Biosynthesis and processing of prostatic and lysosomal acid phosphatases in a prostate carcinoma cell line PC-3SF12

The biosynthesis of distinct prostatic and lysosomal acid phosphatases is demonstrated using a human prostatic carcinoma cell line, PC-3SF12. The biosynthesis and maturation of the acid phosphatases was studied by metabolic labeling with radioactive leucine, specific immunoprecipitation, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and fluorography. Of the tartrate-inhibitable acid phosphatase activity in PC-3SF12 cells, 60% is lysosomal and 10% is prostatic. The lysosomal-type acid phosphatase is synthesized as precursor with a molecular weight of 68,000, some of which is converted to higher-molecular-weight precursor polypeptides (Mr 71,000 and 77,000). The multiple forms of the precursors are due to differences in the carbohydrate chains on the enzyme because biosynthesis in the presence of tunicamycin eliminates the precursor multiplicity. The initial precursor (Mr 68,000) is processed to a mature polypeptide (Mr 49,000), via intermediates with molecular weights of 62,000 and 59,000. The mature polypeptide is degraded to smaller polypeptides with molecular weights of 30,000, 28,000, and 25,000. Precursor polypeptides of the lysosomal-type enzyme are secreted in the medium. Prostatic acid phosphatase is synthesized as a precursor with a molecular weight of 110,000, which is processed via several intermediates (Mr 99,000-93,000, 77,000, and 55,000) to a mature polypeptide with a molecular weight of 49,000. Particularly during cell homogenization, or lysis, the mature polypeptide is rapidly degraded to an immunoprecipitable polypeptide with a molecular weight of 20,000. None of these polypeptides is secreted in detectable amounts into the medium. Precursors and mature and smaller polypeptides are present in human prostate extract and seminal fluid. Proteolytic degradation of prostatic acid phosphatases in cells and tissues is probably catalyzed by a plasmin-like or related trypsin-like enzyme because degradation of the mature prostatic phosphatase polypeptide is completely prevented by addition of the plasmin inhibitor bovine pancreatic trypsin inhibitor. Prostatic- and lysosomal-type acid phosphatases are eventually stored at least in part in two different types of cell organelles. Testosterone does not influence the biosynthesis and secretion of either acid phosphatase in this cell line.