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

Abstract
We investigated expression levels of Na+,K+‐ATPase α‐isoforms and their ATPase activities in human colorectal cancer tissue and the accompanying normal mucosa. A decrease in expression of the α1‐isoform protein was observed in all sampled cancer tissues compared with the normal mucosae. The level of ouabain (5 μM)‐sensitive Na+,K+‐ATPase activity in carcinomas was 81±5% that of in the normal mucosae. The mRNA expression of α2‐ and α4‐isoforms was decreased in almost all the carcinoma samples. Interestingly, the expression level of the α3‐isoform protein in the cancer tissue was higher than that of the normal mucosa. These results indicate that a decrease in the α1‐isoform expression and an increase in the α3‐isoform expression may be associated with colorectal cancer.