Analysis of prostatic fluid: evidence for the presence of a prospective marker for prostatic cancer.

In an endeavor to identify marker(s) for prostatic cancer, proteins in prostatic fluids were analyzed by two-dimensional (2-D) gel electrophoresis. The fluids were obtained from five males who had no prostate lesions and five patients each with benign prostatic hyperplasia (BPH) and prostatic carcinoma (PCA). The specimens were collected directly over a mixture of protease inhibitors and centrifuged, and the supernatants were lyophilized and solubilized in sodium dodecyl sulfate mix. Identical amounts of proteins were pooled according to donors' prostate disease and the resulting samples were subjected to 2-D gel analysis employing the ISO-DALT system. The electrophoretograms were developed by silver or double stain. The samples of each group exhibited distinctive profiles with the exception of similar relative positions of major protein spots. A predominant protein occurring as several charge variants was consistently present in prostatic fluids of patients with PCA. This protein appeared to be a previously unknown constituent that we have called protein D (molecular weight approximately 22 kDa and isoelectric point approximately 4), and was undetectable in the fluids of "normal" men and patients with BPH. An analysis of pooled, unprocessed urine from PCA patients revealed that perhaps this protein is excreted in urine in very low quantities. These results strongly suggest that the potential of this protein as a marker for prostatic cancer should be further explored.