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