Abstract
CD98, also known as SLC3A2, is a multifunctional cell surface molecule consisting of amino acid transporters. CD98 is ubiquitously expressed in many types of tissues, but expressed at higher levels in cancerous tissues than in normal tissues. CD98 is also upregulated in most hepatocellular carcinoma (HCC) patients; however, the function of CD98 in HCC cells has been little studied. In this study, we generated a panel of monoclonal antibodies (MAbs) against surface proteins on human embryonic stem cells (hESCs). NPB15, one of the MAbs, bound to hESCs and various cancer cells, including HCC cells and non-small cell lung carcinoma (NSCLC) cells, but not to peripheral blood mononuclear cells (PBMCs) and primary hepatocytes. Immunoprecipitation and mass spectrometry identified the target antigen of NPB15 as CD98. CD98 depletion decreased cell proliferation, clonogenic survival, and migration and induced apoptosis in HCC cells. In addition, CD98 depletion decreased the expression of cancer stem cell (CSC) markers in HCC cells. In tumorsphere cultures, the expression of CD98 interacting with NPB15 was significantly increased, as were known CSC markers. After cell sorting by NPB15, cells with high expression of CD98 (CD98-high) showed higher clonogenic survival than cells with low expression of CD98 (CD98-low) in HCC cells, suggesting CD98 as a potential CSC marker on HCC cells. The chimeric version of NPB15 was able to induce antibody-dependent cellular cytotoxicity (ADCC) against HCC cells in vitro. NPB15 injection showed antitumor activity in an HCC xenograft mouse model. The results suggest that NPB15 may be developed as a therapeutic antibody for HCC patients.