Immunological quantitation and localization of ACAT-1 and ACAT-2 in human liver and small intestine.
By using specific anti-ACAT-1 antibodies in immunodepletion studies, we previously found that ACAT-1, a 50-kDa protein, plays a major catalytic role in the adult human liver, adrenal glands, macrophages, and kidneys but not in the intestine. Acyl-coenzyme A:cholesterol acyltransferase (ACAT) activity in the intestine may be largely derived from a different ACAT protein. To test this hypothesis, we produced specific polyclonal anti-ACAT-2 antibodies that quantitatively immunodepleted human ACAT-2, a 46-kDa protein expressed in Chinese hamster ovary cells. In hepatocyte-like HepG2 cells, ACAT-1 comprises 85-90% of the total ACAT activity, with the remainder attributed to ACAT-2. In adult intestines, most of the ACAT activity can be immunodepleted by anti-ACAT-2. ACAT-1 and ACAT-2 do not form hetero-oligomeric complexes. In differentiating intestinal enterocyte-like Caco-2 cells, ACAT-2 protein content increases by 5-10-fold in 6 days, whereas ACAT-1 protein content remains relatively constant. In the small intestine, ACAT-2 is concentrated at the apices of the villi, whereas ACAT-1 is uniformly distributed along the villus-crypt axis. In the human liver, ACAT-1 is present in both fetal and adult hepatocytes. In contrast, ACAT-2 is evident in fetal but not adult hepatocytes. Our results collectively suggest that in humans, ACAT-2 performs significant catalytic roles in the fetal liver and in intestinal enterocytes.
Chang
C C
CC
Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
Sakashita
N
N
Ornvold
K
K
Lee
O
O
Chang
E T
ET
Dong
R
R
Lin
S
S
Lee
C Y
CY
Strom
S C
SC
Kashyap
R
R
Fung
J J
JJ
Farese
R V
RV
Patoiseau
J F
JF
Delhon
A
A
Chang
T Y
TY
D000293:Adolescent; D000328:Adult; D000368:Aged; D000818:Animals; D016466:CHO Cells; D006528:Carcinoma, Hepatocellular; D002648:Child; D003001:Cloning, Molecular; D006224:Cricetinae; D006801:Humans; D007413:Intestinal Mucosa / Q000196:embryology / Q000201:enzymology*; D007421:Intestine, Small / Q000196:embryology / Q000201:enzymology*; D007527:Isoenzymes / Q000032:analysis / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000196:embryology / Q000201:enzymology*; D008113:Liver Neoplasms; D008875:Middle Aged; D011994:Recombinant Proteins / Q000032:analysis / Q000378:metabolism; D002785:Sterol O-Acyltransferase / Q000032:analysis* / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D007527:Isoenzymes; D011994:Recombinant Proteins; D002785:Sterol O-Acyltransferase