Activation of IκB Kinase β by Protein Kinase C Isoforms

Abstract

The atypical protein kinase C (PKC) isotypes (lambda/iotaPKC and zetaPKC) have been shown to be critically involved in important cell functions such as proliferation and survival. Previous studies have demonstrated that the atypical PKCs are stimulated by tumor necrosis factor alpha (TNF-alpha) and are required for the activation of NF-kappaB by this cytokine through a mechanism that most probably involves the phosphorylation of IkappaB. The inability of these PKC isotypes to directly phosphorylate IkappaB led to the hypothesis that zetaPKC may use a putative IkappaB kinase to functionally inactivate IkappaB. Recently several groups have molecularly characterized and cloned two IkappaB kinases (IKKalpha and IKKbeta) which phosphorylate the residues in the IkappaB molecule that serve to target it for ubiquitination and degradation. In this study we have addressed the possibility that different PKCs may control NF-kappaB through the activation of the IKKs. We report here that alphaPKC as well as the atypical PKCs bind to the IKKs in vitro and in vivo. In addition, overexpression of zetaPKC positively modulates IKKbeta activity but not that of IKKalpha, whereas the transfection of a zetaPKC dominant negative mutant severely impairs the activation of IKKbeta but not IKKalpha in TNF-alpha-stimulated cells. We also show that cell stimulation with phorbol 12-myristate 13-acetate activates IKKbeta, which is entirely dependent on the activity of alphaPKC but not that of the atypical isoforms. In contrast, the inhibition of alphaPKC does not affect the activation of IKKbeta by TNF-alpha. Interestingly, recombinant active zetaPKC and alphaPKC are able to stimulate in vitro the activity of IKKbeta but not that of IKKalpha. In addition, evidence is presented here that recombinant zetaPKC directly phosphorylates IKKbeta in vitro, involving Ser177 and Ser181. Collectively, these results demonstrate a critical role for the PKC isoforms in the NF-kappaB pathway at the level of IKKbeta activation and IkappaB degradation.

Upregulation of cyclooxygenase-2 is accompanied by increased expression of nuclear factor-κB and IκB kinase-α in human colorectal cancer epithelial cells

“…The IKKs are part of a larger multiprotein complex called the IKK signalsome, which contains the IKK complex-associated protein (IKAP) and IKKg (also called NEMO), which is also crucial for NFkB activation (Cohen et al, 1998;Yamaoka et al, 1998;Bowie and O'Neill, 2000). Many upstream activators and regulators of IKK activity have been identified, including the NF-kB-inducing kinase (NIK) (Nakano et al, 1998), protein kinase Cz (PKCz) (Lallena et al, 1999), transforming growth factor b-activated kinase (TAK-1) (Ninomiya-Tsuji et al, 1999), MEK kinase (MEKK) 1, 2 and 3 (Zhao and Lee, 1999), and S6 kinase (Schouten et al, 1997). NF-kB can induce the expression of numerous target genes, including COX-2.…”

The Drosophila Atypical Protein Kinase C-Ref(2)P Complex Constitutes a Conserved Module for Signaling in the Toll Pathway

“…However, in other tissues, such as lung, in which PKC levels are much higher than in fibroblasts, the lack of PKC also inhibits IKK activation and the nuclear translocation of NF-B (20). Therefore, it seems that in cells in which PKC levels are very on April 27, 2019 by guest http://mcb.asm.org/ low, this PKC isoform plays an essential role in NF-B-dependent transcriptional activation that cannot be compensated for by / PKC, which is ubiquitously and abundantly expressed (20); in cells where PKC levels are higher, it may function upstream of the IKK complex, possibly as an IKK kinase (19). This is reminiscent of, for example, the cell type-dependent role played by IKK␣ in NF-B signaling.…”

Celastrol, a novel triterpene, potentiates TNF-induced apoptosis and suppresses invasion of tumor cells by inhibiting NF-κB–regulated gene products and TAK1-mediated NF-κB activation

“…We also investigated how celastrol suppresses IKK activation. Several kinases, such as MEKK1, 54 MEKK3, 55 PKC, 56 glycogen synthase kinase-3␤, 57 TAK1, 52 PDK1, 58 and Akt 59 have been reported to function upstream of IKK. Recent studies, however, indicate that TAK1 plays a major role in the canonical pathway activated by cytokines through its interaction with TAB1 and TAB2.…”