Studies using chromatin immunoprecipitation and RNA mimicking reveal that miR-423-5p decreases RNA polymerase II occupancy and increases histone H3 lysine 9 dimethylation (H3K9me2) at the progesterone receptor (PR) promoter of human breast cancer cells, indicating a chromatin-level silencing mechanism for the regulation of expression of PR, which mediates endocrinal effects in the development of the mammary gland and breast cancer [97]. This evidence concerns the gene PGR and breast carcinoma.