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J. Biol. Chem., Vol. 279, Issue 10, 9306-9312, March 5, 2004

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Regulatory Interaction between Arylhydrocarbon Receptor and SIM1, Two Basic Helix-Loop-Helix PAS Proteins Involved in the Control of Food Intake^*

Chun Yang, Francine Boucher, André Tremblay, and Jacques L. Michaud, A clinician-scientist of the CIHR

From the Research Center, Hôpital Sainte-Justine, 3175 Côte Sainte-Catherine, Montréal, Québec H3T 1C5, Canada

The basic helix-loop-helix PAS (bHLH-PAS) transcription factors SIM1 and arylhydrocarbon receptor (AHR) are involved in the control of feeding behavior. Sim1 haploinsufficiency causes hyperphagia in mice and humans, most likely by perturbing the hypothalamus function. The administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a ligand of AHR, causes severe anorexia, which also appears to be of central origin. Both SIM1 and AHR require heterodimerization either with ARNT or ARNT2 to function. Here, we characterize the promoter for Sim1 and show that a consensus AHR-ARNT/2 binding site positively regulates its activity in the context of transfection experiments in Neuro-2A cells. A gel shift assay indicated that AHR-ARNT/2 can bind its putative site in the Sim1 promoter. Overexpression of Arnt, Arnt2, or Ahr increased the activity of a reporter construct containing the Sim1 promoter by 1.8-, 1.5-, and 2.2-fold, respectively, but failed to do so when the AHR-ARNT/2 binding site was mutated. Similarly, TCDD increased the activity of the reporter construct by 1.8-fold but not that of its mutated version. Finally, we found that TCDD increased Sim1 expression in Neuro-2A cells and in mouse kidney and hypothalamus by 4-, 3-, and 2-fold, respectively. We conclude that Sim1 expression is regulated by AHR-ARNT/2. This result raises the possibility that Sim1 mediates the effect of TCDD on feeding and points to a complex network of regulatory interactions between bHLH-PAS proteins.

Received for publication, July 21, 2003 , and in revised form, October 8, 2003.

^* This work was supported by Operating Grant MOP-15458 from the Canadian Institutes of Health Research. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed: Research Center, Hôpital Sainte-Justine, 3175 Côte Sainte-Catherine, Montréal, Québec H3T 1C5, Canada. Fax: 514-345-4766; E-mail: jmichaud{at}justine.umontreal.ca.

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