Drug action on poly(A) polymerase activity and isoforms during U937 cell apoptosis

The enzyme poly(A) polymerase (PAP; EC 2.7.7.19) catalyzes the polyadenylat ion of mRNAs. It's activity levels and isoforms vary within the cell cycle (31) and apoptosis (34). The direct effect of most anticancer drugs is cell damage (DNA and RNA synthesis inhibition, DNA breaks and/or cell cycle abe rrations), which then triggers signaling pathways that activate apoptosis a nd eventually lead to regulated cell death. The experiments described here concern the chemotherapeutic agents, interferon (IFN) and 5-fluorouracil (5 -FU), and their action on U937 cells, alone or in various combinations, res ulting in the commitment of cell apoptosis, as observed by the appearance o f DNA fragmentation. Furthermore, examination of U937 cell apoptotic trend in parallel with PAP activity measurements and isoforms detection by immuno blotting, revealed both partial enzyme inactivation and dephosphorylation, in particular after the combined drug action of 5-FU and IFN on U937 cells. Our work on chemotherapeutic drug action at the level of mRNA polyadenylat ion may contribute to new insights into the mechanism of cell apoptosis, as well as provide information on mRNA poly(A) tail formation, removal and fu nction.