title: Expression of pro form of prostate-specific antigen by mammalian cells and its conversion to mature, active form by human kallikrein 2.
abstract: To study the expression, biosynthesis, and processing of prostate-specific antigen (PSA) in mammalian cells, recombinant PSA was expressed in Syrian hamster tumor cell line AV12-664 (AV12-PSA). Expression of PSA was monitored by the Tandem-MP PSA assay. PSA was secreted into the medium during the logarithmic phase of cell growth at >9 microg/ml and was stable. The PSA purified from spent medium of AV12-PSA cells did not exhibit any enzymatic activity and did not complex with the protease inhibitor, alpha-1-antichymotrypsin. These findings indicated that an inactive form of PSA was expressed by AV12-PSA cells. NH2-terminal sequencing confirmed the identity of the PSA purified from the spent medium of AV12-PSA cells to be pro-PSA. This demonstrates that PSA is expressed as pro-PSA by mammalian cells and suggests that pro-PSA may be present in biological fluids. Human kallikrein 2 (hK2), another member of the hK family, is also expressed predominantly in prostate epithelium. Although hK2 has been shown to exhibit trypsin-like activity, little is known about its natural substrates. Using purified proteins, we show that hK2 can convert pro-PSA to mature, enzymatically active PSA, thus establishing a physiological connection between hK2 and PSA. These findings imply that hK2 may be regulating PSA activity in vivo.
authors.affiliation: Hybritech Incorporated, San Diego, California 92196-9006, USA.
authors.forename: A
authors.initials: A
authors.lastname: Kumar
authors.forename: S D
authors.initials: SD
authors.lastname: Mikolajczyk
authors.forename: A S
authors.initials: AS
authors.lastname: Goel
authors.forename: L S
authors.initials: LS
authors.lastname: Millar
authors.forename: M S
authors.initials: MS
authors.lastname: Saedi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D002845:Chromatography; D006224:Cricetinae; D017077:Culture Media, Conditioned / Q000032:analysis; D006801:Humans; D007610:Kallikreins / Q000494:pharmacology*; D008969:Molecular Sequence Data; D017430:Prostate-Specific Antigen / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection
chemical_list: D017077:Culture Media, Conditioned; D011994:Recombinant Proteins; D007610:Kallikreins; D017430:Prostate-Specific Antigen