title: Pituitary corticotroph SOCS-3: novel intracellular regulation of leukemia-inhibitory factor-mediated proopiomelanocortin gene expression and adrenocorticotropin secretion.
abstract: As pituitary leukemia-inhibitory factor (LIF) mediates neuroimmune signals to the hypothalamo-pituitary-adrenal axis, we tested the role of intracellular SOCS-3 in corticotroph function. SOCS-3, a cytokine-inducible protein of the suppressor of cytokine signaling (SOCS) family, is expressed in the murine pituitary in vivo. After i.p. injection of LIF (5.0 micrograms/mouse) or interleukin-1 beta (0.1 microgram/mouse) pituitary SOCS-3 mRNA was stimulated 9-fold and 6-fold, respectively. Also, in corticotroph AtT-20 cells LIF and interleukin-1 beta both potently stimulated SOCS-3 mRNA expression. In AtT-20 cells, stable overexpression of SOCS-3 inhibits basal and LIF-stimulated ACTH secretion in comparison to mock-transfected AtT-20 cells (basal: 4426 +/- 118 vs. 4973 +/- 138 pg/ml, P < 0.05; LIF-induced: 5511 +/- 172 vs. 9308 +/- 465 pg/ml, P < 0.001). Stable overexpression of SOCS-3 cDNA in AtT-20 cells also resulted in a significant 50% decrease of LIF-induced POMC mRNA levels (P < 0.05) and POMC promoter activity (P < 0.001), respectively. Western blot analysis revealed an inhibition of LIF-stimulated gp130 and STAT-3 phosphorylation in SOCS-3 overexpressing AtT-20 cells. Thus, SOCS-3 inhibits the Janus kinase (JAK) and signal transducers and activators of transcription (STAT) pathway, which is known to mediate LIF-stimulated ACTH secretion and POMC gene expression. In conclusion, SOCS-3 functions as an intracellular regulator of POMC gene expression and ACTH secretion, acting as a negative feedback mediator of the cytokine-mediated neuro-immuno-endocrine interface.
authors.affiliation: Division of Endocrinology and Metabolism, Cedars-Sinai Research Institute-UCLA School of Medicine 90048, USA.
authors.forename: C J
authors.initials: CJ
authors.lastname: Auernhammer
authors.forename: V
authors.initials: V
authors.lastname: Chesnokova
authors.forename: C
authors.initials: C
authors.lastname: Bousquet
authors.forename: S
authors.initials: S
authors.lastname: Melmed
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000378:metabolism*; D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D002460:Cell Line; D050822:Cytokine Receptor gp130; D004268:DNA-Binding Proteins / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects*; D006131:Growth Inhibitors / Q000494:pharmacology*; D007031:Hypothalamus / Q000378:metabolism; D007375:Interleukin-1 / Q000494:pharmacology; D015850:Interleukin-6; D053605:Leukemia Inhibitory Factor; D008222:Lymphokines / Q000494:pharmacology*; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D010766:Phosphorylation; D010902:Pituitary Gland / Q000378:metabolism*; D011333:Pro-Opiomelanocortin / Q000235:genetics*; D011506:Proteins / Q000235:genetics / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism; D011994:Recombinant Proteins / Q000494:pharmacology; D012097:Repressor Proteins; D050796:STAT3 Transcription Factor; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors; D014162:Transfection
chemical_list: D015703:Antigens, CD; D004268:DNA-Binding Proteins; D006131:Growth Inhibitors; C494200:Il6st protein, mouse; D007375:Interleukin-1; D015850:Interleukin-6; D053605:Leukemia Inhibitory Factor; C507838:Lif protein, mouse; D008222:Lymphokines; D008562:Membrane Glycoproteins; D011506:Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D012097:Repressor Proteins; D050796:STAT3 Transcription Factor; C491411:Socs3 protein, mouse; C494087:Stat3 protein, mouse; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D050822:Cytokine Receptor gp130; D011333:Pro-Opiomelanocortin; D000324:Adrenocorticotropic Hormone