ABSTRACT
Tenascin-C is an adhesion modulatory matrix protein that is highly expressed in tumors; however, its biochemical activity involved in tumorigenesis is not fully understood. On the other hand, increasing evidence indicates the importance of integrin α5ß1 in cancer development. We previously demonstrated that tenascin-C harbors a functional site that can be released as a proadhesive peptide such as TNIIIA2. Peptide TNIIIA2 is capable of inducing activation of ß1-integrins including α5ß1 via syndecan-4. In this study the proadhesive effect of TNIIIA2 was characterized by potentiated and sustained activation of integrin α5ß1. Based on this effect, TNIIIA2 rendered nontransformed fibroblasts (NIH3T3) resistant to serum deprivation-elicited anoikis through activation of the Akt/Bcl-2 pathway. Moreover, TNIIIA2 hyperstimulated PDGF-dependent proliferation of NIH3T3 by activating integrin α5ß1. Tenascin-C, a parental protein of TNIIIA2, also stimulated PDGF-dependent proliferation, which was blocked by a matrix metalloproteinase-2/9 inhibitor and an anti-TNIIIA2 function-blocking antibody, suggesting proteolytic exposure of the proadhesive effect of TNIIIA2. Mechanistic analyses revealed that TNIIIA2 induced a lateral association of PDGF receptor ß with the molecular complex of activated integrin α5ß1 and syndecan-4 in the membrane microdomains enriched with cholesterol/caveolin-1, resulting in prolonged activation of PDGF receptor ß and the subsequent Ras/mitogen-activated protein kinase pathway in a PDGF-dependent manner. Of note, TNIIIA2 induced continuous proliferation in NIH3T3 in an integrin α5ß1-dependent manner even after they formed a confluent monolayer. Thus, it was proposed that tenascin-C might be involved in deregulated cell growth through potentiated and sustained activation of integrin α5ß1 after exposure of the proadhesive effect of TNIIIA2.
