title: Direct modulation of the protein kinase A catalytic subunit α by growth factor receptor tyrosine kinases.
abstract: The cyclic-AMP-dependent protein kinase A (PKA) regulates processes such as cell proliferation and migration following activation of growth factor receptor tyrosine kinases (RTKs), yet the signaling mechanisms that link PKA with growth factor receptors remain largely undefined. Here we report that RTKs can directly modulate the function of the catalytic subunit of PKA (PKA-C) through post-translational modification. In vitro kinase assays revealed that both the epidermal growth factor and platelet derived growth factor receptors (EGFR and PDGFR, respectively) tyrosine phosphorylate PKA-C. Mass spectrometry identified tyrosine 330 (Y330) as a receptor-mediated phosphorylation site and mutation of Y330 to phenylalanine (Y330F) all but abolished the RTK-mediated phosphorylation of PKA-C in vitro. Y330 resides within a conserved region at the C-terminal tail of PKA-C that allosterically regulates enzymatic activity. Therefore, the effect of phosphorylation at Y330 on the activity of PKA-C was investigated. The K(m) for a peptide substrate was markedly decreased when PKA-C subunits were tyrosine phosphorylated by the receptors as compared to un-phosphorylated controls. Importantly, tyrosine-phosphorylated PKA-C subunits were detected in cells stimulated with EGF, PDGF, and Fibroblast growth factor 2 (FGF2) and in fibroblasts undergoing PDGF-mediated chemotaxis. These results demonstrate a direct, functional interaction between RTKs and PKA-C and identify tyrosine phosphorylation as a novel mechanism for regulating PKA activity.
authors.affiliation: Department of Medical Laboratory and Radiation Sciences, The University of Vermont, Burlington, Vermont 05405, USA.
authors.forename: George B
authors.initials: GB
authors.lastname: Caldwell
authors.forename: Alan K
authors.initials: AK
authors.lastname: Howe
authors.forename: Christian K
authors.initials: CK
authors.lastname: Nickl
authors.forename: Wolfgang R
authors.initials: WR
authors.lastname: Dostmann
authors.forename: Bryan A
authors.initials: BA
authors.lastname: Ballif
authors.forename: Paula B
authors.initials: PB
authors.lastname: Deming
mesh_terms: D000818:Animals; D019556:COS Cells; D002460:Cell Line; D049109:Cell Proliferation; D002522:Chlorocebus aethiops; D054751:Cyclic AMP-Dependent Protein Kinase Catalytic Subunits / Q000235:genetics / Q000378:metabolism*; D066246:ErbB Receptors / Q000378:metabolism; D051379:Mice; D041681:NIH 3T3 Cells; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D017978:Receptors, Growth Factor / Q000378:metabolism; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism; D015398:Signal Transduction; D014443:Tyrosine / Q000378:metabolism
chemical_list: D017978:Receptors, Growth Factor; D014443:Tyrosine; D066246:ErbB Receptors; D020794:Receptor Protein-Tyrosine Kinases; D017479:Receptors, Platelet-Derived Growth Factor; D054751:Cyclic AMP-Dependent Protein Kinase Catalytic Subunits; D011493:Protein Kinase C