Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.1 (protein kinase)
 81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Teleost rod photoreceptors elongate in the light and shorten in darkness. We are investigating the role of cAMP-dependent protein kinase (PKA), phosphatases and target phosphoproteins in the regulation of photoreceptor cell shape. Preparations of rod fragments, consisting of the motile inner segment with attached photosensory outer segment (RIS-ROS), undergo light-stimulated elongation in culture. The PKA-selective inhibitor, H89, enhanced RIS-ROS elongation in both light and darkness, suggesting that elongation is associated with dephosphorylation of PKA substrates. Okadaic acid and calyculin A, inhibitors of type 1 and 2A phosphatases, blocked light-dependent and light-independent elongation with relative potencies suggesting that elongation requires dephosphorylation by type 1 phosphatase in light and type 2A phosphatase in darkness. To identify targets of PKA and phosphatases, RIS-ROS were isolated from retinas prelabeled with 32P-orthophosphate, and then incubated in the presence of kinase inhibitors or phosphatase inhibitors. Two phosphoproteins, PP33 and PP35, were phosphorylated by PKA and dephosphorylated by type 1 or 2A phosphatases in light- and dark-cultured RIS-ROS. PP35 (but not PP33) was immunoprecipitated by an antibody to phosducin, a PKA-regulated modulator of phototransduction (Lee et al., 1992); PP35 was also phosphorylated in vitro by a Ca2+ calmodulin-activated kinase. PP33 further differed from PP35 in its phosphopeptide maps and phosphorylation by PKC. We conclude that RIS-ROS elongation is correlated with the dephosphorylation of PKA substrates by type 1 or 2A phosphatases. Candidate mediator proteins include PP35, a fish phosducin homolog, and PP33, a newly described photoreceptor phosphoprotein.
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PMID:Phosducin and PP33 are in vivo targets of PKA and type 1 or 2A phosphatases, regulators of cell elongation in teleost rod inner-outer segments. 747 10

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.
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PMID:Identification of cyclic nucleotide-regulated phosphoproteins, including phosducin, in motile rod inner-outer segments of teleosts. 815 21