P4HA1 and prostate carcinoma: Next, to determine whether miR-124 represses P4HA1 expression, we treated prostate cancer cells with precursor miRs, miR-124 as well as other miRs such as miR-23a, 23b, 29a, 29b, 29c, 122, and 499a and measured P4HA1 protein levels.