Specific Uncoupling of GRB2 from the Met Receptor

Abstract

The biological effects of hepatocyte growth factor/scatter factor are mediated by autophosphorylation of its receptor, the Met tyrosine kinase, on two carboxyl-terminal tyrosines. These phosphotyrosines (Y1349VHVNATY1356VNV) are multifunctional docking sites for several effectors. Grb2, the adaptor for the Ras guanyl-nucleotide exchanger SOS, binds to Tyr1356 in the YVNV motif. By site-directed mutagenesis we either abrogated or duplicated the Grb2 consensus, without interfering with the other effectors. Loss of the link with Grb2 severely impaired transformation. The same mutation, however, had no effect on the "scattering" response, indicating that the level of signal which can be reached by Grb2-independent routes is permissive for motility. Duplication of the Grb2 binding site enhanced transformation and left motility unchanged. Thus, two Met-mediated biological responses, motility and growth, can be dissociated on the basis of their differential requirement for a direct link with Ras.

Transforming Growth Factor β2 inhibition of Hepatocyte Growth Factor-induced endothelial proliferation and migration

“…In addition, in rat ®broblasts TGF b 1 signi®cantly decreased Src kinase activity and protein abundance, mainly by accelerating Src degradation (Fukuda et al, 1998). The tyrosine receptor induced Ras-MAPK pathway has been shown to be essential for cell proliferation (Ponzetto et al, 1996). Indeed, in the presence of the MEK inhibitor PD098059, HGF did not stimulate endothelial proliferation.…”

“…Various intracellular signalling pathways are activated by Met and mediate a speci®c cell response. In epithelial cells, it is established that scattering is dependent on phosphatidylinositol-3-OH kinase and Rac activation (Ridley et al, 1995), while growth requires the stimulation of the Ras-MAPK (Ponzetto et al, 1996) cascade and the STAT pathway is necessary for tubulogenesis (Boccaccio et al, 1998). To understand how TGF b 2 inhibits HGF, we elucidated which intracellular signalling pathways are able to discriminate between HGF-induced cell migration and proliferation in endothelial cells.…”

“…HGF-induced growth of epithelial cells requires the stimulation of the MAP-kinase cascade (Ponzetto et al, 1996). Since erk-2/p42 MAPK is activated by a kinase cascade that induces phosphorylation of threonine and tyrosine residues, we evaluated the levels of tyrosine phosphorylated erk-2/p42 MAPK in HUVEC treated with HGF and TGF b 2 alone or in combination.…”

Loss of the exon encoding the juxtamembrane domain is essential for the oncogenic activation of TPR-MET

“…Among proteins involved in Met downstream signaling, the two adaptor molecules Grb-2 and Gab-1 play a central role. Binding of Grb-2 to Tyr 489 initiates the sos-ras pathway and is required for TprMet mediated transformation (Ponzetto et al, 1996); the interaction of Gab-1 with Tyr 482 and Tyr 489 promotes the recruitment of transducers such as PI3Kinase that, in turn, control motility and invasion (Giordano et al, 1997;Bardelli et al, 1999). To assess the role of the juxtamembrane domain on the regulation of Tpr-Met signaling, we compared the interaction of Tpr-Met and Tpr-juxtaMet with either Grb-2 and Gab-1 using pull-down experiments.…”

Activating mutations in the Met receptor overcome the requirement for autophosphorylation of tyrosines crucial for wild type signaling

“…In this regard, two tyrosine doublets Y8,9 and Y14,15, have been shown to be essential for Met signaling (Fixman et al, 1997;Ponzetto et al, 1996;Rodrigues and Park, 1994;Weidner et al, 1995). Following their phosphorylation, Y8,9 function to greatly enhance the enzymatic activity of the Met receptor (Naldini et al, 1991a;Rodrigues and Park, 1994), while Y14,15 provide docking sites for a wide array of signaling molecules (Fixman et al, 1995(Fixman et al, , 1996(Fixman et al, , 1997Paio et al, 1996;Ponzetto et al, 1994).…”