A Trk nerve growth factor (NGF) receptor point mutation affecting interaction with phospholipase C-γ1 abolishes NGF-promoted peripherin induction but not neurite outgrowth

We analyzed the function of Trk nerve growth factor (NGF) receptors containing a point mutation (Tyr → Phe) in a major autophosphorylation site (Tyr-785). Tyr-785 is required for phospholipase C-γ1 to interact with Trk and to become tyrosine-phosphorylated in response to NGF. The altered receptors were transfected into a mutant subline of PC12 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 internalization. Moreover, Trk Y785F mediates NGF-stimulated neurite outgrowth as well as a variety of additional responses including induction of immediate-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 observations indicate that phospholipase C-γ1 activation or other signaling pathways dependent on Tyr-785 autophosphorylation are selectively required for regulation of peripherin expression by NGF, but not for many other functional NGF responses. This supports the presence of multiple and separable signaling pathways in the NGF mechanism of action.