Li Q, et al. - Researchers investigated the role of ribosomal protein S6 kinase 4 (RSK4) in estrogen-induced breast cancer development and its underlying mechanism. They performed immunohistochemistry, RT-PCR and Western blotting to determine the expressions of estrogen receptor (ER) and RSK4. Using bisulfite genomic sequencing, they assessed the methylation of RSK4 promoter. They used Western blotting to test the expressions of methyltransferases, such as DNMT1, DNMT3A and DNMT3B. ER positive (ER+) breast cancer tissues and MCF-7 cells exhibited significantly elevated ER expression and RSK4 methylation, but RSK4 expression was attenuated. According to the findings, estrogen acts as a promotor of the progression of breast cancer via methylation-mediated RSK4 inactivation in ER+ breast cancer. A new target for the treatment of ER+ breast cancer might be offered by this investigation.