Reduced G-protein-coupled-receptor kinase 2 activity results in impairment of osteoblast function.
Rapid phosphorylation of many G-protein-coupled receptors (GPCRs) by G-protein-coupled receptor kinases (GRKs) accompanies stimulus-driven desensitization. Recent evidence suggests that GRKs and their associated arresting proteins, beta-arrestins, function as essential elements in the GPCR-mediated mitogen-activated protein (MAP) kinase signaling cascade. We investigated the interaction between GRKs and MAP kinase activation by growth factors in UMR 106-H5 osteoblastic cells stably expressing a dominant negative mutant of GRK2 (K220R). Expression of K220R in osteoblastic cells results in reduced cellular proliferation, both basally and in response to insulin-like growth factor-1 (IGF-1), and blunting of IGF-1- and EGF-induced MAP kinase activation. Reduced MAP kinase activation is not associated with alterations in IGF-1-receptor autophosphorylation. Both a constitutively active Ras mutant and PMA fully activate MAP kinase in K220R cells. We found that disruption of the GRK2 gene results in: (1) reduced osteoblast proliferation in response to growth factors, and (2) impaired receptor tyrosine kinase activation of mitogenic signaling pathways. Thus, GRK2 may regulate growth factor responsiveness in osteoblasts by modulating multiprotein complex formation following receptor tyrosine kinase activation.
Bliziotes
M
M
Portland VA Medical Center, Portland, OR 97201, USA. bliziote@ohsu.edu
Gunness
M
M
Zhang
X
X
Nissenson
R
R
Wiren
K
K
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009154:Mutation; D010006:Osteoblasts / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D051552:beta-Adrenergic Receptor Kinases
D011956:Receptors, Cell Surface; D004815:Epidermal Growth Factor; D007334:Insulin-Like Growth Factor I; D017868:Cyclic AMP-Dependent Protein Kinases; D051552:beta-Adrenergic Receptor Kinases; D020928:Mitogen-Activated Protein Kinases; D019204:GTP-Binding Proteins; D013755:Tetradecanoylphorbol Acetate