Enrichment of Acyl Coenzyme A:Cholesterol O-Acyltransferase Near Trans-Golgi Network and Endocytic Recycling Compartment

N Khelef, TT Soe, O Quehenberger… - … , and vascular biology, 2000 - Am Heart Assoc
N Khelef, TT Soe, O Quehenberger, N Beatini, I Tabas, FR Maxfield
Arteriosclerosis, thrombosis, and vascular biology, 2000Am Heart Assoc
Acyl coenzyme A: cholesterol O-acyltransferase (ACAT) is the enzyme responsible for
cholesterol esterification in macrophages leading to foam cell formation. The determination
of its localization is a critical step in understanding its regulation by cholesterol. Using
immunofluorescence and confocal microscopy, we previously showed that the enzyme
colocalized with markers of the endoplasmic reticulum, but in addition, ACAT was found in
an unidentified paranuclear site. In the present study, we further define the localization of …
Abstract
—Acyl coenzyme A:cholesterol O-acyltransferase (ACAT) is the enzyme responsible for cholesterol esterification in macrophages leading to foam cell formation. The determination of its localization is a critical step in understanding its regulation by cholesterol. Using immunofluorescence and confocal microscopy, we previously showed that the enzyme colocalized with markers of the endoplasmic reticulum, but in addition, ACAT was found in an unidentified paranuclear site. In the present study, we further define the localization of paranuclear ACAT. First, we found that ACAT does not colocalize with sorting endosomes or late endosomes labeled with fluorescent α2-macroglobulin. The paranuclear ACAT is close to the endocytic recycling compartment labeled with fluorescent transferrin. We also show that the paranuclear structure containing ACAT is very close to TGN38, a membrane protein of the trans-Golgi network (TGN), but farther from Gos28, a marker of cis, medial, and trans Golgi. After treatment with nocodazole, the central localization of ACAT did not colocalize with markers of the TGN. These data indicate that a significant fraction of ACAT resides in membranes that may be a subcompartment of the endoplasmic reticulum in proximity to the TGN and the endocytic recycling compartment. Because the TGN and the endocytic recycling compartment are engaged in extensive membrane traffic with the plasma membrane, esterification of cholesterol in these membranes may play an important role in macrophage foam cell formation during atherogenesis.
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