RhoA-dependent switch between alpha 2 beta 1 and alpha 3 beta 1 integrins is induced by laminin-5 during early stage of HT-29 cell differentiation

Integrin-mediated interactions between the basement membrane and epithelial cells control the differentiation of epithelia. We characterized the modul ation of adhesive behaviors to basement membrane proteins and of integrin f unction in the human colon adenocarcinoma HT-29 cell line, which differenti ates into enterocytes after the substitution of galactose for glucose in th e medium. We demonstrate an increased capability of these cells to adhere t o collagen type IV during the early stage of differentiation. This effect o ccurs without any changes in integrin cell surface expression but rather re sults from an alpha2 beta1/alpha3 beta1 integrin switch, alpha3 beta1 integ rin becoming the major collagen receptor. The increase in laminin-5 secreti on and deposit on the matrix is a key factor in the mechanism regulating ce ll adhesion, because it is responsible for the activation of alpha3 beta1 i ntegrin. Furthermore, down-regulation of RhoA GTPase activity occurs during HT-29 cell differentiation and correlates with the activation of the integ rin alpha3 beta1. Indeed, C3 transferase, a RhoA GTPase inhibitor, induces a similar alpha2 beta1/alpha3 beta1 switch in undifferentiated HT-29 cells. These results indicate that the decrease in RhoA activation is the biochem ical mechanism underlying this integrin switch observed during cell differe ntiation. The physiological relevance of such modulation of integrin activi ty in the functioning of the crypt-villus axis is discussed.