Submitted on December 31, 2007
Accepted on May 21, 2008
Sodium arsenite induces orphan nuclear receptor SHP gene expression via AMP-activated protein kinase to inhibit gluconeogenic enzyme gene expression
Dipanjan Chanda1, Sung-Jin Kim2, In-Kyu Lee3, Minho Shong4, and Hueng-Sik Choi5*
1 Hormone Research Center, School of Biological Sciences and Technology, Chonnam National University, Gwangju, Korea, Republic of
2 Department of Internal Medicine, Chungnam National University School of Medicine, Daejon, Korea, Republic of
3 Department of Internal Medicine, Kyungpook National University School of Medicine, Daegu, Korea, Republic of
4 Daejon, Korea, Republic of; Department of Internal Medicine, Chungnam National University School of Medicine, Daejon, Korea, Republic of
5 Hormone Research Center, School of Biological Sciences and Technology, Chonnam National University, Gwangju, Korea, Republic of; Gwangju, Korea, Republic of
* To whom correspondence should be addressed. E-mail: hsc{at}chonnam.ac.kr.
Sodium arsenite (NaArs) has been demonstrated to alter the expression of genes associated with glucose homeostasis in tissues involved in the pathogenesis of type 2 diabetes; however the underlying molecular mechanism has not been fully elucidated yet. Here, we report that the sodium arsenite-induced gene expression of the small heterodimer partner (SHP; NR0B2), an atypical orphan nuclear receptor, regulates the expression of hepatic gluconeogenic genes. Sodium arsenite augments hepatic SHP mRNA levels in an AMP-activated protein kinase (AMPK)-dependent manner. Sodium arsenite activated AMPK and was shown to perturb cellular ATP levels. The arsenite-induced SHP mRNA level was blocked by adenoviral overexpression of dominant negative AMPK (Ad-dnAMPKα) or by the AMPK inhibitor, compound C, in hepatic cell lines. We demonstrated the dose-dependent induction of SHP mRNA levels by sodium arsenite and repressed the forskolin/dexamethasone-induced gene expression of the key hepatic gluconeogenic genes, phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase). Ad-dnAMPKα blocked the repressive effects of arsenite- induced SHP on PEPCK and G6Pase. Sodium arsenite inhibited the promoter activity of PEPCK and G6Pase, and this repression was abolished by siRNA SHP treatments. The knockdown of SHP expression by oligonucleotide siRNA SHP or adenoviral siRNA SHP (Ad-siRNA SHP) released the sodium arsenite-mediated repression of forskolin/dexamethasone-stimulated PEPCK and G6Pase gene expression in a variety of hepatic cell lines. Results from our study suggest that sodium arsenite induces SHP via AMPK to inhibit the expression of hepatic gluconeogenic genes, and also provide us with a novel molecular mechanism of arsenite-mediated regulation of hepatic glucose homeostasis.
