Glycoprotein differences in solid and ascites forms of the 13762 rat mammary adenocarcinoma.

ityisnotabsolute. The blood group Tand MN antigens are also found on the surface of TA3-Ha ascites mammary adenocarcinoma cells (26, 28) and can be released from these cells by proteolysis to give large sialoglycopeptides (5). It has been postulated that the presence of sialoglycoprotein at the cell surface masks histocompatibility antigens and permits transplantation of TA3Ha cells across strain and species barriers (i 8). This sialogly coprotein is essentially absent from the strain-specific TA3-St cells, as determined by lectin (ViCia graminea) hemagglutina tion inhibition assays (4) and by proteolytic release of sialo glycopeptides (6). However, the sialoglycoprotein or its frag ments are also shed from the TA3-Ha cell surfaces (8), a phenomenon which has been postulated to be related to the metastatic potential of these cells (7). In addition, the sialogly coprotein is sensitive to the environment or growth conditions of the cell. Transfer of the TA3-Ha ascites cells to suspension culture causes the loss of sialoglycoprotein (7). The s.c. injec tion of TA3-Ha cells to give a solid tumor causes a decrease in the amount of sialoglycoprotein (ViCia receptors) present, but further transplantation as a solid tumor increases sialoglyco protein to the level of the ascites form. Such results indicate that the expression of sialoglycoprotein is sensitive to the environment in which the cell grows and that it may be con trolled by the cell. To delineate the roles of the cell surface sialoglycoproteins in the processes that contribute to the escape of tumor cells from immune surveillance, it is necessary to determine the factors which contribute to the expression of these glycopro teins at the cell surface. We have used the 13762 mammary adenocarcinoma for investigations of these questions because of several advantages which this system offers: (a) both the parent solid tumor and various ascites sublines are available; (b) the 13762 ascites sublines differ substantially in morpho logical characteristics (3), Con A agglutinability (3), and xenotransplantability (23) properties which are also different for the 2 TA3 ascites sublines (i 8); (c) there is a dominant high-molecular-weight sialoglycoprotein (ASGP-i ) present in the ascites cells, as determined by metabolic, chemical, or enzymatic labeling (23). Both xenotransplantable and non xenotransplantable sublines contain similar amounts of this glycoprotein. This contrasts with the essentially qualitative difference in the expression of sialoglycoprotein found for xenotransplantable and nonxenotransplantable TA3 sublines (i 8); (d) the dominant sialoglycoprotein from both xenotrans plantable and nonxenotransplantable sublines has been pun