The major focus of the study proposed here is to characterize the requirements for the ER associated degradation (ERAD) of the Epithelial Sodium Channel (ENaC). ENaC is responsible for salt reabsorption across the epithelia of the kidney and lung, and plays a critical role in controlling blood pressure and airway fluid volume. Defects in ENaC degradation are associated with Liddle's Syndrome and pseudohypoaldosteronism type I that result in hyper- and hypotension respectively. Because of ENaC's role in salt homeostasis, the synthesis and trafficking are tightly regulated at every level. While ENaC trafficking at the cell surface and more peripheral cellular compartments has been extensively studied, there is currently little known about ENaC biosynthesis and quality control in the ER. ER associated degradation (ERAD) is the process whereby proteins entering the secretory pathway are monitored by the ER quality control system and subject to degradation when they fail to attain a mature conformation. In addition to ENaC, many other disease relevant proteins can also become ERAD substrates, including CFTR (cystic fibrosis), AQP2 (nephrogenic diabetes insipidus), and Pael-R (Parkinson's disease). My previous work has shown that the degradation of ENaC requires a unique complement of molecular chaperones. For example, the ER lumenal Hsp40s are required for ENaC degradation, but the Hsp70, BiP for which Hsp40s serve as co-chaperones are not. The goal of this proposal is to identify and characterize additional effectors of ENaC degradation and biogenesis using two model systems. First, I will use the yeast model system to characterize genes that were upregulated in a transcriptional analysis of ENaC expressing yeast. I will also assay the role of the nucleotide exchange factors Sil1 and Lhs1, as well as the quality control associated lectins in ENaC degradation. Second, I will use the data I obtain in yeast to identify and characterize the human homologues of the ENaC effectors. The role of the human homologues in ENaC degradation will be assessed using a Xenopus oocyte overexpression system to obtain a functional, electrophysiological readout (sodium current) for ENaC surface expression. While I have become proficient in using yeast as a model organism, I am unfamiliar with using electrophysiological techniques. Fortunately, the laboratory of Dr. Tom Kleyman is very experienced with these techniques and has agreed to host this portion of my training. I am extremely motivated to master two- electrode voltage clamp electrophysiology, which will allow me to monitor ENaC trafficking using a functional readout. I believe this, as well as learning to use yeast genetic approaches will complement my current technical skills and provide me with the technical ability to become a successful independent scientist. In addition to acquiring new technical skills this award will enable me to further develop my teaching, mentoring, writing, presenting, and management skills, which are all critical to becoming a well-rounded, independent scientist. I am fortunate to be completing this training under the direction of my co-sponsors, Dr. Jeff Brodsky and Dr. Tom Kleyman, who are both not only well-established investigators, but skilled educators, and I am confident that I will attain the goals outlined in this award. In addition to the technical aspects of this proposal I will take full advantage of the training opportunities this career award will provide for my professional development by participating in journal clubs, local and national meetings, and meeting with my advisory committee on a regular basis. I am confident that the training environment of the University of Pittsburgh, the Department of Biological Sciences, and the Renal-Electrolyte Division provides will help me attain my ultimate goal of becoming an independent scientific investigator, where I will continue to investigate the early folding, trafficking and degradation events of ENaC and other disease relevant proteins.
The current application proposes to investigate early events during the synthesis, folding, and degradation of the Epithelial Sodium Channel (ENaC). ENaC is responsible for the reabsorbtion of sodium in the kidney and is critical for regulating blood pressure. Mutations in ENaC lead to diseases including Liddle's Syndrome and Pseudohypoaldosteronism Type 1; therefore, understanding the early biogenesis events is critical.
