Epidermal growth factor receptor (EGFR) signaling regulates cell survival, migration, proliferation and cell fate specification in animals. The receptor undergoes dimerization and autophosphorylation upon activation by its ligands, and initiates a cascade of downstream signaling events that involves the classical Ras/Raf/MAPK pathway. Aberrant expression of the receptor and pathway components can lead to many human cancers. Hence, EGFR and other pathway components have been intensely studied.
The structure and function of the receptor is conserved among different species. Drosophila melanogaster presents a simplified model to study EGFR signaling with the presence of one receptor and four activating ligands, as opposed to multiple receptors and ligands in mammals. EGFR signaling is used repeatedly during different stages of development, regulated in part by the spatial and temporal expression of the ligands. Pathway activity is further modulated by positive and negative feedback loops, some of which involve the ligands themselves. The neuregulin like agonist vein (vn) was cloned in our lab. vn was shown to be an activator of EGFR and is required for wing disc growth and specification of body wall fate.
Expression of vn is dependent on EGFR pathway activity in embryos and the wing disc. Here we defined an enhancer sequence that is responsible for vn expression in the early wing disc when vn activity is required for subsequent global development of the wing disc. Conserved ETS sites within this enhancer are required for vn expression and are bound by the ETS factor, Pointed P2 (PntP2), in vitro. PntP2 is a known target of EGFR signaling that is activated by MAPK. Our data demonstrate, for the first time, direct regulation of a ligand promoter by EGFR signaling.
Despite its use as a powerful genetic model, the Drosophila field lacks well characterized cell-type specific cell lines. Here, we describe the characterization of a novel epithelial cell line, which endogenously expresses components of the EGFR signaling pathway. This characterization suggests that this cell line will be a valuable model to study EGFR signaling. In particular, it will be useful to address biochemical and cell biological questions pertaining to the pathway and also to isolate novel components of the pathway using high throughput in vitro screens.