A M Teckchandani | PubMed Health

PubMed2001

Beyond the RING: CBL proteins as multivalent adapters.

Following discovery of c-Cbl, a cellular form of the transforming retroviral protein v-Cbl, multiple Cbl-related proteins have been identified in vertebrate and invertebrate organisms. c-Cbl and its homologues are capable of interacting with numerous proteins involved in cell signaling, including various molecular adapters and protein tyrosine kinases. It appears that Cbl proteins play several functional roles, acting both as multivalent adapters and inhibitors of various protein tyrosine kinases. The latter function is linked, to a substantial extent, to the E3 ubiquitin-ligase activity of Cbl proteins. Experimental evidence for these functions, interrelations between them, and their biological significance are addressed in this review, with the main accent placed on the adapter functions of Cbl proteins.

Animals↗

PubMed2001

c-Cbl facilitates fibronectin matrix production by v-Abl-transformed NIH3T3 cells via activation of small GTPases.

The protooncogenic protein c-Cbl has been shown to act as a multivalent adaptor and a negative regulator of protein tyrosine kinase-mediated signaling. Recent studies have implicated it in the regulation of cell adhesion-related events. We have previously shown that c-Cbl facilitates adhesion and spreading of v-Abl-transformed fibroblasts, and that these effects are dependent on its tyrosine phosphorylation. However, the mechanisms mediating effects of c-Cbl on fibroblast adhesion remain poorly understood. In this study we demonstrate that the tyrosine phosphorylation-dependent effect of c-Cbl on adhesion of v-Abl-transformed fibroblasts is primarily mediated by an increase in fibronectin matrix deposition by these cells. This increase in fibronectin matrix deposition and, hence, in cell adhesion is dependent on cytoskeletal rearrangements induced by RhoA, Rac1 and, possibly, Rap1 activation caused by c-Cbl. The observed activation of these GTPases is mediated by the recruitment of phosphatidylinositol-3' kinase, CrkL and Vav2 to the C-terminal tyrosine residues of c-Cbl. The results of this study also demonstrate that ubiquitination is essential for the observed effects of c-Cbl on fibronectin matrix production and cell adhesion.

3T3 Cells↗