PLCγ is a key signaling molecule that regulates pathways required for cell proliferation, differentiation and apoptosis. Various studies have reported PLCγ overexpression to be a key factor in transforming primary tumors to metastatic by affecting these very pathways. A PLCγ-specific inhibitor could therefore be an invaluable tool not only for basic research but also for anti-cancer studies.
Small wing (sl), the Drosophila homolog of PLCγ, plays a dual role. It negatively regulates the EGFR pathway controlling photoreceptor and wing vein differentiation while positively regulating the Insulin pathway affecting growth. An sl null mutant (sl9/sl9) shows a reduced wing size, ectopic veins and rough eyes as a result of extra R7 photoreceptors in ~60% ommatidia. Our objective is to identify a novel small molecule inhibitor of PLCγ using Drosophila as a model system.
In a primary screen, we looked at vein differentiation patterns to identify molecules that alter EGFR signaling. Argos, an inhibitor of EGFR, when overexpressed in wings causes severe loss of venation which is significantly rescued in L3 by a partial loss of Sl function. Thus, drug fed MS1096>Aos flies were used as a sensitive model system to detect potential Sl inhibition by looking for L3 vein recovery. 37 of the 1,596 small molecules, provided by the NCI, showed significant results.
We are currently in the process of performing secondary screens to confirm EGFR inhibition by looking at photoreceptor differentiation in the eye in an sl7 mutant. sl7 is a missense mutation that results in 5-10% ommatidia with extra R7 photoreceptors. Further inhibition of Sl or the EGFR pathway would result in a higher percentage of R7 recruitment. So far, we have identified 7 small molecules as potential inhibitors. In conjunction, these molecules are also being tested on homozygous rolled (rl1) mutants. rl1 flies have a disrupted EGFR pathway and exhibit ~22% ommatidia without R7’s. Amplification of the EGFR pathway, potentially through Sl inhibition would result in a recovery of photoreceptor numbers. Subsequent experiments will try to determine whether any of the small molecules identified do in fact inhibit Sl.