Differences in the rates of protein degradation in untransformed and transformed cell lines

Abstract

The rate of protein degradation in 3T3, 3T3/41, SV40 virus-transformed 3T3, BHK21, Rous sarcoma virus-transformed BHK21 and MRC-5 cells was assayed in monolayer and suspension culture by pre-labeling the cells with radioactive leucine and measuring the loss of radioactivity from the cells. The rate of protein degradation of 3T3 and MRC-5 cells in suspension culture, under which condition they do not grow, was greater than that of other cell lines which are capable of growing in suspension. In all cell lines it was greater in suspension culture than in monolayer culture. There was an inverse correlation between the rate of protein degradation and the growth rate of the cells. The addition of insulin to 3T3 cells in suspension culture causes the reduction of the rate of protein degradation, increase of cellular protein and stimulation of DNA synthesis.