Characteristics of membrane and cytosol forms of the mammary tumor glycoprotein molecule MTGP in human breast carcinoma cell cultures and tumors.

The presence, concentration and selected molecular characteristics of the human mammary carcinoma glycoprotein molecule set MTGP, a trace and apparently tumor-specific molecule, were examined in fifteen cell cultures established from mammary carcinomas, tissue from seven mammary carcinomas and control cultures. Both cytosol and membrane-associated forms of MTGP were analyzed, and each was phenotyped by reference to isoelectric point and buoyant density. All cells or tissues of mammary carcinoma origin contained membrane MTGP, whereas cytosol MTGP was undetectable in cell cultures from half of the mammary carcinomas. Neither membrane nor cytosol MTGP were detectable in cells other than mammary carcinomas. Cytosol MTGP could be assigned to three groups by reference to presence, isoelectric point and buoyant density. Membrane MTGP also exhibited heterogeneity between different tumors and could be assigned to three groups by isoelectric point and buoyant density. Each form of MTGP was homogeneous for a given single tumor or cell culture and retained its phenotypic features with passage and cloning. Four general types of MTGP are proposed, through there may be additional fine heterogeneity that cannot be further resolved at this time. These data provide an initial characterization of the membrane form of MTGP and an integrated characterization that is consistent with the concept that tumor-specific antigens may possess both constant regions by reference to antigens recognized by the antisera and variable structure by reference to physicochemical characteristics.