Signaling Pathways Regulating Proteolysis in Innervated Muscle

University Of Pittsburgh, Pittsburgh PA

Investigators

Abstract

Regulation of proteolytic processes is important in many kinds of physiological adaptations, in development, and in diverse pathological states, including wasting and atrophy in skeletal muscle, and hypertrophy or atrophy in cardiac muscle. Muscle proteolysis is well-known to be promoted by fasting or chronic starvation, by disuse or denervation, in sepsis and in cancer cachexia. Conversely, reduced proteolysis (in addition to increased synthesis) may contribute to cardiac hypertrophy. The mechanisms by which intracellular or extracellular signals are transduced to regulate proteolytic processes in muscle are poorly understood. This project aims to increase our understanding of these processes using the simplest genetically tractable model system available for studying innervated muscle, the nematode Caenorhabditis elegans. The methodology uses transgenic animals in which the level of a 8-galactosidase fusion protein reports" on proteolysis specifically in 95 body-wall muscle and 8 sex-muscle cells. The reporter protein is completely stable in fed animals, but is degraded under conditions of starvation, denervation, mutational activation of the homolog of the Ras proto-oncogene, or mutational hyperactivation of a fibroblast growth factor (FGF) receptor homolog. This research will determine whether control of muscle protein degradation by activated-Ras signals is mediated by the Raf/MEK/MAP kinase pathway, determine how it is affected by activity of the P13 kinase pathway, and determine if the relevant signals from activated FGF receptor are transmitted by way of the Ras/Raf/MEK/MAPK pathway. The roles of intramuscular calcium and diacylglycerol and the possible roles of calcium-activated protein kinases will also be explored. These questions will be approached by epistasis analysis of mutant strains in which one or two signal-transduction proteins are inactivated or hyperactivated, combined with the use of selective inhibitors of individual steps in signal transduction. Analysis of these signaling mechanisms in this simple system will provide paradigms for investigating the signaling pathways that control muscle proteolysis in more complex organisms.