Dissociation of NGF Induced Signal Transduction from Neurite Elongation by Expression of a Mutant Adaptor Protein v-Crk in PC12 Cells

Expression of the adaptor protein v-Crk in PC12 cells results in sustained activation of NGF signaling pathways and augmented neuritogenesis. However, the inhibitory effect of the v-Crk SH2 domain mutant on neurite elongation does not correlate with impaired Trk A dependent signaling events or gene induction. In contrast, immunofluorescence studies and Triton X-100 extraction experiments indicate that v-Crk co-localizes with the cytoskeletal protein paxillin in the actin cytoskeleton whereas the v-Crk SH2 mutant causes aberrant aggregration of actin filaments at the growth cones. Interestingly, the neurotrophin receptor p75 in v-CrkPC12 cells also displays enhanced localization to the cytoskeleton and these cells exhibit an increased rate of NGF internalization. Together our data suggest that v-Crk might target the NGF-activated receptor signaling complex to the cytoskeleton, thereby potentiating neuritogenesis at the growth cone level. However, mutation in the v-Crk SH2 domain uncouples NGF signaling from the cytoskeletal interactions necessary for neurite elongation.