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This Article Full Text Full Text (PDF) All Versions of this Article: JME-09-0025v1 43/1/19    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Selva, D. M Articles by Hammond, G. L Search for Related Content PubMed PubMed Citation Articles by Selva, D. M Articles by Hammond, G. L

¹ Child and Family Research Institute, 950 West 28th Avenue, Vancouver, British Columbia, Canada V5Z 4H4
² Department of Obstetrics and Gynaecology, The University of British Columbia, 4500 Oak Street, Vancouver, British Columbia, Canada V6H 3N1

(Correspondence should be addressed to G L Hammond; Email: ghammond{at}cw.bc.ca)

Thyroid hormones increase hepatic sex hormone-binding globulin (SHBG) production, which is also regulated by hepatocyte nuclear factor-4 (HNF-4) in response to changes in the metabolic state of the liver. Since the human SHBG promoter lacks a typical thyroid hormone response element, and because thyroid hormones influence metabolic state, we set out to determine whether thyroid hormones mediate SHBG expression indirectly via changes in HNF-4 levels in HepG2 human hepatoblastoma cells, and in the livers of transgenic mice that express a 4.3 kb human SHBG transgene under the control of its own 0.8 kb promoter sequence. Thyroid hormones (triiodothyronine (T₃) and thyroxine (T₄)) increase SHBG accumulation in HepG2 cell culture medium over 5 days, and increase cellular SHBG mRNA levels. In addition, T₄ treatment of HepG2 cells for 5 days increased HNF-4 mRNA and HNF-4 levels in concert with decreased cellular palmitate levels. Plasma SHBG levels were also increased in mice expressing a human SHBG transgene after 5 days treatment with T₃ along with increased hepatic HNF-4 levels. In HepG2 cells, the human SHBG promoter failed to respond acutely (within 24 h) to T₄ treatment, but a 4-day pre-treatment with T₄ resulted in a robust response that was prevented by co-treatment with HNF-4 siRNA, or by blocking the β-oxidation of palmitate through co-treatment with the carnitine palmitoyltransferase I inhibitor, etomoxir. These data lead us to conclude that thyroid hormones increase SHBG production indirectly by increasing HNF-4 gene expression, and by reducing cellular palmitate levels that further contribute to increased HNF-4 levels in hepatocytes.