Luteinizing hormone stimulates mammalian target of rapamycin signaling in bovine luteal cells via pathways independent of AKT and mitogen-activated protein kinase: modulation of glycogen synthase kinase 3 and AMP-activated protein kinase.
LH stimulates the production of cAMP in luteal cells, which leads to the production of progesterone, a hormone critical for the maintenance of pregnancy. The mammalian target of rapamycin (MTOR) signaling cascade has recently been examined in ovarian follicles where it regulates granulosa cell proliferation and differentiation. This study examined the actions of LH on the regulation and possible role of the MTOR signaling pathway in primary cultures of bovine corpus luteum cells. Herein, we demonstrate that activation of the LH receptor stimulates the phosphorylation of the MTOR substrates ribosomal protein S6 kinase 1 (S6K1) and eukaryotic translation initiation factor 4E binding protein 1. The actions of LH were mimicked by forskolin and 8-bromo-cAMP. LH did not increase AKT or MAPK1/3 phosphorylation. Studies with pathway-specific inhibitors demonstrated that the MAPK kinase 1 (MAP2K1)/MAPK or phosphatidylinositol 3-kinase/AKT signaling pathways were not required for LH-stimulated MTOR/S6K1 activity. However, LH decreased the activity of glycogen synthase kinase 3Beta (GSK3B) and AMP-activated protein kinase (AMPK). The actions of LH on MTOR/S6K1 were mimicked by agents that modulated GSK3B and AMPK activity. The ability of LH to stimulate progesterone secretion was not prevented by rapamycin, a MTOR inhibitor. In contrast, activation of AMPK inhibited LH-stimulated MTOR/S6K1 signaling and progesterone secretion. In summary, the LH receptor stimulates a unique series of intracellular signals to activate MTOR/S6K1 signaling. Furthermore, LH-directed changes in AMPK and GSK3B phosphorylation appear to exert a greater impact on progesterone synthesis in the corpus luteum than rapamycin-sensitive MTOR-mediated events.
Hou
Xiaoying
X
Professor and Director of Research and Development, 983255 Nebraska Medical Center, Omaha, Nebraska 68198-3255, USA.
Arvisais
Edward W
EW
Davis
John S
JS
D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D002417:Cattle; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D008184:Luteal Cells / Q000187:drug effects / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000494:pharmacology*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011247:Pregnancy; D011374:Progesterone / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D011863:Radioimmunoassay; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D000077191:Wortmannin
D000730:Androstadienes; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D011374:Progesterone; D007986:Luteinizing Hormone; D000242:Cyclic AMP; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases; D038362:Glycogen Synthase Kinase 3; D055372:AMP-Activated Protein Kinases; D020123:Sirolimus; D000077191:Wortmannin