We show that histone deacetylase (HDAC) inhibitors lead to functional expression of MHC class I–related chain A and B (MICA/B) on cancer cells, making them potent targets for natural killer (NK) cell–mediated killing through a NK group 2, member D (NKG2D) restricted mechanism. Blocking either apoptosis or oxidative stress caused by HDAC inhibitor treatment did not affect MICA/B expression, suggesting involvement of a separate signal pathway not directly coupled to induction of cell death. HDAC inhibitor treatment induced glycogen synthase kinase-3 (GSK-3) activity and down-regulation of GSK-3 by small interfering RNA or by different inhibitors showed that GSK-3 activity is essential for the induced MICA/B expression. We thus present evidence that cancer cells which survive the direct induction of cell death by HDAC inhibitors become targets for NKG2D-expressing cells like NK cells, γδ T cells, and CD8 T cells.

Background and aims: Expression of inducible nitric oxide synthase (iNOS) is greatly upregulated in the colonic mucosa of patients with collagenous and ulcerative colitis. As the transcription factor nuclear factor κB (NFκB) is a major inducer of iNOS gene expression, we compared activation and transcriptional activity of NFκB in colonic mucosal biopsies from these patients. Patients: Eight patients with collagenous colitis, six with relapsing ulcerative colitis, and eight with uninflamed bowel were studied. Methods: NFκB DNA binding activity was assessed by electrophoretic mobility shift assay and inhibitor of NFκB (IκB) kinase (IKK) activity by immunocomplex kinase assay. In vivo recruitment of NFκB to the iNOS promoter was determined by chromatin immunoprecipitation analysis and transcriptional activity by NFκB gene expression profiling arrays. Cells showing NFκB activation were identified by immunohistochemistry. Results: In collagenous and ulcerative colitis, as opposed to uninflamed bowel, IKKβ activity and strong NFκB DNA binding gave rise to activation of identical NFκB subunits and recruitment of transcriptionally active p65 to the iNOS promoter. In collagenous colitis, activated NFκB was observed only in epithelial cells while up to 10% of lamina propria macrophages showed activation in ulcerative colitis. Conclusions: In collagenous and ulcerative colitis, colonic mucosal NFκB is activated and recruited to the iNOS promoter in vivo via an IKKβ mediated pathway. As collagenous colitis is not associated with tissue injury, these data challenge the prevailing view that activation of NFκB per se mediates tissue injury. Our results suggest that downstream inflammatory reactions leading to tissue damage originate in lamina propria immune cells, as increased NFκB activity in collagenous colitis was localised solely in epithelial cells, but present also in macrophages in ulcerative colitis.

NKG2D ligand surface expression is important for immune recognition of stressed and neotransformed cells. In this study, we show that surface expression of MICA/B and other NKG2D ligands is dependent on N-linked glycosylation. The inhibitor of glycolysis and N-linked glycosylation, 2-deoxy-d-glucose (2DG), potently inhibited surface expression of MICA/B after histone deacetylase inhibitor treatment; the inhibition occurred posttranscriptionally without affecting MICA promoter activity. Transient overexpression of MICA surface expression was also inhibited by 2DG. 2DG blocks N-linked glycosylation of MICA/B by a reversible mechanism that can be alleviated by addition of d-mannose; this does not, however, affect the inhibition of glycolysis. Addition of d-mannose restored MICA/B surface expression after 2DG treatment. In addition, specific pharmacological or small interfering RNA-mediated targeting of glycolytic enzymes did not affect MICA/B surface expression, strongly suggesting that N-linked glycosylation, and not glycolysis, is essential for MICA/B surface expression. Corroborating this, tunicamycin, a selective inhibitor of N-linked glycosylation, abolished MICA/B surface expression without compromising activation of MICA promoter activity. NK cell-mediated killing assay and staining with a recombinant NKG2D–Fc fusion protein showed that all functional NKG2D ligands induced by histone deacetylase inhibitor treatment were abolished by 2DG treatment and fully reconstituted by further addition of d-mannose. Our data suggest that posttranslational N-linked glycosylation is strictly required for NKG2D ligand surface expression. Cancer and infection often result in aberrant glycosylation, which could likely be involved in modulation of NKG2D ligand expression. Our data further imply that chemotherapeutic use of 2DG may restrict NKG2D ligand surface expression and inhibit secretion of immunoinhibitory soluble NKG2D ligands.

