Anticancer drug action on poly(A) polymerase activity and isoforms during HeLa and WISH cell apoptosis.

Poly(A) polymerase (PAP; EC 2.7.7.19) catalyzes mRNA polyadenylation. Its activity and isoform levels vary during cell cycle transformation and apoptosis. It has become widely accepted that cell death after DNA damage by anticancer agents is primarily the result of apoptosis and that cells able to evade apoptosis will be resistant to cell killing. The therapeutic agents interferon (IFN), 5-fluorouracil (5-FU) and tamoxifen (Tam) with different mechanisms of action mediate both partial dephosphorylation and inactivation of PAP, detected by immunoblotting analysis and PAP enzyme assay, respectively. We examined the apoptotic tendencies of HeLa and WISH cell lines caused by one of the drugs used, 5-FU. The trend in the cells examined, observed by DAPI and/or DNA fragmentation assay, was found to be accompanied by and reversibly related to PAP activity levels and PAP lower mobility phosphorylated forms of 106 and 100 kDa isoforms. Moreover, a cell type-modulated, differential response of HeLa (chemosensitive cells) versus WISH (drug-resistant diploid cells) has been revealed. This finding yields information on the possible use of PAP as a tumor marker involved in cell commitment and/or induction of apoptosis and may help to improve our understanding of tumor cell sensitivity to anticancer agents.