Abstract
NADPH-cytochrome P450 reductase (POR) is essential for the functioning of microsomal cytochrome P450 (P450) monooxygenases and heme oxygenases. The biological roles of the POR-dependent enzymes in the intestine have not been defined, despite the wealth of knowledge on the biochemical properties of the various oxygenases. In this study, cDNA microarray analysis revealed significant changes in gene expression in enterocytes isolated from the small intestine of intestinal epithelium-specific Por knock-out (named IE-Cpr-null) mice compared with that observed in wild-type (WT) littermates. Gene ontology analyses revealed significant changes in terms related to P450s, transporters, cholesterol biosynthesis, and, unexpectedly, antigen presentation/processing. The genomic changes were confirmed at either mRNA or protein level for selected genes, including those of the major histocompatibility complex class II (MHC II). Cholesterol biosynthetic activity was greatly reduced in the enterocytes of the IE-Cpr-null mice, as evidenced by the accumulation of the lanosterol metabolite, 24-dihydrolanosterol. However, no differences in either circulating or enterocyte cholesterol levels were observed between IE-Cpr-null and WT mice. Interestingly, the levels of the cholesterol precursor farnesyl pyrophosphate and its derivative geranylgeranyl pyrophosphate were also increased in the enterocytes of the IE-Cpr-null mice. Furthermore, the expression of STAT1 (signal transducer and activator of transcription 1), a downstream target of geranylgeranyl pyrophosphate signaling, was enhanced. STAT1 is an activator of CIITA, the class II transactivator for MHC II expression; CIITA expression was concomitantly increased in IE-Cpr-null mice. Overall, these findings provide a novel and mechanistic link between POR-dependent enzymes and the expression of MHC II genes in the small intestine.
Highlights
P450 reductase (POR)-dependent enzymes metabolize numerous endogenous compounds
CDNA microarray analysis revealed significant changes in gene expression in enterocytes isolated from the small intestine of intestinal epithelium-specific Por knock-out mice compared with that observed in wild-type (WT) littermates
Microarray Analysis—By using relatively conservative criteria in fold change (Ն1.75 or Յ0.57) and a p value of Յ0.01, we identified a number of mouse small intestine (SI) genes that were differentially expressed in the enterocytes of the intestinal epithelium (IE)-Cpr-null mice, compared with their expression levels in WT mice (34 up-regulated and 17 down-regulated) (Table 1)
Summary
P450 reductase (POR)-dependent enzymes metabolize numerous endogenous compounds. Results: Enterocytes of intestinal Por knock-out mice show up-regulation of genes important for immunity and increased geranylgeranyl pyrophosphate levels. This latter model was found to have partial embryonic lethality, altered steroid hormone homeostasis, and infertility in females, in addition to impairments in drug metabolism and decreases in serum cholesterol In both the liver-Cpr-null and the Cpr-low mice, extensive changes in global gene expression were observed in the livers, which revealed the importance of. Additional studies of the levels of relevant endogenous metabolites (including cholesterol, 24dihydrolanosterol (24-DHL), farnesyl pyrophosphate (FPP), geranylgeranyl pyrophosphate (GGPP), heme, and bilirubin) and signaling proteins (including STAT1 and CIITA (class II major histocompatibility complex transactivator)) provided evidence in support of a novel link between POR-dependent enzymes and expression of the major histocompatibility complex class II (MHC II) genes, which are important for intestinal immunity
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