Derangement of regulation of protein degradation in transforming fibroblasts.

Changes in endogenous protein degradation of stable proteins with growth state have been observed in a number of normal cell lines: increases in degradation of between 15 and 40% occurred in 10 cell lines at confluence. No such regulation of proteolysis was observed in 4 cell lines which were clonogenic in soft agar. We have evidence that this derangement of regulation coincides with the transformation of cells, because such regulation disappears in spontaneously transforming fibroblasts and is decreased by the tumour promoter 12-0-tetradecanoyl-phorbol-13-acetate. In addition, regulation reappears in a growth control revertant of a transformed line.