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 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 demonstrate that the Brg1-CK2 interaction occurred during mitosis in embryonic somites and in primary myoblasts derived from satellite cells isolated from muscle tissue. The interaction of CK2 activity 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 sub-cellular compartments. Thus CK2 acts a mitotic kinase that regulates Brg1 phosphorylation and sub-cellular localization.function of Brg1 and leads to a block of myogenic differentiation [16]. However, dephosphorylation of Brg1 by the phosphatase, calcineurin, opposes the activity of PKCβ1, allowing chromatin remodeling by Brg1 and initiation of myogenesis [16]. Mutagenesis and unbiased mass spectrometry analyses of Brg1 phosphopeptides in the presence and absence of a calcineurin inhibitor identified calcineurin target sequences, but the mass spectrometry data identified additional Brg1 phosphopeptides that were not responsive to calcineurin inhibition [16]. This suggested that Brg1 is a target of additional signal transduction pathways. Our subsequent studies showed that Brg1 was phosphorylated by casein kinase 2 (CK2), a Serine/Threonine kinase, which promoted myoblast proliferation and survival by regulating subnuclear localization and incorporation of one of two related subunits, BAF155/BAF170, into the enzyme complex [17].CK2 is ubiquitously expressed and functions as a tetramer of two catalytic subunits, CK2α or CK2α', and two CK2β regulatory subunits, and it has more than 300 known substrates [29][30][31].CK2 is required for cell cycle progression, survival, apoptosis, and transcriptional regulation.Knockout mice lacking the CK2α subunit show cardiac and neural tube defects and die during embryogenesis, whereas mice lacking the α' subunit have impaired spermatogenesis [32][33][34].Knockout of the CK2β subunit in mice leads to reduced proliferation during embryogenesis, which is reflected in the small size of the animals at embryonic day 6.5 (E6.5) and resorption at E7.5 [35]. Analyses of a murine conditional knockout model showed that CK2β is essential for viability of embryonic stem cells and primary embryonic fibroblasts [35]. In vitro ...

4,5,7‐Trisubstituted indeno[1,2‐b]indole inhibits CK2 activity in tumor cells equivalent to CX‐4945 and shows strong anti‐migratory effects

“…Thus, the obtained high amount of CX-4945 in the nuclear fraction may be responsible for its high impact on apoptosis induction. Recently, an interaction of CK2 and the chromatin remodeling enzyme Brg1 within the nucleus of proliferating myoblasts was observed [64]. Since this interaction takes place in the nucleus, the high amount of CX-4945 in this fraction could be explanatory for its strong anti-proliferative effects.…”

Neuronal Activity-Induced BRG1 Phosphorylation Regulates Enhancer Activation

“…BRG1 has been shown to be phosphorylated during mitosis, which correlates with its dissociation from condensed chromatin and inactivation (Muchardt et al, 1996;Sif et al, 1998). Recent studies showed that Casein kinase 2 phosphorylates BRG1 during mitosis at multiple sites, and that these phosphorylation events are important for myoblast proliferation and survival (Padilla-Benavides et al, 2020;Padilla-Benavides et al, 2017). During myogenesis, phosphorylation of BRG1 by PKCβ1 and dephosphorylation by calcineurin regulates gene expression (Nasipak et al, 2015).…”

“…Phosphorylation of transcription regulators influences a dynamic protein interaction network that allows neurons to produce rapid and diverse responses to enable adaption 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 protein modifications in response to neuron activities or how posttranslational modifications regulate BAF activities.…”