title: Phosphorylation of GRK7 by PKA in cone photoreceptor cells is regulated by light.
abstract: The retina-specific G protein-coupled receptor kinases, GRK1 and GRK7, have been implicated in the shutoff of the photoresponse and adaptation to changing light conditions via rod and cone opsin phosphorylation. Recently, we have defined sites of phosphorylation by cAMP-dependent protein kinase (PKA) in the amino termini of both GRK1 and GRK7 in vitro. To determine the conditions under which GRK7 is phosphorylated in vivo, we have generated an antibody that recognizes GRK7 phosphorylated on Ser36, the PKA phosphorylation site. Using this phospho-specific antibody, we have shown that GRK7 is phosphorylated in vivo and is located in the cone inner and outer segments of mammalian, amphibian and fish retinas. Using Xenopus laevis as a model, GRK7 is phosphorylated under dark-adapted conditions, but becomes dephosphorylated when the animals are exposed to light. The conservation of phosphorylation at Ser36 in GRK7 in these different species (which span a 400 million-year evolutionary period), and its light-dependent regulation, indicates that phosphorylation plays an important role in the function of GRK7. Our work demonstrates for the first time that cAMP can regulate proteins involved in the photoresponse in cones and introduces a novel mode of regulation for the retinal GRKs by PKA.
authors.affiliation: Department of Cell and Developmental Biology, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7090, USA.
authors.forename: Shoji
authors.initials: S
authors.lastname: Osawa
authors.forename: Rebecca
authors.initials: R
authors.lastname: Jo
authors.forename: Ellen R
authors.initials: ER
authors.lastname: Weiss
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D003563:Cyclic CMP / Q000031:analogs & derivatives / Q000494:pharmacology; D054768:G-Protein-Coupled Receptor Kinases / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D008027:Light; D008969:Molecular Sequence Data; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects / Q000528:radiation effects; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D013552:Swine; D013997:Time Factors; D014162:Transfection / Q000379:methods; D014982:Xenopus laevis; D015027:Zebrafish
chemical_list: D010726:Phosphodiesterase Inhibitors; D005576:Colforsin; D003563:Cyclic CMP; D012694:Serine; C053441:dibutyryl cyclic-3',5'-cytidine monophosphate; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D054768:G-Protein-Coupled Receptor Kinases; D015056:1-Methyl-3-isobutylxanthine