The adaptor protein soc-1/Gab1 modifies growth factor receptor output in C. elegans

Previous genetic analysis has shown that dos/soc-1/Gab1 functions positively in receptor tyrosine kinase (RTK) stimulated Ras/Map kinase signaling, through the recruitment of csw/ptp-2/Shp2. Using sensitised assays in Caenorhabditis elegans for let-23/Egfr and daf-2/InsR (Insulin receptor-like) signaling, it is shown that soc-1/Gab1 inhibits phospholipase C-γ (PLCγ) and phosphatidylinositol 3’-kinase (PI3K) mediated signaling. Furthermore, as well as stimulating Ras/Map kinase signaling, soc-1/Gab1 stimulates a poorly defined signaling pathway that represses class 2 daf-2 phenotypes. In addition, it is shown that SOC-1 binds the C-terminal SH3 domain of SEM-5. This binding is likely to be functional as the sem-5(n2195)G201R mutation, which disrupts SOC-1 binding, behaves in a qualitatively similar manner to a soc-1 null allele in all assays for let-23/Egfr and daf-2/InsR signaling examined. Further genetic analysis suggests that ptp-2/Shp2 mediates the negative function of soc-1/Gab1 in PI3K mediated signaling, as well as the positive function in Ras/Map kinase signaling. Other effectors of soc-1/Gab1 are likely to inhibit PLCγ mediated signaling and stimulate the poorly defined signaling pathway that represses class 2 daf-2 phenotypes. Thus, the recruitment of soc-1/Gab1, and its effectors, into the RTK signaling complex modifies the cellular response by enhancing Ras/Map kinase signaling whilst inhibiting PI3K and PLCγ mediated signaling.