Morphologic and Antigenic Properties of Mouse Mammary Tumor Virus Produced in a Hormone-Responsive Fashion by C57B1/10 Mammary Tumors of Non-Viral Origin

Abstract

Bl-MaTU/A1 mouse mammary tumor cells, derived from a C57B1/10 mammary adenocarcinoma induced by dimethylbenzanthracene and mammotropic hormones, express virus particles and proteins related to mouse mammary tumor virus (MMTV). Immunocytochemical analysis by means of monospecific and monoclonal anti-gp52 sera revealed a different localization of the main structural proteins of MMTV in Bl-MaTU/A1 and GR cells (the latter used as a positive virus-producing control). Immunoelectron microscopy of B-type particles budding from the microvilli of dexamethasone-stimulated Bl-MaTU/A1 cells showed remarkably weak reactivity of the viral envelope with anti-gp52-protein A-gold complexes as compared with that of dexamethasone-stimulated GR cells. Since Bl-MaTU/A1-associated MMTV originates from the amplified unit II of endogenous MMTV, which is altered probably within the env gene, the observed antigenic difference in the Bl-MaTU/A1-associated MMTV may be due to altered synthesis of gp52 glycoprotein in these cells.