GIPC and GAIP form a complex with TrkA: A putative link between G protein and receptor tyrosine kinase pathways

NGF initiates the majority of its neurotrophic effects by promoting the act ivation of the tyrosine kinase receptor TrkA. Here we describe a novel inte raction between TrkA and GIPC, a PDZ domain protein. GIPC binds to the juxt amembrane region of TrkA through its PDZ domain. The PDZ domain of GIPC als o interacts with GAIP, an RGS (regulators of G protein signaling) protein. GIPC and GAIP are components of a G protein-coupled signaling complex thoug ht to be involved in vesicular trafficking. In transfected HEK 293T cells G IPC, GAIP, and TrkA form a coprecipitable protein complex. Both TrkA and GA IP bind to the PDZ domain of GIPC, but their binding sites within the PDZ d omain are different. The association of endogenous GIPC with the TrkA recep tor was confirmed by coimmunoprecipitation in PC12 (615) cells stably expre ssing TrkA. By immunofluorescence GIPC colocalizes with phosphorylated TrkA receptors in retrograde transport vesicles located in the neurites and cel l bodies of differentiated PC12 (615) cells. These results suggest that GIP C, like other PDZ domain proteins, serves to cluster transmembrane receptor s with signaling molecules. When GIPC is overexpressed in PC12 (615) cells, NGF-induced phosphorylation of mitogen-activated protein (MAP) kinase (Erk 1/2) decreases; however, there is no effect on phosphorylation of Akt, phos pholipase C-gamma1, or Shc. The association of TrkA receptors with GIPC and GAIP plus the inhibition of MAP kinase by GIPC suggests that GIPC may prov ide a link between TrkA and G protein signaling pathways.