Activated Rac1 selectively up-regulates the expression of integrin alpha 6beta 4 and induces cell adhesion and membrane ruffles of nonadherent coloncancer Colo201 cells

Functions of small GTPases in integrin expression were investigated when th e interaction of nonadherent human colon carcinoma 201 cells with the extra cellular matrix (ECM) was examined. By transfection of the constitutively a ctive form of a small GTPase Rad, Rac Via, adhesion of cells to the ECM inc reased with concomitant cell spreading and formation of membrane ruffles. A ctivated Cdc42 and Cdc42 V12, but not wild-type Rad, Cdc42, or RhoA, also i nduced the adhesion and spreading of Colo201 cells. This adhesion is integr in beta 4 dependent since an antibody for integrin beta 4 inhibited the Rac V12-dependent cell adhesion and numbers of adhesive cells on laminin-coated plates exceeded those on collagen- and fibronectin-coated plates. By immun ofluorescence, in addition to clustering of integrin molecules, expression of integrin alpha 6 beta 4 on the cell surface of Rac V12- and Cdc42 Via-ex pressing cells was selectively up-regulated without an increase in biosynth esis of alpha 6 beta 4 integrin. Treatment of Rac Via-expressing cells with wortmannin or LY294002, specific inhibitors of phosphoinositide 3-OH kinas e, decreased the up-regulated (alpha 6 beta 4 and cell adhesion. In light o f this evidence, we propose that the regulation of integrin alpha 6 beta 4 expression induced by Rad and Cdc42 may play an important role in cell adhe sion and tumorigenesis of colon carcinoma cells. (C) 1999 Academic Press.