Bombesin, Lysophosphatidic Acid, and Epidermal Growth Factor Rapidly Stimulate Focal Adhesion Kinase Phosphorylation at Ser-910

Abstract

A rapid increase in the tyrosine phosphorylation of the nonreceptor tyrosine kinase FAK 1 (1, 2), which localizes to focal adhesion plaques (3), has been identified as a prominent early event in cells stimulated by diverse signaling molecules that regulate cell proliferation, migration, and apoptosis (4, 5 (14,27). Phosphorylation at Tyr-925 within the focal adhesion targeting (FAT) domain creates a binding site for the Src homology 2 domain of the adapter protein Grb2-SOS (Ras exchange factor) complex and provides a possible mechanism of activation of the Ras/Raf/MEK/ERK pathway (36). The FAT domain binds paxillin and talin, which are responsible for targeting FAK to the focal adhesions and for promoting downstream signaling (36 -38). The importance of FAK-mediated signal transduction is underscored by experiments showing that this tyrosine kinase is implicated in embryonic development (39) and in the control of cell migration (27, 40 -42), proliferation (40, 43), and apoptosis (44, 45). It is increasingly recognized that overexpression of FAK is linked to the invasive properties of cancer cells (46,47).In addition to being phosphorylated at multiple tyrosines in response to external stimuli, FAK is also phosphorylated at serine residues (48, 49). Recently, Ser-722 and Ser-910, in the COOH-terminal, noncatalytic region of FAK (termed FAK-related nonkinase (FRNK)), have been identified as prominent phosphorylation sites (49). Despite the importance of FAK in signal transduction, virtually nothing is known about the regulation of these phosphorylation events. In particular, none of the previous studies demonstrated that the phosphorylation of any of these serine residues of FAK can be regulated in re-

Differential FAK phosphorylation at Ser-910, Ser-843 and Tyr-397 induced by angiotensin II, LPA and EGF in intestinal epithelial cells

“…Interestingly, both Ser-910 and Ser-843, located in the COOH-terminal region of FAK, have been identified as prominent phosphorylation sites during mitosis [33]. Recent results from our laboratory demonstrated that FAK phosphorylation at Ser-910 was strikingly stimulated by GPCR agonists, tumor promoting phorbol esters and growth factors in Swiss 3T3 fibroblasts [34][35][36]. Furthermore, phosphorylation of FAK at Ser-843 was induced by GPCR agonists, including bombesin, vasopressin and bradykinin in Swiss 3T3 fibroblasts [37].…”

“…In fibroblasts, we proposed that FAK serves as a point of integration of signals transmitted via Gα q , leading to PKC/ERK-dependent FAK phosphorylation at Ser-910 [34][35][36] and to Ca 2+ /calmodulin/CaMKII-dependent FAK phosphorylation at Ser-843 [37]. Here, we examined whether these pathways also operate in intestinal epithelial cells.…”

“…Given that PKCs lead to ERK activation in response to ANGII in IEC-18 cells and that activated ERKs directly phosphorylate FAK at Ser-910 in vitro [34], we determined whether FAK phosphorylation at Ser-910 in GPCR-stimulated intestinal epithelial cells is mediated also through an ERK-dependent pathway. In line with this possibility, treatment of IEC-18 cells with U0126, a potent inhibitor of MEK-mediated ERK activation, prevented FAK phosphorylation at Ser-910 induced by subsequent addition of either ANGII or PDB to these cells.…”

“…The proximity of these phosphorylated serine residues to sites at which FAK interacts with other proteins suggests a possible function in the regulation of the assembly of FAK signaling complexes [6]. Recent results from our laboratory demonstrated that FAK phosphorylation at Ser-910 is strikingly stimulated by GPCR agonists, tumor promoting phorbol esters and growth factors through an ERK-dependent pathway in Swiss 3T3 fibroblasts [34][35][36]. In another study, we demonstrated that stimulation of 3T3 fibroblasts with bombesin, bradykinin or vasopressin induced a rapid and transient increase in FAK phosphorylation at Ser-843 through a Ca 2+ /calmodulin/CaMKII-dependent pathway [37].…”

“…More recently, it has become clear that FAK is also phosphorylated at multiple serine residues [32][33][34][35][36][37]. The proximity of these phosphorylated serine residues to sites at which FAK interacts with other proteins suggests a possible function in the regulation of the assembly of FAK signaling complexes [6].…”