549 BLADDER CANCER CELLS EVADE NK CELL IMMUNITY BY USING CELL-SURFACE O-GLYCANS

Abstract

INTRODUCTION AND OBJECTIVES: To explore the detailed molecular mechanisms underlying bladder cancer metastasis, we focused on the role of cell-surface carbohydrates. We immunohistochemically analyzed paraffin-embedded bladder cancer specimens for the expression of a glycosyltransferase, core2 -1,6-N-acetylglucosminyltransferase (C2GnT) which forms core2 branch on O-glycans (A). We discovered that C2GnT expression was closely related with highly metastatic phenotypes of bladder cancer and that C2GnT-expressing cancer cells possessed high ability to evade NK cell immunity. We then aimed to elucidate their evasion mechanisms. There are two major ways of NK attacking cancer cells. Cancer cell-expressing ligands bind NK-activating receptors, thereby activating NK cells to attack cancer cells. NK cell-expressing ligands such as TNF-related apoptosis inducing ligand (TRAIL) bind death receptors in tumor cells, thereby inducing apoptosis of tumor cells. An NK-activating receptor, natural killer group 2 member D (NKG2D) and TRAIL play a major role in tumor rejection (B). METHODS: A primary ligand for NKG2D in cancer cells is MHC class I-related chain A (MICA). We analyzed O-glycans of MICA and MUC1 (a cancer cell-surface major mucin) by Western blotting and lectin column chromatography. We then examined the roles of Oglycans in evasion from NK cell immunity by tumor formation assay and cytotoxicity assay. RESULTS: In C2GnT-expressing cancer cells, poly N-acetyllactosamine was present on core2 O-glycans on MICA and MUC1, and galectin-3 bound MICA and MUC1 through this poly N-acetyllactosamine. We discovered that C2GnT-expressing bladder cancer cells took two different strategies to evade NK cell attack. One is that modification of MICA with poly N-acetyllactosamine and galectin-3 reduces the affinity of MICA for NKG2D, thereby severely impairing NK cell activation (C) (Tsuboi, S. et al. 2011 EMBO J 30:3173-3185). Another one is that modification of MUC1 with poly N-acetyllactosamine and galectin-3 reduces the accessibility of NK cells to the cancer cell surface, thereby shielding cancer cells from NK cell attack by TRAIL (D). CONCLUSIONS: The immunoevasion mechanisms using core2 O-glycans (C and D) allow bladder cancer cells to survive longer in the circulation, resulting in metastasis. Source of Funding: None