The KDM2B- Let-7b -EZH2 Axis in Myelodysplastic Syndromes as a Target for Combined Epigenetic Therapy

Abstract

Both DNA and histone methylation are dysregulated in the myelodysplastic syndromes (MDS). Based on preliminary data we hypothesized that dysregulated interactions of KDM2B, let-7b and EZH2 signals lead to an aberrant epigenetic landscape. Gene expression in CD34+ cells from MDS marrows was analyzed by NanoString miR array and validated by real-time polymerase chain reaction (PCR). The functions of KDM2B, let-7b and EZH2 were characterized in myeloid cell lines and in primary MDS cells. Let-7b levels were significantly higher, and KDM2B and EZH2 expression was lower in primary CD34+ MDS marrow cells (n = 44) than in healthy controls (n = 21; p<0.013, and p<0.0001, respectively). Overexpression of let-7b reduced EZH2 and KDM2B protein levels, and decreased cells in S-phase while increasing G0/G1 cells (p = 0.0005), accompanied by decreased H3K27me3 and cyclin D1. Silencing of KDM2B increased let-7b expression. Treatment with the cyclopentanyl analog of 3-deazaadenosine, DZNep, combined with the DNA hypomethylating agent 5-azacitidine, decreased levels of EZH2, suppressed methylation of di- and tri-methylated H3K27, and increased p16 expression, associated with cell proliferation. Thus, KDM2B, via let-7b/EZH2, promotes transcriptional repression. DZNep bypassed the inhibitory KDM2B/let-7b/EZH2 axis by preventing H3K27 methylation and reducing cell proliferation. DZNep might be able to enhance the therapeutic effects of DNA hypomethylating agents such as 5-azacitidine, currently considered standard therapy for patients with MDS.

Down-regulation of EZH2 expression in myelodysplastic syndromes

“…Karoopongse et al showed that EZH2 expression is lower in CD34+ MDS cells and that this downregulation was related to inflammatory and immune responses [24]. Mechanistically, SRSF2 mutation was recently shown to lead to the mis-splicing of EZH2 RNA and consequent nonsense-mediated decay (NMD) of the transcript [25].…”

Association of EZH2 protein expression by immunohistochemistry in myelodysplasia related neoplasms with mutation status, cytogenetics and clinical outcomes

“…EZH2 (Enhancer of Zester homolog 2) encodes the catalytic subunit of the PRC2 complex methylating H3K27 influencing stem cell renewal by epigenetic transcriptional repression. EZH2 is mutated in ~10% of MDS or myelodysplastic/myeloproliferative neoplasms (MPN) with unknown function, demonstrating a need for characterization in disease modulation or prognostication (Xu & Li, ; Karoopongse et al , ; Sashida et al , ). We explored EZH2 protein expression by immunohistochemistry (IHC) in patient bone marrow (BM) samples with regard to mutation status, clinical characteristics and outcome.…”

Histone demethylase KDM2B upregulates histone methyltransferase EZH2 expression and contributes to the progression of ovarian cancer in vitro and in vivo

“…Karoopongse et al found that EZH2 expression in myelodysplastic syndrome cells was decreased after KDM2B knockdown 19. This result suggests that EZH2 expression may be regulated by KDM2B.…”