N⁶-Methylation of Adenosine of <i>FZD10</i> mRNA Contributes to PARP Inhibitor Resistance.

Abstract

Despite the high initial response rates to PARP inhibitors (PARPi) in <i>BRCA</i>-mutated epithelial ovarian cancers (EOC), PARPi resistance remains a major challenge. Chemical modifications of RNAs have emerged as a new layer of epigenetic gene regulation. N⁶-methyladenosine (m⁶A) is the most abundant chemical modification of mRNA, yet the role of m⁶A modification in PARPi resistance has not previously been explored. Here, we show that m⁶A modification of <i>FZD10</i> mRNA contributes to PARPi resistance by upregulating the Wnt/β-catenin pathway in <i>BRCA</i>-mutated EOC cells. Global m⁶A profile revealed a significant increase in m⁶A modification in <i>FZD10</i> mRNA, which correlated with increased <i>FZD10</i> mRNA stability and an upregulation of the Wnt/β-catenin pathway. Depletion of FZD10 or inhibition of the Wnt/β-catenin sensitizes resistant cells to PARPi. Mechanistically, downregulation of m⁶A demethylases FTO and ALKBH5 was sufficient to increase <i>FZD10</i> mRNA m⁶A modification and reduce PARPi sensitivity, which correlated with an increase in homologous recombination activity. Moreover, combined inhibition of PARP and Wnt/β-catenin showed synergistic suppression of PARPi-resistant cells <i>in vitro</i> and <i>in vivo</i> in a xenograft EOC mouse model. Overall, our results show that m⁶A contributes to PARPi resistance in BRCA-deficient EOC cells by upregulating the Wnt/β-catenin pathway via stabilization of <i>FZD10</i>. They also suggest that inhibition of the Wnt/β-catenin pathway represents a potential strategy to overcome PARPi resistance. SIGNIFICANCE: These findings elucidate a novel regulatory mechanism of PARPi resistance in EOC by showing that m⁶A modification of FZD10 mRNA contributes to PARPi resistance in BRCA-deficient EOC cells via upregulation of Wnt/β-catenin pathway.