The role of the chromatin protein HMGN3 in cytokine induced gene expression

QH301 Biology;QH426 Genetics

Davis, Craig Stewart ; West, Katherine L.

University:University of Glasgow

Department:Institute of Cancer Sciences

关键词: HMGN3, CCL1, chromatin, epigenetics, gene regulation, histone modification;   

Others  :  http://theses.gla.ac.uk/795/1/2008CraigMSc.pdf.pdf

来源: University of Glasgow

【 摘 要 】

HMGN proteins modulate chromatin structure by binding to chromatin, unfolding nucleosome arrays and altering the pattern of histone modifications.HMGN3 is unique amongst the HMGN family as two splice variants are produced from the HMGN3 transcript.HMGN3 was shown to regulate TNFα-induced expression of the murine chemokine gene CCL1 which is implicated in conditions such as asthma, atherosclerosis and cancer.However, the mechanism by which HMGN3 modulates gene expression was unknown.This investigation studied the role of HMGN3 in modulating TNFα-induced expression of the mCCL1 gene, and identified changes in histone modifications associated with the mCCL1 gene during expression.Quantitative real-time PCR (QRT-PCR) results show that over-expression of HMGN3 in MEFs reduces mCCL1 induction by TNFα.Chromatin immunoprecipitation (ChIP) assays show HMGN3 binds to the mCCL1 gene.Peaks in Histone H3 lysine 14 acetylation (H3K14ac) coincide with peaks of HMGN3 binding at the mCCL1 gene.TNFα stimulation leads to decreased HMGN3 binding and this correlates with reduced H3K14ac at the mCCL1 gene.This is reminiscent of a previous study that showed HMGN1 inhibits anisomycin-stimulated fosB transcription.Taken together, this shows that HMGN3 fine-tunes TNFα-induced gene expression, and suggests it may be necessary to remove HMGN3 from the mCCL1 gene in order to get efficient transcription.mCCL1 is known to contain an inducible NF-kappaB site.TNFα induces the NF-kappaB signalling cascade.TNFα stimulation leads to the translocation of NF-kappaB to the nucleus, as well as the kinase IKKα.IKKα can directly phosphorylate H3S10 and enhance acetylation of H3K14 at NF-kappaB regulated promoters.p38 also induces phosphorylation of H3S10, which may improve access for NF-kappaB to bind the NF-kappaB site.To investigate whether HMGN3 has an indirect role in regulating gene expression, NF-kappaB and p38 luciferase assays were performed.Results show that HMGN3 does not significantly affect either the NF-kappaB or p38 signalling pathways.Based on this work and other published data, the following model is proposed: HMGN3 binds mCCL1 chromatin, enhances acetylation of H3K14 as shown by ChIP, and may inhibit TNFα-induced H3S10 phosphorylation, possibly mediated by IKKα, thus inhibiting mCCL1 expression as shown by RNA data.However, following TNFα stimulation, HMGN3 may become phosphorylated, possibly by IKKα or MSK1, reducing HMGN3 binding to chromatin as suggested by the ChIP results, enhancing the accessibility of H3S10 phosphorylation, possibly by IKKα.The reduced binding of HMGN3 may be necessary for efficient expression of the mCCL1 gene.