title: 17β-Estradiol positively modulates growth hormone signaling through the reduction of SOCS2 negative feedback in human osteoblasts.
abstract: Recent evidence demonstrated an interplay between estrogens and growth hormone (GH) at cellular level. To investigate the possible mechanism/s involved, we studied the effect of 17β-estradiol (E2) on GH signaling pathways in primary culture of human osteoblasts (hOBs). Exposure of hOBs to E2 (10(-8) M) 60 min before GH (5 ng/ml) significantly increased phosphorylated STAT5 (P-STAT5) levels compared with GH alone. E2 per se had no effect on P-STAT5. E2-enhanced GH signaling was effective in increasing osteopontin, bone-sialoprotein, and IGF II mRNA expression to a greater extent than GH alone. We then studied the effect of E2 on the protein levels of the negative regulator of GH signaling, suppressor of cytokine signaling-2 (SOCS2). E2 (10(-11) M-10(-7) M) reduced dose-dependently SOCS2 protein levels without modifying its mRNA expression. The silencing of SOCS2 gene prevented E2 positive effect on GH induced P-STAT5 and on GH induced bone-sialoprotein and osteopontin mRNA expression. Treatment with the inhibitor of DNA-dependent RNA synthesis, actinomycin-D, did not prevent E2 induced decrease of SOCS2, thus suggesting a non-genomic effect. E2 promoted an increase in SOCS2 ubiquitination. To determine if increased ubiquitination of SOCS2 by E2 led to degradation by proteasome, hOBs were pretreated with the proteasome inhibitor MG132 (5 μM) which blocked E2 reduction of SOCS2. These findings demonstrate for the first time that E2 can amplify GH intracellular signaling in hOBs with an essential role played by the reduction of the SOCS2 mediated feedback loop.
authors.affiliation: Bone Metabolism Unit, San Raffaele Scientific Institute, Via Olgettina 60, 20132 Milano, Italy.
authors.forename: Simona
authors.initials: S
authors.lastname: Bolamperti
authors.forename: Emanuela
authors.initials: E
authors.lastname: Mrak
authors.forename: Gianluigi
authors.initials: G
authors.lastname: Moro
authors.forename: Paolo
authors.initials: P
authors.lastname: Sirtori
authors.forename: Gianfranco
authors.initials: G
authors.lastname: Fraschini
authors.forename: Francesca
authors.initials: F
authors.lastname: Guidobono
authors.forename: Alessandro
authors.initials: A
authors.lastname: Rubinacci
authors.forename: Isabella
authors.initials: I
authors.lastname: Villa
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D003609:Dactinomycin / Q000494:pharmacology; D004958:Estradiol / Q000494:pharmacology*; D025461:Feedback, Physiological / Q000187:drug effects*; D005786:Gene Expression Regulation / Q000187:drug effects; D019382:Human Growth Hormone / Q000378:metabolism*; D006801:Humans; D007335:Insulin-Like Growth Factor II / Q000235:genetics / Q000378:metabolism; D058574:Integrin-Binding Sialoprotein / Q000235:genetics / Q000378:metabolism; D007976:Leupeptins / Q000494:pharmacology; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D053495:Osteopontin / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D059748:Proteolysis / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D050799:STAT5 Transcription Factor / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects* / Q000235:genetics; D000071222:Suppressor of Cytokine Signaling 1 Protein; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000378:metabolism*; D014162:Transfection; D054875:Ubiquitination / Q000187:drug effects
chemical_list: D058574:Integrin-Binding Sialoprotein; D007976:Leupeptins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; C108944:SOCS1 protein, human; C106643:SOCS2 protein, human; C106644:SOCS3 protein, human; D050799:STAT5 Transcription Factor; D000071222:Suppressor of Cytokine Signaling 1 Protein; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D053495:Osteopontin; D019382:Human Growth Hormone; D003609:Dactinomycin; D004958:Estradiol; D007335:Insulin-Like Growth Factor II; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde