Differential Expression Patterns of <scp>SLCO</scp> Solute Carriers in Human Breast Cancer Cell Lines and Tumour Samples

The cellular uptake of nutrients essential for cell growth and survival is facilitated by solute carrier (SLC) transporters. Members of the SLCO subfamily of SLCs mediate the uptake of substrates relevant to breast cancer (BC), including steroid hormones and anticancer drugs. Accumulating evidence suggests that altered expression of these transporters may affect BC pathogenesis by influencing cell proliferation and anticancer drug resistance. In this study, we investigated differential expression of 11 SLCO transporters using semi-quantitative and quantitative PCR in MCF-7 and MDA-MB-231 BC cell lines and in human BC tissue samples. Eight SLCO transporters were expressed in at least one cell line. Of these, SLCO1B1 and SLCO1B3 showed higher expression in MDA-MB-231 than MCF-7 cells. Conversely, SLCO2A1, SLCO4C1 and SLCO5A1 showed higher expression in MCF-7 than MDA-MB-231 cells. Quantitative PCR analysis of 18 patients' BC tissue samples revealed variable expression of a number of SLCO transporters, regardless of patients having been treated with or without endocrine therapy prior to tumour excision. Proliferation and gene expression studies were conducted on the cell lines following exposure to β-estradiol, which stimulated cell proliferation in MCF-7 cells, as well as causing a significant increase in SLCO4C1 gene expression.