title: Trk is a calmodulin-binding protein: implications for receptor processing.
abstract: The tyrosine kinase receptors for the neurotrophins (Trk) are a family of transmembrane receptors that regulate the differentiation and survival of different neuronal populations. Neurotrophin binding to Trk leads to the activation of several signalling pathways including a rapid, but moderate, increase in intracellular calcium levels. We have previously described the role of calcium and its sensor protein, calmodulin, in Trk-activated intracellular pathways. Here we demonstrate that calmodulin is able to precipitate TrkA from PC12 cell lysates. Using recombinant GST-fusion proteins containing the complete intracellular domain of TrkA, or fragments of this region, we show that calmodulin binds directly to the C-terminal domain of TrkA in a Ca2+-dependent manner. We have also co-immunoprecipitated endogenous Trk and calmodulin in primary cultures of cortical neurones. Moreover, we provide evidence that calmodulin is involved in the regulation of TrkA processing in PC12 cells. Calmodulin inhibition results in the generation of a TrkA-derived p41 fragment from the cytosolic portion of the protein. This fragment is autophosphorylated in tyrosines and can recruit PLCgamma and Shc adaptor proteins. These results suggest that calmodulin binding to Trk may be important for the regulation of Trk intracellular localization and cleavage.
authors.affiliation: Grup de Neurobiologia Molecular, Departament de Ciències Mèdiques Bàsiques, Facultat de Medicina, Universitat de Lleida, Lleida, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Llovera
authors.forename: Yolanda
authors.initials: Y
authors.lastname: de Pablo
authors.forename: Joaquim
authors.initials: J
authors.lastname: Egea
authors.forename: Mario
authors.initials: M
authors.lastname: Encinas
authors.forename: Sandra
authors.initials: S
authors.lastname: Peiró
authors.forename: Dionisio
authors.initials: D
authors.lastname: Martín-Zanca
authors.forename: Nativitat
authors.initials: N
authors.lastname: Rocamora
authors.forename: Joan X
authors.initials: JX
authors.lastname: Comella
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D002148:Calmodulin-Binding Proteins / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D016716:PC12 Cells; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D020917:Receptor, trkA
chemical_list: D002148:Calmodulin-Binding Proteins; D002352:Carrier Proteins; D008565:Membrane Proteins; D020794:Receptor Protein-Tyrosine Kinases; D020917:Receptor, trkA; D002118:Calcium