In our study, we investigated (i) whether miR-454-3p is able to regulate MED12 and/or AR expression, (ii) whether the inhibition of MED12 by siRNA or the overexpression of miR-454-3p has a functional effect on the viability of EnzR PCa cell lines and (iii) the effects of siMED12 and miR-454-3p on the expression of selected proteins (MED12, AR, AR-V7, and c-Myc) in EnzR PCa cell lines. The gene discussed is AR; the disease is posterior cortical atrophy.