title: Evidence of heterogeneity of protein-turnover states in cultured cells.
abstract: Previous studies on L-cell cultures [Amenta & Sargus (1979) Biochem. J. 182, 847--859] have suggested: (a) that degradation of slow-turnover proteins occurs in a distinct cell state (D-state); (b) that cells randomly enter the D-state with a first-order transition constant, rapidly degrade cell protein, and return to a quiescent G0-state. In the present study we have tested the hypothesis that the putative D-state exists as a substate within A-state (non-replicating) fibroblasts. Rat-embryo fibroblasts were prelabelled with [14C]leucine and [3H]thymidine, 'chased' for 24 h, and then placed in fresh growth medium containing either vinblastine (10 microM) or colchicine (25 microM) for three successive 24 h periods. Cells trapped in mitosis were separated from the residual non-replicating cells and rates of protein synthesis, degradation and net accumulation were measured in both populations. We observed that significant protein degradation occurred only in the non-replicating population, although both populations showed equally high rates of protein synthesis induced by fresh growth medium. These data support the hypothesis that degradation of slow-turnover protein is heterogeneous, occurring only in A-state cells. A model that proposes a separate D-state within G0-phase successfully accounts for these observations and previous reports on this cell line [Amenta, Sargus & Baccino (1978) J. Cell. Physiol. 97, 267--283] showing no differences in degradation of the slow-turnover protein pool in growth-stimulated and stationary-phase fibroblast cultures.
mesh_terms: D000818:Animals; D002455:Cell Division; D002478:Cells, Cultured; D003078:Colchicine / Q000494:pharmacology; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism*; D008938:Mitosis; D008954:Models, Biological; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D014747:Vinblastine / Q000494:pharmacology
chemical_list: D011506:Proteins; D014747:Vinblastine; D003078:Colchicine