IndraLab
Statements
"Among other effectors, active ras binds and activates the raf kinase, iniziating a kinase cascade involving serine phosporylation of mek1/2 (mapkk) and tyrosine and threonine phosphorylation of erk1/2 ras activation leads to raf and subsequently mek activation. Phospholipide analysis demostrated that serine residues 218 and 222 of human mek1 are the primary sites for phosphorylation by c-raf."
rlimsp
"This strategy revealed that MEK1 is constitutively and mainly phosphorylated at the Thr-292, Ser-298, Thr-386, and Thr-388 residues in vivo, and that combinations of phosphorylations at these four residues produce at least six phosphorylated variants of MEK1. Like the levels of phosphorylation of the Ser-218 and Ser-222 residues by RAF1, which have been well studied, the phosphorylation statuses of Thr-292, Ser-298, Thr-386, and Thr-388 residues vary widely during activation and deactivation of the MAPK pathway."
"Protein kinase C (PKC) regulates activation of the Raf-1 signaling cascade by growth factors, but the mechanism by which this occurs has not been elucidated. Here we report that one mechanism involves dissociation of Raf kinase inhibitory protein (RKIP) from Raf-1. Classic and atypical but not novel PKC isoforms phosphorylate RKIP at serine 153 (Ser-153). RKIP Ser-153 phosphorylation by PKC either in vitro or in response to 12-O-tetradecanoylphorbol-13-acetate or epidermal growth factor causes release of RKIP from Raf-1"
"Despite remarkable progress in dissecting the signaling pathways that are crucial for the metabolic effects of insulin, the molecular basis for the specificity of its cellular actions is not fully understood. One clue might lie in the spatial and temporal aspects of signaling. Recent evidence suggests that signaling molecules and pathways are localized to discrete compartments in cells by specific protein interactions. Also, the rapid termination of tyrosine or lipid phosphorylation by phosphatases or serine kinases might tightly control the strength of a signaling pathway, thus determining its effect on growth, differentiation and metabolism. Insulin is the most potent anabolic hormone known, promoting the synthesis and storage of carbohydrates, lipids and proteins and inhibiting their degradation and release back into the circulation. Decreased secretion of insulin, coupled with resistance to its actions, results in type 2 diabetes, a devastating disease that is reaching epidemic proportions [1]. Even in the absence of diabetes, insulin resistance is often associated with central obesity, hypertension, polycystic ovarian syndrome, dyslipidemia and atherosclerosis. At the cellular level, insulin action is characterized by diverse effects, including changes in vesicle trafficking, stimulation of protein kinases and phosphatases, promotion of cellular growth and differentiation and activation or repression of transcription. This complexity suggests that insulin action must involve multiple signaling pathways that diverge at or near the activation of its tyrosine kinase receptor. In fact, it is likely that even individual effects of the hormone require multiple signaling inputs. Evidence is emerging that the coordination of these pathways might be governed by their intracellular compartmentalization or duration of action. Here, we consider how temporal and spatial aspects of signal transduction play a crucial role in determining the specificity of insulin action, focusing on signal initiation from the receptor that is spatially segregated into discrete domains of the plasma membrane, as well as the mechanisms that determine the duration of individual signaling pathways. Together, these factors help to differentiate insulin from other hormones that share some of the same overall signaling properties. Divergent signaling pathways are initiated by insulin receptor substrates. The insulin receptor is a tyrosine kinase that catalyzes the phosphorylation of several intracellular substrates, including the insulin receptor substrate (IRS) proteins [2], GAB-1 [3], Shc [4], APS [5], p60DOK [6], SIRPS [7] and c-Cbl [8] (Fig. 1). Each of these substrates recruits a distinct subset of signaling proteins containing Src homology 2 (SH2) domains, which interact specifically with sequences surrounding the phosphotyrosine residue. Moreover, each of these substrates can be confined to distinct locations in the cell by specific sequences that direct interactions with other proteins or lipids. Most attention in the field of insulin receptor substrates has focused on the IRS family of proteins. Mice lacking the IRS-1 protein are insulin resistant but do not develop overt diabetes [9,10]. By contrast, animals lacking IRS-2 exhibit both impaired glucose tolerance and diabetes [11], which appears to result from a defect in insulin secretion as well as insulin resistance, presumably owing to decreased b-cell proliferation in the pancreas in the face of increased demand for insulin. Despite the similarity in structure and function, the apparent differences in phenotype between IRS1 and IRS2 knockout mice underscore a specific signaling specificity that probably results from their tissue distribution, subcellular location, activation–inactivation kinetics and combinatorial interactions with downstream effectors [12]. The tyrosine phosphorylation of IRS family members generates docking sites for sev..."
"Western blot analysis was performed on protein extracts isolated from HPECs overexpressing Cdc37 or the vector only (Fig. 1C) ? .Raf-1 steady-state levels were unchanged. However, Raf-1 activity, measured by the abundance of phosphorylated S217/221 MEK1/2, a direct target of Raf-1 (30) , was consistently elevated in Cdc37-overexpressing cells, whereas total MEK1/2 levels were unchanged. Increases in Cdk4 levels and markedly reduced p16 expression were also consistently observed in Cdc37-overexpressing HPECs. "
"To address a possible role of mutant C-RAF proteins in the constitutive phosphorylation of ERK1/2, kinase assays were done with Myc-tagged C-RAF proteins immunoprecipitated from transiently transfected Cos-7 cells. Strong constitutive kinase activity was shown for S427GC-RAF whereas I448VC-RAF did not significantly differ from wt C-RAF (Fig. 3A)."
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RAF1 phosphorylated on an unknown residue, an unknown residue, an unknown residue, an unknown residue, an unknown residue, an unknown residue, an unknown residue, and an unknown residue phosphorylates MAP2K1. 1 / 1
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"acti-Fig. 3. PKCb in insulin signal-ing. Insulin-stimulated insulin receptor (IR) phosphorylates IRS1. IRS1 recruit various signaling molecules through SH2-phos-photyrosine interactions. IRS1-binding proteins containing an SH2 domain include Grb2, PI3K, SHP-2, and Nck. Insulin-induced ERK activation in L6 myocytes occurs largely through Raf-1 rather than Ras activation. In contrast, EGF-induced ERK acti-vation is dependent on Grb2/Sos-mediated Ras activation."