title: Altered degradation of proteins microinjected into senescent human fibroblasts.
abstract: Ribonuclease A was introduced into the cytoplasm of IMR-90 human diploid fibroblasts by red cell-mediated microinjection. Early passage fibroblasts degraded ribonuclease A with a half-life of approximately 90 h in the presence of 10% fetal calf serum and enhanced the degradative rate 1.6-fold upon serum withdrawal. Senescent cells degraded ribonuclease A more slowly with half-lives ranging between 125 and 250 h and had diminished capacities to enhance the catabolism of this protein during serum starvation. Decreased protein degradation in senescent cells was also evident for microinjected RNase S-protein, RNase B, aldolase, lysozyme, and the synthetic copolymer polyglutamate: tyrosine:alanine (1:1:1). These alterations in the mechanisms and regulation of intracellular protein degradation may contribute to several biochemical abnormalities characteristic of aging cells and organisms.
mesh_terms: D002460:Cell Line; D004722:Endoribonucleases / Q000378:metabolism; D004910:Erythrocyte Membrane; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008168:Lung; D008845:Microinjections; D011506:Proteins / Q000378:metabolism*; D012259:Ribonuclease, Pancreatic
chemical_list: D011506:Proteins; D004722:Endoribonucleases; D012259:Ribonuclease, Pancreatic