Antonio C. Bianco

Department of Medicine
Brigham and Women's Hospital
Harvard Institutes of Medicine, Room 643
77 Avenue Louis Pasteur
Boston, MA 02115
Tel: (617) 525-5153
Fax: (617) 731-4718
Email: abianco@deiodinase.org
Web Page: The Bianco Lab Page
3 postdoctoral fellows, 2 graduate students, 2 research assistants

Thyroid hormone modulates gene expression in virtually every vertebrate cell through ligand-dependent transcription factors, the T3 receptors. Thyroid hormone is secreted as a pro-hormone (T4) that can be activated to T3 in a stage- and tissue-specific manner by two iodothyronine deiodinases, D1 and D2, while a third deiodinase, D3, prevents T4 activation and terminates T3 action. These three deiodinases are dimeric integral membrane proteins composed of a single N-terminal trans-membrane segment connected to a larger globular domain that contains the active center embedded in a thioredoxin fold. A striking feature of this pocket is the presence of the rare amino acid Selenocysteine (Sec) that is critical for catalysis.

One of the aims of our lab is to study D2, the key thyroid hormone activating enzyme. D2 is localized in the endoplasmic reticulum (ER) and thus increases the supply of T3 to the cell nucleus, affecting the expression of T3-responsive genes. Our studies have shown that D2 regulation is achieved primarily by ubiquitination, i.e. the covalent attachment of mono- or polyubiquitin chains to proteins, known in eukaryotic cells as a critical method by which the function and fate of proteins may be altered. Ubiquitination inactivates D2 and targets the protein for degradation in the proteasomes. However, we have also found that inactive ubiquitinated D2 can be reactivated by the VDU1/2 deubiquitinating enzymes and rescued from terminal proteasomal degradation. D2 ubiquitination is mediated by WSB-1, a SOCS-box-containing WD-40 protein that is induced by hedgehog signaling in embryonic structures during development. WSB-1 is the substrate recognition subunit of a much larger ubiquitinating catalytic core complex, modeled as Elongin BC-Cul5-Rbx1 (ECSWSB-1). In collaboration with the Tabin lab we showed that in the developing tibial growth plate, hedgehog-stimulated D2 ubiquitination via ECSWSB-1 regulates chondrocyte differentiation and thus mediates a mechanism by which thyroid hormone can effect local control of skeletogenesis.

Another aim of our lab is to study these processes that regulate D2 activity in a physiological and pathophysiological context focusing primarily on energy expenditure and insulin action. One of the goals is to develop novel pharmacological tools to treat insulin resistance and obesity. The rationale is that mammals can rapidly increase the utilization of energy substrates and metabolic rate in response to different signals, including thyroid hormone. D2 is expressed in tissues that promote these changes such as skeletal muscle in humans and brown adipose tissue in rodents. We have shown that targeted disruption of the Dio2 gene in mice is associated with impaired adaptive thermogenesis and, in humans, a decrease in D2 activity resulting from a Dio2 gene polymorphism is associated with insulin resistance. In contrast, pharmacological D2 activation increases energy expenditure in human skeletal muscle cells and, in mice, promotes resistance to diet-induced obesity.

References:

• Curcio-Morelli C, Zavacki AM, Christofollete M, Gereben B, Freitas B, Harney JW, Li Z, Wu G, Bianco AC. Deubiquitination of type 2 iodothyronine deiodinase by pVHL-interacting deubiquitinating enzymes regulates thyroid hormone activation. J Clin Invest 2003;112:189-96.
• Callebaut I, Curcio-Morelli C, Mornon JP, Gereben B, Buettner C, Huang S, Castro B, Fonseca TL, Harney JW, Larsen PR, Bianco AC. The iodothyronine selenodeiodinases are thioredoxin-fold family proteins containing a glycoside hydrolase-clan GH-A-like structure. J Biol Chem 2003; 278:36887-96
• Dentice M, Bandyopadhyay A, Gereben B, Callebaut I, Christoffolete MA, Kim BW, Nissim S, Mornon J-P, Zavacki AM, Zeöld A, Curcio-Morelli C, Ribeiro R, Harney JW, Tabin CJ and Bianco AC. The Hedgehog-inducible WSB-1 is an E3 ubiquitin ligase adaptor that modulates thyroid hormone activation and PTHrP secretion in the developing growth plate. Nature Cell Biol 2005; 7:698-705
• Watanabe M, Houten SM, Mataki C, Christoffolete MA, Kim BW, Bianco AC, Auwerx J. Bile acids induce energy expenditure by promoting intracellular thyroid hormone activation. Nature 2006; 439:484-489