Raf Kinase Inhibitor Protein Interacts with NF-κB-Inducing Kinase and TAK1 and Inhibits NF-κB Activation

Abstract

The transcriptional activator nuclear factor kappa B (NF-B) is required for the upregulation of a large number of genes in response to inflammation, viral and bacterial infection, and other stress stimuli. Genes that respond to NF-B encode a variety of cytokines, cell adhesion molecules, and acute-phase response proteins as well as apoptotic suppressor and effector proteins. It is believed that this reprogramming of gene expression is essential for cell survival during situations of physiological crisis (61). The activation of NF-B in response to stimulation by the proinflammatory cytokines tumor necrosis factor alpha (TNF-␣) and interleukin 1 beta (IL-1␤) has been extensively studied (17, 30); however, the mechanisms that modulate and eventually limit these responses are still poorly understood (61).We report here that the recently discovered protein kinase inhibitor protein RKIP (Raf kinase inhibitor protein) acts to inhibit NF-B activation. RKIP was first identified as an interacting partner of Raf-1 and shown to function as a negative regulator of the mitogen-activated protein (MAP) kinase (MAPK) cascade initiated by 76). The Raf-1-initiated pathway is comprised of three sequentially acting protein kinases: a MAP kinase kinase kinase (MAPKKK), a MAP kinase kinase (MAPKK), and a MAPK. This basic relationship has now been found to be conserved in several protein kinase pathways. In the Raf-1 pathway the MAPK is ERK1/2 (extracellular signal-regulated kinase 1 and 2), the MAPKK is MEK1 (MAP/ERK kinase 1), and the MAPKKK is Raf-1 itself. Functional studies using both gain-of-function and loss-of-function approaches demonstrated that RKIP disrupts the interaction between 76). Depletion of endogenous RKIP upregulated Raf-1 kinase activity and MAPK signaling, whereas ectopic expression of RKIP suppressed Raf-1 kinase activity and MAPK signaling as well as v-Raf-mediated transformation. Biochemical studies showed that RKIP efficiently dissociated preformed Raf/MEK complexes and behaved kinetically as a competitive inhibitor of MEK phosphorylation. In vivo, the association of endogenous RKIP with Raf-1 correlated inversely with Raf-1 kinase activity during serum stimulation of quiescent cells.Active NF-B is a dimer that can be assembled from several members of the Rel family of transcription factors, and some form of NF-B is expressed in most cell types (61). In unstimulated cells, NF-B is retained in the cytoplasm in an inactive form bound to a family of inhibitory proteins known as IB (inhibitors of B). Activation of NF-B requires the phosphorylation and degradation of IB, which allows the NF-B dimer to translocate into the nucleus. Virtually all of the many stimuli that can activate NF-B cause the phosphorylation of IB on

Absence of RKIP expression is an independent prognostic biomarker for gastric cancer patients

“…Currently, is known that RKIP also suppresses the activation of the nuclear factor κB (NF-κB) (10) and the regulator of G-protein coupled receptors (GRK-2) (11), and may be involved in regulation of the cell cycle (12). Thus, RKIP mediates important cellular mechanisms, including cell differentiation, cell cycle, apoptosis and cell migration, and is deregulated in several human disorders (13).…”

Promoter methylation and expression of Raf kinase inhibitory protein in esophageal squamous cell carcinoma

“…RKIP inhibits Raf-1-mediated phosphorylation and activation of mitogen-activated protein kinase (MAPK) kinase (MEK)-1, as well as the subsequent MAPK and extracellular signal-regulated kinase activities (8). RKIP also negatively regulates nuclear factor (NF)-κB signaling and the signaling downstream of G protein-coupled receptor kinase (9,10). During cancer development, RKIP is characterized as a tumor suppressor gene because of its maintenance of chromosome stability, inhibition of cellular proliferation, promotion of cell differentiation and dynamic balancing of oncogene activities (11).…”

The role of Raf-1 kinase inhibitor protein in the regulation of pancreatic beta cell proliferation in mice

“…In a similar way, deletion of Raf-1 does not result in decreased ERK1/2 phosphorylation in pancreatic islets, indicating that other Raf-1-dependent pathways may be operative in beta cells [25]. Additionally, RKIP1 may function through Raf-1 independent mechanisms involving NF-κB [8], GSK3β [9] or G protein-coupled receptors [11]. Apoptotic rates are comparable between Rkip1 −/− and WT P28 pancreases, implying that NF-κB-dependent survival pathways are not affected by Rkip1 deletion.…”

“…However, upon phosphorylation by protein kinase C, RKIP1 can dissociate from Raf-1 and inhibit G protein-coupled receptor kinase 2 (GRK2) [7], a negative regulator of G protein-coupled receptors. Additionally, RKIP1 has been implicated as a negative regulator of nuclear factor κB (NF-κB)-signalling pathways and an activator of glycogen synthase kinase 3β (GSK3β)-dependent signalling pathways [8,9]. Therefore, RKIP1 mediates the crosstalk between various important cellular signalling pathways and, consequently, can influence a wide array of cellular functions including cell proliferation, differentiation and apoptosis.…”