Histone H1 variant-specific lysine methylation by G9a/KMT1C and Glp1/KMT1D

Abstract

BackgroundThe linker histone H1 has a key role in establishing and maintaining higher order chromatin structure and in regulating gene expression. Mammals express up to 11 different H1 variants, with H1.2 and H1.4 being the predominant ones in most somatic cells. Like core histones, H1 has high levels of covalent modifications; however, the full set of modifications and their biological role are largely unknown.ResultsIn this study, we used a candidate screen to identify enzymes that methylate H1 and to map their corresponding methylation sites. We found that the histone lysine methyltransferases G9a/KMT1C and Glp1/KMT1D methylate H1.2 in vitro and in vivo, and we mapped this novel site to lysine 187 (H1.2K187) in the C-terminus of H1. This H1.2K187 methylation is variant-specific. The main target for methylation by G9a in H1.2, H1.3, H1.5 and H1.0 is in the C-terminus, whereas H1.4 is preferentially methylated at K26 (H1.4K26me) in the N-terminus. We found that the readout of these marks is different; H1.4K26me can recruit HP1, but H1.2K187me cannot. Likewise, JMJD2D/KDM4 only reverses H1.4K26 methylation, clearly distinguishing these two methylation sites. Further, in contrast to C-terminal H1 phosphorylation, H1.2K187 methylation level is steady throughout the cell cycle.ConclusionsWe have characterised a novel methylation site in the C-terminus of H1 that is the target of G9a/Glp1 both in vitro and in vivo. To our knowledge, this is the first demonstration of variant-specific histone methylation by the same methyltransferases, but with differing downstream readers, thereby supporting the hypothesis of H1 variants having specific functions.

Basic concepts of epigenetics

“…111,115 Other identified HMG proteins include HMGN3a/3b and HMGN5, 115 which are present in euchromatin. 116 There is very little information at this point about the regulatory roles of post-translational modifications to the H1 linker, such as ADP-ribosylation or methylation, 117 but there is some indication that phosphorylation of H1 increases the dissociation rate of unstable cores within nucleosomes. 118 However, most studies allude to the importance as phosphorylation of H2Av in flies, can lead to active recruitment of HATs and proteins containing bromodomains (BRDs), such as Tip60/ATPase/helicases (in eukaryotes) and the NuA4 acetyltransferase/Swr1 complex (in yeast).…”

Stimulation of β-catenin and colon cancer cell growth by the KDM4B histone demethylase

“…These include the four related lysine-specific demethylase 4 (KDM4) proteins, KDM4A-D (8). They can demethylate histone H3 on lysines 9 and 36 as well as histone H1.4 on lysine 26 (9)(10)(11)(12)(13)(14)(15). Notably, KDM4A, B and C are overexpressed in human breast tumors and promote proliferation of breast tumor cells, in part due to their ability to function as cofactors of estrogen receptor α (16)(17)(18)(19)(20)(21).…”

A Role for Widely Interspaced Zinc Finger (WIZ) in Retention of the G9a Methyltransferase on Chromatin

“…These enzymes are implicated in a variety of disease and biological processes (6); they demonstrate both co-activator and co-repressor functions (6 -8) and interact with other SET domain-containing proteins including SETDB1, Suv39H1, and the PRC2 complex (9,10). G9a and GLP show similar substrate specificities (11-13); they methylate histones H1 (11,12,14), H3K27 (11,15) and H3K56 (16), as well as a number of non-histone proteins (17)(18)(19)(20)(21), but are best characterized as the major lysine methyltransferases involved in mono-and di-methylation of H3K9 (11,(22)(23)(24)(25).…”