ISOLATION AND CHARACTERIZATION OF OVARIAN-CANCER ANTIGEN CA-125 USINGA NEW MONOCLONAL-ANTIBODY (VK-8) - IDENTIFICATION AS A MUCIN-TYPE MOLECULE

A new murine monoclonal antibody (MAb VK-8), detecting the CA 125 ovar ian cancer antigen, was used to purify this antigen from OVCAR-3 ovari an cancer cells by affinity chromatography. The biochemical properties of the purified antigen are characteristic of a mucin-type glycoprote in: (I) the molecule is highly glycosylated (77% w/w), mainly with gal actose, N-acetylglucosamine, and N-acetylgalactosamine, (2) the protei n moiety is rich in serine, threonine and proline, (3) many of the ser ine and threonine residues are glycosylated, (4) the glycan chains are almost entirely O-linked, with core 2 [Gal beta 1 --> 3(GlcNAc beta 1 --> 6)GalNAc] structures predominating and (5) these chains carry fuc osylated Type 2 (Le(y) and Le(x), and H type 2) blood group structures . The antigen exhibited a very high m.w. (> 10(3) kDa) in aqueous buff er as well as in urea, but was degraded by proteolytic enzymes to smal ler fragments that no longer reacted with the antibody. Although this result, and other immunochemical data, indicate that OC125, the origin al MAb to CA125, and VK-8 antibodies detect epitopes on the protein po rtion of the molecule, the involvement of carbohydrate cannot be ruled out. Further insight into the structure and function of the CA 125 an tigen will come from cloning the gene coding for the peptide backbone, and from more detailed carbohydrate structural analysis. (C) 1997 Wil ey-Liss, Inc.