Peroxisome proliferator enhances gene expression of cellular retinol-binding protein, type II in Caco-2 cells

doi:10.1016/S0024-3205(98)00003-4

Life Sciences

Volume 62, Issue 10, 30 January 1998, Pages 861-871

https://doi.org/10.1016/S0024-3205(98)00003-4 Get rights and content

Abstract

Both the mRNA and protein of cellular retinol-binding protein, type two (CRBP(II)) are induced in rat intestine by high fat (corn oil) diet (Biochim. Biophys. Acta 1200, 34–40, 1994) as well as by dietary unsaturated long-chain fatty acids (J. Nutr. 125, 2039–2044, 1995). To gain an insight into the mechanism for this induction, we investigated whether CRBP(II) gene was activated by exposure of the human intestinal cell line, Caco-2 to a peroxisome proliferator (clofibric acid) and/or 9-cis retinoic acid. Northern blot hybridization revealed that Caco-2 cells endogenously expressed the mRNAs of peroxisome proliferator-activated receptor α (PPARα) and retinoid X receptor α (RXRα). The expression of the genes encoding CRBP(II), PPARα, and RXRα increased progressively during differentiation of Caco-2 cells. The cells exposed to 100 μM clofibric acid exhibited 70% greater CRBP(II) mRNA and the exposure of the cells to 100 μM clofibric acid in combination with 100 nM 9-cis retinoic acid exhibited 130% greater CRBP(II) mRNA level, indicating that the effect of the combination of them was additive. Neither PPARα mRNA nor RXRα mRNA level was enhanced by clofibric acid. In conclusion, our data suggested that the CRBP(II) gene expression may be enhanced by an activation of PPARα-RXRα heterodimer through some putative metabolite(s) formed via fatty acid-related metabolic pathway in the clofibric acid-treated cells.

