A NOVEL JUXTAMEMBRANE DELETION IN RAT TRKA BLOCKS DIFFERENTIATIVE BUTNOT MITOGENIC CELL SIGNALING IN RESPONSE TO NERVE GROWTH-FACTOR

We have generated a novel rat TrkA receptor mutant (TrkAS3) by deletio n of five conserved residues ((IMENP497)-I-493) in the juxtamembrane d omain. TrkAS3 receptors cannot support nerve growth factor (NGF)-induc ed cell cycle arrest or neuronal differentiation but retain cell survi val responses as well as Ras-dependent mitogenic signaling. Cells of t he nnr5 line stably expressing TrkAS3 induce NGF-dependent SHC phospho rylation and phosphatidylinositol 3-kinase, phospholipase Cy-l, and pr olonged mitogen-activated protein kinase activation to absolute levels comparable to those in PC12 cells. Although the stoichiometry of TrkA S3-SHC binding is reduced, cells overexpressing TrkAS3 exhibit NGF-dep endent SHC-Grb-2/Sos binding, essential for Ras activation, as well as NGF-dependent SNT phosphorylation to absolute levels comparable to th ose in PC12 cells. Collectively, these data suggest that the TrkAS3 de letion either directly affects a novel Ras-independent TrkA binding pr otein or that the decrease in TrkAS3-SHC association affects a Res-ind ependent SHC binding protein essential for cell cycle arrest and/or ne urite outgrowth.