Background: Superoxide (O₂⁻) generation through the activity of reduced nicotinamide dinucleotide (NADH) or reduced nicotinamide dinucleotide phosphate (NADPH) oxidases has been demonstrated in a variety of cell types, but not in human colonic epithelial cells. Aims: To measure O₂⁻ production and effects of modulators of NAD(P)H oxidase activity and inhibitors of potential O₂⁻ generating enzymes in cultures of human colonic epithelial cells. Expression of the catalytic subunits of NAD(P)H oxidase, Nox1 and gp91^phox (phox, phagocytic oxidase), and the membrane bound subunit p22^phox was assessed. Methods: The transformed colonic epithelial cell lines (DLD-1, HT-29, and Caco-2) were studied at subconfluence, confluence, and after differentiation. Primary colonic epithelial cells were isolated from mucosal biopsies from the normal human colon. Extracellular O₂⁻ production was measured by the cytochrome c reduction assay or luminol enhanced luminescence. Nox1, gp91^phox, and p22^phox mRNA expression was assessed in colonic epithelial cells and blood neutrophils by reverse transcriptase-polymerase chain reaction. Results: Production rates of O₂⁻ were higher in subconfluent transformed cells (mean (SEM) 35.8 (4.2) nmol/mg of protein/h) and primary cells (40.4 (5.9)) than in confluent transformed cells (6.0 (0.9); p<0.01). The oxidoreductase inhibitor diphenylene iodonium significantly inhibited O₂⁻ production whereas NADPH and NADH increased production rates. In contrast, O₂⁻ was unaffected by phorbol myristate ester, N^G-nitro-l-arginine methyl ester, indomethacin, or allopurinol. Nox1 mRNA was expressed in all colonic epithelial cells whereas gp91^phox was detected only in HT-29 cells and neutrophils. p22^phox was expressed in all cell types. Conclusions: Cultures of transformed and primary epithelial cells from human colon may produce extracellular O₂⁻ through an NAD(P)H oxidase expressing Nox1 and p22^phox.

BACKGROUND AND AIMS: Luminal nitric oxide (NO) is greatly increased in the colon of patients with collagenous and ulcerative colitis. To define the source and consequence of enhanced NO production we have studied expression of NO synthase (NOS) isoforms and nitrotyrosine in mucosal biopsies from these patients. In addition, effects on colonic fluid transfer caused by manipulating the substrate of NOS were studied in patients with collagenous colitis. PATIENTS: Eight patients with collagenous colitis, nine with active ulcerative colitis, and 10 with uninflamed bowel were included. METHODS: Expression of NOS isoforms was quantified by western blotting. Inducible NOS (iNOS) and nitrotyrosine were localised by immunohistochemistry. Modulation of NOS activity by topical N ^G -monomethyl- l -arginine ( l -NMMA) or l -arginine was assessed during perfusion of whole colon. Plasma and perfusate nitrite/nitrate (NO _x ) was measured by Griess' reaction. RESULTS: Both in collagenous and ulcerative colitis, expression of iNOS was 10 ² –10 ³ higher (p<0.001) than in uninflamed bowel and localised primarily to the epithelium. Endothelial NOS was evenly expressed in all groups while neuronal NOS was undetectable. Nitrotyrosine was markedly expressed in active ulcerative colitis but rarely detected in collagenous colitis and never in uninflamed bowel. In collagenous colitis, the output of NO _x was markedly increased compared with uninflamed bowel (283 (58) v <37 nmol/min; p<0.01) and fluid was net secreted. l -NMMA reduced the output of NO _x by 13–66% (95% confidence intervals) and secretion of fluid by 25–109% whereas l -arginine increased the output of NO _x by 3–39% and secretion of fluid by 15–93%. CONCLUSIONS: In collagenous colitis, as opposed to ulcerative colitis, upregulation of iNOS occurs in the absence of nitrotyrosine formation and mucosal damage. Excess generation of NO may be the primary cause of diarrhoea in this condition.