Retinoid, Retinoic Acid Receptor β and Breast Cancer

Retinoids have been reported to inhibit the growth of several breast cancer cell lines in culture and to reduce breast tumor growth in animal models. Furthermore, retinoic acid (RA) can augment the action of other breast cancer cell growth inhibitors both in vitro and in vivo. Clinically, interest has increased in the potential use of retinoids for the prevention and treatment of human breast cancer. The regulation of cell growth and differentiation of normal, premalignant, and malignant cells by retinoids is mediated by the RA receptors (RARs) and retinoid X receptor. One of the target genes of retinoid receptors is RARβ2. A growing body of evidence supports the hypotheses that the RARβ2 gene is a tumor suppressor gene and the chemopreventive effects of retinoids are due to induction of RARβ2. RARβ2 expression is reduced in many malignant tumors including breast carcinoma. This paper will briefly discuss basic aspects of retinoids and retinoid acid receptor. In particular, we review what is now known for inactivation mechanism of RARβ2 and its role in tumor cell growth inhibition.