NEUROTROPHINS INDUCE SPHINGOMYELIN HYDROLYSIS - MODULATION BY COEXPRESSION OF P75(NTR) WITH TRK RECEPTORS

We examined neurotrophin-induced sphingomyelin hydrolysis in cells exp ressing solely the law affinity neurotrophin receptor, p75(NTR), and i n PC12 cells that coexpress p75(NTR) and Trk receptors, Nerve growth f actor (NGF), brain-derived neurotrophic factor, neurotrophin-3 (NT-3), and NT-5 stimulated sphingomyelin hydrolysis with similar kinetics in p75(NTR)-NIH-3T3 cells, Although brain-derived neurotrophic factor (1 0 ng/ml) was slightly more potent than NGF at inducing sphingomyelin h ydrolysis, NT-3 and NT-5 induced significant hydrolysis (30-35%) at 0. 1 to 1 ng/ml in p75(NTR)-NIH-3T3 cells, NT-3 did not induce sphingomye lin hydrolysis in Trk C-NIH-3T3 cells nor in cells expressing a mutate d p75(NTR) containing a 57-amino acid cytoplasmic deletion, thus demon strating the role of p75(NTR) in this signal transduction pathway, In p75(NTR)-NIH-3T3 cells, neurotrophin-induced sphingomyelin hydrolysis 1) localized to an internal pool of sphingomyelin, 2) was not a conseq uence of receptor internalization, and 3) showed no specificity with r espect to the molecular species of sphingomyelin hydrolyzed, In contra st to cells expressing solely p75(NTR), NGF (100 ng/ml) did not induce sphingomyelin hydrolysis in PC12 cells, Interestingly, NT-3 (10 ng/ml ) induced the same extent of sphingomyelin hydrolysis in PC12 cells as was apparent in p75(NTR)-NIH-3T3 cells. However, in the presence of N GF, NT-3 was unable to induce sphingomyelin hydrolysis, raising the po ssibility that Trk was modulating p75(NTR)-dependent sphingomyelin hyd rolysis, Inhibition of Trk tyrosine kinase activity with 200 nM K252a enabled both NGF and NT-3 in the presence of NGF to induce sphingomyel in hydrolysis, These data support that p75(NTR) serves as a common sig naling receptor for neurotrophins through induction of sphingomyelin h ydrolysis and that crosstalk pathways exist between Trk and p75(NTR)-d ependent signaling pathways.