after 2008, micrornas (mirnas) were identified as new players in regulating the expression of p-gp in both transcriptional and post-transcriptional levels. some mirnas decrease the expression of p-gp. for example, mir-200c down-regulates the expression of p-gp through the jnk signaling pathway or zeb1 and zeb2; mir-145 down-regulates the mrna of p-gp by directly binding to the 3'-utr of the gene of p-gp and thus suppresses the translation of p-gp. some other mirnas increase the expression of p-gp. for example, mir-27a up-regulates p-gp expression by suppressing the raf kinase inhibitor protein (rkip); alternatively, mir-27a can also directly bind to the promoter of the p-gp gene, which works in a similar way with the mechanism of action of transcriptional factors.