Interleukin (IL) 1beta induction of IL-6 is mediated by a novel phosphatidylinositol 3-kinase-dependent AKT/IkappaB kinase alpha pathway targeting activator protein-1.
Here we describe a novel role for the phosphatidylinositol 3-kinase/AKT pathway in mediating induction of interleukin-6 (IL-6) in response to IL-1. Pharmacological inhibition of phosphatidylinositol 3-kinase (PI3K) inhibited IL-6 mRNA and protein production. Overexpression of either dominant-negative AKT or IkappaB kinase alpha mutant, IKKalphaT23A, containing a mutation in a functional AKT phosphorylation site, shown previously to be important for NFkappaB activation, completely abrogated IL-6 promoter activation in response to IL-1. However, mutation of the consensus NFkappaB site on the IL-6 promoter did not abrogate promoter activation by IL-1 in contrast to the AP-1 site mutation. IL-1 induces phosphorylation of IKKalpha on the NFkappaB inducing kinase (NIK) phosphorylation sites Ser(176)/Ser(180) and on the Thr(23) site, and although phosphorylation of IKKalphaT23 is inhibited both by LY294002 and wortmannin, phosphorylation of Ser(176)/Ser(180) is not. Neither inhibition of PI 3-kinase/AKT nor IKKalphaT23A overexpression affected IkappaBalpha degradation in response to IL-1. Only partial inhibition by dominant-negative AKT and no inhibitory effect of IKKalphaT23A was observed on an IL-6 promoter-specific NFkappaB site in contrast to significant inhibitory effects on the AP-1 site. Taken together, we have discovered a novel PI 3-kinase/AKT-dependent pathway in response to IL-1, encompassing PI 3-kinase/AKT/IKKalphaT23 upstream of AP-1. This novel pathway is a parallel pathway to the PI 3-kinase/AKT upstream of NFkappaB and both are involved in IL-6 gene transcription in response to IL-1.
Neurochemistry Laboratory, Department of Psychiatry-Neuroscience and Genetics and Aging Research Unit, Massachusetts General Hospital (East), Charlestown, Massachusetts 02129, USA. ccahill@rics.bwh.harvard.edu
Catherine M
CM
Cahill
Jack T
JT
Rogers
D018938:Caco-2 Cells; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D020672:I-kappa B Proteins / Q000378:metabolism*; D007375:Interleukin-1 / Q000378:metabolism; D053583:Interleukin-1beta / Q000378:metabolism*; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D009154:Mutation; D000072000:NF-KappaB Inhibitor alpha; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction; D018808:Transcription Factor AP-1 / Q000378:metabolism*
D004791:Enzyme Inhibitors; D020672:I-kappa B Proteins; D007375:Interleukin-1; D053583:Interleukin-1beta; D015850:Interleukin-6; C000606204:NFKBIA protein, human; D018808:Transcription Factor AP-1; D000072000:NF-KappaB Inhibitor alpha; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt