Carbonic anhydrase-related protein VIII increases invasiveness of non-small cell lung adenocarcinoma

Carbonic anhydrase-related protein VIII (CA-RP VIII) is believed to be an oncofetal antigen and is overexpressed in colorectal and non-small cell lung cancer. However, the pathobiological properties of CA-RP VIII in lung cancer remain unclear. In the present study, we examined ultrastructural changes caused by exogenous CA-RP VIII expression in a well-differentiated lung adenocarcinoma cell line, PC-9. Many vacuoles lined by cilia, sometimes large vacuoles pushing the nuclei to one side, were found in the cytoplasm of CA-RP VIII-expressing PC-9 cells, but not in control PC-9 cells. Moreover, signet-ring cells containing abundant intracytoplasmic mucin were often found among CA-RP VIII-expressing PC-9 cells, but rarely among control PC-9 cells. We subsequently examined CA-RP VIII expression in atypical adenomatous hyperplasia and early-stage lung adenocarcinoma (Stage Ia). Significant expression of CA-RP VIII was observed in invasive lung adenocarcinoma but not in noninvasive adenocarcinoma. Interestingly, CA-RP VIII was strongly expressed in signet-ring cell cancer and invasive mucinous adenocarcinoma components. CA-RP VIII also appeared to enhance the invasiveness of PC-9 cells in Matrigel invasion assay. The present findings suggest that CA-RP VIII expression in lung adenocarcinoma is related to cancer cell invasion.