Adenosine A(2b) receptor is highly expressed in human hepatocellular carcinoma

High levels of adenosine accumulate in hypoxic tissues during the rapid growth of tumors, suggesting activation of adenosine receptors may facilitate tumor progress. The relevance of adenosine receptors to hepatocellular carcinoma (HCC), in particular the adenosine A(2b) receptor (A(2b)), is not yet fully understood. The aim of this study was to assess whether A(2b) was differentially expressed in normal and cancerous tissues and evaluate the clinicopathological correlation of A(2b) level in HCC. Expression of A(2b) in tumor cells was investigated by immunohistochemical staining. Protein analysis was done by Western blotting and evaluation of A(2b) mRNA expression levels utilized quantitative real-time PCR analysis of tissue samples of 64 hepatocellular carcinomas and in their paired adjacent normal tissues. Western blot data suggested that A(2b) was expressed predominantly in the cell membrane and cytoplasm of tumor cells and that the intensity of A(2b) protein expression was consistently higher in HCC than in adjacent normal tissues. Levels of A(2b) mRNA in HCC were significantly higher than in adjacent tissues, as measured by real-time PCR (P<0.001). With regard to venous invasion, satellite lesions and advanced pathologic Tumor-Node-Metastasis (pTNM) stage, the A(2b) level tended to be higher than that seen in negative cases (P<0.05). Our findings demonstrate that A(2b) expression is up-regulated in HCC, the expression level of A(2b) is correlated to tumor progression in HCC, and suggest that A(2b) may be a novel target for HCC therapeutic strategy.