Detection of the steroidogenic acute regulatory protein, StAR, in human liver cells

• Published in: Biochimica et biophysica acta Vol. 1733; no. 2; pp. 111 - 119
• Main Authors: Hall, E.A., Ren, S., Hylemon, P.B., Rodriguez-Agudo, D., Redford, K., Marques, D., Kang, D., Gil, G., Pandak, W.M.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15.04.2005
• Subjects: Bile acid; Bile Acids and Salts - biosynthesis; Blotting, Western; Cell Line; Cholestanetriol 26-Monooxygenase; Cholesterol; Electrophoresis, Gel, Two-Dimensional; Hepatocytes - chemistry; Hepatocytes - metabolism; Humans; Hydroxycholesterols - pharmacology; Lipid transport; Liver - chemistry; Liver - metabolism; Mitochondrial Proteins - metabolism; Phosphoproteins - analysis; Phosphoproteins - biosynthesis; Phosphoproteins - genetics; Recombinant Proteins - biosynthesis; Regulation; RNA, Messenger - biosynthesis; Steroid Hydroxylases - biosynthesis; Steroid Hydroxylases - genetics; Steroidogenic acute regulatory protein; Regulation; Steroidogenic acute regulatory protein; Lipid transport; Bile acid; Cholesterol
• ISSN: 1388-1981; 0006-3002; 1879-2618; 1878-2434
• DOI: 10.1016/j.bbalip.2005.01.004

Overexpressing StAR (a mitochondrial cholesterol transporter) increases (>5-fold) the rate of 27-hydroxylation of cholesterol and the rates of bile acid synthesis in primary rat hepatocytes; suggesting that the transport of cholesterol into mitochondria is rate-limiting for bile acid biosynthesis via the CYP27A1 initiated ‘acidic’ pathway. Our objective was to determine the level of StAR expression in human liver and whether changes in StAR would correlate with changes in CYP27A1 activity/bile acid synthesis rates in human liver tissues. StAR mRNA and protein were detected in primary human hepatocytes and HepG2 cells by RT-PCR/Northern analysis and by Western analysis, respectively. In immunocompetition assays, liver StAR was competed away with the addition of purified human adrenal StAR. Overexpressing CYP27A1 in both cell types led to >2-fold increases in liver StAR concentration. StAR protein levels also increased ∼2-fold with the addition of 27-hydroxycholesterol to HepG2 cell culture medium. Overexpressing StAR increased the rates of 27-hydroxylation of cholesterol/bile acid synthesis in both cell lines and increased intracellular levels of 27-hydroxycholesterol. In conclusion, human liver cells contain regulable StAR protein whose level of expression appears capable of regulating cellular cholesterol homeostasis, representing a potential therapeutic target in the management of hyperlipidemia.