Prostate-specific antigen triggers transformation of seminal α2-macroglobulin (α2-M) and its binding to α2-macroglobulin receptor/low-density lipoprotein receptor-related protein (α2-M-R/LRP) on human spermatozoa
✍ Scribed by Birkenmeier, Gerd; Usbeck, Elke; Schäfer, Angelika; Otto, Andreas; Glander, Hans-Jürgen
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 348 KB
- Volume
- 36
- Category
- Article
- ISSN
- 0270-4137
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✦ Synopsis
The aim of this study was to identify the proteolytic activity which triggers the transformation of human ␣2-macroglobulin (␣2-M) in seminal fluid and its binding to its receptor. METHODS. Measurement of the concentrations of total and transformed ␣2-M in seminal fluid was accomplished by ELISA. Zymography of seminal plasma was performed in SDSpolyacrylamide gels containing casein as proteolytic substrate. Rate electrophoresis, SDS-PAGE, and Western blotting were applied to study the complex formation of prostate-specific antigen (PSA) with ␣2-M. Ligand-binding analysis of sperm cells was performed using [ 125 I]labeled proteins. Detection of receptor on sperm cells was achieved by immunofluorescence. RESULTS. The mean concentration of total ␣2-M in a random collection of seminal plasma was 4.6 g/ml. On average, between 33-98% of the inhibitor was found to be transformed. Zymography of seminal plasma revealed a proteolytic activity which is associated with a 33-kDa protein identified as PSA. Its proteolytic activity could be inhibited by ␣2-M. Both purified PSA and seminal plasma were capable of transforming native ␣2-M. Binding of PSA to ␣2-M triggers the exposition of receptor binding sites in the inhibitor molecule, which causes binding of the complex to ␣2-M-R/LRP identified on spermatozoa. CONCLUSIONS. PSA, the main proteinase in seminal fluid, is responsible for the transformation of ␣2-M and for its binding to ␣2-M-R/LRP present on spermatozoa. The binding of ␣2-M-PSA complexes to the spermatozoa receptor may exert an impact on normal sperm-cell functions.