MLH1 mediates PARP-dependent cell death in response to the methylating agent N-methyl-N-nitrosourea

J. R. McDaid, J. Loughery, P. Dunne, J. C. Boyer, Stephen Downes, R. A. Farber, Colum Walsh

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15 Citations (Scopus)


BACKGROUND: Methylating agents such as N-methyl-N-nitrosourea (MNU) can cause cell cycle arrest and death either via caspase-dependent apoptosis or via a poly(ADP-ribose) polymerase (PARP)-dependent form of apoptosis. We wished to investigate the possible role of MLH1 in signalling cell death through PARP. METHODS: Fibroblasts are particularly dependent on a PARP-mediated cell death response to methylating agents. We used hTERT-immortalised normal human fibroblasts (WT) to generate isogenic MLH1-depleted cells, confirmed by quantitative PCR and western blotting. Drug resistance was measured by clonogenic and cell viability assays and effects on the cell cycle by cell sorting. Damage signalling was additionally investigated using immunostaining. RESULTS: MLH1-depleted cells were more resistant to MNU, as expected. Despite having an intact G(2)/M checkpoint, the WT cells did not initially undergo cell cycle arrest but instead triggered cell death directly by PARP overactivation and nuclear translocation of apoptosis-inducing factor (AIF). The MLH1-depleted cells showed defects in this pathway, with decreased staining for phosphorylated H2AX, altered PARP activity and reduced AIF translocation. Inhibitors of PARP, but not of caspases, blocked AIF translocation and greatly decreased short-term cell death in both WT and MLH1-depleted cells. This MLH1-dependent response to MNU was not blocked by inhibitors of ATM/ATR or p53. CONCLUSION: These novel data indicate an important role for MLH1 in signalling PARP-dependent cell death in response to the methylating agent MNU. British Journal of Cancer (2009) 101, 441-451. doi:10.1038/sj.bjc.6605186 Published online 28 July 2009 (C) 2009 Cancer Research UK
Original languageEnglish
Pages (from-to)441-451
Issue number3
Publication statusPublished (in print/issue) - Jul 2009


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