NUCLEAR-LOCALIZATION OF BRAIN-TYPE GLYCOGEN-PHOSPHORYLASE IN SOME GASTROINTESTINAL CARCINOMA

Our previous reports have demonstrated frequent and strong expression of glycogen phosphorylase (EC 2.4.1.1) activity mainly in the cytoplas m of gastric carcinoma. Although previous studies have suggested the p hosphorylase glycosyltransferase system to be in the nucleus from enzy me histochemical analyses, intranuclear localization of the phosphoryl ase has not been fully established. The aims of the present study are to investigate the nuclear localization of glycogen phosphorylase and to identify the isoform of phosphorylase in the nucleus of gastrointes tinal carcinoma. The activity of glycogen phosphorylase in carcinoma c ells corresponding to the nucleus was demonstrated using enzyme cytoch emical analysis. The phosphorylase activity coincided with localizatio n revealed by immunocytochemistry using affinity-purified specific ant i-human brain-type glycogen phosphorylase antibody. The isoform expres sed in the nuclei of carcinoma cells was identified as being only the brain type according to a polymerase chain reaction-based assay using RNA obtained from gastric carcinoma cells and primers specific to musc le, liver and brain types of glycogen phosphorylase. The intranuclear localization of the brain-type isoform was confirmed by immunoelectron microscopical analyses. Further investigation to examine the nuclear localization in human carcinoma tissue (145 and 25 specimens with gast ric and colonic carcinoma respectively) was carried out by immunohisto chemistry using specific anti-brain-type antibody. Nuclear immunostain ing was observed in seven cases out of 145 gastric carcinoma. The pres ent study is the first to clarify the nuclear localization of glycogen phosphorylase with enzymatic activity in gastrointestinal carcinoma. The isoform of the enzyme expressed in the carcinoma was identified as the brain type. These results warrant further studies on the mechanis ms for transporting the large molecule of brain-type glycogen phosphor ylase to nuclei and its function in the nucleus of carcinoma cells. (C ) 1998 Chapman & Hall.