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Heterogeneity of Expression and Induction of Mouse Mammary Tumor Virus Antigens in Mouse Mammary Tumors¹

Department of Cell Biology, AMC Cancer Research Center and Hospital, Lakewood, Colorado 80214 [J. C. H.] and Department of Immunology, Michigan Cancer Foundation, Detroit, Michigan 48201 [G. H. H.]

Seven spontaneous BALB/cfC₃H mouse mammary tumors were heterogeneous in expression of murine mammary tumor virus-associated cell surface antigens. To determine the basis of this heterogeneity, cells from spontaneous tumors and from five subpopulations isolated from a single spontaneous tumor were examined for expression of viral antigens under both conventional conditions and conditions known to induce synthesis of murine mammary tumor virus antigens (5-iodo-2'-deoxyuridine and dexamethasone). Induction with 5-iodo-2'-deoxyuridine resulted in further manifestation of the antigenic heterogeneity of spontaneous tumors. The five subpopulations from a single tumor differed in the amount of viral antigens present in untreated and in induced cultures. Coculturing showed that viral antigen expression was independent in each subpopulation within a heterogeneous mixture and was not influenced by the presence of other subpopulations with different potentials for viral antigen synthesis. The expression of murine mammary tumor virus structural antigens, a protein with a molecular weight of 28,000 and a glycoprotein with a molecular weight of 52,000, differed within the heterogeneous subpopulations, and was noncoordinate. The data suggest that the antigenic heterogeneity in spontaneous tumors reflects the existence of cells within them that differ in both expression of viral antigens and in their response to inducers of viral antigen synthesis.

¹ Supported by Grants CA 27419 and CA 13943 from the NIH, a bequest from E. Walter Albachten, and an institutional grant to the Michigan Cancer Foundation from the United Foundation of greater Detroit.

² To whom requests for reprints should be addressed, at 6401 West Colfax Avenue, Lakewood, Colorado, 80214.

Received 3/18/82. Accepted 7/29/82.