Transforming growth factor-beta overrides the adhesion requirement for surface expression of alpha(5)beta(1) integrin in normal rat kidney fibroblasts - A necessary effect for induction of anchorage-independent growth

We have previously shown that the expression of alpha(5)beta(1) integrin on the cell surface is dependent upon cell adhesion to the extracellular matr ix, and we report here that transforming growth factor-beta (TGF-beta) over comes this requirement in normal rat kidney (NRK) fibroblasts. Thus, suspen ded NRK cells treated with TGF-beta show levels of surface alpha(5)beta(1) integrin that are equivalent to those seen in adherent cells. Moreover, sev eral experiments showed that this effect is necessary for the induction of anchorage-independent growth by TGF-beta. First, a kinetic analysis showed that surface expression of alpha(5)beta(1) integrin was restored in TGF-bet a-treated NRK cells prior to the induction of anchorage-independent growth. Second, NRK cell mutants that have lost their TGF-beta requirement for sur face expression of alpha(5)beta(1) integrin were anchorage-independent in t he absence of TGF-beta, Third, an antisense oligonucleotide to the beta(1) integrin subunit or, fourth, stable expression of an alpha(5)-antisense cDN A blocked the ability of TGF-beta to stimulate anchorage-independent growth . Thus, TGF-beta overrides the adhesion requirement for surface expression of alpha(5)beta(1) integrin in NRK cells, and this effect is necessary for the induction of anchorage-independent growth.