Investigation of cell death induced by N-methyl-N-nitrosourea in cell lines of human origin and implication of RNA binding protein alterations.

Methylating agents, a widely used class of anticancer drugs, induce DNA methylation adducts, the most biologically significant being O(6)-methylguanine. The efficacy of these drugs depends on the interplay of three DNA repair systems: base excision repair (BER), methyl-directed mismatch repair (MMR) and direct damage reversal by O(6)-methylguanine-DNA methyltransferase (MGMT). An MGMT-inducible, MMR- and BER-proficient HeLa cell line was treated with different concentrations of N-methyl-N-nitrosourea (MNU), a model S(N)1 methylating agent, analogous to widely used methylating cancer chemotherapeutic drugs, under different expression levels of the repair enzyme (MGMT). MNU induced MGMT-dependent apoptotic cell death. In this particular cellular context, the induction of apoptosis was accompanied by modifications of the RNA binding protein poly(A)polymerase and significant down-regulation of the heterogeneous nuclear ribonucleoprotein (hnRNP) C1/C2. These results implicate alterations of the above mentioned RNA binding proteins in S(N)1 methylating agent-induced cell death and apoptosis, providing a possible perspective regarding their use as biomarkers of tumor resistance/sensitivity to chemotherapy.