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 n umber of nuclear retinoid receptors, including RAR alpha, beta and gam ma, and RX R alpha, beta and gamma. RAR alpha, RAR gamma, RXR alpha an d 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. Tr eatment of 3T3-L1 cells with 1 muM RA led to a 4-5-fold increase in th e RAR gamma mRNA level, but only a trace amount of RAR beta mRNA was d etected. RAR MRNA expression was rapidly (within 2 h) induced by physi ological concentrations of RA in a dose-dependent manner. The response of RAR gamma mRNA expression to RA was reversible; rapid disappearanc e of RAR gamma mRNA occurred on RA removal. In addition. the induction of RAR gamma expression did not require de novo protein synthesis. hu t 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 absenc e of RA were examined,. RAR gamma1 mRNA was detected in 3T3-L1 cells b ut was not affected by RA treatment, however. RAR gamma2 mRNA was stro ngly induced by RA.