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 a ctivity and isoform levels vary during cell cycle transformation and apopto sis. It has become widely accepted that cell death after DNA damage by anti cancer agents is primarily the result of apoptosis and that cells able to e vade apoptosis will be resistant to cell killing. The therapeutic agents in terferon (IFN), 5-fluorouracil (5-FU) and tamoxifen (Tam) with different me chanisms of action mediate both partial dephosphorylation and inactivation of PAP, detected by immunoblotting analysis and PAP enzyme assay, respectiv ely. We examined the apoptotic tendencies of HeLa and WISH cell lines cause d 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 phosphory lated forms of 106 and 100 kDa isoforms. Moreover, a cell type-modulated, d ifferential response of HeLa (chemosensitive cells) versus WISH (drug-resis tant diploid cells) has been revealed. This finding yields information on t he 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.