EZH2 or HDAC1 Inhibition Reverses Multiple Myeloma–Induced Epigenetic Suppression of Osteoblast Differentiation

Abstract

In multiple myeloma (MM) osteolytic lesions rarely heal because of persistent suppressed osteoblast differentiation resulting in a high fracture risk. Herein, chromatin immunoprecipitation analyses reveal that MM cells induce repressive epigenetic histone changes at the Runx2 locus that prevent osteoblast differentiation. The most pronounced MM-induced changes were at the Runx2-P1 promoter, converting it from a poised bivalent state to a repressed state. Previously it was observed that MM induce the transcription repressor GFI1 in osteoblast precursors, which correlates with decreased Runx2 expression. Thus, prompting detailed characterization of the MM and TNFα-dependent GFI1-response element within the Runx2-P1 promoter. Further analyses reveal that MM-induced GFI1 binding to Runx2 in osteoblast precursors and recruitment of the histone modifiers HDAC1, LSD1, and EZH2 is required to establish and maintain Runx2 repression in osteogenic conditions. These GFI1-mediated repressive chromatin changes persist even after removal of MM. Ectopic GFI1 is sufficient to bind to Runx2, recruit HDAC1 and EZH2, increase H3K27me3 on the gene, and prevent osteogenic induction of endogenous Runx2 expression. Gfi1 knockdown in MC4 cells blocked MM-induced recruitment of HDAC1 and EZH2 to Runx2, acquisition of repressive chromatin architecture, and suppression of OB differentiation. Importantly, inhibition of EZH2 or HDAC1 activity in pre-osteoblasts after MM exposure in vitro or in osteoblast precursors from MM patients reversed the repressive chromatin architecture at Runx2 and rescued osteoblast differentiation. Implications This study suggests that therapeutically targeting EZH2 or HDAC1 activity may reverse the profound MM-induced osteoblast suppression and allow repair of the lytic lesions.

Epigenetic‐Based Mechanisms of Osteoblast Suppression in Multiple Myeloma Bone Disease

“…Direct MM‐BMSC interactions and soluble cytokine‐mediated cross‐talk combine to alter BMSCs into a chronically pro‐adipogenic and senescence‐like phenotype with suppressed osteogenesis . In fact, the observations that myeloma‐exposed BMSCs (MM‐BMSCs) undergo long‐term phenotypic changes in the absence of myeloma signals suggested that epigenetic modifications direct the cellular reprogramming and osteogenic suppression of MM‐BMSCs . In such a way, myeloma‐induced alterations of chromatin structure in BMSCs can be epigenetically propagated as a heritable memory regulating the transcriptional signature in the absence of continuous MM signals.…”

Mechanisms of bone destruction in multiple myeloma

“…Interestingly, Gfi1 knockdown in MC4 cells blocked MM-induced recruitment of HDAC1and EZH2 to Runx2, acquisition of repressive chromatin architecture, and suppression of osteoblast differentiation(Adamik et al, 2017). Elevated Gfi1 blocks Runx2 induction by osteogenic signals.…”

Maternal regulation of SATB2 in osteo‐progeniters impairs skeletal development in offspring

“…The polycomb group protein enhancer of zeste homologue 2 (Ezh2), a histone lysine methyltransferase associated with transcriptional repression, catalyzes the addition of methyl groups to histone H3 at Lys 27 (H3K27me3) in target genes involved in numerous cellular processes, predominantly leading to gene repression . There is evidence that loss or inhibition of Ezh2 leads to enhanced osteogenic but inhibited adipogenic differentiation of bone marrow‐derived mesenchymal stem cells (BMSCs) both from rodents and humans, as well as in murine pre‐osteoblastic cell line MC3T3 . Expression of Ezh2 suppresses the osteogenic genes and ligand‐dependent signaling pathways (eg, WNT, PTH, and BMP2) to favor adipogenic differentiation .…”