Differential expression of ACAT1 and ACAT2 among cells within liver, intestine, kidney, and adrenal of nonhuman primates

Two closely related enzymes with more than 50% sequence identity have been identified that catalyze the esterification of cholesterol using acyl-CoA s ubstrates, namely acyl-CoA:cholesterol acyltransferase 1 (ACAT1) and ACAT2. Both are membrane-spanning proteins believed to reside in the endoplasmic reticulum of cells. ACAT2 has been hypothesized to be associated with lipop rotein particle secretion whereas ACAT1 is ubiquitous and may serve a more general role in cellular cholesterol homeostasis. We have prepared and affi nity purified rabbit polyclonal antibodies unique to either ACAT enzyme to identify their cellular localization in liver and intestine, the two main l ipoprotein-secreting tissues of the body, and for comparison, kidney and ad renal. In the liver, ACAT2 was identified in the rough endoplasmic reticulu m of essentially all hepatocytes whereas ACAT1 was confined to cells lining the intercellular spaces among hepatocytes in a pattern typical of Kupffer cells. In the intestine, ACAT2 signal was strongly present in the apical t hird of the mucosal cells, whereas ACAT1 staining was diffuse throughout th e mucosal cell, but with strong signal in goblet cells, Paneth cells, and v illus macrophages. In the kidney, ACAT1 immunostaining was specific for the distal tubules and podocytes within the glomerulus. In the adrenal, ACAT1 signal was strongly present in the cells of the cortex, and absent from oth er adrenal cell types. No ACAT2 signal was identified in the kidney or adre nal. We conclude that only the cells of the liver and intestine that secret e apolipoprotein B-containing lipoproteins contain ACAT2, whereas ACAT1 is present in numerous other cell types The data clearly suggest separate func tions for these two closely related enzymes, with ACAT2 being most closely associated with plasma cholesterol levels.