Inhibition of Src tyrosine kinases suppresses activation of nuclear factor-κB, and serine and tyrosine phosphorylation of IκB-α in lipopolysaccharide-stimulated raw 264.7 macrophages

Involvement of protein tyrosine kinases (PTK) in lipopolysaccharide (LPS)-induced nuclear factor-kappa B (NF- B) activation has been demonstrated. Studies investigated the role of PTK and the underlying mechanisms by which PTK play a role in LPS induction of pathways leading to NF- B activation in macrophages. Inhibitors of PTK - genistein, herbimycin A, or AG126 - blocked LPS-induced NF- B activation. Genistein also blocked pervanadate-induced NF- B activation. Furthennore, Src TK selective inhibitors - damnacanthal or PP1 - blocked LPS-induced NF- B activation over a range of nanomolar concentrations. Genistein, damnacanthal, or PP1 blocked the LPS-induced serine phosphorylation, the degradation of I B- , and the consequent translocation of the p65 subunit of NF- B to the nucleus. In addition to serine phosphorylation of I B- , LPS-induced NF- B activation also required tyrosine phosphorylation of I B- . These TK inhibitors blocked substantially LPS induction of tyrosine phosphorylation of I B- . Furthermore, cSrc and Lck were physically associated with I B- . These results suggest that the LPS-induced NF- B pathways are dependent on both serine and tyrosine phosphorylation of I B- , and that Src TK, such as cSrc and Lck, are key components of the LPS signaling pathway through at least two different mechanisms associated with NF- B activation. Copyright