title: MHC class I expression protects rat colon carcinoma cells from hepatic natural killer cell-mediated apoptosis and cytolysis, by blocking the perforin/granzyme pathway.
abstract: BACKGROUND: Hepatic natural killer (NK) cells, the most cytotoxic cells of the natural occurring NK cells, are located in the liver sinusoids and are thus in a strategic position to kill arriving metastasising tumour cells, like colon carcinoma cells. It is known that major histocompatibility complex (MHC) class I on tumour cells negatively regulates NK cell-mediated cytolysis, but this is found using blood- or spleen-derived NK cells. Therefore, using isolated rat hepatic NK cells and the syngeneic colon carcinoma cell line CC531s, we investigated whether this protective role of MHC class I is also operative in hepatic NK cells, and addressed the mechanism of MHC class I protection. RESULTS: When MHC class I on CC531s cells was masked by preincubation with monoclonal antibody OX18, hepatic NK cell-mediated cytolysis (51Cr release) as well as apoptosis (DNA fragmentation, nucleus condensation and fragmentation) increased. When hepatic NK cells were preincubated with the granzyme inhibitor 3,4-dichloroisocoumarin, or when extracellular Ca2+ was chelated by ethylene glycol-bis(beta-aminoethyl ether)-N, N-tetraacetic acid, the enhanced cytolysis and apoptosis were completely inhibited. The involvement of the perforin/granzyme pathway was confirmed by showing that the enhanced cytolysis was caspase-independent. CONCLUSIONS: MHC class I expression protects CC531s colon carcinoma cells from hepatic NK cell-mediated apoptosis and cytolysis, by blocking the perforin/granzyme pathway.
authors.affiliation: Laboratory for Cell Biology and Histology, Vrije Universiteit Brussel (VUB), Laarbeeklaan 103, 1090 Brussels, Belgium. dvermijl@cyto.vub.ac.be
authors.forename: Dianzhong
authors.initials: D
authors.lastname: Luo
authors.forename: David
authors.initials: D
authors.lastname: Vermijlen
authors.forename: Peter JK
authors.initials: PJ
authors.lastname: Kuppen
authors.forename: Eddie
authors.initials: E
authors.lastname: Wisse