Protein synthesis inhibition in mouse peritoneal macrophages results in increased acyl coenzyme A:cholesterol acyl transferase activity and cholesteryl ester accumulation in the presence of native low density lipoprotein.

I Tabas,G C Boykow

doi:10.1016/s0021-9258(18)45333-1

Abstract

Cholesteryl ester (CE) accumulation in arterial wall macrophages (foam cells), mediated by the intracellular enzyme acyl coenzyme A:cholesterol acyl transferase (ACAT), is a prominent feature of atherosclerotic lesions. However, native low density lipoprotein (LDL) does not cause activation of ACAT or CE accumulation in cultured mouse peritoneal macrophages despite both substantial LDL uptake and degradation and the presence of ACAT in these cells. We now report that when protein synthesis is inhibited in mouse peritoneal macrophages by treatment with cycloheximide, puromycin, or actinomycin D, native LDL-induced whole-cell ACAT activity and CE accumulation is 10-fold higher than that seen in LDL-treated control cells. The enhancement of ACAT activity was seen 4 h after the addition of cycloheximide, and ACAT activity returned to control values 4 h after the withdrawal of cycloheximide. Postnuclear supernatants and microsomes from cycloheximide-treated mouse peritoneal macrophages also had higher ACAT activity than microsomes from control cells, but the relative enhancement (maximum 3.3-fold) was less than that seen when ACAT was assayed in the intact cell. In contrast to the situation with mouse peritoneal macrophages, cycloheximide treatment of J774 macrophages, which under normal conditions display high ACAT activity and CE accumulation in the presence of native LDL, did not result in further enhancement of either ACAT activity or LDL-induced CE accumulation. From these data we postulate that mouse peritoneal macrophages have a short-lived protein that inhibits ACAT-mediated cholesterol esterification which is responsible for their lack of ACAT response and CE accumulation in the presence of native LDL. The explanation for high ACAT activity and LDL-induced CE accumulation in J774 macrophages may be that these cells lack the putative mouse peritoneal macrophage cholesterol esterification inhibitor.

Highlights

Cholesteryl ester (CE) accumulation in arterial wall been investigatedby several laboratories [5]
Effect of Protein Synthesis Inhibitionon Whole-Cell accumulationonly ase (ACAT) Activity in Mouse Peritoneal Macrophages-As demonstrated previously,ACAT-mediated cholesterol esterification activity in LDL-treated mouse peritoneal macrophages is relatively low despite the fact that these cells both have ACAT as well asinternalizeand degrade substantialamounts of LDL
On LDL-induced whole-cell ACAT activity in mouse peritoneal macrophages,cells were incubated with LDL (200 pg/ ml)alone(control) or inthepresence of threedifferent inhibitors of protein synthesis, the translational inhibitors cycloheximide and puromycin and the transcriptional inhibitor actinomycinD (Fig. 1).The cells were pulse-labeled with [14C]oleate,and whole-cell ACAT activity was assayed by measuring the formation of cholesteryl[I4C]oleate

Summary

RESULTS

Effect of Protein Synthesis Inhibitionon Whole-Cell ACAT Activity in Mouse Peritoneal Macrophages-As demonstrated previously (ll),ACAT-mediated cholesterol esterification activity in LDL-treated mouse peritoneal macrophages is relatively low despite the fact that these cells both have ACAT as well asinternalizeand degrade substantialamounts of LDL.

ELControl Puromycin Actlnornycln D

The data show that in those cells initially treated with

Ratio CHXCon

DISCUSSION