Gab2 requires membrane targeting and the met binding motif to promote lamellipodia, cell scatter, and epithelial morphogenesis downstream from the met receptor

Abstract

Gab1 and Gab2 are conserved scaffolding proteins that amplify and integrate signals stimulated by many growth factor receptors including the Met receptor. Gab1 acts to diversify the signal downstream from Met through the recruitment of multiple signaling proteins, and is essential for epithelial morphogenesis. However, whereas Gab1 and Gab2 are both expressed in epithelial cells, Gab2 fails to support a morphogenic response. We demonstrate that Gab1 and Gab2 are divergent in their function whereby Gab1, but not Gab2, promotes lamellipodia formation, and is localized to the membrane of lamellipodia upon Met activation. We have identified activation of ERK1/2 as a requirement for lamellipodia formation. Moreover, activated ERK1/2 are localized to lamellipodia in Gab1 expressing cells but not in cells that overexpress Gab2. By structure-function studies, we identify that enhanced membrane localization conferred through the addition of a myristoylation signal, together with the addition of the direct Met binding motif (MBM) from Gab1, are required to promote lamellipodia and confer a morphogenic signaling response to Gab2. Moreover, the morphogenesis competent myristoylated Gab2MBM promotes localization of activated ERK1/2 to the leading edge of lamellipodia in a similar manner to Gab1. Hence, subcellular localization of the Gab scaffold, as well as the ability of Gab to interact directly with the Met receptor, are both essential components of the morphogenic signaling response which involves lamellipodia formation and the localization of ERK1/2 activation in membrane ruffles.

Met receptor tyrosine kinase signals through a cortactin-Gab1 scaffold complex, to mediate invadopodia

“…Following Gab1 knockdown in MKN45 cells or in fibroblasts expressing a Tpr-Met mutant unable to recruit Gab1 Y1349F/Y1356FY, the inability to produce invadopodia and/or actin rosettes (Figs 3, 4) is due to decreased assembly of actin-rich core structures (supplementary material Movies 2,3), consistent with a role for Met-Gab1 signaling in the regulation of an early step in invadopodia formation. This supports previous reports that Gab1 plays a role in Met-dependent regulation of other actin-rich cellular structures, such as lamellipodia (Frigault et al, 2008) and circular dorsal ruffles (Abella et al, 2010). Hence, depending on the cellular context, Gab1 provides a common link between Met signals and assembly of actin-rich structures at the cell periphery.…”

PECAM1 regulates flow-mediated Gab1 tyrosine phosphorylation and signaling

“…Membrane targeting of Gab1 plays a critical role in mediating tyrosine kinase receptors-triggered signaling [24, 25]. To show Gab1 subcellular localization in the cell-cell contacts by both flow and HGF, we infected HUVECs with adenoviral GFP-tagged Gab1 (Ad-GFP-Gab1) followed by exposure to flow or treatment with HGF for 15 min.…”

Function, regulation and pathological roles of the Gab/DOS docking proteins

“…As already discussed above, the generation of knock-in -mice carrying mutations in either the SHP2 or the p85 binding sites of Gab1 revealed that these interactions play distinct roles in embryonic development [32]. Interestingly, enforced membrane localization of Gab2 through the addition of a myristoylation signal together with the introduction of the MBD from Gab1 is sufficient to confer a Gab1-like behaviour to Gab2 in HGF-stimulated MDCK cells [146]. These findings indicate that in the case of Gab1 and Gab2, differences in their subcellular compartmentalization, rather than in coupling to effectors, leads to distinct biological properties.…”