Identification of novel LRH-1 target genes in breast cancer cells (#71)
The orphan receptor Liver Receptor Homologue-1 (LRH-1) has roles in development, bile-acid homeostasis and steroidogenesis. It also promotes tumourigenesis in gastric, colon, pancreatic and breast cancer. In breast cancer epithelial cells LRH-1 stimulates cell proliferation while in the tumour associated stroma it is critical in increasing local estrogen production by activating expression of the aromatase (CYP19A1) gene. Our previous expression profiling of breast cancer cells identified the heterogeneous ribonucleoprotein hnRNPs as potential LRH-1 target genes. Here, we aimed to determine the effects of LRH-1 and hnRNPs on breast cancer cell proliferation and invasiveness. Expression of LRH-1 and/or hnRNPA1 was knocked down in MDA-MB-231 breast cancer cells. Cy-Quant assay and wound healing assay were performed to assess the cell proliferation and invasiveness. To understand the potential mechanism of LRH-1 and hnRNPs on cell proliferation, mRNA levels of pyruvate kinase isoform I and II were measured using real time PCR. Silencing LRH-1 resulted in a 50% (p<0.01) decrease in cell proliferation and a 20% reduction in cell invasiveness, compared to cells transfected with control shRNA. Silencing hnRNPA1 led to a 25% (p<0.01) decrease cell proliferation. When both LRH-1 and hnRNPA1 were knocked down, cell proliferation was reduced by 30% (p<0.01). We also detected a shift in pyruvate kinase isoform expression from type II to type I in LRH-1 and hnRNPA1 knockdown cells (60% and 30% reduced respectively, p<0.01). The actions of LRH-1 in breast cancer progression are poorly understood. Here we identified hnRNPA1 and hnRNPA2/B1 as novel LRH-1 target genes. Inhibition of LRH-1 and hnRNPA1 expression decreases cell proliferation and invasiveness in breast cancer cells. Although the underlying mechanism for this regulation is not clear, our data suggest that a metabolic pathway switch through pyruvate kinase isoform expression may be involved.