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ACAT-2, a second mammalian acyl-CoA:cholesterol acyltransferase. Its cloning, expression, and characterization
1Gladstone Institute of Cardiovascular Disease, University of California, San Francisco, California 94141, USA.
The Journal of Biological Chemistry
|October 3, 1998
Summary
Scientists discovered a new enzyme, acyl-CoA:cholesterol acyltransferase-2 (ACAT-2), crucial for cholesterol esterification in the liver and intestines. This finding aids in understanding cholesterol metabolism and developing targeted ACAT inhibitors.
Area of Science:
- Biochemistry
- Molecular Biology
- Genetics
Background:
- Acyl-CoA:cholesterol acyltransferase (ACAT) is vital for cellular cholesterol homeostasis and implicated in cholesterol absorption, lipoprotein production, and atherosclerosis.
- Mammalian ACAT research suggested the existence of multiple ACAT enzymes, with evidence pointing to distinct roles in mouse liver and intestine.
Purpose of the Study:
- To identify and characterize a second mammalian ACAT enzyme, designated ACAT-2.
- To investigate the tissue-specific expression and functional role of ACAT-2 in cholesterol esterification.
Main Methods:
- Cloning and expression of the ACAT-2 gene in H5 insect cells using a recombinant baculovirus.
- Assaying cholesterol esterification activity and substrate specificity for ACAT-1 and ACAT-2.
- Evaluating the differential inhibition of ACAT-1 and ACAT-2 activities using specific inhibitors.
- Mapping the ACAT-2 gene (Acact2) to mouse chromosome 15.
Main Results:
- ACAT-2 was identified as a distinct enzyme, 44% identical to ACAT-1, and expressed as a ~46-kDa protein in cell membranes with high cholesterol esterification activity.
- Both ACAT-1 and ACAT-2 esterified oxysterols, but exhibited different IC50 values with specific ACAT inhibitors, enabling selective targeting.
- ACAT-2 expression was predominantly observed in mouse liver and small intestine, supporting its role in these tissues.
- The mouse ACAT-2 gene (Acact2) was mapped to chromosome 15, a region linked to plasma cholesterol regulation.
Conclusions:
- ACAT-2 is a newly identified mammalian enzyme that plays a significant role in cholesterol esterification, particularly in the liver and intestine.
- The distinct properties and expression patterns of ACAT-1 and ACAT-2 offer opportunities for developing selective ACAT inhibitors.
- The discovery of ACAT-2 provides a molecular basis for further research into cholesterol metabolism, lipoprotein dynamics, and the pathogenesis of diseases like atherosclerosis.
