Up-regulation of Na+K+-ATPase α3-isoform and down-regulation of the α1-isoform in human colorectal cancer

We investigated expression levels of Na+,K+-ATPase alpha-isoforms and their ATPase activities in human colorectal cancer tissue and the accompanying normal mucosa. A decrease in expression of the alpha1-isoform protein was observed in all sampled cancer tissues compared with the normal mucosae. The level of ouabain (5 muM)-sensitive Na+,K+-ATPase activity in carcinomas was 81 +/- 5% that of in the normal mucosae. The mRNA expression of alpha2- and alpha4-isoforms was decreased in almost all the carcinoma samples. Interestingly, the expression level of the alpha3-isoform protein in the cancer tissue was higher than that of the normal mucosa. These results indicate that a decrease in the alpha1-isoform expression and an increase in the alpha3-isoform expression may be associated with colorectal cancer. (C) 2004 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.