RETINOIC ACID RECEPTOR GAMMA-2 GENE-EXPRESSION IS UP-REGULATED BY RETINOIC ACID IN 3T3-L1 PREADIPOCYTES

Retinoids, especially all-trans retinoic acid (RA), have been shown to inhibit the differentiation of preadipose cells. In the present study, the expression of retinoic acid receptors (RAR alpha, beta and gamma) and retinoid X receptors (RXR alpha, beta and gamma) was examined by Northern blot analysis in rat adipose tissue and mouse 3T3-L1 adipose cells. The adipose tissue and/or 3T3-L1 cells expressed mRNAs for a number of nuclear retinoid receptors, including RAR alpha, beta and gamma, and RX R alpha, beta and gamma. RAR alpha, RAR gamma, RXR alpha and RXR beta mRNAs were abundant in adipose tissue and 3T3-L1 cells. RXR gamma mRNA was detected in adipose tissue but not in 3T3-L1 cells. Treatment of 3T3-L1 cells with 1 muM RA led to a 4-5-fold increase in the RAR gamma mRNA level, but only a trace amount of RAR beta mRNA was detected. RAR MRNA expression was rapidly (within 2 h) induced by physiological concentrations of RA in a dose-dependent manner. The response of RAR gamma mRNA expression to RA was reversible; rapid disappearance of RAR gamma mRNA occurred on RA removal. In addition. the induction of RAR gamma expression did not require de novo protein synthesis. hut was completely abolished by an inhibitor of RNA synthesis. Using RAR gamma1 and gamma2 isoform-specific probes. the patterns of RAR gamma1 and gamma2 mRNA expression in 3T3-L1 cells in the presence and absence of RA were examined,. RAR gamma1 mRNA was detected in 3T3-L1 cells but was not affected by RA treatment, however. RAR gamma2 mRNA was strongly induced by RA.