GIPC Is Recruited by APPL to Peripheral TrkA Endosomes and Regulates TrkA Trafficking and Signaling

Abstract

GIPC is a PDZ protein located on peripheral endosomes that binds to the juxtamembrane region of the TrkA nerve growth factor (NGF) receptor and has been implicated in NGF signaling. We establish here that endogenous GIPC binds to the C terminus of APPL, a Rab5 binding protein, which is a marker for signaling endosomes. When PC12(615) cells are treated with either NGF or antibody agonists to activate TrkA, GIPC and APPL translocate from the cytoplasm and bind to incoming, endocytic vesicles carrying TrkA concentrated at the tips of the cell processes. GIPC, but not APPL, dissociates from these peripheral endosomes prior to or during their trafficking from the cell periphery to the juxtanuclear region, where they acquire EEA1. GIPC's interaction with APPL is essential for recruitment of GIPC to peripheral endosomes and for TrkA signaling, because a GIPC PDZ domain mutant that cannot bind APPL or APPL knockdown with small interfering RNA inhibits NGF-induced GIPC recruitment, mitogen-activated protein kinase activation, and neurite outgrowth. GIPC is also required for efficient endocytosis and trafficking of TrkA because depletion of GIPC slows down endocytosis and trafficking of TrkA and APPL to the early EEA1 endosomes in the juxtanuclear region. We conclude that GIPC, following its recruitment to TrkA by APPL, plays a key role in TrkA trafficking and signaling from endosomes.

Endogenous Vascular Endothelial Growth Factor-A (VEGF-A) Maintains Endothelial Cell Homeostasis by Regulating VEGF Receptor-2 Transcription

“…APPL has also been correlated with GIPC/synectin in the control of TrkA trafficking and signaling (58), and GIPC is another important protein involved in VEGFR-2 trafficking (59). We also knocked down GIPC in HUVECs and found that the VEGFR-2 mRNA level was unmodified (data not shown).…”

All known patient mutations in the ASH-RhoGAP domains of OCRL affect targeting and APPL1 binding

“…Genetic disruption of both GIPC and megalin in mice yields low molecular weight proteinuria, a defect also seen in Lowe Syndrome and Dent Disease [20,21]. Additionally, APPL1 could link OCRL to TrkA, which could help explain the cognitive manifestations of Lowe Syndrome [11,22,23]. Dual color immunofluorescence of cells expressing Myc-APPL1 (red) and wild type HA-OCRL or HA-OCRL with patient mutations (green).…”

Directing traffic in neural cells: determinants of receptor tyrosine kinase localization and cellular responses

“…GIPC interacts with the juxtamembrane region of TrkA (Liu et al 2001). Characterization of this interaction demonstrated that knock-down of GIPC results in the slowed internalization and retrograde trafficking of TrkA, as well as in the inhibition of NGF-mediated Akt and ERK phosphorylation (Varsano et al 2006). The Xenopus homolog of mammalian GIPC, xGIPC, or Kermit 2, also has been implicated in IGF-IR signaling by directly interacting with the IGF-IR and promoting IGF-I stimulated MAPK signaling and Xenopus oocyte maturation (Booth et al 2002).…”