MULTIPLE PATHWAYS ARE INVOLVED IN PROTECTION OF MCF-7 CELLS AGAINST DEATH DUE TO PROTEIN-SYNTHESIS INHIBITION

Previously we have shown that IGF-1 protected MCF-7 cells against deat h induced by the protein synthesis inhibitor cycloheximide (CHX). In t he present study we investigated the ability of protein kinase C activ ator 12-O-tetradecanoyl-phorbol-13-acetate (TPA), the protein kinase A activator 8-bromoadenosine 3'5'-cyclic monophosphate (Br-cAMP), and t he enzyme inhibitor aurintricarboxylic acid (ATA) to protect MCF-7 cel ls against death, due to a continuous presence of CHX. Cell death was evaluated after 48 h of incubation by several techniques (trypan blue staining, release of lactic dehydrogenase, cellular ATP content, trans mission electron microscopy, and DNA fragmentation). Apoptosis which t erminates in necrosis, characterized this mode of cell death. TPA and ATA at optimal concentrations of 40 ng/ml and 100 mu g/ml, respectivel y, reduced cell death to the control level (without CHX), while Br-cAM P at an optimal concentration of 650 mu g/ml reduced cell death only p artially. IGF-1, TPA, and ATA, which stimulated protein synthesis in t he control MCF-7 cells, had no effect on protein synthesis in the CHX- treated cells, indicating that the survival effect is not due to new p rotein synthesis. The protein kinase C inhibitor staurosporine blocked the survival effect of TPA and IGF-1 in a dose-dependent manner, howe ver did not affect the survival effect of ATA. The tyrosine kinase inh ibitor genistein blocked the survival effect of IGF-1, but not that of TPA and ATA. Our results provide evidence for several distinctive pat hways, the activation of which protects MCF-7 cells against death, due to protein synthesis inhibition. (C) 1995 Wiley-Liss, Inc.