The long-range objective of this project is to understand the external and intramuscular signals and signal-transduction networks that regulate protein degradation in muscle. Previous studies in this laboratory have identified and characterized the proteasome-mediated degradation induced by starvation or functional denervation and the non-proteasomal degradation induced by Fibroblast Growth Factor (FGF) signaling via a Ras-MAP kinase cascade, and shown a role of Insulin-like Growth Factor receptor signaling in opposing FGF-promoted degradation. These studies made it clear not only that protein degradation in muscle responds to multiple external and autocrine signals and is mediated by multiple proteolytic mechanisms, but also that the state of protein catabolism may be determined by the balance between opposing signals rather than by the intensity of a single signal. This proposal focuses on elucidating the observations that degradation of transgene-coded reporter proteins in muscles of Caenorhabditis elegans is negatively regulated by a Transforming Growth Factor Beta (TGF-beta) receptor, and is promoted by excess signal from a calcium-calmodulin dependent protein kinase (CaMKII). The methodologies used are primarily those of genetics (particularly suppression and epistasis analysis), biochemistry (measurement of reporter proteins and molecular correlates of signaling) and molecular biology. Potentially novel signaling pathways will be elucidated, effectors downstream of the TGF-beta receptor and CaM kinase will be characterized, and the relation of these pathways to others in the cell will be explored. The broader impact of this project, in the short-to-medium term, will be to provide a keener understanding of how complex networks of signals and signal-transduction pathways, operating in at least two distinct cell types (neurons and muscles) and possibly a third (hypodermis), are coordinated to regulate protein stability in the target tissue (muscle). There will also be significant educational impacts: Undergraduate researchers will be an integral part of the project team. The senior scientific personnel will make strong efforts to incorporate aspects of C. elegans biology and neuromuscular biology in general into undergraduate courses they teach (Genetics, Introductory Biology) and into other undergraduate courses (Developmental Biology, Cell Biology). Modules using C. elegans as a model for insulin signaling and lipid metabolism are incorporated into workshops for high-school teachers and live C. elegans are provided for K-12 school visits. In the longer term, the impact of this project on clinically important issues of muscle health could become substantial, since the catabolism of muscle proteins is important both for normal adaptive physiology and for a variety of pathological states.
