MOLECULAR-CLONING, FUNCTIONAL EXPRESSION AND TISSUE DISTRIBUTION OF RAT ACYL-COENZYME A-CHOLESTEROL ACYLTRANSFERASE

Acyl-coenzyme A:cholesterol acyltransferase (ACAT) is an enzyme cataly zing the intracellular formation of cholesteryl esters from free chole sterol and fatty acyl-CoA. In the present study, we cloned rat ACAT cD NA and determined its tissue distribution. Rat ACAT cDNA, having a cod ing region of 1635 bp with its deduced protein sequence of 545 amino a cids and two typical motifs such as signature sequences and leucine he ptad motif, showed 83, 92 and 90% identity with human, mouse, and hams ter ACAT, respectively. Expression of rat ACAT cDNA in A293 cells and CHO cells resulted in a 3.0 to 3.5-fold increase in the enzyme activit y. Among twelve tissues examined, ACAT activity was highest in adrenal followed by liver and intestine while that of aorta was extremely low . The mRNA level was also the highest in adrenal among four tissues ex amined. However, in contrast to its high ACAT activity, the liver mRNA level was extremely low (adrenal >> intestine > aorta >> liver). Cons istent with mRNA levels, immunohistochemical analyses with a specific ACAT antibody detected significant ACAT signals in adrenal and intesti ne but a negligible signal in liver. These results indicate that adren al most abundantly expresses ACAT in rat. Furthermore, rat liver showe d a high ACAT activity but an extremely low ACAT mRNA and negligible i mmunohistochemical reactivity, suggesting the presence of a structural ly different ACAT protein(s) in rat liver. (C) 1998 Elsevier Science B .V.