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Endocrinology. 2006 Jul;147(7):3211-8. Epub 2006 Mar 30.

The thyroid hormone receptor-beta agonist GC-1 induces cell proliferation in rat liver and pancreas.

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Department of Toxicology, Oncology, and Molecular Pathology Unit, University of Cagliari, Via Porcell 4, 09124 Cagliari, Italy.


Thyroid hormones regulate cell growth, cell differentiation, and metabolic functions via interaction with the thyroid hormone nuclear receptors (TRs). Recently, a small class of halogen-free high-affinity thyroid hormone agonists has been developed that are highly selective for the TRbeta subtype. Because of the selective hyperthyroidism generated by one of these agonists, GC-1, this compound has the potential to be developed as a new therapeutic agent for the treatment of a variety of metabolic disturbances, including lipid disorders and obesity; thus, it becomes important to determine whether GC-1 has other unknown effects on potential target organs. The purpose of this study was to investigate the effect of GC-1 on cell proliferation in rat liver and pancreas. Rats treated with GC-1 (50 or 100 mug/100 g body weight) were killed at different time points. Hepatic and pancreatic cell proliferation was monitored by immunohistochemical determination of bromodeoxyuridine incorporation. The expression of cell cycle-related genes was analyzed by Northern and Western analysis. The results show that GC-1 strongly stimulates rat hepatocyte proliferation in the absence of tissue injury. Although GC-1-induced hepatocyte proliferation was associated with a rapid increase in cyclin D1 mRNA levels, no change in the expression of c-jun and c-fos was observed. GC-1 also induced massive pancreatic cell proliferation. The results indicate that the TRbeta-selective agonist GC-1 is a strong mitogen for hepatocytes and pancreatic acinar cells. Furthermore, they suggest that the TRbeta receptor is the mediator for the mitogenic activity of thyroid hormone and other thyromimetics.

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