Differential degradation of [35S]methionine polypeptides in Duchenne muscular dystrophy skin fibroblasts in vitro.

Rates of protein turnover have been measured in three normal and three Duchenne muscular dystrophy (DMD) skin fibroblast cell lines. Cell populations were analyzed at identical states with regard to cell number, state of topoinhibition, and cumulative population doublings (CPD). Net protein synthesis measured by the incorporation of [35S]methionine in an 18-hr pulse was reduced by an average of 34%; degradation of total cellular protein measured after an 18-hr pulse with [35S]methionine and a 24-hr chase was enhanced by an average of 50% in DMD fibroblasts. Two-dimensional gel electrophoresis analyses revealed that the breakdown of the majority of [35S]methionine polypeptides was markedly increased in DMD fibroblasts. Quantitative determinations of the differential degradation rates of 10 selected proteins in the tropomyosin region of two-dimensional gels were undertaken by scintillation counting and computer analyses. In three series of experiments, the degradation of the 10 proteins in DMD fibroblasts was enhanced by individual polypeptides between 12.0% and 151.2% as measured by scintillation counting or between 0.8% and 128% as determined by computer analyses.