Induction of acyl-coenzyme A : cholesterol acyltransferase-1 by 1,25-dihydroxyvitamin D-3 or 9-cis-retinoic acid in undifferentiated THP-1 cells

We have previously shown that acyl-coenzyme A: cholesterol acyltransferase- 1 (ACAT-1) protein content increases significantly during the human monocyt e-macrophage differentiation process, To gain further insight, we used undi fferentiated human monocytic THP-1 cells as a model system with which to ex amine whether ACAT-1 mRNA and protein content can be increased by treating cells with 1,25-dihydroxyvitamin D-3 [1,25-(OH)(2)D-3] or with 9-cis-retino ic acid (9-cis-RA), two agents known to upregulate the expression of variou s genes during the monocyte-macrophage differentiation process, Immunoblot analysis with anti-human ACAT-1 antibodies revealed that ACAT-1 protein was increased by 2.6-fold, using 1,25-(OH)(2)D-3 at a physiological concentrat ion (100 pM), ACAT-1 protein was also increased when using 9-cis-RA, but on ly at relatively high concentrations (0.1-1 muM). Northern blot analysis re vealed that among the four ACAT-1 mRNA transcripts (2.8, 3.6, 4.2, and 7.0 kb) examined, only the 2.8- and 3.6-kb transcripts were selectively increas ed. On the basis of enzyme assays in vitro, ACAT activity was increased 3.0 -fold by using 100 nM 1,25-(OH)2D3, and 1.8-fold by using 1 muM 9-cis-RA. T ogether, our results suggest that 1,25-(OH)(3) participates in ACAT-1 gene expression during the monocyte-macrophage differentiation process.