c-Src enhances the spreading of src-/- fibroblasts on fibronectin by a kinase-independent mechanism.

Abstract

We have explored the role of the tyrosine kinase c-Src in cellular adhesion. Fibroblasts derived from src-~-mice (src-/-fibroblasts) exhibit a reduced rate of spreading on fibronectin. This defect is rescued by expression of wild-type chicken c-Src. Analyses of mutants suggest that c-Src increases the rate of cell spreading in src-/-fibroblasts through a kinase-independent mechanism requiring both the SH3 and SH2 domains. To further address the role of c-Src in adhesion, we examined the activity and subcellular distribution of c-Src during the adhesion of fibroblasts on fibronectin. We observed a transient increase in the specific kinase activity of c-Src accompanied by the partial dephosphorylation of the negative regulatory site Y527. Activation of c-Src is followed by its redistribution to newly formed focal adhesions. These results suggest that the enzymatic activity and subcellular distribution of c-Src are coordinately regulated during cellular adhesion and that c-Src can affect adhesion by a kinase-independent mechanism.

Tumorigenesis mediated by MET mutant M1268T is inhibited by dominant-negative Src

“…Anti-avian Src antibody recognized only exogenous Src protein Oncogene Dominant negative Src inhibits bioactivity of M1268T MET N Nakaigawa et al tumors in vivo were dependent, at least in part, on the binding and activation of c-Src. Kaplan et al (1995) focused attention on the seemingly paradoxical e ects of c-Src and v-Src on cellular adhesion. Kaplan et al (1995) found that c-Src positively in¯uenced cellular adhesion, while v-Src resulted in morphogic transformation and an apparent reduction in cellular adhesion.…”

“…Kaplan et al (1995) focused attention on the seemingly paradoxical e ects of c-Src and v-Src on cellular adhesion. Kaplan et al (1995) found that c-Src positively in¯uenced cellular adhesion, while v-Src resulted in morphogic transformation and an apparent reduction in cellular adhesion. The authors suggested that di erent levels of kinase activity in the two proteins in focal adhesions might partially explain the paradox.…”

The many faces of Src: multiple functions of a prototypical tyrosine kinase

“…In particular, signaling from integrin receptors involves Src family kinases, but may not require Src's kinase activity. Upon crosslinking of integrins, Src is transiently activated and is found in a detergent insoluble fraction, enriched in focal adhesions, the sites where integrins help organize cytoskeletal and signaling proteins in response to adhesion (Kaplan et al, 1995). Fibroblasts derived from src7/7 mice exhibit a defect in initial cell spreading (Kaplan et al, 1995), defects in phosphorylation of an adaptor molecule pp130cas (Bockholt and Burridge, 1995;Hamasaki et al, 1996;Vuori et al, 1996) and a 10-fold attenuation of MAPK activation in response to plating on ®bronectin (Schlaepfer et al, 1997), indicating that Src is critical in pathways downstream of integrin crosslinking.…”

“…In fact, defects in integrin signaling in src7/7 cells are actually complemented, in part, by kinase-inactive molecules. For example, either a kinase-inactive point mutant of Src or a truncated molecule that removes the entire kinase domain will complement the cell-spreading defect (Kaplan et al, 1995); these molecules will also increase pp130cas phosphorylation in response to ®bronectin (Schlaepfer et al, 1997 and P Schwartzberg, unpublished observations). A truncated Src molecule lacking the kinase domain has also been demonstrated to restore partial activation of MAPK (Mitogen Activated Protein Kinase) in response to plating on ®bronectin (Schlaepfer et al, 1997).…”

“…Activated or`open conformation' Src is not only associated with an increase in kinase activity, but also with an accompanying change in protein localization (Kaplan et al, 1995). Src in its`closed conformation' is constitutively found associated with endosomal membranes in a detergent soluble fraction.…”