Inhibition of polo-like kinase 4 manifests anti-leukemic effects through remodelling histone methylation

Abstract

Current treatment for acute myeloid leukemia (AML) comprises intensive chemotherapy (IC) and allogeneic hematopoietic stem cell transplantation (HSCT). However, these approaches have not been successful in patients with TP53 mutated AML with less than 25% of them maintain long-term remission. Recent findings suggested that targeting polo-like kinase 4 (PLK4), a centriole duplication and cytokinesis regulator, might be a promising cancer treatment strategy including TP53 mutated AML. However, the therapeutic mechanism of this novel target has not been fully elucidated. Herein, we reported the hitherto undescribed effect of PLK4 inhibition on the epigenetic regulation of leukaemogenesis.

Transcriptome analysis was performed in KO52, a TP53 mutated AML cell line, upon treatment of PLK4 inhibitor CFI-400945. Leukemic cells were purified based on the ploidy status (2N and 4N) before RNA-sequencing to avoid the confounding effects of polyploidy. The molecular and cellular effects of CFI-400945 were subsequently examined.

Gene set enrichment analysis (GSEA) was performed on the differentially expressed genes (DEGs) induced by CFI-400945 and revealed that genes associated with histone 3 lysine 27 trimethylation (H3K27me3) and polycomb repressive complex 2 (PRC2), were negatively enriched upon CFI-400945 treatment. Consistently, the global H3K27me3 levels in 2N, 4N and polyploidy populations were increased after treatment. By comparing our transcriptome data with public datasets, the DEGs identified upon PLK4 inhibition were found to be positively correlated with those induced by protein arginine methyltransferase 5 (PRMT5) inhibition. Mechanistically, PLK4 was found to bind with PRMT5 by co-immunoprecipitation (Co-IP), and inhibition of PLK4 significantly suppressed PRMT5 phosphorylation. Increases in global O-GlcNAcylation level, protein expression of enhancer of zeste 2 (EZH2) and global H3K27me3 level were also observed in KO52 cells upon PLK4 or PRMT5 inhibition, which were ameliorated by O-linked N-acetylglucosamine transferase (OGT) inhibitor. To ascertain the role of histone modification by PLK4 inhibition in anti-leukemic effects, a panel of genes associated with leukemic stem cell signature, apoptosis, cellular proliferation, DNA damage and immune surveillance were investigated. These genes were downregulated with increased H3K27me3 enrichment upon PLK4 or PRMT5 inhibition, which were ameliorated by PRC2 or OGT inhibitors. It was consistent with the observations that the increased DNA damage, apoptosis, and suppressed proliferation upon PLK4 or PRMT5 inhibition were alleviated by PRC2 inhibitor.

To conclude, the observations supported a novel PLK4/PRMT5/EZH2/H3K27me3 axis that might account for the anti-leukemic effects of PLK4 inhibition, and strengthen its therapeutic potential in TP53 mutated AML.