AJP - Cell Physiology, Vol 251, Issue 5 748-C753, Copyright © 1986 by American Physiological Society
Proteolysis in cultured cells during prolonged serum deprivation and replacement
J. J. Berger and J. F. Dice
Cells in culture show a series of changes in intracellular protein
degradation in response to serum deprivation and replacement that are
similar to alterations in degradation in tissues of starved and refed
animals. Rates of intracellular protein degradation are increased in
confluent cultures of IMR-90 human diploid fibroblasts when deprived of
serum, but this enhanced proteolysis is transient. By 24-48 h, rates of
protein degradation decline to values comparable to or below those for
cells incubated in the presence of serum. Longer serum deprivation leads to
further reductions in proteolysis. The reduced proteolysis after long-term
deprivation cannot be explained by experimental artifacts or by gradual
depletion of glucocorticoids or thyroid hormones from cells. Readdition of
serum to deprived cells that are still in the enhanced phase of proteolysis
restores degradation rates to values comparable to those in nondeprived
cells. However, in cells deprived of serum for 24-48 h or longer,
readdition of serum to the medium results in a marked reduction in
proteolysis to rates below those observed in nondeprived cells. These
responses of cultured cells to long-term serum deprivation and readdition
may be of considerable physiological importance in that the proteolytic
responses of tissues in starved and refed animals may be at least partially
due to mechanisms operating at the cellular level.