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Isolation and characterization of unsaturated fatty acids as natural ligands for the retinoid-X receptor
2003, Archives of Biochemistry and Biophysics
Citation Excerpt :
The rat cellular retinol-binding protein II gene (rCRBPII) and apolipoprotein AI have been implicated as containing a DR1-type RXRE [33,34]. The evidence supporting these as true RXR homodimer response elements is somewhat controversial and the involvement of other DR1 heterodimer partners, such as PPARs, cannot be excluded [35,36]. Since fatty acids are known ligands of the PPARs, analysis of RXR homodimer-dependent activation of DR1-type RXREs must be evaluated with caution.
The retinoid-X receptor (RXR) is a ligand activated nuclear receptor that is the heterodimer partner for many class II nuclear receptors. Previously identified natural ligands for this receptor include 9-cis retinoic acid (9cRA), docosahexaenoic acid, and phytanic acid. Our studies were performed to determine if there are any unidentified, physiologically important RXR ligands. Agonists for RXR were purified from rat heart and testes lipid extracts with the use of a cell-based reporter assay to monitor RXR activation. Purified active fractions contained a variety of unsaturated fatty acids and components were quantified by gas–liquid chromatography of derivatized samples. The corresponding fatty acid standards elicited a similar response in the reporter cell assay. Competition binding analysis revealed that the active fatty acids compete with [³H]9cRA for binding to RXR. Non-esterified fatty acids were analyzed from lipid extracts of isolated heart and testes nuclei and endogenous concentrations were found to be within the range of their determined binding affinities. Our studies reveal tissue dependent profiles of RXR agonists and support the idea of unsaturated fatty acids as physiological ligands of RXR.
PPARβ regulates vitamin A metabolism-related gene expression in hepatic stellate cells undergoing activation
2003, Journal of Lipid Research
Activation of cultured hepatic stellate cells correlated with an enhanced expression of proteins involved in uptake and storage of fatty acids (FA translocase CD36, Acyl-CoA synthetase 2) and retinol (cellular retinol binding protein type I, CRBP-I; lecithin:retinol acyltransferases, LRAT). The increased expression of CRBP-I and LRAT during hepatic stellate cells activation, both involved in retinol esterification, was in contrast with the simultaneous depletion of their typical lipid-vitamin A (vitA) reserves. Since hepatic stellate cells express high levels of peroxisome proliferator activated receptor β (PPARβ), which become further induced during transition into the activated phenotype, we investigated the potential role of PPARβ in the regulation of these changes. Administration of L165041, a PPARβ-specific agonist, further induced the expression of CD36, B-FABP, CRBP-I, and LRAT, whereas their expression was inhibited by antisense PPARβ mRNA. PPARβ-RXR dimers bound to CRBP-I promoter sequences.
Our observations suggest that PPARβ regulates the expression of these genes, and thus could play an important role in vitA storage. In vivo, we observed a striking association between the enhanced expression of PPARβ and CRBP-I in activated myofibroblast-like hepatic stellate cells and the manifestation of vitA autofluorescent droplets in the fibrotic septa after injury with CCl₄ or CCl₄ in combination with retinol.
Modulation of the expression of peroxisome proliferator-activated receptor-dependent genes through disproportional expression of two subtypes in the small intestine
2001, Archives of Biochemistry and Biophysics
We have reported that dietary long-chain triacylglycerols (LCT) enhance the transcription of cellular retinol-binding protein, the type II (CRBPII) gene, and the liver-type fatty acid-binding protein (L-FABP) gene in the small intestine. Because the cis elements on the CRBPII gene consisting of two AGGTCA motifs separated by a single nucleotide are known to bind not only the 9-cis-retinoic acid receptor (RXR) homodimer, but also the peroxisome proliferator-activated receptor (PPAR)-RXR heterodimer, it has been implicated that the unsaturated long-chain fatty acids, as the ligands of the PPAR, might activate the transcription of the CRBPII gene, thereby making use of the RXR-response elements (RXRE and RE3) as the PPAR-response element (PPRE). In this study, we found that the PPARα mRNA level in the rat jejunum was elevated by dietary fat, whereas the PPARδ mRNA level was reduced under this condition. Electrophoretic mobility-shift assay revealed that both PPARα-RXRα and PPARδ-RXRα heterodimers, specifically and in a dose-dependent manner, bound to the two PPRE-like elements of the rat CRBPII gene as well as the known PPREs in the L-FABP and acyl-CoA oxidase genes. The binding of the PPARα-RXRα heterodimer to the CRBPII-RXRE, the CRBPII-RE3, and the PPREs of L-FABP, HMG-CoA synthase, and acyl-CoA oxidase was gradually diminished by the addition of increasing amounts of PPARδ. The binding of the PPARδ-RXRα heterodimer to CRBPII-RXRE, CRBPII-RE3, and other PPREs was also gradually reduced by the addition of increasing amounts of PPARα. Using Escherichia coli-expressed RXRα, we showed that the mutual competition for RXRα with PPARα and PPARδ occurred at the protein level. These results suggest that the transcriptions of CRBPII, L-FABP, and the other PPAR-dependent genes in the small intestine may be coordinately regulated by the disproportional expression of PPARα and PPARδ.
Transcriptional regulation of cellular retinol-binding protein, type II gene expression in small intestine by dietary fat
1999, Archives of Biochemistry and Biophysics
We have previously demonstrated that dietary fat, especially unsaturated fatty acids, induces cellular retinol-binding protein, type II (CRBPII) gene expression in rat jejunum. In the present study, we showed that feeding a high-fat diet caused parallel increases in jejunal CRBPII mRNA and CRBPII pre-mRNA levels. Nuclear run-on assay also revealed that this increase of CRBPII mRNA level by high-fat diet was, at least in part, triggered at a transcription level. Moreover, peroxisome proliferator-activated receptor alpha (PPARα) mRNA level was also increased in the jejunum by high-fat diet. Gel shift assay showed that the binding activity of rat jejunal nuclear protein to the nuclear receptor response elements located in the rat CRBPII gene (RXRE and RE3) was greater in rats fed high-fat diet than in those fed fat-free diet and were enhanced by addition of bacterially expressed PPARα protein. Also PPARα-retinoid X receptor alpha (RXRα) heterodimer was capable of binding to the CRBPII-RXRE and RE3 elements and these binding activities were enhanced by addition of some PPARα ligands in the gel shift assay. Taken together, these studies suggest that dietary fatty acids may lead to induction of CRBPII gene transcription through increases of PPARα as well as its ligand levels.
Pharmacogenomics - It's not just pharmacogenetics
1998, Current Opinion in Biotechnology
Differential regulation of intestinal and liver fatty acid-binding proteins in human intestinal cell line (Caco-2): Role of collagen
1998, Experimental Cell Research
Fatty acid-binding proteins (FABP) are small cytosolic proteins which are thought to play a key role in fatty acid metabolism. The intestine contains the intestinal (I-FABP) and the liver (L-FABP) isoforms, but their regulation is still poorly documented. In order to find suitable conditions for studying the regulation of the two FABP isoforms in Caco-2 cells, we investigated the effects of the presence of collagen during cell proliferation or differentiation. When collagen was present only during cell proliferation on culture dishes, I-FABP expression was enhanced, whereas sucrase-isomaltase was unaffected and L-FABP expression was merely accelerated. In contrast, when collagen was present during cell differentiation on filter inserts, both I-FABP and sucrase-isomaltase were strongly reduced, but L-FABP was not affected. Under the former conditions (the more suitable for studying FABP regulation), the peroxysome proliferator-activated receptor (PPAR) activators, clofibrate and α-bromopalmitate, enhanced the two isoforms. This study, which is the first one providing a quantitative protein analysis of I-FABP and L-FABP in Caco-2 cells, demonstrates different time courses of expression of these proteins during cell differentiation. It also shows that I-FABP is specifically regulated by collagen and that, under conditions optimal for their expression, both isoforms are modulated by metabolic factors.

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Peroxisome proliferator enhances gene expression of cellular retinol-binding protein, type II in Caco-2 cells

Abstract

J. Biol. Chem.

J. Lipid Res.

J. Biol. Chem.

J. Biol. Chem.

Biochim. Biophys. Acta

Biochim. Biophys. Acta

J. Nutr.

Cell

Analyt. Biochem.

J. Steroid Bbchem. Mol. Biol.

J. Biol. Chem.

J. Biol. Chem.

Biochem. Biophys. Res. Commun.

J. Nutr.

J. Nutr.

Biochemistry

J. Nutr. Sci. Vitaminol.