MEK Kinase 1 Interacts with Focal Adhesion Kinase and Regulates Insulin Receptor Substrate-1 Expression

Abstract

MEK kinase 1 (MEKK1) has been shown to contribute to the regulation of cell migration, whereas focal adhesion kinase (FAK) is a major player involved in both cell migration and integrin signaling. Here we show that MEKK1 and FAK are co-immunoprecipitated from mouse fibroblasts. Moreover, the association between MEKK1 and FAK appears to be physiologically relevant, as it is enhanced by treatment with epidermal growth factor (EGF). Targeting FAK to the membrane also enhanced its association with MEKK1, indicating that MEKK1 is localized to a membrane-related subcellular domain, perhaps focal adhesions. Interestingly, the expression of insulin receptor substrate-1 (IRS-1) was diminished in MEKK1-deficient fibroblasts, which is similar to an earlier finding in FAK-deficient fibroblasts. Insulin-like growth factor 1 (IGF-1)-induced ERK activation was diminished in MEKK1-deficient cells, but MEKK11 is a 196-kDa serine-threonine kinase activated in response to a variety of stimuli, including EGF, lysophosphatidic acid, osmotic stress, and microtubule toxins (1, 2). Upon activation, MEKK1 participates in the regulation of the JNK and ERK pathways and is involved in the activation of . In addition, MEKK1 senses microtubule integrity, protects cells from committing to apoptosis, and contributes to the migration of fibroblasts and epithelial cells. The phenotype of the MEKK1-null mouse includes an eyelid closure defect that is also seen in mice lacking the EGF receptor and TGF-␣ (6). This suggests the possibility that MEKK1 is required for EGF receptor control of cell migration. Consistent with that idea, overexpression of MEKK1 induces the formation of a large lamellipodia-like structure in epithelial cells (6). Still, the mechanism by which MEKK1 influences cell motility remains unclear.FAK is protein tyrosine kinase found at sites of adhesion (7). It is activated by integrin-mediated adhesion and serves as a signaling protein within cytoskeleton-associated networks (7). The Src-family protein tyrosine kinases p130 Cas, Shc, and Grb2 act in concert with FAK to transduce integrin-generated signals to the ERK/JNK MAP kinase cascades (7). Experiments using FAK-deficient cells have established that FAK is essential for integrin-stimulated cell migration and important for linking activation of the PDGF and EGF receptors to the cellular machinery that promotes directed cell migration (8). The fact that MEKK1 is enriched in membranes and colocalizes with ␣-actinin along actin stress fibers at focal adhesions (9, 10) prompted us to investigate the possibility that MEKK1 is associated with FAK.Insulin and IGF-1 exert diverse biological effects by binding to and activating their cognate tyrosine kinase receptors. IRS-1 is a major substrate for the insulin and IGF-1 receptors, which rapidly phosphorylate it on multiple tyrosine residues upon ligand binding. Recently, it was reported that targeted disruption of FAK eliminates IRS-1 expression in MEFs and that interactions between cells and the extracellular matrix regulate the tran...

MAP kinases and cell migration

“…Also, in cerebellar granule neurons, active JNK is predominantly localized in cytoplasmic compartments (Coffey et al, 2000). Furthermore, active JNK is localized at focal adhesions, and MEKK1, a kinase upstream of JNK, is associated with α-actinin and FAK (Almeida et al, 2000;Christerson et al, 1999;Yujiri et al, 2003). The observations that active JNK is found in cytoplasmic locations provide additional evidence for cytoplasmic functions of JNK, in addition to its established nuclear functions.…”

Stress-induced corneal epithelial apoptosis mediated by K+ channel activation

“…On the other hand, scaffold protein MEKK1, an upstream mitogen activated protein kinase K (MAPKK) kinase of JNK cascades, is also associated with cytoskeleton reorganization and activated in response to cell volume changes (Kwan et al, 2001;Cross and Templeton, 2004;Lieber et al, 2004). Recent studies found that FAK physiologically inter acts with MEKK1 identified by immunocoprecipitation and co-localization in response to EGF stimulation (Yujiri et al, 2003). Thus, it is very likely in the corneal epithelium that FAK coordinates signals from inputs of UV-induced volume shrinkage to the JNK signaling pathway.…”

Focal adhesion kinase regulates insulin resistance in skeletal muscle

“…In addition, regulation of FAK phosphorylation by insulin stimulation in non-muscle cells has been reported [8][9][10]. A regulatory role of FAK in IRS-1 levels [11,12] and hepatic insulin action [13,14] has also been reported. Genetic studies have provided evidence for interaction between integrin and insulin signalling [15,16].…”