Novel Mechanisms for the Alteration of RET Receptor Tyrosine Kinase Signal Transduction.

Abstract

Receptor tyrosine kinases (RTKs) are the second largest family of transmembrane receptors, and these proteins regulate numerous cellular processes including cell survival, metabolism, proliferation and differentiation. Mutations that affect the activity, abundance, cellular distribution or regulation of these receptors often leads to diseases such as cancer, making our understanding of the basic biology of these receptors, especially the regulation of their expression and signaling, critically important. One such RTK, RET, is a receptor for glial cell line-derived neurotrophic factor (GDNF) family ligands (GFLs) and has several functions in the developing embryo, including crucial roles in kidney morphogenesis, spermatogenesis and development of numerous neuronal populations. Regulation of RET through mechanisms such as intracellular trafficking, turnover and activation change the signaling capabilities of RET and have been well studied. Here I present two additional novel mechanisms of action of RET. In the first investigation, I explored the effects of novel 5’-alternative splicing on RET protein structure and function. These isoforms, which arise from exon skipping, are full-length RET proteins with deletions in the extracellular domain and are referred to as RETΔE3 and RETΔE345. I found that these isoforms differ from full-length RET in both their biochemical properties as well as their signaling capabilities. In the second study, I investigated the interaction of RET with p75, a pro-apoptotic protein that is a member of the tumor necrosis factor receptor (TNFR) superfamily. While I discovered that RET and p75 interact, and that this association is increased by the presence of pro-apoptotic stimuli in vitro, I identified a p75-independent role for RET in programmed cell death in the sympathetic nervous system during development in vivo. These data provide two novel mechanisms for the regulation of RET which, along with future studies, will further our understanding of RET biology under physiologic and pathologic conditions.