Expression of Aggrus/podoplanin in bladder cancer and its role in pulmonary metastasis.

Platelet aggregation-inducing factor Aggrus, also known as podoplanin, is associated with tumor malignancy by promoting hematogenous metastasis. Aggrus overexpression has been reported in some tumor tissues including lung, esophagus, head and neck and brain. We here found the frequent upregulation of aggrus mRNA in urinary bladder cancers using cancer tissue panels from various organs. Immunohistochemical analysis confirmed Aggrus protein expression in urinary bladder cancers and suggested a positive correlation between Aggrus expression and metastatic tendency in bladder cancers. Endogenous expression of Aggrus protein on the cell surface was found in the mouse bladder cancer MBT-2 cell line and human bladder cancer SCaBER cell lines. Knockdown of Aggrus expression in MBT-2 cells decreased their ability to induce platelet aggregation and form pulmonary metastasis in syngeneic mouse models. Knockdown of Aggrus expression in the human bladder cancer SCaBER cells also attenuated their ability to induce platelet aggregation and form pulmonary metastasis in mice. Moreover, pulmonary metastasis of SCaBER cells was prevented by prior administration of our generated anti-Aggrus neutralizing monoclonal antibodies by attenuating their retention in lung. These results indicate that Aggrus plays an important role in bladder cancer metastasis. Thus, anti-Aggrus neutralizing antibodies would be useful for the prevention of hematogenous metastasis of Aggrus-positive bladder cancer.