Activation of Prostate-Specific Antigen Precursor (pro-PSA) by Prostin, a Novel Human Prostatic Serine Protease Identified by Degenerate PCR,

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Abstract
A novel serine protease was found in human prostate by degenerate oligonucleotide PCR amplification and cloned. The zymogen form of this enzyme, named prostinogen, is composed of 240 amino acid residues with an amino-terminal propiece of 5 residues and a 235-residue mature enzyme. The transcript has a signal peptide of 15 amino acid residues. The mature enzyme has 41% sequence identity with prostate specific antigen (PSA). Prostinogen was expressed in Escherichia coli and refolded from inclusion bodies. The zymogen, with a molecular mass of 28 kDa, was readily activated by agarose-immobilized trypsin to generate prostin, a serine protease, which cleaves the chromogenic substrate (N-benzoyl-L-Ile-L-Glu-L-Gly-L-Arg-p-nitroaniline hydrochloride) (S-2222). Recombinant prostin readily activates the precursor of PSA (pro-PSA) by cleavage of the amino terminal Arg(7)-Ile(8) peptide bond. These results indicate that prostin may be a physiological activator of pro-PSA following its own proteolytic activation, as part of a cascade system involving a series of serine protease precursor proteins in the prostate.