Nm23-H1 expression of metastatic tumors in the lymph nodes is a prognostic indicator of oral squamous cell carcinoma

We recently reported that low Nm23-H1 expression of primary oral squamous cell carcinoma (OSCC) was correlated with the occurrence of lymphatic metastasis. However, little is known about whether Nm23-H1 level of metastatic tumors in the cervical lymph nodes is reduced in comparison with primary oral cancers and its significance for patients' prognosis. By immunohistochemistry, we analyzed the Nm23-H1 expression in 52 pairs of OSCC specimens from primary oral cancers and their metastatic lymph nodes. Western blot analysis further confirmed the immunohistochemical interpretation. To verify the effects of Nm23-H1 on cell migration and invasion, we established several stable clones derived from a human OSCC cell line (SAS) by knockdown and overexpression. Wound-healing closure, transwell migration and invasion assays were performed to determine cell motility, migratory and invasive activities. Western blot analysis was carried out to evaluate cyclin A expression of OSCC cells with the altered Nm23-H1 levels following knockdown and overexpression. By immunohistochemistry, Nm23-H1 expression of metastatic lymph nodes was significantly lower than that of their primary oral cancers, supporting a role of Nm23-H1 in metastasis suppression. Negative Nm23-H1 interpretation of OSCC specimens, in either primary oral cancers or metastatic lymph nodes, indicated a poor survival outcome of patients. On the basis of in vitro studies of Nm23-H1 knockdown and overexpression, we demonstrated an inverse correlation between Nm23-H1 expression and the invasiveness of OSCC cells. Moreover, we observed the concomitant reduction in Nm23-H1 and cyclin A levels of metastatic tumors in both results of in vitro OSCC cells and ex vivo tumor specimens.