Visit our Expo - Redox and Inflammation signaling 2012

Chromatin impact on NF-kB-driven gene expression
Guy HAEGEMAN, Wim VANDEN BERGHE, Ruben HOYA ARIAS, ‘Matladi
NDLOVU & Linda VERMEULEN
Laboratory for Eukaryotic Gene Expression and Signal Transduction (LEGEST),
Department of Molecular Biology, Ghent University, Ledeganckstraat 35, 9000 GENT
(Belgium)
E-mail: guy.haegeman@ugent.be
Interleukin-6 (IL6) is a pluri-potent cytokine, of which the expression needs to be tightly
regulated in order to keep the organism in a balanced and homeostatic condition. Indeed,
dysregulation of IL6 leads to a variety of affections, like chronic inflammation, autoimmune
and cardiovascular diseases, cancer progression, osteoporosis, etc.
The IL6 gene promoter contains a plethora of transcription factor-binding sites, among which
NF-kB is the most important factor for induction of the gene by infammatory stimuli, like e.g.
TNF. NF-kB is in majority a cytoplasmic protein complex (composed of a p50 and a p65
subunit), which upon inflammatory stimulation migrates to the nucleus and occupies its
position on a variety of gene promoters. In previous work, we have shown that, in addition to
this cytoplasmic activation step, the transcriptional potency of NF-kB is codetermined by the
activated MAP kinase pathway, more particularly by the nuclear kinase MSK1, that
phosphorylates the p65 subunit at Ser 276 (to generate a fully transcription-competent
enhanceosome), as well as the Histon-3 tails at Ser 10 (which is the onset of chromatin
relaxation).
As it was recently published that IKK-a is the Histon-3 phosphorylating kinase after TNF
induction, we investigated the role and impact of these two different kinases for IL6 gene
expression. We found that MSK1 is the primary initiating kinase for temporary chromatin
opening and relaxation (even in the absence of activated NF-kB), whereas IKK-a (only
released after TNF induction) takes over and continues the status of chromatin relaxation,
when activated MSK1 levels off. Sustained chromatin opening and arrival of NF-kB at the
gene promoter upon TNF induction thus lead to abundant IL6 gene expression, whereas
enhanced IL6 gene expression and/or temporary chromatin relaxation by MSK1 extinguishes
in the absence of TNF signalization.
Not only the local (i.e. the gene-specific) chromatin relaxation, but also the entire
nucleosomal arrangement along the chromatin fiber is determinative for the (cell-specific)
levels of gene expression. Indeed, upon comparison of the IL6 gene promoter status in two
different breast cancer cell lines, i.e. the benign, low IL6-expressing cell type MCF-7 and the
aggressive tumor cell line MDA-MB-231 that shows abundant IL6 expression, we found that,
upon DNaseI digestion and restriction enzyme accessibility assays, high IL6 expression
correlates with an increased number of hypersensitive sites, constitutive NF-kB/DNA binding,
and elevated MSK1 activity. Moreover, chromatin of the low-expressing cell line can be
converted to a more open configuration upon treatment of the cells with inhibitors of DNA
methylation, thus leading to augmented levels of IL6 gene expression in the restrictive cell
type MCF-7.
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