The protein tyrosine phosphatase, Shp2, is required for the complete activation of the RAS/MAPK pathway by brain-derived neurotrophic factor.
Brain-derived neurotrophic factor (BDNF) and other neurotrophins induce a unique prolonged activation of mitogen-activated protein kinase (MAPK) compared with growth factors. Characterization and kinetic and spatial modeling of the signaling pathways underlying this prolonged MAPK activation by BDNF will be important in understanding the physiological role of BDNF in many complex systems in the nervous system. In addition to Shc, fibroblast growth factor receptor substrate 2 (FRS2) is required for the BDNF-induced activation of MAPK. BDNF induces phosphorylation of FRS2. However, BDNF does not induce phosphorylation of FRS2 in cells expressing a deletion mutant of TrkB (TrkBDeltaPTB) missing the juxtamembrane NPXY motif. This motif is the binding site for SHC. NPXY is the consensus sequence for phosphotyrosine binding (PTB) domains, and notably, FRS2 and SHC contain PTB domains. This NPXY motif, which contains tyrosine 484 of TrkB, is therefore the binding site for both FRS2 and SHC. Moreover, the proline containing region (VIENP) of the NPXY motif is also required for FRS2 and SHC phosphorylation, which indicates this region is an important component of FRS2 and SHC recognition by TrkB. Previously, we had found that the phosphorylation of FRS2 induces association of FRS2 and growth factor receptor binding protein 2 (Grb2). Now, we have intriguing data that indicates BDNF induces association of the SH2 domain containing protein tyrosine phosphatase, Shp2, with FRS2. Moreover, the PTB association motif of TrkB containing tyrosine 484 is required for the BDNF-induced association of Shp2 with FRS2 and the phosphorylation of Shp2. These results imply that FRS2 and Shp2 are in a BDNF signaling pathway. Shp2 is required for complete MAPK activation by BDNF, as expression of a dominant negative Shp2 in cells attenuates BDNF-induced activation of MAPK. Moreover, expression of a dominant negative Shp2 attenuates Ras activation showing that the protein tyrosine phosphatase is required for complete activation of MAPKs by BDNF. In conclusion, Shp2 regulates BDNF signaling through the MAPK pathway by regulating either Ras directly or alternatively, by signaling components upstream of Ras. Characterization of MAPK signaling controlled by BDNF is likely to be required to understand the complex physiological role of BDNF in neuronal systems ranging from the regulation of neuronal growth and survival to the regulation of synapses.
Easton
John B
JB
Department of Molecular Pharmacology, St Jude Children's Research Hospital, North Lauderdale, Memphis, Tennessee, USA.
Royer
Amanda R
AR
Middlemas
David S
DS
D020816:Amino Acid Motifs / Q000502:physiology; D000818:Animals; D000831:Animals, Newborn; D015153:Blotting, Western / Q000379:methods; D019208:Brain-Derived Neurotrophic Factor / Q000494:pharmacology*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D004789:Enzyme Activation / Q000187:drug effects; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation / Q000379:methods; D047908:Intracellular Signaling Peptides and Proteins / Q000502:physiology*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed / Q000379:methods; D009447:Neuroblastoma; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D017027:Protein Tyrosine Phosphatases / Q000502:physiology*; D051381:Rats; D020318:Rats, Long-Evans; D020813:Receptor, trkB / Q000378:metabolism; D054593:SH2 Domain-Containing Protein Tyrosine Phosphatases; D015398:Signal Transduction / Q000187:drug effects*; D013997:Time Factors; D014162:Transfection / Q000379:methods; D014443:Tyrosine / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism*
D019208:Brain-Derived Neurotrophic Factor; D047908:Intracellular Signaling Peptides and Proteins; D049452:Green Fluorescent Proteins; D014443:Tyrosine; D020813:Receptor, trkB; D020929:Mitogen-Activated Protein Kinase Kinases; C516724:PTPN11 protein, human; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D017027:Protein Tyrosine Phosphatases; C516727:Ptpn11 protein, rat; D054593:SH2 Domain-Containing Protein Tyrosine Phosphatases; D018631:ras Proteins