HDAC4 and breast cancer: miR-22-3p has a dual role in re-sensitizing fulvestrant (FUL)-resistant BC cells through a p21cip1-dependent mechanism, as it targets their transcriptional repressors forkhead box P1 (FOXP1) and Histone Deacetylase 4 (HDAC4), and also through p53 acetylation, leading to activation of p21cip1 [34].