Expression of carbonic anhydrase-related protein CA-RP VIII in non-small cell lung cancer

Carbonic anhydrase-related protein (CA-RP VIII) lacks a Zn-binding motif which is essential for carbonic anhydrase activity. Therefore, CA-RP VIII is believed to have a no catalytic activity and a new biological property. In the present study, CA-RP VIII expression in non-tumorous lung and non-small cell lung carcinomas was investigated. Little or no expression of CA-RP VIII was observed in human lungs by Northern-blot analysis. Reverse-transcription polymerase chain reaction analysis demonstrated CA-RP VIII mRNA in developing human lungs and, to a lesser extent, in normal lungs. Subsequent immunohistochemical staining revealed that CA-RP VIII was expressed in the pulmonary epithelium in developing lungs; however, CA-RP VIII expression was restricted in bronchial ciliated cells in adult lungs. Neither bronchial gland nor squamous metaplasia of interstitial pneumonia expressed CA-RP VIII. In contrast, CA-RP VIII was strongly expressed in almost all archival lung cancer specimens, which included 24 squamous cell carcinomas, 25 adenocarcinomas, and 6 adenosquamous cell carcinomas. Cancer cells at the front of tumor progression expressed CA-RP VIII in particular abundance. The present findings suggest that CA-RP VIII may play a role in non-small lung cell carcinomas.