Hedgehog (Hh) signaling is critical for many developmental events and must be restrained to prevent cancer. The ultimate goal of our research is to solve the mystery of the Hh signal reception, the actions of the two transmembrane proteins, Smoothened (Smo) and Patched (Ptc). Currently our laboratory is using Drosophila model system to understand the significance of the trafficking of Smo protein and the transporter activity of Ptc protein during animal development.
Regulators for Smo protein movement: We showed previously that movement of Smo protein to the plasma membrane is a pre-requisite for activating Hh signaling in vivo. Since hyper-activation of the Hh pathway causes cancer, a good understanding of Smo trafficking is likely to provide clues for improved treatment for human disorders. We conducted a cell-based RNA interference (RNAi) screen to look for novel proteins regulating Smo trafficking. We have chosen several candidates for further characterization using genetic, biochemical and cell biological approaches.
Transporter activity of Ptc protein: The Hh receptor Ptc antagonizes Smo activity, but the exact mechanism remains a mystery. Ptc protein shares similarity with the RND transporters. We have shown that Ptc may behave as a transporter when assayed in vitro. Currently we are testing Ptc transporter activity in vivo, using transgenic flies expressing various Ptc SSD mutations. The identification of Ptc as a transporter opens up a whole new set of opportunities for dissecting Hh signal transduction.
The construction of an animal, with a single fertilized egg cell becoming tens of trillions of cells, requires exquisite coordination. At almost every stage in development, cells emit, receive and interpret signals from other nearby cells, and these signals are necessary for normal differentiation and function. Remarkably, only a few protein signals are required to coordinate cell fate decisions, tissue patterning and organ growth. These include Hedgehog, Notch, Wnt, and growth factor signals. My lab utilizes Drosophila wing development as a simple model system to study developmental signaling, not only because the fly wing morphogenesis requires interplay among major signaling processes, but more importantly, the stereotypical morphology of the adult wing allows us to conduct simple but efficient genetic screens to uncover conserved regulatory mechanisms underlying metazoan development. Our genetic screens led us to identify two protein modification events, reversible phosphorylation and ubiquitination, that are important to regulate Hedgehog and Notch signaling activation. The goal of our study is to better understand the mechanisms of how these two protein modification events regulate components of the Hedgehog and Notch pathways to assure appropriate signaling outcomes, with the hope that they will provide effective therapeutic targets for preventing birth defects and tumorigenesis.
Zhu, A. J., Zheng, L., Suyama, K. and Scott, MP. (2003) Altered localization of Drosophila Smoothened protein activates Hedgehog signal transduction. Genes & Development 17:1240-1252.
Huang X., Suyama, K., Buchanan, J., Zhu, AJ. and Scott, MP. (2005) A Drosophila model of the Niemann-Pick type C lysosome storage disease: dnpc1a is required for molting and sterol homeostasis. Development 132:5115-5124.
Su, Y., Ospina, JK., Zhang, J., Michelson, A., Schoen, AM. and Zhu, AJ. (2011) Sequential phosphorylation of Smoothened transduces graded Hedgehog signaling. Science Signaling 4:ra43.
Du, J., Zhang, J., Su, Y., Liu, M., Ospina, JK., Yang, Y. and Zhu, A. J. (2011) In vivo RNAi screen reveals neddylation genes as novel regulators of Hedgehog signaling. PLoS ONE 6:e2416.
Zhang, J., Liu, M., Su, Y., Du, J. and Zhu, AJ. (2012) A targeted in vivo RNAi screen reveals deubiquitinases as new regulators of Notch signaling. G3 (in press).