title: SLAM-associated protein as a potential negative regulator in Trk signaling.
abstract: Neurotrophin signaling plays important roles in regulating the survival, differentiation, and maintenance of neurons in the nervous system. Binding of neurotrophins to their cognate receptors Trks induces transactivation and phosphorylation of the receptor at several tyrosine residues. These phosphorylated tyrosine residues then serve as crucial docking sites for adaptor proteins containing a Src homology 2 or phosphotyrosine binding domain, which upon association with the receptor initiates multiple signaling events to mediate the action of neurotrophins. Here we report the identification of a Src homology 2 domain-containing molecule, SLAM-associated protein (SAP), as an interacting protein of TrkB in a yeast two-hybrid screen. SAP was initially identified as an adaptor molecule in SLAM family receptor signaling for regulating interferon-gamma secretion. In the current study, we found that SAP interacted with TrkA, TrkB, and TrkC receptors in vitro and in vivo. Binding of SAP required Trk receptor activation and phosphorylation at the tyrosine 674 residue, which is located in the activation loop of the kinase domain. Overexpression of SAP with Trk attenuated tyrosine phosphorylation of the receptors and reduced the binding of SH2B and Shc to TrkB. Moreover, overexpression of SAP in PC12 cells suppressed the nerve growth factor-dependent activation of extracellular signal-regulated kinases 1/2 and phospholipase Cgamma, in addition to inhibiting neurite outgrowth. In summary, our findings demonstrated that SAP may serve as a negative regulator of Trk receptor activation and downstream signaling.
authors.affiliation: Department of Biochemistry, Biotechnology Research Institute and Molecular Neuroscience Center, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
authors.forename: Kin Yip
authors.initials: KY
authors.lastname: Lo
authors.forename: Wing Hong
authors.initials: WH
authors.lastname: Chin
authors.forename: Yu Pong
authors.initials: YP
authors.lastname: Ng
authors.forename: Albert W
authors.initials: AW
authors.lastname: Cheng
authors.forename: Zelda H
authors.initials: ZH
authors.lastname: Cheung
authors.forename: Nancy Y
authors.initials: NY
authors.lastname: Ip
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015139:Blotting, Southern; D015153:Blotting, Western; D001921:Brain / Q000378:metabolism; D002460:Cell Line; D018076:DNA, Complementary / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D007371:Interferon-gamma / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D008856:Microscopy, Fluorescence; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D009414:Nerve Growth Factors / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D016716:PC12 Cells; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051381:Rats; D020917:Receptor, trkA / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D015398:Signal Transduction; D000071179:Signaling Lymphocytic Activation Molecule Associated Protein; D020798:Two-Hybrid System Techniques; D014443:Tyrosine / Q000737:chemistry; D018909:src Homology Domains
chemical_list: D018076:DNA, Complementary; D005656:Fungal Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009414:Nerve Growth Factors; D011993:Recombinant Fusion Proteins; C114953:SH2D1A protein, human; D000071179:Signaling Lymphocytic Activation Molecule Associated Protein; D014443:Tyrosine; D007371:Interferon-gamma; D020917:Receptor, trkA