Abstract 9513596 Dobrowsky The objectives of this proposal are to determine the structural components and the molecular mechanisms which regulate the coupling of the low affinity neurotrophin receptor, p75NTR, to the activation of a novel lipid second messenger system, the sphingomyelin (SM) cycle. Activation of the SM cycle produces ceramide which has been implicated in mediating the growth suppressing or apoptotic effects of specific cytokines and growth factors. Neurotrophins are growth factors which are necessary for the differentiation and maintenance of neuronal cells. The PI has recently demonstrated that neurotrophins induce SM hydrolysis through p75NTR. The cellular location of this SM pool will be determined. The structural requirements for the interaction of sphingomyelinase with the the p75 NTR will be determined, and their interaction will be studied in the presence and absence of the neurotrophin ligand. Since activation may also occur through intermediary molecules, the effect of neurotrophins on p75NTR dependent phospholipase A2 activation and arachidonic acid production a potential physiologic activator of SMase) will be examined. Since there are some indications of crosstalk between this pathway and tyrosine kinase, p75NTR dependent SM hydrolysis will be examined in tyrosine kinase receptor mutants, or by using inhibitors to uncouple tyrosine kinase from downstream signaling proteins. These studies will provide mechanistic insights into factors which regulate the coupling of p75NTR to SMase and elucidate the functional role of crosstalk pathways in the coordinate regulation of neurotrophin signaling pathways. They will also provide information on the role of lipids in intracellular signaling. ***
