Cloning and characterization of the α1‐antichymotrypsin produced by human prostate tissue

BACKGROUND: alpha 1-antichymotrypsin (ACT) forms stable complexes with prostate-specific antigen (PSA), a serine protease, and this complex is the major form of PSA in the blood circulation. alpha 1-antichymotrypsin occurs in the blood in approximately 10(5) molar excess to PSA, mainly due to hepatic production, but local prostatic production of ACT has been demonstrated by immunohistochemistry and in situ hybridization. The present study was performed to further characterize this prostate-produced ACT. METHODS: The nucleotide structure of the prostatic transcript was determined from ACT coding clones isolated from prostatic cDNA. The occurrence of a prostatic ACT transcript was analyzed by Northern blot. RT-PCR was used to detect ACT transcripts in cultured prostatic cancer cells. RESULTS: Screening of two prostatic cDNA libraries showed the frequency of ACT transcripts to be about 1 clone in 40,000. The cDNA sequence of prostatic ACT is identical to that of the previously published hepatic ACT. Northern blot analysis of mRNA extracted from prostatic tissue showed a single transcript of approximately 1.5 kb. RT-PCR analysis demonstrated an ACT transcript in cultured prostatic cancer cells. CONCLUSIONS: In this study we provide further evidence for a local, prostatic production of ACT. The cDNA sequence data suggest that the peptide backbone of prostatic ACT is identical to the protein derived from the liver, and thus may be functional as a protease inhibitor.