Suppression of TNF-alpha mediated apoptosis by EGF in TNF-alpha sensitive human cervical carcinoma cell line.

The tumor suppressor protein p53 is the most frequently mutated gene in human cancer. The function of p53 is not restricted to "guarding" against oncogenic stress, but also p53 can guard against the presence of DNA damage. One of the principal mechanisms by which cells achieve this is by regulating the p53 protein level although its phosphorylation and cellular localization also contribute to the regulation of its function. Since many tumors secrete growth factor(s) that inhibit apoptosis and support the growth of cancer cells, we investigated the effects of human epidermal growth factor (EGF) on human TNF-alpha-mediated induction of p53 and its transcriptional target, p21 in TNF-alpha sensitive human cervical carcinoma cell line, ME180S. We found that TNF-alpha can increase the cellular levels of p53, p21 and induce apoptosis in ME180S cells. However, pretreatment of cells with EGF can suppress all these effects of TNF-alpha. To determine which kinase(s) pathway was utilized by EGF to show these suppressive effects, cells were pretreated with inhibitors of MAPK, PI3K and PKC pathways. Among these only PKC inhibitor reversed all the suppressive effects of EGF. We also found that ME180S cells express only zeta, lambda, epsilon, iota, delta, theta, beta PKC subtypes and among these EGF treatment activate only PKC-delta redistribution to the membrane from the cytosol. An inhibitor of PKC, GF 109203X inhibited EGF-mediated suppression of TNF-alpha-induced accumulation of p53, p21 and induction of apoptosis. In summary, we concluded that EGF can protect ME180S cells from TNF-alpha-induced apoptosis through activation of PKC-delta.