TRANSFORMING GROWTH-FACTOR BETA(1) SUPPRESSES TRANSFORMATION IN HEPATOCYTES BY REGULATING ALPHA(1)BETA(1) INTEGRIN EXPRESSION

We previously reported that (a) treatment of the ras-transformed hepat ocyte cell line NR4 with transforming growth factor (TGF) beta(1) supp resses many characteristics associated with the transformed phenotype including altered morphology, actin cytoskeleton reorganization, and a nchorage-independent growth such that the cells more closely resemble the immortalized CWSV1 parent cell line; (b) transformed NR4 cell expr essed significantly less alpha(1) integrin RNA than the immortalized C WSV1 cells; and (c) TGF-beta(1) treatment of NR4 cells stimulated the express of alpha(1) and beta(1) integrin in TGF-beta(1)-mediated suppr ession of the ras-transformed phenotype was investigated. We determine d that (a) the cell surface integrin that increased in response to TGF -beta(1) treatment of NR4 cells was alpha(1) integrin; (b) TGF-beta(1) altered the ability of NR4 cells to attach to collagen and laminin, t he extracellular matrix components that interact with the alpha(1) bet a(1) integrin receptor; (c) TGF-beta(1) treatment resulted in relocali zation of the alpha(1) integrin on the NR4 cell surface; and (d) TGF-b eta(1)-mediated inhibition of anchorage-independent growth was blocked by the presence of alpha(1) integrin antibody. A cell lin that overex presses alpha(1) integrin was derived from NR4 cells; characterization of these cells indicated that they continued to express H-ras RNA but were less transformed than the parent NR4 cells. Specifically, they h ad an altered morphology, an organized actin cytoskeleton, and reduced ability to demonstrate anchorage-independent growth. We conclude that functional alpha(1) beta(1) integrin is necessary for TGF-beta(1)-med iated suppression of the ras-transformed phenotype in the ras-transfor med hepatocyte cell line NR4.