Genetic Dissection of Signalling From Phosphotyrosine Residue 1201 of the Oncogenic Neu Receptor Tyrosine Kinase

Abstract

<p> The ErbB2/Neu orphan receptor tyrosine kinase is amplified in 20-30% of breast and ovarian cancers and predicates poor patient prognosis. Five conserved tyrosine residues, autophosphorylated by Neu catalytic activity, "dock" adaptors and second messengers that activate discrete signalling pathways, most prominently the Ras/MAPK pathway, to regulate cell survival and proliferation. </p> <p> Genetic analysis using Drosophila provides an efficient means for identifying evolutionarily conserved signalling components. Neu and Drosophila EGFR overexpression directs Drosophila tissue development synonymously. Consistent with biochemical evidence, genetic analysis ofNeu signalling through individual pTyr revealed activating signals for 4(Yl144, YB; Y1201, YC; Y1226/7, YD; Y1253, YE) of the 5 sites. Strong Ras-dependent signalling was mediated through adaptors Grb-2 (YB) and SHC (YD). In contrast to biochemical evidence, a strong Ras component was not genetically detected for YC or YE. </p> <p> We have conducted two enhancer-suppressor screens to identify novel Ras and non-Ras requirements for YC signalling. For the first screen, a quantitative approach was designed to identify modification of an YC-specific wing notch phenotype. Thirty-two members of the Ras/MAPK signalling cassette were assessed. Sensitivity to Ras, Raf, MAPK and the Ras-related GTPase R-Ras was identified downstream ofYC. The second screen, a large-scale mutagenesis, took advantage of an YC-induced rough eye phenotype. From over 19 000 screened flies, 11 enhancers and 6 suppressors were isolated. One strong suppressor has been genetically mapped to the dual transcription factor and phosphatase eyes absent. Other promising Ras-dependent and Ras-independent modifiers await farther mapping. Results from both screens point to YC as a unique pTyr that uses both Ras-dependent and Ras-independent outputs. </p>