title: Localization and regulation of bovine eye calmodulin-dependent cyclic nucleotide phosphodiesterase by cyclic AMP-dependent protein kinase.
abstract: Calmodulin-dependent cyclic nucleotide phosphodiesterase is one of the key enzymes involved in the complex interactions, which occur between the cyclic nucleotide and Ca2+ second-messenger systems. In eye, cAMP regulation is important in a variety of physiological processes such as aqueous humor regulation, photoreceptor signal transduction and retinal blood flow. Bovine eye calmodulin-dependent cyclic nucleotide phosphodiesterase was purified to apparent homogeneity and the isolated enzyme had a significantly higher affinity for calmodulin and Ca2+. Immunohistology revealed calmodulin-dependent cyclic nucleotide phospho-diesterase expression in corneal epithelium, retina and optic nerve of the eye. The cAMP-dependent protein kinase was found to catalyze the phosphorylation of bovine eye calmodulin-dependent cyclic nucleotide phosphodiesterase and the following observations were made. Firstly, the phosphorylation resulted in the incorporation of 1 mol of phosphate per mol of subunit, resulting in higher calmodulin and Ca2+ concentration requirement for calmodulin-dependent cyclic nucleotide phosphodiesterase activation. Secondly, Ca2+ and calmodulin prevented the phosphorylation. Thirdly, the phosphorylation of calmodulin-dependent cyclic nucleotide phosphodiesterase could be reversed by the calmodulin-dependent phosphatase, calcineurin. Analysis of the complex regulatory properties of the calmodulin-dependent cyclic nucleotide phosphodiesterase in the eye has led to the suggestion that fluxes of cAMP and Ca2+ during cell activation are closely coupled and that calmodulin-dependent cyclic nucleotide phosphodiesterase plays a key role in this signal coupling phenomenon.
authors.affiliation: Department of Pathology, College of Medicine, University of Saskatchewan and Cancer Research Unit, Saskatchewan Cancer Agency, Saskatoon, Saskatchewan S7N 4H4, Canada. rsharma@scf.sk.ca
authors.forename: Rajendra K
authors.initials: RK
authors.lastname: Sharma
authors.forename: Dallas P
authors.initials: DP
authors.lastname: Seitz
authors.forename: Baljit
authors.initials: B
authors.lastname: Singh
authors.forename: Yingchun
authors.initials: Y
authors.lastname: Tan
mesh_terms: D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism*; D002417:Cattle; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D054677:Cyclic Nucleotide Phosphodiesterases, Type 1; D005123:Eye / Q000201:enzymology*; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D009928:Organ Specificity; D010766:Phosphorylation
chemical_list: D002147:Calmodulin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D054677:Cyclic Nucleotide Phosphodiesterases, Type 1; D002118:Calcium