Differential expression of cytoplasmic carbonic anhydrases, CA I and II, and membrane-associated isozymes, CA IX and XII, in normal mucosa of large intestine and in colorectal tumors

This study compares the localization of carbonic anhydrase isozymes (CA) I and II and that of IX and XII in normal large intestine and in colorectal t umors. Immunohistochemical studies were performed on 69 colorectal lesions. While the normal mucosa of the large intestine showed high expression for CA I and II, the intensity of the immunostaining for both isozymes decrease d in benign lesions and was very weak in malignant tumors. The reciprocal p attern of expression observed for these cytoplasmic isozymes and transmembr ane CA IX and XII in intestinal tissue specimens supports the suggestion th at CA IX and XII may be functionally involved in tumor progression to malig nancy and/or in invasion. By contrast, while CA I and II are prominent in n ormal colorectal mucosa, where they play a role in regulation of pH homeost asis and water and ion transport, loss of expression of these cytoplasmic i sozymes consistently accompanies progression to malignant transformation.