PDCD4 and hepatocellular carcinoma: Zhu et al. found that miR-21 was up-regulated in HCC cells and tissues, which was associated with the capacity of cancer cell migration and invasion in HCC, where the miR-21 expression was inversely correlated with the protein expression of its targeted gene, programmed cell death 4 (PDCD4) and signaling molecules of its downstream pathway [13].