Type I collagen synergistically enhances PDGF-induced smooth muscle cell proliferation through pp60src-dependent crosstalk between the alpha2beta1 integrin and PDGFbeta receptor.
Smooth muscle cells (SMCs) are exposed to both platelet-derived growth factor (PDGF) and type I collagen (CNI) at the time of arterial injury. In these studies we explore the individual and combined effects of these agonists on human saphenous vein SMC proliferation. PDGF-BB produced a 5.5-fold increase in SMC DNA synthesis whereas CNI stimulated DNA synthesis to a much lesser extent (1.6-fold increase). Alternatively, we observed an 8.3-fold increase in DNA synthesis when SMCs were co-incubated with CNI and PDGF-BB. Furthermore, stimulation of SMCs with PDGF-BB produced a significant increase in ERK-2 activity whereas CNI alone had no effect. Co-incubation of SMCs with PDGF-BB and CNI resulted in ERK-2 activity that was markedly greater than that produced by PDGF-BB alone. In a similar fashion, PDGF-BB induced phosphorylation of the PDGF receptor beta (PDGFRbeta) and CNI did not, whereas concurrent agonist stimulation produced a synergistic increase in receptor activity. Blocking antibodies to the alpha2 and beta1 subunits eliminated this synergistic interaction, implicating the alpha2beta1 integrin as the mediator of this effect. Immunoprecipitation of the alpha2beta1 integrin in unstimulated SMCs followed by immunoblotting for the PDGFRbeta as well as Src family members, pp60(src), Fyn, Lyn, and Yes demonstrated coassociation of alpha2beta1 and the PDGFRbeta as well as pp60(src). Incubation of cells with CNI and/or PDGF-BB did not change the degree of association. Finally, inhibition of Src activity with SU6656 eliminated the synergistic effect of CNI on PDGF-induced PDGFRbeta phosphorylation suggesting an important role for pp60(src) in the observed receptor crosstalk. Together, these data demonstrate that CNI synergistically enhances PDGF-induced SMC proliferation through Src-dependent crosstalk between the alpha2beta1 integrin and the PDGFRbeta.
Hollenbeck
Scott T
ST
Columbia Weill Cornell Division of Vascular Surgery, Weill Medical College of Cornell University, USA. sth9005@med.cornell.edu
Itoh
Hiroyuki
H
Louie
Otway
O
Faries
Peter L
PL
Liu
Bo
B
Kent
K Craig
KC
D000818:Animals; D000077214:Becaplermin; D049109:Cell Proliferation; D002478:Cells, Cultured; D024042:Collagen Type I / Q000378:metabolism*; D024141:Collagen Type IV / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D038982:Integrin alpha2beta1 / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000502:physiology*; D010982:Platelet-Derived Growth Factor / Q000378:metabolism*; D020574:Proto-Oncogene Proteins c-sis; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism*; D020797:Receptor, Platelet-Derived Growth Factor beta / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D014680:Veins / Q000033:anatomy & histology
D024042:Collagen Type I; D024141:Collagen Type IV; D038982:Integrin alpha2beta1; D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; D000077214:Becaplermin; D020797:Receptor, Platelet-Derived Growth Factor beta; D016392:Proto-Oncogene Proteins pp60(c-src); D020928:Mitogen-Activated Protein Kinases