EXPRESSION OF THE RETINOIC ACID NUCLEAR RECEPTORS (RARS) AND RETINOID X-RECEPTOR (RXR) GENES IN ESTROGEN-RECEPTOR POSITIVE AND NEGATIVE BREAST-CANCER

Abstract

Retinoid inhibition of breast carcinoma growth correlates with the estrogen receptor (ER) positivity and elevated retinoic acid nuclear receptor (RARalpha) mRNA levels. We therefore examined retinoid nuclear receptor mRNA levels in patient breast carcinoma biopsy specimens to determine if such a correlation exists between ER positivity and RARalpha mRNA levels. We have now shown that RARalpha mRNA levels are significantly higher in ER positive samples. RARgamma mRNA is expressed at relatively high levels in a majority of the tumor samples independent of the ER-status while RARbeta mRNA was expressed at low levels in only one tumor sample. We also found high RXRalpha mRNA levels in all of the tumor samples examined while RXRgamma mRNA could not be detected. Our study demonstrates that RARalpha mRNA levels are either low or absent in ER-negative patient samples and that RARalpha levels may serve as a potential marker to determine patient responsiveness to RA therapy.