Regulation and function of interphase histone H1 phosphorylation in pluripotent cell differentiation

Histone H1 phosphorylation is thought to be involved in multiple cellular processes including chromatin condensation and transcriptional regulation. Recent studies revealed changes in the expression and genomic distributions of H1 variants during cell differentiation which appear to contribute to phenotypic differences between cell types, but the functional significance of phosphorylation at specific sites in individual H1 variants and their dynamic regulation in this process has not been investigated. Here we show that the global levels of phosphorylation of H1.5-Ser18 (pS18-H1.5), H1.2/H1.5-Ser173 (pS173-H1.2/5) and H1.4-Ser187 (pS187-H1.4) are regulated differentially during pluripotent cell differentiation. Enrichment of pS187-H1.4, but not pS18-H1.5, near the transcription start sites (TSSs) of pluripotency factor genes is diminished after differentiation. Selective inhibition of CDK7 and CDK9, or siRNA depletion of CDK9 rapidly diminishes both the global levels and the enrichment of pS187-H1.4 at housekeeping genes. Moreover, inhibiting transcription with actinomycin D induces the accumulation of pS187-H1.4 at promoters and gene bodies. Notably, the levels of pS187-H1.4 enrichment after actinomycin D treatment or cell differentiation reflect the extent of CDK9 recruitment at the same loci. Remarkably, the global levels of H1.5-S18 and H1.2/H1.5-S173 phosphorylation are not affected by these transcription inhibitor treatments, and selective inhibition of CDK2 does not affect global phosphorylation of H1.4-S187 or H1.5-S18. Although Erk phosphorylates S187-H1.4 in vitro, our data with Erk inhibitor treatments and EGF stimulation suggest that Erk does not phosphorylate S187-H1.4 in vivo. Studies of cells expressing H1.4 mutants that mimic constitutive dephosphorylation and phosphorylation at one or two interphase sites reveal that interphase phosphorylation of H1.4 affects transcription in a gene-specific manner. Taken together, our data provide strong evidence that H1 variant phosphorylations are dynamically regulated in a site-specific and gene-specific fashion during pluripotent cell differentiation, and that the enrichment of pS187-H1.4 at genes is positively related to their transcription. H1.4-S187 is likely to be a direct target of CDK9 during interphase in vivo while other H1 variant phosphorylations appear to be mediated by distinct kinases.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Cell and Developmental Biology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2017

Author dc:creator

• Liao, Ruiqi

Contributors dc:contributor

• Mizzen, Craig
• Stubbs, Lisa
• Katzenellenbogen, Benita
• Belmont, Andrew

• Histone H1
• Phosphorylation
• Embryonic stem cell
• Differentiation
• Cyclin dependent kinases (CDK)
• Transcriptional regulation

Statement dc:rights

• Copyright 2017 Ruiqi Liao

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/97720

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/97720