A novel role for a Drosophila homologue of cGMP-specific phosphodiesterase in the active transport of cGMP.
cGMP was first discovered in urine, demonstrating that kidney cells extrude this cyclic nucleotide. Drosophila Malpighian tubules provide a model renal system in which a homologue of mammalian PDE (phosphodiesterase) 6 is expressed. In humans, this cG-PDE (cGMP-specific PDE) is specifically expressed in the retinal system, where it controls visual signal transduction. In order to gain insight into the functional role of DmPDE6 (Drosophila PDE6-like enzyme) in epithelial function, we generated transgenic animals with targeted expression of DmPDE6 to tubule Type I (principal) cells. This revealed localization of DmPDE6 primarily at the apical membranes. As expected, overexpression of DmPDE6 resulted in elevated cG-PDE activity and decreased tubule cGMP content. However, such targeted overexpression of DmPDE6 creates a novel phenotype that manifests itself in inhibition of the active transport and efflux of cGMP by tubules. This effect is specific to DmPDE6 action, as no effect on cGMP transport is observed in tubules from a bovine PDE5 transgenic line which display reduced rates of fluid secretion, an effect not seen in DmPDE6 transgenic animals. Specific ablation of DmPDE6 in tubule principal cells, via expression of a targeted DmPDE6 RNAi (RNA interference) transgene, conferred increased active transport of cGMP, confirming a direct role for DmPDE6 in regulating cGMP transport in tubule principal cells. Pharmacological inhibition of DmPDE6 in wild-type tubules using the cG-PDE inhibitor, zaprinast, similarly results in stimulated cGMP transport. We provide the first demonstration of a novel role for a cG-PDE in modulating cGMP transport and efflux.
Day
Jonathan P
JP
Institute of Biomedical and Life Sciences, Division of Molecular Genetics, University of Glasgow, Glasgow G11 6NU, UK. s.a.davies@bio.gla.ac.uk
Houslay
Miles D
MD
Davies
Shireen-A
SA
D000818:Animals; D001693:Biological Transport, Active; D016764:Cell Polarity; D006152:Cyclic GMP / Q000378:metabolism*; D054707:Cyclic Nucleotide Phosphodiesterases, Type 6; D004331:Drosophila melanogaster / Q000166:cytology / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D008317:Malpighian Tubules / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010727:Phosphoric Diester Hydrolases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D011688:Purinones / Q000494:pharmacology
D010726:Phosphodiesterase Inhibitors; D011688:Purinones; D010727:Phosphoric Diester Hydrolases; D054707:Cyclic Nucleotide Phosphodiesterases, Type 6; C011145:zaprinast; D006152:Cyclic GMP