The Histone Variant MacroH2A1.2 Is Necessary for the Activation of Muscle Enhancers and Recruitment of the Transcription Factor Pbx1

Abstract

SUMMARY Histone variants complement and integrate histone post-translational modifications in regulating transcription. The histone variant macroH2A1 (mH2A1) is almost three times the size of its canonical H2A counterpart due to the presence of a ~25kDa evolutionarily conserved non-histone macro domain. Strikingly, mH2A1 can mediate both gene repression and activation. However, the molecular determinants conferring these alternative functions remain elusive. Here, we report that mH2A1.2 is required for the activation of the myogenic gene regulatory network and muscle cell differentiation. H3K27 acetylation at prospective enhancers is exquisitely sensitive to mH2A1.2, indicating a role of mH2A1.2 in imparting enhancer activation. Both H3K27 acetylation and recruitment of the transcription factor Pbx1 at prospective enhancers are regulated by mH2A1.2. Overall, our findings indicate a role of mH2A1.2 in marking regulatory regions for activation.

Regulation of Breast Cancer-Induced Osteoclastogenesis by MacroH2A1.2 Involving EZH2-Mediated H3K27me3

“…One important initial result obtained using this assay system was that mH2A1.2 significantly decreases osteoclastogenic potential of soluble factors secreted by MDA-MB-468 breast cancer cells. The observation that two other mH2A isoforms, mH2A1.1 and mH2A2, do not participate in regulating osteoclastogenesis is important in light of several recent reports suggesting that mH2A isoforms are dedicated to regulatory roles in specific gene expression (Dell’Orso et al, 2016; Gamble et al, 2010; Kapoor et al, 2010; Kim et al, 2013). In agreement with these observations, our secretome analysis of microarray data demonstrates that mH2A1.2 is essential for keeping inactive the genes encoding the factors that influence osteo- clastogenesis and metastasis in MDA- MB-468 breast cancer cells.…”

“…This accumulation of mH2A has been proposed to contribute to long-term maintenance of gene silencing in these genomic regions. Beside its role in X chromosome inactivation, mH2A can also modulate specific gene transcription both negatively and positively (Dell’Orso et al, 2016; Gamble et al, 2010; Kapoor et al, 2010; Kim et al, 2013). These properties of mH2A may be generated through physical and functional interactions with gene specific regulators, as supported by previous studies showing that HDAC1/2, PARP1, and Pbx1 are recruited by mH2A1 and necessary for establishing distinct transcription states (Buschbeck et al, 2009; Chakravarthy et al, 2005; Chen et al, 2014; Dell’Orso et al, 2016; Kim et al, 2013).…”

Temporal regulation of chromatin during myoblast differentiation

“…The histone H2A variant macroH2A (mH2A) is characterized by the presence of a ∼25 kDa evolutionarily conserved carboxyl-terminal domain called the macro domain, which makes the protein nearly three times larger than its canonical counterpart. Evidence suggests the genome-wide distribution of mH2A is similar in myoblasts and in differentiated myotubes and is predominantly associated with regions of active transcription (43). Regions of co-localization of mH2A with trimethylated H3K27 in myoblasts was also reported, but knockdown of mH2A has no effect on this modification and no major effect on gene expression, suggesting that it is not required or is redundant for repression of gene expression in the undifferentiated state (43).…”

“…Evidence suggests the genome-wide distribution of mH2A is similar in myoblasts and in differentiated myotubes and is predominantly associated with regions of active transcription (43). Regions of co-localization of mH2A with trimethylated H3K27 in myoblasts was also reported, but knockdown of mH2A has no effect on this modification and no major effect on gene expression, suggesting that it is not required or is redundant for repression of gene expression in the undifferentiated state (43). This finding is consistent with reports from other systems (44).…”

“…This finding is consistent with reports from other systems (44). However, mH2A is necessary for the recruitment of the homeodomain transcription factor Pbx1 to some myogenic promoters and enhancers, which then contributes to the recruitment of MyoD and expression of differentiation-specific gene expression (43, 45-47). In addition, mH2A promotes inclusion of an activating histone mark, acetylated H3K27, at myogenic enhancers and promoters (48).…”