Abstract
Receptor-binding cancer antigen expressed on SiSo cells (RCAS1) is a type II membrane protein isolatedas a human tumor-associated antigen against a human uterine adenocarcinoma cell line, SiSo. RCAS1 acts asa ligand for a putative receptor present on immune cells such as T, B, and NK cells and inhibits the growth ofreceptor-expressing cells, further inducing apoptotic cell death. These observations suggest a role of RCAS1 in theimmune escape of tumor cells. Although a variety of cancer tissues have been screened and found to be positivefor RCAS1 expression, whether RCAS1 is expressed in head and neck cancer remains unclear. This study examinedwhether RCAS1 is expressed in adenoid cystic carcinoma (ACC) tissues or various cell lines (HSG, AZA1, AZA3, and HSY) derived from human salivary glands and whether tumor cells that express RCAS1 induce apoptosisof its receptor-positive cells, peripheral blood lymphocytes (PBLs). RCAS1 transcripts and proteins weredetected in 4 cell lines. Immunohistochemical examinations revealed that RCAS1 was slightly to moderately positivein 11 of 13 cases (84.6 %) of ACC. Confocal laser microscopy showed that PBLs stimulated with interleukin (IL)-2 undergo apoptosis by co-culturing with HSG or HSY cells. Our results of TUNEL showed that apoptotictumor-infiltrating lymphocytes were distinctly observed around RCAS1-positive tumor cells in ACC tissues. Theseresults suggest that RCAS1 expression might be associated with the progression of salivary gland tumors and apossible mechanism for oral cancer immune escape.
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