Alteration of the hormonal bioactivity of parathyroid hormone-related protein (PTHrP) as a result of limited proteolysis by prostate-specific antigen.
OBJECTIVE
To discover whether the proteolytic activity of prostate-specific antigen (PSA) affects the structure and function of parathyroid hormone-related protein (PTHrP), as both are abundant components of human seminal plasma.


METHODS
The ability of PTHrP to act as a substrate was studied by incubating a synthetic polypeptide, consisting of 34 amino acid residues of the amino-terminal domain of PTHrP, with purified PSA. The incubate was then analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, high-pressure liquid chromatography separation, amino-terminal peptide sequencing, and mass spectrometry. The physiologic effect of the proteolytic activity of PSA on PTHrP was studied by measuring any alteration in PTHrP (1-34)-induced elevation of cyclic adenosine monophosphate (cAMP) production by UMR-106 rat osteosarcoma cells in culture. All cell culture experiments were performed with PSA and PTHrP (1-34) at physiologic concentrations. RESULTS. Our data show that PSA proteolytically cleaves PTHrP (1-34) after either residue 22 or 23, generating three peptide fragments. Both cleavages occur carboxy terminally of a phenylalanine residue. The cAMP production in rat osteosarcoma cells, induced by the amino-terminal portion of PTHrP (1-34), as a result of its structural similarity with parathyroid hormone (PTH), was abated by PSA in a dose- and time-dependent fashion. In contrast, heat-inactivated PSA had no effect on cAMP production.


CONCLUSIONS
Our study demonstrates that PTHrP is a substrate for PSA. The cleavage of the amino-terminal portion of PTHrP completely disrupts its ability to interact with the PTH/PTHrP receptor and thus inhibits its PTH-like activity. The proteolytic processing of PTHrP by PSA may play an important role in the post-translational/post-secretional regulation of prostatic PTHrP activities, which are believed to include regulation of prostate growth and differentiation.
Iwamura
M
M
Department of Urology, University of Rochester Medical Center, New York, USA.
Hellman
J
J
Cockett
A T
AT
Lilja
H
H
Gershagen
S
S
D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D006801:Humans; D006868:Hydrolysis; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins / Q000378:metabolism*; D044162:Parathyroid Hormone-Related Protein; D017430:Prostate-Specific Antigen / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D051381:Rats
D009363:Neoplasm Proteins; C470121:PTHLH protein, human; D044162:Parathyroid Hormone-Related Protein; D011506:Proteins; D017430:Prostate-Specific Antigen