Functional Roles of NYD-SP8 in Cancer Development and Progression

Cancer/testis (CT) antigens are encoded by genes that are normally expressed only in the human germ-line, but are also expressed in various tumor types. CT antigens are also being studied for their roles in carcinogenesis as well as for their potentials as targets for anti-cancer therapy. A novel CT gene, NYD-SP8, (Accession No. AY014285.1) has recently been identified. It is located to human chromosome 19q13.31 and encodes a 27 kDa glucosylphosphatidylinositol (GPI) anchored cell surface protein, which shows structural homology to urokinase plasminogen activator receptor (uPAR). This thesis describes the characterization and functional roles of NYD-SP8 involved in cancer development.;In the first set of experiments, the possible role(s) and underlying mechanism(s) of NYD-SP8 in regulating cell proliferation and apoptosis were investigated. Flow cytometric analysis, cell proliferation assay and Western blot analysis showed that NYD-SP8 promoted cell proliferation and protected cells against TNFalpha-induced apoptosis in Human embryonic kidney cells (HEK293) and human hepatocellular carcinoma cells (hHCC). In vitro studies showed that NYD-SP8 enhanced anchorage-independent growth of hHCC, further suggesting the pro-survival effect of NYD-SP8. These data demonstrated important functions of NYD-SP8 in promoting cell growth and preventing apoptosis during cancer development.;In the second sets of experiments, the possible role(s) and underlying mechanism(s) of NYD-SP8 in regulating cancer invasion and metastasis were investigated. The results showed that NYD-SP8 could suppress multiple "tumor associated" proteases. Overexpression of NYD-SP8 resulted in reducing activities of the three major classes of proteases known to be involved in ECM degradation, including uPA, matrix metalloproteinases (MMPs) and cathepsin B, leading to suppression of both in vitro and in vivo cancer cell invasion and metastasis. Co-immunoprecipitation experiments showed binding of NYD-SP8 to uPA/uPAR complexes and interfering with active uPA production. These data demonstrated an important function of NYD-5P8 in regulating ECM degradation, providing a novel mechanism that modulates uPA/uPAR signaling in the suppression of cancer progression.;In the last part of thesis, the involvement of NYD-SP8 in epithelial-mesenchymal transitions (EMTs) was demonstrated. Upon TGFbeta stimulation or TGFbeta/TNFalpha co-stimulation, the mRNA and protein expression of NYD-SP8 was decreased in LIM1863 cells. Cell adhesion assay showed that the attachment ability of hHCC-SP8 was lowered in laminin and fibronectin coated plate, suggesting the possible role of NYD-SP8 in affecting cell-matrix interaction. These data indicate that NYD-SP8 is involved in the EMTs process and may serve as potential EMTs markers during cancer development.;In summary, the present findings have demonstrated the roles of NYD-SP8 in multi-step cancer development. Further investigations of NYD-SP8 in cancer development may provide new insights and ground for potential use of CT antigens in anti-cancer therapy. (Abstract: 428 words)...