Promotor specific regulation of NF-kappaB mediated transcription by the phosphorylation of p65 on Ser547.

NF-kappaB (p50/p65) is an important regulator of gene transcription as it controls the
expression of hundred of genes involved in inflammatory and innate responses, proliferation,
survival, cancer initiation and progression. Several modes of NF-kappaB activation are known
among which the classical pathway induced by pro-inflammatory cytokines and a complex atypical
pathway induced by DNA damage. Both pathways converge on the IKK activation. The stimulidependent
p65 phosphorylation on several serine can control its transcriptional potential either
globally or often in a gene specific manner.
Lately, we have reported a direct interaction between p65 and ATM and the in vitro
phosphorylation of Ser547 by this kinase. A comparative transcriptomic analysis performed in
HEK-293 cells expressing either p65WT or p65S547A identified several differentially transcribed
genes (IL8, A20, SELE…) after an Etoposide treatment. Substitution of Ser547 to Ala does not
affect p65 binding on the kappaB site of the IL8 promoter but it reduces p65 interaction with
HDAC1 leading to a higher level of histone H3 acetylated on Lys9 and therefore a higher gene
induction. These data indicate that ATM regulates a sub-set of NF-kappaB dependent genes after a
genotoxic stress by direct phosphorylation of p65 (1).
We are now investigating the impact of the S547A mutation in the context of an
inflammatory response. Mefs p65KO expressing recombinant p65WT or p65S547A were treated with
TNFalpha. No differences were observed in the kinetic of degradation of IkBa or the nuclear
translocation of p65. The level of transcription of a few selected genes is presently under
investigation. Contrary to another study, we did not observed any role of ATM in NF-kappaB
activation by TNFalpha