Abstract 454: ADAM proteases shed UL-16-binding protein 2 in human lung cancer cell lines.

Abstract

Abstract NKG2D is an activating receptor that is expressed in immune effector cells, and the ligands for which are expressed in transformed cells. NKG2D-NKG2D ligand system might play an essential role in the tumor immunity of host cells. We have previously reported that a member of NKG2D ligand family, UL-16-binding protein 2 (ULBP2), is predominantly expressed on the surface of lung cancer cells, and is shed and solubilized into the sera of the lung cancer patients. In addition, we showed that the soluble form of ULBP2 (sULBP2) aggravates the cytotoxicity of host immune effector cells. Therefore, shedding of ULBP2 from the surface of cancer cells might be a critical component of the immune escape mechanisms employed in lung cancer. In this study, we investigated the mechanism of ULBP2 shedding from the cell surfaces in human lung cancer cell lines. First, we compared the amount of ULBP2 expression on the surface of normal cells and that in the culture medium of various lung cancer cell lines. We observed a significant correlation among non-small-cell lung cancer (NSCLC) cell lines (r=0.835, P<0.01), but not small-cell lung cancer (SCLC) cell lines (r=-0.154). These observations suggest that the ULBP2 shed in the culture medium is proportional to the level of its cell surface expression by NSCLC cell lines, but this does not apply in case of SCLC cell lines. Next, we examined the expression levels and activation status of A Disintegrin and Metalloproteinase (ADAM) families in the cell lines as candidates that execute the shedding of ULBP2 proteases. We found that ADAM17 was abundantly expressed and activated in NSCLC cell lines, but not in SCLC cell lines. Finally, we directly confirmed the shedding of ULBP2 by the enzyme ADAM metallopeptidase domain 17 (ADAM17) by using gene silencing and overexpression of ADAM17 in NSCLC and SCLC cell lines, respectively. Our data indicated that the expression of ADAM17 is a crucial determining factor in the heterogeneous shedding of ULBP2, which is observed in the lung cancer cell lines. ULBP2 shedding, and the resultant sULBP2 formation, is one of the determining factors of host tumor cell immunity; hence, developing a form of intervention to act on the shedding step by using ADAM protease inhibitors would be a promising and novel immunomodulatory therapy. Citation Format: Kosuke Yamaguchi, Hiroki Hikumi, Shinji Matsumaga, Miyako Takata, Naoki Kinoshita, Kiyoshi Hashimoto, Masaki Nakamoto, Jun Kurai, Masanari Watanabe, Akira Yamasaki, Tadashi Igishi, Naoto Burioka, Eiji Shimizu. ADAM proteases shed UL-16-binding protein 2 in human lung cancer cell lines. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 454. doi:10.1158/1538-7445.AM2013-454