Friday, April 8, 2011

Expression and Roles of Pannexins in ATP Release in the Pituitary Gland

Shuo Li, Ivana Bjelobaba, Zonghe Yan, Marek Kucka, Melanija Tomic and Stanko S. Stojilkovic

Section on Cellular Signaling (S.L., Z.Y., M.K., M.T., S.S.S.), Program in Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-4510; and Department of Neurobiology (I.B.), Institute for Biological Research "Sinisa Stankovic," University of Belgrade, 11000 Belgrade, Republic of Serbia

Address correspondence and reprint requests to: Dr. Stanko Stojilkovic, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Building 49, Room 6A-36, 49 Convent Drive, Bethesda, Maryland 20892-4510. E-mail: stankos@helix.nih.gov or stojilks@mail.nih.gov .

Pannexins are a newly discovered three-member family of proteins expressed in the brain and peripheral tissues that belong to the superfamily of gap junction proteins. However, in mammals pannexins do not form gap junctions, and their expression and function in the pituitary gland have not been studied. Here we show that the rat pituitary gland expresses mRNA and protein transcripts of pannexins 1 and 2 but not pannexin 3. Pannexin 1 was more abundantly expressed in the anterior lobe, whereas pannexin 2 was more abundantly expressed in the intermediate and posterior pituitary. Pannexin 1 was identified in corticotrophs and a fraction of somatotrophs, the S100-positive pituicytes of the posterior pituitary and AtT-20 (mouse pituitary adrenocorticotropin-secreting cells) and rat immortalized pituitary cells secreting prolactin, whereas pannexin 2 was detected in the S100-positive folliculostellate cells of the anterior pituitary, melanotrophs of the intermediate lobe, and vasopressin-containing axons and nerve endings in the posterior lobe. Overexpression of pannexins 1 and 2 in AtT-20 pituitary cells enhanced the release of ATP in the extracellular medium, which was blocked by the gap junction inhibitor carbenoxolone. Basal ATP release in At-T20 cells was also suppressed by down-regulating the expression of endogenous pannexin 1 but not pannexin 2 with their short interfering RNAs. These results indicate that pannexins may provide a pathway for delivery of ATP, which is a native agonist for numerous P2X cationic channels and G protein-coupled P2Y receptors endogenously expressed in the pituitary gland.

From http://endo.endojournals.org/cgi/content/abstract/en.2010-1216v1