The expression of orphan nuclear receptor Liver Receptor Homolog-1 (LRH-1) is elevated in breast cancer and promotes proliferation, migration and invasion in vitro. LRH-1 expression is regulated by oestrogen (E-2), with LRH-1 mRNA transcript levels higher in oestrogen receptor alpha (ER alpha) positive (ER+) breast cancer cells compared to ER- cells. However, the presence of LRH-1 protein in ER- cells suggests discordance between mRNA transcript levels and protein expression. To understand this, we investigated the impact of mRNA and protein stability in determining LRH-1 protein levels in breast cancer cells. LRH-1 transcript levels were significantly higher in ER+ versus ER- breast cancer cells lines; however LRH-1 protein was expressed at similar levels. We found LRH-1 mRNA and protein was more stable in ER- compared to ER+ cell lines. The tumor-specific LRH-1 variant isoform, LRH-1v4, which is highly responsive to E-2, showed increased mRNA stability in ER- versus ER+ cells. In addition, in MCF-7 and T47-D cell lines, LRH-1 total mRNA stability was reduced with E-2 treatment, this effect mediated by ER alpha. Our data demonstrates that in ER- cells, increased mRNA and protein stability contribute to the abundant protein expression levels. Expression and immunolocalisation of LRH-1 in ER- cells as well as ER- tumors suggests a possible role in the development of ER- tumors. The modulation of LRH-1 bioactivity may therefore be beneficial as a treatment option in both ER- and ER+ breast cancer. (C) 2013 Elsevier Inc. All rights reserved.