The RNA-binding protein HuR regulates GATA3 mRNA stability in human breast cancer cell lines

Meta-analyses of microarray data indicate that GATA3 is co-expressed with estrogen receptor alpha (ER) in breast cancer cells. While the significance of this remains unclear, it is thought that GATA3 may serve as a prognostic indicator in breast tumors and may play a role in ER signaling. Recently, reciprocal regulation of GATA3 and ER transcription was demonstrated, suggesting that control of their expression is intertwined. We sought to determine whether GATA3 and ER expression was also coordinately regulated at other levels. Unlike ER, GATA3 was not under epigenetic control and was not re-expressed in the presence of DNMT or HDAC inhibitors in ER/GATA3-negative cells. However, like ER, these inhibitors decreased GATA3 expression in ER/GATA3-positive cell lines. We have previously reported that ER mRNA stability is increased through binding of the RNA-binding protein HuR/ELAV1 to the 3untranslated region (UTR) and that DNMT and HDAC inhibitors reduce ER expression by altering this interaction. Biotin pull-down assays using a biotinylated GATA3 RNA probe confirmed that HuR also binds to the GATA3 3UTR. Inhibition of HuR using siRNA probes decreased GATA3 mRNA, mRNA stability and protein expression, indicating that HuR plays a role in regulating GATA3 expression. Inhibition of either HuR or GATA3 reduced cell growth of MCF7 cells. Based on our findings, it is clear that coordinate regulation of ER and GATA3 occurs, however differences do exist. These findings may aid in identification of new targets that control cell growth of breast cancer cells.