Chmp1 may negatively regulate DER and Notch signaling. Meagan Valentine, Simon Collier. Dept Biomedical Sciences, Marshall University, Huntington, WV.

   Chmp1 is a component of ESCRT-III, a conserved protein complex required for degradation of activated membrane receptors. The ESCRT complexes downregulate many pathways involved in development and growth, and several components, Chmp1 included, have been linked to human cancer. Chmp1 has not been studied in Drosophila, so we are investigating Chmp1 function with knockdown and over-expression. Our results suggest that Chmp1 negatively regulates Epidermal Growth Factor Receptor (DER) and Notch signaling. We used VDRC and TRiP RNAi fly lines to knock Chmp1 down in the Drosophila wing. The result was wider wing veins. Since the DER pathway regulates wing vein size, we tested for interactions with both positive and negative regulators of DER signaling. Our results suggest that Chmp1 negatively regulates DER signaling. We are evaluating the effect of Chmp1 knockdown on expression of Blistered (Bs), which is negatively regulated by DER signaling, by generating clones of Chmp1 knockdown in the wing. Preliminary results suggest that Chmp1 knockdown reduces Bs, supporting the conclusion that Chmp1 negatively regulates DER signaling. We created fly lines to over-express Chmp1 or His-Myc-tagged Chmp1 (HM-Chmp1). Both of these lines display activity, as they can partially rescue the Chmp1 knockdown phenotype. Over-expression of Chmp1 in the wing results in wing vein deltas, suggesting that Notch signaling may be altered as well. Notch signaling affects wing vein size, so we are testing for interactions between Chmp1 knockdown and Notch. So far, it seems that Chmp1 knockdown reduces the frequency of notches normally observed with the hypomorphic N^55e11 allele, suggesting that Chmp1 negatively regulates Notch signaling. We are also using HM-Chmp1 to investigate Chmp1 localization. HM-Chmp1 localizes apically and to the membrane in multiple Drosophila tissues. Overall, our results suggest that Chmp1 negatively regulates Notch and DER signaling. Likely, the role Chmp1 plays in growth is at least in part due to regulation of DER and Notch signaling through its involvement in ESCRT function.