Activation of the Drosophila C3G leads to cell fate changes and overproliferation during development, mediated by the RAS-MAPK pathway and RAP1

Abstract

The cellular signal transduction pathways by which C3G, a RAS family guanine nucleotide exchange factor, mediates v-crk transformation are not well understood. Here we report the identification of Drosophila C3G, which, like its human cognate, specifically binds to CRK but not DRK/GRB2 adaptor molecules. During Drosophila development, constitutive membrane binding of C3G, which also occurs during v-crk transformation, results in cell fate changes and overproliferation, mimicking overactivity of the RAS-MAPK pathway. The effects of C3G overactivity can be suppressed by reducing the gene dose of components of the RAS-MAPK pathway and of RAP1. These findings provide the first in vivo evidence that membrane localization of C3G can trigger activation of RAP1 and RAS resulting in the activation of MAPK, one of the hallmarks of v-crk transformation previously thought to be mediated through activation of SOS.

Crk family adaptors–signalling complex formation and biological roles

“…In the fruit¯y, genes for Crk (Galletta et al, 1999), DC3G (Ishimaru et al, 1999) and the DOCK180-homologue MBC (myoblast city; Erickson et al, 1997;Nolan et al, 1998) were cloned and functionally characterized. MBC is important for myoblast fusion, dorsal closure and neural development, phenotypes which may be linked at least in part to a role of MBC in the migration of speci®c cells.…”

“…DC3G appears to play a role in the regulation of cell fates and proliferation since a membrane-tagged full-length DC3G, which is believed to function as a constitutively active form of DC3G, leads to phenotypes mimicking an overactivation of the Ras1 ± MAPK pathway. A truncated (dominant negative) version, lacking the catalytic domain, leads to morphogenetic defects (Ishimaru et al, 1999). Reduc-tion of the gene doses of Rap1 or Ras diminished the e ects induced by expression of`overactivated' DC3G.…”

A Misexpression Screen to Identify Regulators of Drosophila Larval Hemocyte Development

“…This is the largest class of EP/EY insertions and includes genes that may regulate the adherent or migratory properties of hemocytes, for example, scab (scb, EY10270); C3G (EP1613), a Ras family guanine nucleotide exchange factor (Ishimaru et al 1999); RhoGEF2 (EY08391), which has been shown to direct cell shape changes (Barrett et al 1997) and control invagination of mesodermal and endodermal primordia during gastrulation (Hacker and Perrimon 1998); and tousled-like kinase (tlk, EP1200), which has been identified as a regulator of Rho signaling (Gregory et al 2007). …”

C3G-mediated suppression of oncogene-induced focus formation in fibroblasts involves inhibition of ERK activation, cyclin A expression and alterations of anchorage-independent growth

“…C3G is activated by multiple signals depending on the cell type (McLeod et al, 1998;Reedquist and Bos, 1998;Sakkab et al, 2000;Yokote et al, 1998;York et al, 1998;Zhu et al, 1998), and can also act as a mediator in the activation of several pathways, including the JNK, ERK and Rac signaling pathways (York et al, 1998;Ishimaru et al, 1999;Mochizuki et al, 2000;Abassi and Vuori, 2002).…”