Genomic dissection of receptor tyrosine kinase activation of extracellular signal-regulated kinase in Drosophila

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Receptor tyrosine kinase (RTK) signalling through extracellular signal-regulated kinases (ERKs) plays pivotal roles in development and disease, most notably in oncogenic transformation. While the core signalling cassette has been extensively investigated, this pathway is likely regulated by a larger network of moderate, context-specific proteins. To obtain a global view of RTK/ERK signalling, we performed a genome-wide RNAi screen in Drosophila cells using a quantitative cellular assay monitoring ERK activation. We show that ERK pathway output integrates a wide array of conserved cellular processes. Further analysis of selected components in multiple cell types with different RTK ligands validates and classifies 331 pathway regulators, several of which also demonstrate activity in vivo . The relevance of these genes is highlighted by our isolation of a novel Ste20-like kinase and PPM-family phosphatase which appear to regulate RTK/ERK signalling in vivo and in mammalian cells. We also provide evidence for an in vivo role for twenty other genes isolated from our screen. Because novel regulators which modulate specific pathway output may be potential selective targets for drug discovery, we have conducted two additional genome-wide RNAi screens for regulators of RTK specificity in Drosophila , including genes regulating ERK activation downstream of epidermal growth factor or insulin receptor and genes required specifically for sustained but not transient ERK activation. Our quantitative, unbiased screening approach reveals that the protein networks surrounding signal transduction cascades are large and, more importantly, impose a quantitatively variable effect on output.