Mono-(adenosine 5'-diphosphate) (ADP)-ribosylation, which transfers an
ADP-ribose from
nicotinamide adenine dinucleotide (
NAD) to an acceptor
protein, is an important post-translational modification of cellular
proteins. Several
bacterial toxins are known to possess the
mono-ADP-ribosyltransferase activity to catalyze this reaction as a possible pathogenic factor. Therefore, the aim of this study was to examine whether H. pylori may also induce mono-ADP-ribosylation in a human gastric mucosal
protein in association with
gastric cancer development. Tumorous and adjacent non-tumorous mucosal tissue specimens were obtained from the surgically removed stomachs of 5 patients with gastric
adenocarcinoma, and then were homogenized into cytosolic and membranous fractions. Each homogenate or an H. pylori extract was assayed for mono-ADP-ribosylation with [adenylate-(32)P]-
NAD and
3-aminobenzamide, a potent inhibitor of poly-ADP-ribosylation. The radiolabeled
proteins were separated by
sodium dodecylsulfate-
polyacrylamide gel electrophoresis followed by radio-image analysis. In the extracts from H. pylori, a strain-dependent, endogenous radiolabeling of 70-kDa
protein was detected. An assay of the membranous fractions from 5 gastric
adenocarcinomas with the extract of OMH4, a clinical H. pylori isolate, revealed notable radiolabelings of 55- and 45-kDa
proteins, which were not found without the OMH4 extract. In contrast, the radiolabelings were minimal in the membranous fractions from respective non-tumorous mucosae, and they were not detected in any of the examined cytosolic fractions. All three radiolabelings of 70-, 55-, and 45-kDa
proteins were dependent on
NAD, but not on
ADP-ribose.
Snake venom phosphodiesterase digestion of the 3 radiolabeled
proteins released only
AMP. We thus found that H. pylori had an enzymatic
mono-ADP-ribosyltransferase activity which enabled it to modify the 55- and 45-kDa membranous
proteins of human gastric
adenocarcinoma, as well as the 70-kDa
protein of H. pylori itself. The possible roles underlying our observations on
carcinogenesis or development of human gastric
carcinoma are yet to be elucidated.