DOT1L Regulates Ovarian Cancer Stem Cells by Activating β-catenin Signaling.

Cancer stem cells (CSC) represent a population of cancer cells responsible for tumor initiation, chemoresistance and metastasis. Here we identified the H3K79 methyltransferase disruptor of telomeric silencing-1-like (DOT1L) as a critical regulator of self-renewal and tumor initiation in ovarian CSCs. DOT1L was upregulated in ovarian CSCs vs. non-CSCs. shRNA-mediated DOT1L knockdown decreased the aldehyde dehydrogenase (ALDH) + cell population, impaired the tumor initiation capacity of ovarian CSCs, and blocked the expression of stemness-associated genes. Inhibition of DOT1L's methyltransferase activity by the small molecule inhibitor (DOT1Li) EPZ-5676 also effectively targeted ovarian CSCs. Integrated RNA-sequencing analyses of ovarian cancer (OC) cells in which DOT1L was knocked down vs. control cells and of ovarian CSCs vs. non-CSCs, identified Wnt signaling as a shared pathway deregulated in both CSCs and in DOT1L-deficient OC cells. β-catenin, a key transcription factor regulated by Wnt, was downregulated in OC cells in which DOT1L was knocked down and upregulated in DOT1L overexpressing OC cells. Chromatin immunoprecipitation (ChIP) revealed enrichment of the H3K79Me3 mark at the β-catenin promoter, suggesting that its transcription is regulated by DOT1L. Our results suggest that DOT1L is critical for the self-renewal and tumor initiation capacity (TIC) of ovarian CSCs by regulating β-catenin signaling. Targeting DOT1L in OC could be a new strategy to eliminate CSCs. Implications: This study found that the histone methyltransferase DOT1L regulates the self-renewal and tumor initiation capacity of ovarian CSCs and suggests DOT1L as a new cancer target.