title: AMP-activated protein kinase is a key intermediary in GnRH-stimulated LHβ gene transcription.
abstract: GnRH regulation of pituitary gonadotropin gene transcription is critical for fertility, and metabolic dysregulation is associated with reproductive disorders and altered hypothalamic-pituitary responses. Here, we examined signaling pathways in gonadotropes through which GnRH modulates gonadotropin levels, and potential common signaling pathways with insulin. Using LβT2 cells, we show that GnRH rapidly (5 minutes) triggers activating phosphorylation of AMP-activated protein kinase (AMPK) up to 5-fold; this stimulation is enhanced by insulin through increased total AMPKα levels and activity. GnRH also stimulated c-Jun N-terminal kinase (JNK) and ERK activation, whereas insulin alone stimulated Akt. Inhibition of AMPK activity by compound C, or diminishing AMPK levels by small interfering RNA against AMPKα, prevented GnRH-stimulated transcription of the endogenous LHβ gene and transfected LHβ promoter. Egr-1 (early growth response-1), a transcription factor required for LHβ expression, is synthesized in response to GnRH, and compound C prevents this induction. However, overexpression of Egr-1 in the presence of compound C did not restore GnRH stimulation of LHβ, suggesting that AMPK stimulation of transcription also occurs through additional mechanisms or signaling pathways. One such pathway may be JNK activation, because GnRH stimulation of JNK activity and LHβ transcription occurs more slowly than stimulation of AMPK activity, and AMPK inhibition by compound C or small interfering RNA also prevented GnRH-stimulated JNK phosphorylation. Finally, in primary mouse pituitary cells, GnRH also stimulates AMPK, and AMPK inhibition suppresses GnRH-stimulated LHβ transcription. These studies indicate a novel role for AMPK in GnRH-stimulated transcription in pituitary gonadotropes and a potential common mechanism for GnRH and metabolic modulation of fertility.
authors.affiliation: Division of Endocrinology and Metabolism, Department of Internal Medicine, University of Virginia, Charlottesville, VA 22903, USA.
authors.forename: Josefa
authors.initials: J
authors.lastname: Andrade
authors.forename: Jessica
authors.initials: J
authors.lastname: Quinn
authors.forename: Richad Z
authors.initials: RZ
authors.lastname: Becker
authors.forename: Margaret A
authors.initials: MA
authors.lastname: Shupnik
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000818:Animals; D051766:Early Growth Response Protein 1 / Q000378:metabolism; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D007986:Luteinizing Hormone / Q000378:metabolism; D037101:Luteinizing Hormone, beta Subunit / Q000235:genetics* / Q000378:metabolism; D008297:Male; D051379:Mice; D010766:Phosphorylation / Q000187:drug effects; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D011401:Promoter Regions, Genetic / Q000235:genetics; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects*
chemical_list: D051766:Early Growth Response Protein 1; D007328:Insulin; D037101:Luteinizing Hormone, beta Subunit; D034741:RNA, Small Interfering; D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone; D048031:JNK Mitogen-Activated Protein Kinases; D055372:AMP-Activated Protein Kinases