Isoform-specific phosphorylation of human linker histone H1.4 in mitosis by the kinase Aurora B

Abstract

The linker histone H1 plays an essential role in maintaining and establishing higher-order chromatin structure. As with core histones, histone H1 is also extensively covalently modified. We showed previously that phosphorylation of S27 in human histone H1.4 (H1.4S27-P), prevents binding of heterochromatin protein 1 (HP1) family members (officially known as chromobox protein homologs) to the neighboring dimethylated K26. Here, we present the first functional characterization of H1.4S27-P in vivo and in vitro. We show that H1.4S27 phosphorylation is cell-cycle-regulated and its levels peak on metaphase chromosomes. We identify further Aurora B as the kinase phosphorylating H1.4S27. We demonstrate that histone H1.4 is the only somatic linker histone variant targeted by Aurora B and that Aurora B exclusively phosphorylates S27. Adjacent K26 dimethylation can regulate Aurora B activity towards S27, uncovering a crosstalk between these modifications. Finally, our fluorescence recovery after photobleaching (FRAP) analysis on histone H1.4 mutants suggests a role of S27 phosphorylation in the regulation of histone H1.4 mobility and chromatin binding in mitosis.

Preferential Phosphorylation on Old Histones during Early Mitosis in Human Cells

“…Enrichment of Histone Phosphorylation Marks on Old Histones in Mitosis-We also investigated the distribution of serine/threonine phosphorylations, which in principle do not require inheritance as they are mostly mitosis-specific (15)(16)(17)(18)(19)(20)(21). Surprisingly, four out of five Ser/Thr phosphorylations analyzed, namely H3S10ph, H3.1/2S28ph, H3T3/T6ph, and H1.4S26ph, were enriched on the old histones in early mitosis (Table 1 and Fig.…”

“…Several phosphorylation marks are implicated in transcriptional regulation of individual genes during interphase (58 -63). However, their roles in mitosis remain elusive, despite the fact that the abundance of these marks is generally much higher in mitosis than in interphase (15)(16)(17)(18)(19)(20)(21). Our discovery about the asymmetric distribution of these marks might provide the first step toward understanding their function in mitosis.…”

“…Furthermore, a handful of histone phosphorylation (ph) marks are highly abundant in mitosis and are present at very low levels in the interphase, including H3S10ph, H3S28ph, H3T3ph, H1.4S26ph, etc. (15)(16)(17)(18)(19)(20)(21). The major kinase for these histone phosphorylation marks is Aurora B, which is part of the chromosomal passenger complex and plays essential roles in chromosome condensation, segregation, and cytokinesis during mitotic progression (22).…”

“…The major kinase for these histone phosphorylation marks is Aurora B, which is part of the chromosomal passenger complex and plays essential roles in chromosome condensation, segregation, and cytokinesis during mitotic progression (22). Aurora B phosphorylates histones directly (17,21,(23)(24)(25)(26) or indirectly through activation of another kinase Haspin (27). The levels of these phosphorylation marks peak after the new histones are synthesized in S phase; therefore, they are not likely being transmitted from old to new histones.…”

Dynamics and dispensability of variant‐specific histone H1 Lys‐26/Ser‐27 and Thr‐165 post‐translational modifications

“…We show that phosphorylation of these amino acids occurs during the G2/M phase of the cell cycle. In fact, H1.4-S27 phosphorylation by Aurora B over the course of mitosis has been previously reported [24]. While the global increase in H1 phosphorylation during mitosis was expected, the decrease in K46-ubiquitination is more surprising and needs further investigation.…”