Identification of signal-induced I kappa B-alpha kinases in human endothelial cells

Activation of the nuclear transcription factor-kappa B is an early event in endothelial activation. NF-kappa B activation is regulated by the inducible phosphorylation and subsequent degradation of the inhibitory subunit I kappa B-alpha. We identified two discrete kinases of approximately 36 and 41 kDa in the cytoplasm of human umbilical vein endothelial cells that specifically bind to and phosphorylate the I kappa B-alpha subunit. I kappa B-alpha kinase activity is transiently elevated following treatment with either tumor necrosis factor alpha, interleukin-1 beta, or bacterial lipopolysaccharides and precedes activation of either mitogen-activated kinase or Jun kinase. Furthermore, activation of the I kappa B-alpha kinases precedes both the appearance of hyperphosphorylated I kappa B-alpha and its subsequent degradation, as well as the translocation of NF-kappa B to the nucleus, Deletion mutagenesis of the I kappa B-alpha polypeptide revealed that these kinases bind in or around the ankyrin repeat domains and phosphorylate residues within the C terminus. These kinases, however, were not identical to casein kinase II and displayed a pharmacologic profile distinct from other known kinases. These kinases may represent components of a signal transduction pathway regulating I kappa B-alpha levels in vascular endothelium.