A TRK NERVE GROWTH-FACTOR (NGF) RECEPTOR POINT MUTATION AFFECTING INTERACTION WITH PHOSPHOLIPASE C-GAMMA-1 ABOLISHES NGF-PROMOTED PERIPHERIN INDUCTION BUT NOT NEURITE OUTGROWTH

We analyzed the function of Trk nerve growth factor (NGF) receptors co ntaining a point mutation (Tyr --> Phe) in a major autophosphorylation site (Tyr-785). Tyr-785 is required for phospholipase C-gamma 1 to in teract with Trk and to become tyrosine-phosphorylated in response to N GF. The altered receptors were transfected into a mutant subline of PC 12 rat pheochromocytoma cells (designated PC12nnr5) that, unlike wild- type PC12 cells, lack expression of endogenous Trk and responsiveness to NGF. PC12nnr5 cells permanently transfected with Trk Y785F exhibit NGF-dependent autophosphorylation and normal NGF binding and internali zation. Moreover, Trk Y785F mediates NGF-stimulated neurite outgrowth as well as a variety of additional responses including induction of im mediate-early and late genes. However, in contrast to cells expressing wild-type Trk, cells expressing Trk Y785F lack NGF-promoted elevation of peripherin intermediate filament mRNA and protein. These observati ons indicate that phospholipase C-gamma 1 activation or other signalin g pathways dependent on Tyr-785 autophosphorylation are selectively re quired for regulation of peripherin expression by NGF, but not for man y other functional NGF responses. This supports the presence of multip le and separable signaling pathways in the NGF mechanism of action.