Actually, miR-421 overexpression by transient transfection suppressed ATM protein expression in both LNCaP and C4–2 cells (Fig. 3d), suggesting that miR-421 negatively regulates ATM expression in both androgen-dependent and -independent prostate cancer cells, and N-Myc -induced ATM up-regulation in C4–2 cells is caused by down-regulation of miR-421 and de-repression of ATM expression. This evidence concerns the gene MYCN and Familial prostate cancer.