N-myc downstream-regulated gene 1 downregulates cell proliferation, invasiveness, and tumorigenesis in human oral squamous cell carcinoma.

Oral squamous cell carcinoma (OSCC) is the most common phenotype of oral cancer. N-myc downstream regulated gene 1 (NDRG1) is a modulator for cell proliferation, differentiation, and invasion. The role and function of NDRG1 in OSCC cells remain inconclusive. The (3)H-thymidine incorporation and in vitro matrigel invasion assays revealed NDRG1-knockdown significantly enhanced OSCC cell proliferation and invasion. Overexpressed NDRG1 arrested the cell cycle at the S-phase, thus attenuated cell proliferation in OECM-1 cells. The NDRG1-knockdown enhanced tumorigenesis of OECM-1 cells in the xenograft animal model. Western-blot and zymographic assays revealed that NDRG1 downregulated the gelatinase activities and protein levels of metalloproteinase-2 (MMP-2) and metalloproteinase-9 (MMP-9). NDRG1 modulated epithelial-mesenchymal transition (EMT) through upregulation of the E-cadherin expression, but downregulation of the N-cadherin, Vimentin, Snail-1, and Slug. Immunofluorescence staining indicated knockdown of NDRG1 enhanced F-actin expression and polymerization. Our results indicated NDRG1 attenuated OSCC cell growth in vitro and in vivo. The downregulation of EMT, MMP-2, and MMP-9 may explain the role of anti-invasion of NDRG1 in human OSCC cells. The experiments recognize that NDRG1 is an antitumor gene in OSCC cells.