PDCD4 and neoplasm: Additional research demonstrated that miR-21 could down-regulate the expression of putative tumor-suppressive genes, such as programmed cell death 4 (PDCD4)14, phosphatase and tensin (PTEN)15, maspin16, NFIB17, etc. Our previous study revealed that miR-21 enhanced stretch-induced osteogenic differentiation in human periodontal ligament stem cells (hPDLSCs)18.