The human mismatch repair interactome


Session type:

Josef Jiricny1
1Institute of Molecular Cancer Research, Zurich, Switzerland


Mismatch repair (MMR) is a complex pathway of DNA metabolism that has evolved to increase the fidelity of DNA replication by removing misincorporated nucleotides from the newly-synthesized strand. The importance of this pathway to human health is highlighted by the fact that loss of mismatch repair, either through mutation or transcriptional silencing of MMR genes, predisposes to cancer of the colon, endometrium and ovary. However, MMR proteins also help control recombination fidelity, and recent findings implicate MMR proteins also in DNA damage signalling, somatic hypermutation and class switch recombination of immunoglobulin genes, as well as in the processing of oxidative DNA damage. In an attempt to understand how MMR participates in such diverse pathways of DNA metabolism, we carried out high-throughput assays designed to identify novel interacting partners of MMR proteins.

We screened a library of mgt1-deficient S. cerevisiae deletion mutants for resistance to MNNG, a general hallmark of MMR deficiency. This screen identified a number of interesting genes involved in DNA damage processing and chromatin remodelling. In the human proteomic screen, we identified FANCJ as an interactor of the MMR protein MLH1. FANCJ is a 5’ to 3’ DNA helicase that participates in the Fanconi anaemia (FA) pathway. The significance of this interaction is unclear as yet, given that MLH1-deficient cells do not display sensitivity to cisplatin and mitomycin C (MMC) typical of FA cells, nor do FANCJ-deficient cells display a defect in MMR. We also identified FAN1, a novel DNA endonuclease. An MLH1 pull-down assay identified several other polypeptides, some with an unknown function, which we are currently following up. In this presentation, I shall focus on some of our most recent findings in the above research projects.