CK2-Dependent Phosphorylation of the Brg1 Chromatin Remodeling Enzyme Occurs during Mitosis

Abstract

Brg1 (Brahma-related gene 1) is one of two mutually exclusive ATPases that can act as the catalytic subunit of mammalian SWI/SNF (mSWI/SfigureNF) chromatin remodeling enzymes that facilitate utilization of the DNA in eukaryotic cells. Brg1 is a phospho-protein, and its activity is regulated by specific kinases and phosphatases. Previously, we showed that Brg1 interacts with and is phosphorylated by casein kinase 2 (CK2) in a manner that regulates myoblast proliferation. Here, we use biochemical and cell and molecular biology approaches to demonstrate that the Brg1-CK2 interaction occurred during mitosis in embryonic mouse somites and in primary myoblasts derived from satellite cells isolated from mouse skeletal muscle tissue. The interaction of CK2 with Brg1 and the incorporation of a number of other subunits into the mSWI/SNF enzyme complex were independent of CK2 enzymatic activity. CK2-mediated hyperphosphorylation of Brg1 was observed in mitotic cells derived from multiple cell types and organisms, suggesting functional conservation across tissues and species. The mitotically hyperphosphorylated form of Brg1 was localized with soluble chromatin, demonstrating that CK2-mediated phosphorylation of Brg1 is associated with specific partitioning of Brg1 within subcellular compartments. Thus, CK2 acts as a mitotic kinase that regulates Brg1 phosphorylation and subcellular localization.

Neuronal activity-induced BRG1 phosphorylation regulates enhancer activation

“…Phosphorylation of transcription regulators influences a dynamic protein interaction network that allows neurons to produce rapid and diverse responses to enable adaptation to the changing environment. Despite the identification of phosphorylation sites in BAF subunits in various conditions ( Kimura et al, 2014 ; Kwon et al, 2015 ; Padilla-Benavides et al, 2020 ; Wang et al, 2013 ), it is not clear whether BAF subunits undergo activity-induced protein modifications nor how post-translational modifications regulate BAF activities. Here, we examined how BRG1 coordinates co-factor activities in ARG regulation.…”

Regulation of the Mammalian SWI/SNF Family of Chromatin Remodeling Enzymes by Phosphorylation during Myogenesis

“…Subunit composition is not the only mechanism by which chromatin remodeling enzyme function can be regulated. Post-transcriptional modifications such as acetylation, methylation, sumoylation, phosphorylation, among others, modulate the activity of the mSWI/SNF complex [46][47][48][49][50][51][52][53][54]. Signaling pathways involve a fine-tuned, differential regulation of kinases and phosphatases that are essential for lineage determination and tissue development and maturation [55][56][57].…”

“…Recent studies have demonstrated that casein kinase 2 (CK2) phosphorylates BRG1 in proliferating primary myoblasts derived from mouse satellite cells [50,51]. CK2 is a serine/threonine kinase that exists as a tetramer of two catalytic subunits, CK2α or CK2α', and two regulatory subunits (CK2β).…”

“…Deletion of Pax7 in mice resulted in a decreased number of satellite cells that were progressively lost with aging, and the animals had an impaired ability to regenerate muscle tissue in response to injury [88][89][90]161]. Recent studies demonstrated that the physical interaction between CK2 and BRG1 occurs specifically during mitosis [51]. Confocal microscopy and co-immunoprecipitation analyses showed that CK2 and BRG1 co-localize in cells undergoing mitosis in developing somites of mouse embryos and in primary myoblasts isolated from satellite cells [51].…”

“…Recent studies demonstrated that the physical interaction between CK2 and BRG1 occurs specifically during mitosis [51]. Confocal microscopy and co-immunoprecipitation analyses showed that CK2 and BRG1 co-localize in cells undergoing mitosis in developing somites of mouse embryos and in primary myoblasts isolated from satellite cells [51]. Importantly, the mitotic CK2-dependent phosphorylation of BRG1 was conserved across different cell lineages.…”