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DHRS3, a retinal reductase, is regulated by retinoic acid and lipopolysaccharide in THP1 cells and rat liver in vivo

Microarray analysis of THP‐1 cells, a human monocytic leukemia cell line, identified DHRS3 as a possible target of all‐trans‐retinoic acid (RA). DHRS3 has been described as a microsomal enzyme capable of catalyzing the reduction of retinal to retinol. Treatment of THP‐1 cells with as little as 20 nM RA for 24 h increased DHRS3 mRNA by 40 times as measured by real‐time PCR. There was no significant effect of either TNF‐a or lipopolysaccharide (LPS) alone or in combination with RA in THP‐1 cells. The level of DHRS3 protein was similarly increased by RA, but not by TNF‐a or LPS, as measured by Western blot analysis using an anti‐human DHRS3 antibody. Next, we determined that DHRS3 mRNA is expressed at a relatively high level in the liver as compared to the other tissues. Using the predicted sequence from GenBank database we cloned the full‐length sequence of DHRS3 with a size of 2111 bases from rat liver RNA; the predicted open reading frame was 912 bases. By in vitro transcription‐translation assay of DHRS3 cDNA in pcDNA3.1 vector, 2 major proteins were detected with sizes in the range of 30 to 35 kDa. To determine whether DHRS3 is regulated by RA and/or by inflammation in the liver, we measured DHRS3 mRNA expression by real‐time RT‐PCR in the liver of rat treated either concurrently or sequentially with RA (6 h or 16 h, p.o.) or LPS (6 h or 12 h, i.p.). Whereas RA treatment increased DHRS3 mRNA by only ~30% in liver, LPS suppressed the mRNA expression by >90% both in the absence and presence of RA. The results suggest: 1) Regulation of DHRS3 mRNA expression by RA is tissue or cell line specific. 2) Down‐regulation of DHRS3 by LPS in the liver may contribute to the perturbation of vitamin A metabolism as has been shown during infection and inflammation.