ABSTRACT
All-trans-retinoic acid (at-RA) induces cell differentiation in a wide variety of cell types, including F9 embryonic teratocarcinoma cells, and can influence axial pattern formation during embryonic development. We now identify a novel retinoid synthetic pathway in differentiating F9 cells that results in the intracellular production of 4-oxoretinol (4-oxo-ROL) from retinol (vitamin A). Approximately 10-15% of the total retinol in the culture is metabolized to 4-hydroxyretinol and 4-oxo-ROL by the at-RA-treated, differentiating F9 cells over an 18-hr period, but no detectable metabolism of all-trans-retinol to at-RA or 9-cis-retinoic acid is observed in these cells. Remarkably, we show that 4-oxo-ROL can bind and activate transcription of the retinoic acid receptors whereas all-trans-retinol shows neither activity. Low doses of 4-oxo-ROL (e.g., 10(-9) or 10(-10 M) can activate the retinoic acid receptors even though, unlike at-RA, 4-oxo-ROL does not contain an acid moiety at the carbon 15 position. 4-oxo-ROL does not bind or transcriptionally activate the retinoid X receptors. Treatment of F9 cells with 4-oxo-ROL induces differentiation without conversion to the acid and 4-oxo-ROL is active in causing axial truncation when administered to Xenopus embryos at the blastula stage. Thus, 4-oxo-ROL is a natural, biologically active retinoid that is present in differentiated F9 cells. Our data suggest that 4-oxo-ROL may be a novel signaling molecule and regulator of cell differentiation.
Subject(s)
Receptors, Retinoic Acid/metabolism , Vitamin A/analogs & derivatives , Animals , Cell Differentiation/drug effects , Cell Line , Gene Expression/drug effects , Humans , Mice , Receptors, Retinoic Acid/drug effects , Receptors, Retinoic Acid/genetics , Retinoids/pharmacology , Signal Transduction , Stereoisomerism , Trans-Activators/metabolism , Trans-Activators/pharmacology , Transfection , Tumor Cells, Cultured , Vitamin A/chemistry , Vitamin A/metabolism , Vitamin A/pharmacology , Xenopus laevis/embryology , Xenopus laevis/metabolismABSTRACT
F9 embryonic teratocarcinoma stem cells differentiate into an epithelial cell type called extraembryonic endoderm when treated with retinoic acid (RA), a derivative of retinol (vitamin A). This differentiation is presumably mediated through the actions of retinoid receptors, the RARs and RXRs. To delineate the functions of each of the different retinoid receptors in this model system, we have generated F9 cell lines in which both copies of either the RAR alpha gene or the RAR gamma gene are disrupted by homologous recombination. The absence of RAR alpha is associated with a reduction in the RA-induced expression of both the CRABP-II and Hoxb-1 (formerly 2.9) genes. The absence of RAR gamma is associated with a loss of the RA-inducible expression of the Hoxa-1 (formerly Hox-1.6), Hoxa-3 (formerly Hox-1.5), laminin B1, collagen IV (alpha 1), GATA-4, and BMP-2 genes. Furthermore, the loss of RAR gamma is associated with a reduction in the metabolism of all-trans-RA to more polar derivatives, while the loss of RAR alpha is associated with an increase in metabolism of RA relative to wild-type F9 cells. Thus, each of these RARs exhibits some specificity with respect to the regulation of differentiation-specific gene expression. These results provide an explanation for the expression of multiple RAR types within one cell type and suggest that each RAR has specific functions.
Subject(s)
Cell Differentiation/drug effects , Receptors, Retinoic Acid/metabolism , Tretinoin/metabolism , Animals , Base Sequence , Cell Division , Cell Line , Chromatography, High Pressure Liquid , DNA Primers , Gene Expression/drug effects , Kinetics , Mice , Molecular Sequence Data , Mutagenesis , Polymerase Chain Reaction , Receptors, Retinoic Acid/biosynthesis , Recombinant Proteins/biosynthesis , Recombinant Proteins/metabolism , Recombination, Genetic , Retinoic Acid Receptor alpha , Retinoids/isolation & purification , Retinoids/metabolism , Retinoids/pharmacology , Teratocarcinoma , Transfection , Tretinoin/pharmacology , Tumor Cells, Cultured , Retinoic Acid Receptor gammaABSTRACT
All trans-retinoic acid (tr-RA) has been used to induce leukemic cell differentiation in patients with acute promyelocytic leukemia (APL). However, the duration of remission is brief and is associated with a progressive decrease in peak plasma concentrations following chronic dosing. 9-Cis-retinoic acid (9-cis-RA) has the potential to elicit the same effects as tr-RA, because it can bind and activate the same family of nuclear receptors. It is not known whether the pharmacokinetics of this novel compound resemble those of tr-RA. In this study, we report major differences in the uptake and pharmacokinetics between orally administered tr-RA and 9-cis-RA in the plasma of nude mice. Following a single initial oral administration of either isomer, the plasma peak time of 9-cis-RA (15-30 min) occurred earlier than that of tr-RA (60-180 min), but with lower plasma concentrations and area under the concentration-time curve (AUC) value. A decrease in the AUC of plasma tr-RA was seen in animals that were given a second dose 2 days after the first dose. In contrast, an increase in the AUC of plasma 9-cis-RA was seen in animals that were given a second dose 2 days after the first dose. This increase was due to the appearance of a second 9-cis-RA peak at 180 min. When liarozole, an inhibitor of tr-RA metabolism, was coadministered with the initial tr-RA dose or a second tr-RA dose 2 weeks later, the AUC of plasma tr-RA was increased relative to tr-RA alone.(ABSTRACT TRUNCATED AT 250 WORDS)
