Some miRNAs target the messenger RNAs for DNA methyltransferase genes DNMT1, DNMT3A and DNMT3B, whose gene products are needed for initiating and stabilizing promoter methylations.  As summarized in three reviews, miRNAs miR-29a, miR-29b and miR-29c target DNMT3A and DNMT3B; miR-148a and miR-148b target DNMT3B; and miR-152 and miR-301 target DNMT1.  In addition, miR-34b targets DNMT1 and the promoter of miR-34b itself is hypermethylated and under-expressed in the majority of prostate cancers.  When expression of these microRNAs is altered, they may also be a source of the hyper/hypo-methylation of the promoters of protein-coding genes in cancers.