title: Purification and first characterization of the secreted and cellular 52-kDa proteins regulated by estrogens in human-breast cancer cells.
abstract: An estrogen-regulated 52-kDa glycoprotein secreted by MCF7 breast cancer cells was first purified from serum-free conditioned medium by concanavalin-A--Sepharose (ConA--Sepharose). The 13% pure protein was then used to obtain monoclonal antibodies to the 52-kDa protein [Garcia et al. (1985) Cancer Res. 45, 709-716]. Using ConA--Sepharose and monoclonal antibody affinity chromatographies, the secreted 52-kDa protein was finally purified to homogeneity as verified by silver staining of sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE) and one single N-terminal amino acid. The purification factor was approximately 1400 and the yield 40%. The same two-step procedure, applied to MCF7 cell extracts, yielded four immunologically related proteins of 52 kDa, 48 kDa, 34 kDa and 17 kDa, which were purified 1250-fold with a yield of 30%. These components were further separated by high-performance liquid chromatography gel filtration under denaturing conditions. The final products were homogeneous on the basis of silver-stained SDS-PAGE and gel filtration. However, isoelectrofocusing showed that the pI of the secreted 52-kDa protein and the cellular 34-kDa protein varied from 5.5 to 6.5. Amino acid analysis of the secreted and the related cellular 34-kDa protein is given. Western immunoblotting, pulse chase studies and post-translational studies indicate that the 52-kDa protein is the precursors of a lysosomal enzyme which is partially secreted and partially processed into smaller cellular forms.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000911:Antibodies, Monoclonal; D001943:Breast Neoplasms / Q000378:metabolism*; D002846:Chromatography, Affinity; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D004967:Estrogens / Q000502:physiology*; D006801:Humans; D007120:Immunochemistry; D008970:Molecular Weight; D009363:Neoplasm Proteins / Q000302:isolation & purification* / Q000378:metabolism
chemical_list: D000596:Amino Acids; D000911:Antibodies, Monoclonal; D004967:Estrogens; D009363:Neoplasm Proteins