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Characterization of IkappaB kinases - IkappaB-a is not phosphorylated by Raf-1 or protein kinase C isozymes, but is a casein kinase II substrate.

J. Biol. Chem. 271, 13868-13874 (1996)
Verlagsversion DOI PMC
Open Access Gold
The NF-kappaB transcription factor is activated by a wide variety of stimuli, including phorbol esters such as 12-O-tetradecanoylphorbol-13-acetate. In its inactive state, NF-kappaB is sequestered in the cytoplasm tethered to an inhibitor protein, IkappaB. Activation comprises the rapid phosphorylation of IkappaB-alpha at N-terminal sites, which presumably marks IkappaB-alpha for proteolytic degradation and leads to release of NF-kappaB into the nucleus. In addition, IkappaB-alpha is constitutively phosphorylated at the C terminus, which may be a prerequisite for proper IkappaB function. Protein kinase C (PKC) is activated by 12-O-tetradecanoylphorbol-13-acetate and has been previously reported to phosphorylate IkappaB-alpha in vitro. As PKC has turned out to constitute a multigene family encoding isozymes with different biological functions, we have reinvestigated IkappaB-alpha phosphorylation by PKC using recombinant PKC isozymes expressed in insect cells. While crude PKC preparations were efficient IkappaB-alpha kinases, highly purified PKC isozymes completely failed to phosphorylate IkappaB-alpha. Biochemical separation of porcine spleen yielded at least two fractions with IkappaB-alpha kinase activity, both of which were devoid of detectable PKC isozymes. One peak contained both Raf-1 and casein kinase II (CKII). Purified Raf-1 does not phosphorylate IkappaB-alpha directly, but associates with CKII, which efficiently phosphorylates the C terminus of IkappaB-alpha. Two-dimensional phosphopeptide mapping and high pressure liquid chromatography-mass spectroscopy analysis showed that all IkappaB-alpha kinases induced phosphorylation at the same prominent sites in the C terminus. Our results clearly indicate that PKC isozymes alpha, beta, gamma, delta, epsilon, eta, and zeta as well as Raf-1 are not IkappaB-alpha kinases. They furthermore demonstrate that IkappaB-alpha is targeted by several kinases, one of which appears to be CKII.
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Publikationstyp Artikel: Journalartikel
Dokumenttyp Wissenschaftlicher Artikel
Sprache englisch
Veröffentlichungsjahr 1996
HGF-Berichtsjahr 0
ISSN (print) / ISBN 0021-9258
e-ISSN 1083-351X
Quellenangaben Band: 271, Heft: 23, Seiten: 13868-13874 Artikelnummer: , Supplement: ,
Verlag American Society for Biochemistry and Molecular Biology
Begutachtungsstatus Peer reviewed
PubMed ID 8662925
Erfassungsdatum 1996-12-31