Molecular characterisation and functional interrogation of a local natriuretic peptide system in rodent pituitaries, alphaT3-1 and LbetaT2 gonadotroph cells.
In the pituitary, C-type natriuretic peptide (CNP) has been implicated as a gonadotroph-specific factor, yet expression of the CNP gene (Nppc) and CNP activity in gonadotrophs is poorly defined. Here, we examine the molecular expression and putative function of a local gonadotroph natriuretic peptide system. Nppc, along with all three natriuretic peptide receptors (Npr1, Npr2 and Npr3), was expressed in both alphaT3-1 and LbetaT2 cells and primary mouse pituitary tissue, yet the genes for atrial-(ANP) and B-type natriuretic peptides (Nppa and Nppb) were much less abundant. Putative processing enzymes of CNP were also expressed in alphaT3-1 cells and primary mouse pituitaries. Transcriptional analyses revealed that the proximal 50 bp of the murine Nppc promoter were sufficient for GNRH responsiveness, in an apparent protein kinase C and calcium-dependent manner. Electrophoretic mobility shift assays showed Sp1/Sp3 proteins form major complexes within this region of the Nppc promoter. CNP protein was detectable in rat anterior pituitaries, and electron microscopy detected CNP immunoreactivity in secretory granules of gonadotroph cells. Pharmacological analyses of natriuretic peptide receptor activity clearly showed ANP and CNP are potent activators of cGMP production. However, functional studies failed to reveal a role for CNP in regulating cell proliferation or LH secretion. Surprisingly, CNP potently stimulated the human glycoprotein hormone alpha-subunit promoter in LbetaT2 cells but not in alphaT3-1 cells. Collectively, these findings support a role for CNP as the major natriuretic peptide of the anterior pituitary, and for gonadotroph cells as the major source of CNP expression and site of action.
Thompson
Iain R
IR
Endocrine Signalling Group, Veterinary Basic Sciences, Royal Veterinary College, University of London, Royal College Street, London NW1 0TU, UK.
Chand
Annisa N
AN
Jonas
Kim C
KC
Burrin
Jacky M
JM
Steinhelper
Mark E
ME
Wheeler-Jones
Caroline P
CP
McArdle
Craig A
CA
Fowkes
Robert C
RC
D000818:Animals; D002478:Cells, Cultured; D006152:Cyclic GMP / Q000378:metabolism; D005260:Female; D005786:Gene Expression Regulation; D015292:Glycoprotein Hormones, alpha Subunit / Q000235:genetics; D052681:Gonadotrophs / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000378:metabolism; D008297:Male; D051379:Mice; D020098:Natriuretic Peptide, C-Type / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D010902:Pituitary Gland / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D017461:Receptors, Atrial Natriuretic Factor / Q000032:analysis / Q000235:genetics
D015292:Glycoprotein Hormones, alpha Subunit; D020098:Natriuretic Peptide, C-Type; D007986:Luteinizing Hormone; D017461:Receptors, Atrial Natriuretic Factor; D006152:Cyclic GMP