title: Identification of cyclic nucleotide-regulated phosphoproteins, including phosducin, in motile rod inner-outer segments of teleosts.
abstract: In teleost retinas, rods elongate in the light and shorten in the dark. Rod motility is mediated by the actin cytoskeleton of the inner segment and is regulated by cyclic AMP- or cyclic GMP-stimulated phosphorylation of target proteins. In this study, we have identified the target proteins of cyclic nucleotide-dependent kinases in rods, using preparations of isolated, motile rod inner-outer segments (RIS-ROS). Five proteins found in Percoll-purified RIS-ROS were phosphorylated in the presence of cAMP (> 10 nM), cGMP (> or = 10 microM) and exogenous catalytic subunit of cAMP-dependent protein kinase (PKA). The PKA inhibitor, PKI, blocked stimulation of phosphorylation by both cAMP and cGMP. Three cAMP-stimulated phosphoproteins were detected in cytoskeletal fractions of light- and dark-adapted RIS-ROS. One of these, PP33, appears to be a fish homologue of mammalian phosducin, based on immunolabeling by two different antibodies against mammalian phosducin and on electrophoretic characteristics in 2-D gels. Two additional phosducin immunoreactive bands were detected in Western blots. One, at 35 kDa, comigrated with a second cAMP-stimulated RIS-ROS phosphoprotein, PP35, which was also detected in the cytoskeleton. The other, at 37 kDa, was present in whole teleost retinas but not in purified RIS-ROS. Our results suggest that the effects of both cAMP and cGMP on teleost rod motility are mediated through PKA modulation of target phosphoproteins. These phosphoproteins include a cytoskeleton-associated phosducin homologue.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley 94720.
authors.forename: K
authors.initials: K
authors.lastname: Pagh-Roehl
authors.forename: E
authors.initials: E
authors.lastname: Han
authors.forename: B
authors.initials: B
authors.lastname: Burnside
mesh_terms: D000818:Animals; D046508:Culture Techniques; D000242:Cyclic AMP / Q000502:physiology*; D006152:Cyclic GMP / Q000502:physiology*; D004591:Electrophoresis, Polyacrylamide Gel; D005136:Eye Proteins / Q000378:metabolism; D020555:GTP-Binding Protein Regulators; D015151:Immunoblotting; D010473:Perciformes / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000378:metabolism
chemical_list: D005136:Eye Proteins; D020555:GTP-Binding Protein Regulators; D010750:Phosphoproteins; C065631:phosducin; D000242:Cyclic AMP; D006152:Cyclic GMP