Submitted on June 29, 2007
Revised on September 20, 2007
Accepted on September 20, 2007
Biosynthesis of regulatory oxysterol, 5-cholesten-3
, 25-diol 3-sulfate, in hepatocytes
Xiaobo Li, William M. Pandak, Sandra K. Erickson, Yongjie Ma, Lianhua Yin, Phillip Hylemon, and Shunlin Ren
Medicine, McGuire VA Medical Center, Richmond, VA 23249
Corresponding Author: shunlin.ren{at}va.gov
Cellular cholesterol homeostasis is maintained through coordinated regulation of cholesterol synthesis, degradation, and secretion. Nuclear receptors for oxygenated cholesterol derivatives (oxysterols) are known to play key roles in the regulation of cholesterol homeostasis. We have recently identified a sulfated oxysterol, 5-cholesten-3, 25-diol 3-sulfate (25HC3S), that is localized to liver nuclei. The present study reports a biosynthetic pathway for 25HC3S in hepatocytes. Assays using mitochondria isolated from rats and Cyp27A1 gene knock-out mice indicated that 25-hydroxycholesterol (25HC) is synthesized by CYP27A1. Incubation of cholesterol or 25HC with mitochondrial and cytosolic fractions in the presence of 3’-phosphoadenosyl 5’-phosphosulfate resulted in the synthesis of 25HC3S. Real time RT-PCR and Western blot analysis showed the presence of insulin-regulated hydroxycholesterol sulfotransferase 2B1b (SULT2B1b) in hepatocytes. 25HC3S, but not 25HC, decreased SULT2B1b mRNA and protein levels. Specific siRNA decreased SULT2B1b mRNA, protein, and activity levels. These findings demonstrate that mitochondria synthesize 25HC, which is subsequently 3-sulfated to form 25HC3S.
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