic of LPA-stimulated retraction of fibroblast dendritic extensions is a Rho activity independent from and not for floating matrix contraction (10Lee D.J. Ho C.-H. Grinnell F. Exp. 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Mol. Biol. Cell. 2002; 13: PubMed Scopus Google Scholar). the molecular of LPA-stimulated floating matrix is from LPA-stimulated matrix contraction. as can Jr., R.J. Wang Y. Proc. Natl. Acad. Sci. U. S. A. PubMed Scopus Google Scholar, Cell. Full Text Full Text PDF PubMed Scopus Google Scholar, Yamada K.M. J. Cell Biol. 2002; PubMed Scopus Google Scholar), the of force generation by fibroblasts in collagen matrices in response to increased of the matrix F. Trends Cell Biol. 2003; 13: 264-269Abstract Full Text Full Text PDF PubMed Scopus (668) Google Scholar, D.J. Ho C.-H. Grinnell F. Exp. Cell Res. 2003; 289: 86-94Crossref PubMed Scopus (25) Google Scholar, E. Grinnell F. Mol. Biol. Cell. 2002; 13: PubMed Scopus Google Scholar). As by and by matrix contraction depends on Rho kinase M. J.J. Exp. Cell Res. 2000; PubMed Scopus Google Scholar, M. H. A. H. E. T. M. T. Shibata M. M. Fujiwara K. M. Biochem. 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Physiol. 2001; 280: C1669-C1679Crossref PubMed Google Scholar, 17Totsukawa G. Yamakita Y. Yamashiro S. Hartshorne D.J. Sasaki Y. Matsumura F. J. Cell Biol. 2000; 150: 797-806Crossref PubMed Scopus (541) Google Scholar). molecular of force generation was with floating matrix contraction by floating matrix contraction myosin II from to by blebbistatin and the Rho kinase MLC kinase not to be and stimulation of was with of cells on S. Kuzuya M. Koike T. Asai T. Kanda S. Maeda K. Shibata T. Iguchi A. Atherosclerosis. 2001; 155: 321-327Abstract Full Text Full Text PDF PubMed Scopus (81) Google Scholar, G. Ho C.H. Grinnell F. J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus (26) Google Scholar). PDGF of fibroblasts in collagen matrices Rac and not Rho (9Grinnell F. Ho C.H. Tamariz E. Lee D.J. Skuta G. Mol. Biol. Cell. 2003; 14: 384-395Crossref PubMed Scopus (177) Google Scholar), as has been for cells on S. R.A. J. Cell Biol. 1999; PubMed Scopus Google Scholar, D.J. A. J. 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Hinz B. Chaponnier C. Brown R.A. Nat. Rev. Mol. Cell. Biol. 2002; 3: 349-363Crossref PubMed Scopus (3189) Google Scholar, B. Chaponnier C. Gabbiani G. Am. J. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, B. Gabbiani G. Chaponnier C. J. Cell Biol. 2002; PubMed Scopus Google Scholar), are not for B. 1998; PubMed Scopus Google Scholar, J. P. R. R. Proc. Natl. Acad. Sci. U. S. A. 1995; PubMed Scopus Google Scholar). fibroblasts to move and remodel the matrix is not well The and kinase-independent mechanisms as to We are to and for and

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