Retinoic acids differentially regulate NOR-1 and its closely related orphan nuclear receptor genes in breast cancer cell line MCF-7.

NOR-1, NGFI-B, and Nurr1 are closely related orphan nuclear receptors implicated in diverse biological processes including cell growth and differentiation. We examined the effect of retinoic acids on the expression of these putative transcription factor genes in the breast cancer cell line MCF-7 by a quantitative reverse transcription and polymerase chain reaction. Both all-trans and 9-cis retinoic acids markedly induced NOR-1 mRNA and slightly increased Nurr1 mRNA. In contrast, NGFI-B mRNA was decreased. In the presence of cycloheximide, all-trans retinoic acid superinduced NOR-1 mRNA, whereas all-trans and 9-cis retinoic acids strongly suppressed the NGFI-B mRNA accumulation. The differential effects of retinoic acids on the expression of these genes are in contrast with the effects of forskolin and 12-O-tetradecanoylphorbol-13-acetate, both of which induced mRNAs of all three genes. These findings suggest that NOR-1, NGFI-B, and Nurr1 play distinct roles in the retinoic acid signaling in MCF-7 cells.