Abstract
Cystinotic fibroblasts accumulate lysosomal cystine from the degradation of endogenous and exogenous cystine-containing proteins. Lysosomal cystine accumulation can be modulated by the addition of cystine rich proteins to the culture medium or by labelling the endogenous protein pool with 35(S)-cystine for varying periods.Cultures of cystinotic fibroblasts were incubated in 35(S) -cystine-containing medium (40 mCi/mmol) for 4,24, or 48 hr;treated with cysteamine for 30 min. to produce cystine depletion, and replaced in unlabelled medium with or without 100μM cycloheximide (CHx). The plates were harvested after 24 hr in unlabelled medium and the amount of 35(S)-cystine accumulation determined by high voltage electrophoresis. 100μM CHx inhibited 35(S)-cystine accumulation from all labelling periods. Results are expressed as CPM/106 cells of 35(S)-cystine X 104:4 hrs-control 1.46±.50, CHx 0.34±0.27 p 0.5 n=3. CHx, a known inhibitor of protein synthesis, also inhibits the lysosomal degradation of endogenous but not exogenous proteins,yet appears to enhance overall proteolysis.
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