Differences in turnover rates of vinculin and talin caused by viral transformation and cell density

Vinculin and talin are two major components of focal contacts which interact with each other. In order to understand how the relative levels of these proteins are maintained under various conditions, the synthesis rates and half-lives of vinculin and talin in chick embryonic fibroblasts were determined by autoradiography combined with immunoblotting. High cell density and transformation by Rous sarcoma virus decreased the vinculin synthesis rate by 40%. Upon viral transformation, the synthesis rate of talin decreased by 30%. In contrast to vinculin, the synthesis rate of talin was not affected by cell density. The effect of cell density on the synthesis rate of vinculin was retained after viral transformation, suggesting that cell density and viral transformation affect vinculin synthesis by two independent mechanisms. The synthesis rate of vinculin was approximately two to three times greater than that of talin under all conditions tested. The half-lives of vinculin and talin remained constant at different cell densities in untransformed cells (t1/2 = 18-21 h), but transformation slightly decreased half-lives of both proteins (t1/2 = 16-18 h). These results suggest that the decreased expression of vinculin and talin in transformed chick fibroblasts can be attributed mainly to changes in their biosynthesis rates rather than degradation. This may contribute to a decrease in the number of focal contacts in transformed cells.