Expression of estrogen receptor α, retinoic acid receptor α and cellular retinoic acid binding protein II genes is coordinately regulated in human breast cancer cells

Human breast cancer cell lines expressing the estrogen receptor alpha (ER alpha), all-trans-retinoic acid (ATRA) receptor alpha (RAR alpha) and cellular retinoic acid binding protein II (CRABPII) genes are sensitive to ATRA-mediated growth inhibition. To study the relationship among ER alpha, RAR alpha and CRABPII expression, the protein levels of each member were compared in five breast cancer cell lines (T47D, MCF-7, ZR-75-1, Hs587T and MDA-MB-231 cells) and two immortalized nontumorigenic breast epithelial cell lines (MTSV1.7 and MCF-10A). ER alpha, RAR alpha and CRABPII proteins were detected in T47D, MCF-7 and ZR-75-1 cells but not in other tested cell lines. RAR alpha and CRABPII proteins were either reduced or undetectable in T47D/C4:2W and MCF-7/ADR cells with lost expression of ER alpha. Estradiol increased and antiestrogens (tamoxifen and ICI 164,384) downregulated the expression of both RAR alpha and CRABPII proteins in T47D and MCF-7 cells. RAR alpha antagonist Ro-41-5253 inhibited CRABPII expression, but not RAR alpha expression in estradiol-treated T47D and MCF-7 cells. Suppression of ER alpha by small interfering RNA (siRNA) reduced RAR alpha and CRABPII gene expression and siRNA suppression of RAR alpha reduced CRABPII expression while having no effect on ER alpha in T47D cells. Transient transfection of either RAR alpha or ER alpha expression vectors increased CRABPII expression in MDA-MB-231 cells but only RAR alpha, not ER alpha, activated hCRABPII promoter reporter. These results indicate that there is a gene activation pathway in which ERa drives RAR alpha transcription and RAR alpha drives CRABPII transcription in ER alpha-positive human breast cancer cells.