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Title: Effect of serum starvation on expression and phosphorylation of PKC-alpha and p53 in V79 cells: implications for cell death
Authors: Hasan, Nael M. 
Adams, Gerald E. 
Joiner, Michael C. 
Keywords: Phosphorylation of PKC;Serum starvation;PKC-a AND p53 IN V79 Cells;PKC-a Cells
Issue Date: 1999
Abstract: The effect of serum starvation on the expression and phosphorylation of PKC-a and p53 in Chinese hamster V79 cells was investigated. Serum starvation led to growth arrest, rounding up of cells and the appearance of new PKC-a and p53 bands on Western blots. Prolonged incubation (H48 hr) in serum-deprived medium led to cell detachment and death. Moving cells to fresh medium containing 10% serum before, but not after, cell detachment reversed the changes observed in PKC-a and p53, and also prevented later cell detachment. Radiolabelling studies showed that the higher-molecular weight PKC-a and p53 bands result from increased phosphorylation, while a lower-molecular-weight PKC-a band reflects newly synthesized protein. Immunocomplex kinase assays have shown that the increased phosphorylation of PKC-a is associated with its increased activity. To study the relationship between PKC-a, p53 and cell death, cells were treated either with TPA, to down-regulate PKC or with staurosporine, to inhibit PKC activity. Staurosporine, a potent PKC inhibitor and inducer of programmed cell death, caused the appearance of new PKC-a and p53 bands similar to those induced by serum starvation. If serum starvation was preceded by prolonged (48 hr) TPA treatment to down-regulate PKC-a, cell detachment and death did not take place within the same time frame. Intracellular fractionation of cells demonstrated that increased expression of PKC-a and the appearance of the associated higher and lower molecular weight bands occurred in the nucleus. These data highlight the association of PKC-a and p53 with cellular events leading to cell death. Int. J. Cancer 80:400–405, 1999.
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