Intracellular protein degradation in serum-deprived human fibroblasts.
IMR90 human fibroblasts were labelled by incubation of cells for 48 h in medium containing 10% serum and [3H]leucine. The labelled protein was degraded at a rate of 1%/h during a subsequent incubation in medium with 10% serum. Incubation in medium without serum caused a transient enhancement of the degradation of endogenous protein, which was also found in cells labelled in medium without serum. The degradation of micro-injected haemoglobin was enhanced by serum deprivation in a non-transient manner. These results suggest that enhanced degradation in serum-free medium occurs only for a subpopulation of cell proteins and that it appears transient because the major part of the pool of susceptible endogenous proteins is being degraded during the first 20-30 h in serum-free unlabelled medium. Protein turnover in various cell compartments was measured by a double-labelling technique. Most of the enhanced degradation in serum-deprived cultures (73-83%) was due to breakdown of cytosolic proteins. The enhanced degradation of cytosolic proteins seemed to affect several proteins irrespective of their molecular mass or metabolic stability.
D001769:Blood; D002478:Cells, Cultured; D002498:Centrifugation / Q000379:methods; D003470:Culture Media; D003600:Cytosol / Q000378:metabolism; D005347:Fibroblasts / Q000201:enzymology / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D011506:Proteins / Q000378:metabolism*; D012313:RNA / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism
D003470:Culture Media; D006454:Hemoglobins; D011506:Proteins; D012313:RNA