Phosphorylation of Histones by Tissue Transglutaminase

Abstract

Tissue transglutaminase 2 (TG2) has recently been shown to have intrinsic serine/threonine kinase activity. Since histones are known to be cross-linked by TG2, we investigated whether histones are also substrates for TG2 kinase activity. TG2 was able to phosphorylate H1, H2A, H2B, H3, and H4 histones in vitro. Using peptide substrates and phosphospecific antibodies we demonstrated that TG2 phosphorylated Ser 10 in H3 and that this phosphorylation was reduced by acetylation, whereas phosphorylation of Ser 10 by TG2 enhanced acetylation. Furthermore we demonstrated that exogenous TG2 phosphorylated H1 and H3 in nucleosome preparations. We examined the abundance of TG2 in DNA-associated proteins from MCF-7 cells treated with phorbol ester (TPA) and 17␤-estradiol (E2). TG2 abundance was significantly reduced in E2-treated cells and enhanced in TPA-treated cells. In summary we have demonstrated that TG2 is able to phosphorylate purified histone proteins, and H3 and H1 in chromatin preparations, and it is associated with chromatin in breast cancer cells. These studies suggest a novel role for TG2 in the regulation of chromatin structure and function. Tissue transglutaminase 2 (TG2)4 is a ubiquitously expressed, calcium-dependent trans-amidating acyltransferase that cross-links proteins resulting in polymerization (1). In addition, it has other less characterized functions including as a protein-disulfide isomerase (2), as a G protein-coupled membrane receptor (3) and as a serine/threonine kinase (4). It is localized to many compartments in the cell including the cell membrane, the cytoplasm, and the nucleus (1). TG2 is involved in a multitude of cellular process of which the best studied is apoptosis where it is responsible for the formation of apoptotic bodies.TG2 is translocated to the nucleus by a mechanism that involves importin-␣3 (5, 6), where it can cross-link histones (7,8). Cross-linking of the core histone subunits, H2A and H2B, by TG2 appears to involve glutamine and lysine residues at COOH-terminal domain (9). Histone H1, has also been shown to be a substrate for TG2 (9). Histones bind in a sequence-independent manner to DNA to form chromatin. They are subject to extensive post-translational modification that appears to be important in regulating chromatin function. For example, the aminoterminal tails of histones can be both phosphorylated and acetylated and these modifications are thought to regulate chromatin structure to facilitate transcription, DNA replication, mitosis, and DNA repair.Histone cross-linking by TG2 may be responsible for the changes in DNA function such as transcription and replication (11), although the exact molecular mechanisms responsible have not been elucidated, and many apparently contradictory data exist. For example, it appears that TG2 can only cross-link histones when released from the nucleosome. Since cross-linking of histone by TG2 does not occur when the histones were organized in nucleosome (9), it is not immediately obvious how this cross-linking activity of TG2 could ...

Functional characterization of naturally occurring transglutaminase 2 mutants implicated in early-onset type 2 diabetes

“…5, 10 mM magnesium chloride, [g-32 P]ATP (25 mCi/ml)) for 30 min at 30 8C as described previously (Mishra & Murphy 2004, Mishra et al 2006. The reaction was stopped by the addition of SDS-PAGE sample buffer and the samples were boiled for 5 min.…”

“…In addition, we have reported that TG2 has intrinsic kinase activity and phosphorylates a number of proteins including insulin-like growth factor binding protein-3 (IGFBP3; Mishra & Murphy 2004, Mishra et al 2006, 2007a. We have recently found that IGFBP3 has a role in insulin secretion (Nguyen et al 2011).…”

Roles of transglutaminases in cardiac and vascular diseases

“…The roles of TG2-mediated polyamination or deamidation of glutamine residues and acylation of lysine residues are not fully known. Furthermore, TG2 also acts as a protein disulfide isomerase (194) and as a protein kinase (195)(196)(197) for certain Effects of transglutaminases on vascular and cardiac diseases. The inset depicts a coronary artery with an atheroma that has undergone plaque rupture, with subsequent thrombus formation in the arterial lumen and within the lipid core.…”

Transglutaminase 2, a double face enzyme

“…But the Tgase enzyme disclosed itself further as a rich fertile mine, although a careful skepticism is always required in dealing with new astonishing "discoveries". This particularly applies to the reports that Tgase2 can display two additional activities, the former as protein kinase (Mishra et al 2006), the latter as protein disulfide isomerase (Hasegawa et al 2003). At the eyes of one of us (CMB), these activities still require much research to be definitively proved, although it is interesting to note that these activities do not require calcium and for this reason can potentially play important regulatory functions in physiological cellular conditions.…”