Opposite Regulation of Nuclear Factor-kB (NF-kB) Biological Activity by

ERLEJMAN AG, DE LEO SA, MAZAIRA GI, MOLINARI AM, COX M, GALIGNIANA MD

Les Diablerets

Conferencia; The 6 th. International Conference on the Hsp90-Chaperone Machine; 2012

NF-kB is a heterodimeric protein belonging to the Rel family of transcription factors involved in stress-induced, immune, and inflammatory responses. NF-kB plays important roles during development, programmed cell death, proliferation control, and tumourigenesis. In unstimulated cells, NF-kB dimers are sequestered in the cytosol via IkB. NF-kB activation causes IkB phosphorylation, complex dissociation, and NF-kB nuclear translocation. Because the Hsp90-binding immunophilins FKBP51 and FKBP52 regulate and command the subcellular localization of other nuclear factors such as steroid receptors and p53, we hypothesized that they could similarly modulate NF-kB signalling. In unstimulated cells, FKBP51 co-immunoprecipitates with the RelA/p65 subunit of NF-kB in an Hsp90-independent manner. Upon cell stimulation, NF-kB exchanges FKBP51 by FKBP52. FKBP51 overexpression impairs the nuclear translocation rate of RelA/p65 and inhibits NF-kB transcriptional activity in a peptidylprolyl-isomerase-independent and TPR domain-dependent manner. On the other hand, FKBP52 overexpression increases the nuclear retention time of RelA/p65, and favors both p65 association to a DNA consensus binding sequence and transcriptional activity, the latter being an effect that is entirely dependent on the peptidylprolyl-isomerase activity of FKBP52. Competition assays demonstrate that both immunophilin antagonize one another, and binding assays with purified proteins suggest that the association of p65 and immunophilins is direct. Therefore, we conclude that the biological activity of NF-kB is favored by a higher FKBP52/FKBP51 ratio. This is the first evidence showing that the balance between both immunophilins regulates straightly NF-kB function by direct association to the p65 subunit, and also that immunophilins bind to NFkB nuclear sites of action.