Person:

Sagawa, Morihiko

Recent studies have delineated cancer type-specific roles of histone 3 lysine 27 (H3K27) demethylase KDM6B/JMJD3 depending on its H3K27 demethylase activity. Here we show that KDM6B is expressed in multiple myeloma (MM); and that shRNA-mediated knockdown and CRISPR-mediated knockout of KDM6B abrogate MM cell growth and survival. TNFα or bone marrow stromal cell culture supernatants induce KDM6B, which is blocked by IKKβ inhibitor MLN120B, suggesting KDM6B is regulated by NF-κB signaling in MM cells. RNA-sequencing and subsequent ChIP-qPCR analyses reveal that KDM6B is recruited to the loci of genes encoding components of MAPK signaling pathway including ELK1 and FOS, and upregulates these genes expression without affecting H3K27 methylation level. Overexpression of catalytically-inactive KDM6B activates expression of MAPK pathway-related genes, confirming its function independent of demethylase activity. We further demonstrate that downstream targets of KDM6B, ELK1 and FOS, confer MM cell growth. Our study therefore delineates KDM6B function that links NF-κB and MAPK signaling pathway mediating MM cell growth and survival, and validates KDM6B as a novel therapeutic target in MM.

Epigenetic signaling pathways are implicated in tumorigenesis and therefore histone deacetylases (HDACs) represent novel therapeutic targets for cancers, including multiple myeloma (MM). Although non-selective HDAC inhibitors show anti-MM activities, unfavorable side effects limit their clinical efficacy. Isoform- and/or class-selective HDAC inhibition offers the possibility to maintain clinical activity while avoiding adverse events attendant to broad non-selective HDAC inhibition. We have previously reported that HDAC3 inhibition, either by genetic knockdown or selective inhibitor BG45, abrogates MM cell proliferation. Here we show that knockdown of HDAC3, but not HDAC1 or HDAC2, as well as BG45, downregulate expression of DNA methyltransferase 1 (DNMT1) mediating MM cell proliferation. DNMT1 expression is regulated by c-Myc, and HDAC3 inhibition triggers degradation of c-Myc protein. Moreover, HDAC3 inhibition results in hyperacetylation of DNMT1, thereby reducing the stability of DNMT1 protein. Combined inhibition of HDAC3 and DNMT1 with BG45 and DNMT1 inhibitor 5-azacytidine (AZA), respectively, triggers synergistic downregulation of DNMT1, growth inhibition and apoptosis in both MM cell lines and patient MM cells. Efficacy of this combination treatment is confirmed in a murine xenograft MM model. Our results therefore provide the rationale for combination treatment using HDAC3 inhibitor with DNMT1 inhibitor to improve patient outcome in MM.