2-Aminopurine Inhibits Lipid Accumulation Induced by Apolipoprotein E-Deficient Lipoprotein in Macrophages: Potential Role of Eukaryotic Initiation Factor-2␣ Phosphorylation in Foam Cell Formation

ABSTRACT We previously reported that apolipoprotein (Apo) E-deficient, ApoB48-containing (E Ϫ /B48) lipoproteins inhibited expression of lysosomal hydrolase and transformed mouse peritoneal macrophages (MPMs) into foam cells. The present study examined the effect of 2-aminopurine (2-AP), an inhibitor of eukaryotic initiation factor (eIF)-2␣ phosphorylation, on E Ϫ /B48 lipoprotein-induced changes in gene expression and foam cell formation. Our data demonstrated that E Ϫ /B48 lipoproteins enhanced phosphorylation of eIF-2␣ in macrophages. Incubation of MPMs with E Ϫ /B48 lipoproteins inhibited the translation efficiency of mRNAs encoding lysosomal acid lipase, cathepsin B, and cation-dependent mannose 6 phosphate receptor, with a parallel reduction in the level of these proteins. Addition of 2-AP to the culture media alleviated the suppressive effect of E Ϫ /B48 lipoproteins on lysosomal hydrolase mRNA translation, increased macrophage degradation of E Ϫ /B48 lipoproteins, and inhibited foam cell formation. Transfection of MPMs with a nonphosphorylatable eIF-2␣ mutant also attenuated the suppressive effect of E Ϫ /B48 lipoproteins on expression of lysosomal acid lipase, associated with a reduced accumulation of cellular cholesterol esters. This is the first demonstration that ApoE-deficient lipoproteins inhibit lysosomal hydrolase synthesis and transform macrophages into foam cells through induction of eIF-2␣ phosphorylation

Arrest of Viral Proliferation by Ectopic Copies of Its Cognate Replication Origin

The initiation step of DNA replication is the crucial determinant of proliferation in all organisms. This step depends on the specific interaction of DNA sequences present at origins of DNA replication and their cognate activators. We wished to explore the hypothesis that the presence of ectopic origin copies may interfere with proper genome duplication. Bacteriophage λ was used as a model system. To this end, the outcome of an infection of an E. coli strain harboring ectopic copies of the λ origin region was analyzed. By measuring the effect on the host growth, viral production, and electro-microscopic visualization of the resulting λ replicative intermediates, we concluded that the ectopic copies had prevented the normal initiation step of λ DNA replication. These results suggest that DNA decoys encoding viral origins could constitute effective tools to specifically arrest viral proliferation