title: The protein phosphatase 2A regulatory subunits B'beta and B'delta mediate sustained TrkA neurotrophin receptor autophosphorylation and neuronal differentiation.
abstract: Nerve growth factor (NGF) is critical for the differentiation and maintenance of neurons in the peripheral and central nervous system. Sustained autophosphorylation of the TrkA receptor tyrosine kinase and long-lasting activation of downstream kinase cascades are hallmarks of NGF signaling, yet our knowledge of the molecular mechanisms underlying prolonged TrkA activity is incomplete. Protein phosphatase 2A (PP2A) is a heterotrimeric Ser/Thr phosphatase composed of a scaffolding, catalytic, and regulatory subunit (B, B', and B" gene families). Here, we employ a combination of pharmacological inhibitors, regulatory subunit overexpression, PP2A scaffold subunit exchange, and RNA interference to show that PP2A containing B' family regulatory subunits participates in sustained NGF signaling in PC12 cells. Specifically, two neuron-enriched regulatory subunits, B'beta and B'delta, recruit PP2A into a complex with TrkA to dephosphorylate the NGF receptor on Ser/Thr residues and to potentiate its intrinsic Tyr kinase activity. Acting at the receptor level, PP2A/ B'beta and B'delta enhance NGF (but not epidermal growth factor or fibroblast growth factor) signaling through the Akt and Ras-mitogen-activated protein kinase cascades and promote neuritogenesis and differentiation of PC12 cells. Thus, select PP2A heterotrimers oppose desensitization of the TrkA receptor tyrosine kinase, perhaps through dephosphorylation of inhibitory Ser/Thr phosphorylation sites on the receptor itself, to maintain neurotrophin-mediated developmental and survival signaling.
authors.affiliation: Department of Pharmacology, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Van Kanegan
authors.forename: Stefan
authors.initials: S
authors.lastname: Strack
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D020932:Nerve Growth Factor / Q000494:pharmacology; D016501:Neurites / Q000187:drug effects / Q000201:enzymology; D009474:Neurons / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology*; D016716:PC12 Cells; D010766:Phosphorylation / Q000187:drug effects; D010768:Phosphoserine / Q000378:metabolism; D010769:Phosphothreonine / Q000378:metabolism; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D021122:Protein Subunits / Q000378:metabolism*; D051381:Rats; D020917:Receptor, trkA / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D021122:Protein Subunits; D010769:Phosphothreonine; D010768:Phosphoserine; D020932:Nerve Growth Factor; D020917:Receptor, trkA; D020928:Mitogen-Activated Protein Kinases; D054648:Protein Phosphatase 2