(A) ERα 3′ UTRs is a target of miR-222-3p. P3′UTR-ERα luciferase constructs, containing a wild type or mutated type ERα 3′ UTRs, were transfected into RL95-2 cells. Relative repression of firefly luciferase expression was standardized to a transfection control. The reporter assays were performed three times with essentially identical results. (B and C) MiR-222-3p and ERα levels were analyzed by qRT–PCR and western blot method, respectively. ERα levels decreased when miR-222-3p was upregulated in response to the miR-222m in RL95-2 cells, whereas the reverse was observed for ERα expression when miR-222-3p was knocked down in AN3CA cells. (D) The expression of pS2, cyclin D1 and PR was down regulated after miR-222m transfection in RL95-2 cell lines. Oppositely, in AN3CA cells, these ERα downstream genes were increased with miR-222-3p dampened. * P<0.05, ** P<0.01, *** P<0.001, **** P<0.0001.