Cytokine dependent inverse regulation of CD54 (ICAM1) and major histocompatibility complex class I antigens by nuclear factor κB in HEp2 tumor cell line: effect on the function of natural killer cells

Abstract

The aim of this study is to investigate the mechanisms by which elevated nuclear factor κB (NFκB) activity in HEp2 cells can modulate the function and survival of immune effector cells. Inhibition of NFκB functional activity by stable expression of IκB super-repressor rendered HEp2 cells (HEp2-IκB (S32AS36A)) susceptible to natural killer (NK) cell mediated cytotoxicity. Increase in surface ICAM1 expression was greater on HEp2-IκB (S32AS36A) cells than on the surface of vector alone transfected HEp2 cells when these cells were treated with IFN-γ. In contrast, tumor necrosis factor α (TNF-α) treatment augmented ICAM-1 expression on the surface of vector-alone transfected HEp2 cells and not on the HEp2-IκB (S32AS36A) cells. Moreover, synergistic augmentation of ICAM-1 by a combination of TNF-α and interferon-γ (IFN-γ) treatment was completely abrogated on the surface of HEp2-IκB (S32AS36A) cells. The addition of blocking antibody to ICAM-1 surface antigen partially inhibited the increased cytotxicity mediated by interleukin-2 treated NK cells against HEp2-IκB (S32AS36A) cells. In contrast to ICAM-1, the expression of major histocompatibility complex (MHC) class I antigens were downregulated when the function of nuclear NFκB was inhibited in HEp2 cells. The addition of IFN-γ to HEp2-κB (S32AS36A) cells increased the expression of MHC class I antigen and rendered these cells less susceptible to NK cell mediated cytotoxicity. Secretion of IFN-γ and granulocyte macrophage–colony-stimulating factor (GM-CSF) by NK cells was also significantly increased in the presence of HEp2-IκB (S32AS36A) cells, and the treatment of these tumor cells with IFN-γ prior to their addition to the cultures of NK cells decreased the released IFN-γ and GM-CSF by NK cells. However, the levels of NK cell mediated cytotoxicity and IFN-γ secretion remained significantly higher in the presence of both untreated and IFN-γ treated HEp2-IκB (S32AS36A) cells when compared with vector-alone transfected HEp2 cells. Thus, NFκB regulates inversely the expression of ICAM-1 and MHC class I antigens on HEp2 tumor cells and this may contribute to the resistance of these cells to NK cell mediated cytotoxicity.