Protein oxidation and degradation during proliferative senescence of humanMRC-5 fibroblasts

One of the highlights of age-related changes of cellular metabolism is the accumulation of oxidized proteins. The aging process on a cellular level ca n be treated either as the ongoing proliferation until a certain number of cell divisions is reached (the Hayflick Limit) or as the aging of nondividi ng cells, that is, the age-related changes in cells without proliferation. The present investigation was undertaken to reveal the changes in protein t urnover, proteasome activity, and protein oxidation status during prolifera tive senescence. We were able to demonstrate that the activity of the cytos olic proteasomal system declines dramatically during the proliferative sene scence of human MRC-5 fibroblasts. Regardless of the loss in activity, it c ould be demonstrated that there are no changes in the transcription and tra nslation of proteasomal subunits. This decline in proteasome activity was a ccompanied by an increased concentration of oxidized proteins. Cells at hig her proliferation stages were no longer able to respond with increased degr adation of endogenous [S-35]-Met-radiolabeled proteins after hydrogen perox ide- or quinone-induced oxidative stress. It could be demonstrated that oxi dized proteins in senescent human MRC-5 fibroblasts are not as quickly remo ved as they are in young cells. Therefore, our study demonstrates that the accumulation of oxidized proteins and decline in protein turnover and activ ity of the proteasomal system are not only a process of postmitotic aging b ut also occur during proliferative senescence and result in an increased ha lf-life of oxidized proteins. (C) 2000 Elsevier Science Inc.