title: Retrograde TrkAIII transport from ERGIC to ER: a re-localisation mechanism for oncogenic activity.
abstract: In human SH-SY5Y neuroblastoma (NB) cells, nascent immature N-glycosylated 110kDa TrkA moves rapidly from the endoplasmic reticulum (ER) to the Golgi Network (GN), where it matures into the 140kDa receptor prior to being transported to the cell surface, creating GN and cell surface pools of inactive receptor maintained below the spontaneous activation threshold by a full compliment of inhibitory domains and endogenous PTPases. In contrast, the oncogenic alternative TrkAIII splice variant is not expressed at the cell surface but re-localises to intracellular membranes, within which it exhibits spontaneous ERGIC/COPI-associated activation and oncogenic Akt signalling. In this study, we characterise the mechanism responsible for TrkAIII re-localisation. Spontaneous TrkAIII activation, facilitated by D4 IG-like domain and N-glycosylation site omission, increases spontaneous activation potential by altering intracellular trafficking, inhibiting cell surface expression and eliminating an important inhibitory domain. TrkAIII, spontaneously activated within the permissive ERGIC/COPI compartment, rather than moving in an anterograde direction to the GN exhibits retrograde transport back to the ER, where it is inactivated. This sets-up self-perpetuating TrkAIII re-cycling between the ERGIC and ER, that ensures continual accumulation above the spontaneous activation threshold of the ERGIC/COPI compartment. This is reversed by TrkA tyrosine kinase inhibitors, which promote anterograde transport of inactivated TrkAIII to the GN, resulting in GN-associated TrkAIII maturation to a 120kDa species that is degraded at the proteasome.
authors.affiliation: Department of Applied Clinical and Biotechnological Sciences, University of L'Aquila, L'Aquila, Italy.
authors.forename: Antonietta Rosella
authors.initials: AR
authors.lastname: Farina
authors.affiliation: Department of Applied Clinical and Biotechnological Sciences, University of L'Aquila, L'Aquila, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Cappabianca
authors.affiliation: Department of Applied Clinical and Biotechnological Sciences, University of L'Aquila, L'Aquila, Italy.|Department of Medical-Surgical Science and Biotechnology, University of Rome "La Sapienza", Latina, Italy.
authors.forename: Pierdomenico
authors.initials: P
authors.lastname: Ruggeri
authors.affiliation: Department of Applied Clinical and Biotechnological Sciences, University of L'Aquila, L'Aquila, Italy.
authors.forename: Luciana
authors.initials: L
authors.lastname: Gneo
authors.affiliation: Department of Applied Clinical and Biotechnological Sciences, University of L'Aquila, L'Aquila, Italy.
authors.forename: Rita
authors.initials: R
authors.lastname: Maccarone
authors.affiliation: Department of Applied Clinical and Biotechnological Sciences, University of L'Aquila, L'Aquila, Italy.
authors.forename: Andrew Reay
authors.initials: AR
authors.lastname: Mackay
mesh_terms: D017398:Alternative Splicing / Q000235:genetics; D063646:Carcinogenesis / Q000235:genetics; D045744:Cell Line, Tumor; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006031:Glycosylation / Q000187:drug effects; D006056:Golgi Apparatus / Q000378:metabolism*; D006801:Humans; D009154:Mutation / Q000235:genetics; D009447:Neuroblastoma / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism*; D051058:Oncogene Protein v-akt / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology / Q000627:therapeutic use; D017434:Protein Structure, Tertiary / Q000235:genetics; D021381:Protein Transport / Q000187:drug effects / Q000235:genetics; D020917:Receptor, trkA / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics
chemical_list: D047428:Protein Kinase Inhibitors; D020917:Receptor, trkA; D051058:Oncogene Protein v-akt
keywords: TrkAIII oncoprotein; activation mechanism; endoplasmic reticulum intermediate compartment; neuroblastoma; retrograde transport