Presence and enzymatic activity of prostate-specific antigen in archival prostate cancer samples
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Patients with advanced prostate cancer frequently have a poor prognosis as a result of metastasis. The serum prostate-specific antigen (PSA) test is widely used for the diagnosis of prostate cancer. The enzymatic activity of PSA may be involved in the invasion of prostate cancer. We set out to determine the prevalent form of PSA in human prostate adenocarcinoma samples by ELISA and Western blot analysis and its enzymatic activity using a synthetic substrate S-2586 and fibronectin. Our results show that in serum from prostate cancer patients and in tumour homogenates, the prevalent form was PSA bound to alpha1-antichymotrypsin. All homogenates showed enzymatic activity towards a synthetic PSA substrate, whereas only five samples showed activity at 28 kDa towards fibronectin as determined by enzymography, which is most likely due to active PSA. Human prostate cancer LNCaP cells produced largely inactive PSA. In comparison, 22Rv1 cells produced 29-fold less PSA, but with high specific activity. Similarly, our results from the human prostate cancer tissue samples also show that free PSA appears to exist in diverse forms of very different specific activity. Since PSA, as a serine protease, may be involved in the invasion of prostate cancer, our results suggest that prostate cancers have potentially diverse invasive capacity due to differences in specific enzymatic activity of PSA.