title: Homologous and heterologous desensitization of guanylyl cyclase-B signaling in GH3 somatolactotropes.
abstract: The guanylyl cyclases, GC-A and GC-B, are selective receptors for atrial and C-type natriuretic peptides (ANP and CNP, respectively). In the anterior pituitary, CNP and GC-B are major regulators of cGMP production in gonadotropes and yet mouse models of disrupted CNP and GC-B indicate a potential role in growth hormone secretion. In the current study, we investigate the molecular and pharmacological properties of the CNP/GC-B system in somatotrope lineage cells. Primary rat pituitary and GH3 somatolactotropes expressed functional GC-A and GC-B receptors that had similar EC50 properties in terms of cGMP production. Interestingly, GC-B signaling underwent rapid homologous desensitization in a protein phosphatase 2A (PP2A)-dependent manner. Chronic exposure to either CNP or ANP caused a significant down-regulation of both GC-A- and GC-B-dependent cGMP accumulation in a ligand-specific manner. However, this down-regulation was not accompanied by alterations in the sub-cellular localization of these receptors. Heterologous desensitization of GC-B signaling occurred in GH3 cells following exposure to either sphingosine-1-phosphate or thyrotrophin-releasing hormone (TRH). This heterologous desensitization was protein kinase C (PKC)-dependent, as pre-treatment with GF109203X prevented the effect of TRH on CNP/GC-B signaling. Collectively, these data indicate common and distinct properties of particulate guanylyl cyclase receptors in somatotropes and reveal that independent mechanisms of homologous and heterologous desensitization occur involving either PP2A or PKC. Guanylyl cyclase receptors thus represent potential novel therapeutic targets for treating growth-hormone-associated disorders.
authors.affiliation: Endocrine Signaling Group, Comparative Biomedical Sciences, Royal Veterinary College, University of London, Royal College Street, London, NW1 0TU, UK.
authors.forename: Iain R
authors.initials: IR
authors.lastname: Thompson
authors.forename: Samantha M
authors.initials: SM
authors.lastname: Mirczuk
authors.forename: Lorna
authors.initials: L
authors.lastname: Smith
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Lessey
authors.forename: Bigboy
authors.initials: B
authors.lastname: Simbi
authors.forename: Andrew
authors.initials: A
authors.lastname: Sunters
authors.forename: Gary F
authors.initials: GF
authors.lastname: Baxter
authors.forename: Victoria J
authors.initials: VJ
authors.lastname: Lipscomb
authors.forename: Imelda M
authors.initials: IM
authors.lastname: McGonnell
authors.forename: Caroline P
authors.initials: CP
authors.lastname: Wheeler-Jones
authors.forename: Abir
authors.initials: A
authors.lastname: Mukherjee
authors.forename: Mark S
authors.initials: MS
authors.lastname: Roberson
authors.forename: Craig A
authors.initials: CA
authors.lastname: McArdle
authors.forename: Robert C
authors.initials: RC
authors.lastname: Fowkes
mesh_terms: D000818:Animals; D009320:Atrial Natriuretic Factor / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D004705:Endocytosis / Q000187:drug effects; D052682:Lactotrophs / Q000187:drug effects / Q000201:enzymology*; D008024:Ligands; D051379:Mice; D020098:Natriuretic Peptide, C-Type / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017461:Receptors, Atrial Natriuretic Factor / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013107:Sphingolipids / Q000378:metabolism; D013973:Thyrotropin-Releasing Hormone / Q000378:metabolism; D000099242:Atrial Natriuretic Factor Receptor B
chemical_list: D009320:Atrial Natriuretic Factor; D000242:Cyclic AMP; D008024:Ligands; D020098:Natriuretic Peptide, C-Type; D011493:Protein Kinase C; D012333:RNA, Messenger; D017461:Receptors, Atrial Natriuretic Factor; D013107:Sphingolipids; D013973:Thyrotropin-Releasing Hormone; D000099242:Atrial Natriuretic Factor Receptor B