Extraribosomal function of metallopanstimulin-1: reducing paxillin in head and neck squamous cell carcinoma and inhibiting tumor growth.

Metallopanstimulin-1 (MPS-1) is a multifunctional ribosomal protein RPS27 that contains a zinc finger domain of the C(4) type. MPS-1 has been found to be increased in the sera of a number of different cancers, including head and neck squamous cell carcinoma (HNSCC). However, little is known about the effect of a high-level MPS-1 in regulating cancer cell behavior. In this study, we overexpressed MPS-1 protein in the HNSCC cell line UMSCC-1. We found MPS-1 distributes not only in the cytosol, but also in the nuclei. In addition, MPS-1 is secreted into the culture medium. In vitro and in vivo experiments show that growth of UMSCC-1 cells transfected with MPS-1 is dramatically inhibited. Moreover, we also found that with overexpressing MPS-1, UMSCC-1 cells were arrested on G0/G1 phase, cell proliferation rate was reduced, and tumor angiogenesis was impaired. Further gene array analysis, immunohistochemistry staining and Western blotting reveal that MPS-1 reduces paxillin mRNA and protein levels in UMSCC-1 cells both in vitro and in vivo. Together, these data indicate that when MPS-1 is overexpressed, it has an extraribosomal function as a strong inhibitor of HNSCC tumor cell growth, which may be exerted by reduced paxillin gene expression.