Abstract
SMYD3 is a methyltransferase highly expressed in many types of cancer. It usually functions as an oncogenic protein to promote cell cycle, cell proliferation, and metastasis. Here, we show that SMYD3 modulates another hallmark of cancer, DNA repair, by stimulating transcription of genes involved in multiple steps of homologous recombination. Deficiency of SMYD3 induces DNA-damage hypersensitivity, decreases levels of repair foci, and leads to impairment of homologous recombination. Moreover, the regulation of homologous recombination-related genes is via the methylation of H3K4 at the target gene promoters. These data imply that, besides its reported oncogenic abilities, SMYD3 may maintain genome integrity by ensuring expression levels of HR proteins to cope with the high demand of restart of stalled replication forks in cancers.