Cell Adhesiveness Is Related in Malignant Lymphoid Cells to Tumorigenicity

Mouse lymphoma cells ($49) that grow in suspension culture were selected for increased tumorigenicity through continuous passages in syngeneic BALB/c mice. Developing tumors were classified as high grade malignant lymphoma, small noncleaved type. Variants were selected from these tumorigenic cells that were able to grow as a monolayer attached to their substrate, resembling, in this respect, fibroblastoid cells. Whereas the tumorigenic suspension-growing parental cells were able to induce progressive tumors with an inoculum as low as 100 cells per mouse, the adherent cells were unable to develop as tumors even at an inoculum of 1 x 108 cells per mouse. In addition, mice inoculated once with live adherent cells were immunized against 1 x 107 suspension-growing cells. Involvement of an immune response in the rejection of tumorigenic $49 cells was suggested by (a) adoptive transfer experiments in which spleen cells from immunized mice protected naive mice and (b) the appearance of antibodies in the sera of immunized syngeneic mice that specifically recognized both adherent and suspension-growing $49 cells and detected differences in [35S]methioninelabeled antigens from these cells. Antibodies raised in rabbits against adherent cells recognized three proteins of 34,000, 61,000, and 72,000 apparent molecular weight in radiolabeled adherent cell extracts that are either absent or present in small amounts in extracts of suspension-growing tumorigenic $49 cells. These findings, taken together with our previous report (Hochman, J., A. Katz, E. Levy, and S. Eshel, 1981, Nature (Lond.), 290:248-249), suggest the $49 system as a novel system for studying growth control in malignant lymphoid cells. The relationship among cell adhesiveness (the ability to adhere to other cells and to extracellular substrata), transformation, tumor development, and the metastatic behavior of malignant cells is a well-known but complex phenomenon that has been studied extensively (l, 3, 5, 9, 18, 20, 24) since Ludford (17) and Cowdry (6) first suggested that membranes of tumor cells had lower general adhesive properties than the normal cells from which they were derived. These previous studies have all been carried out on cells grown as monolayers (i.e., fibroblastoid) attached to their substratum and to each other. We have undertaken to study this relationship in malignant lymphoid cells that grow attached neither to each other nor to their substratum. Our working hypothesis is that if in fibroblasts decreased cell adhesiveness correlates with in1282 creased tumorigenicity (3, 18) and vice versa, then isolation of adherent variants from malignant lymphoid cells may result in decreased tumorigenicity. Such a model would be of potential significance in the study of in vitro growth regulation of malignant lymphoid cells. To test this approach, we have used $49 cells--a mouse lymphoma cell line of BALB/c origin (13). We have first demonstrated that stable variants can be isolated, characterized by their ability to adhere to their substratum (bottom of culture flask) and divide while attached to it (11). Using the same approach, we have subsequently isolated substrate-adhering variants from tumorigenic $49 cells, previously selected through continuous in vivo passages in BALB/c mice (12). We have also found that the adherent $49 variants demonstrated impaired tumorigenicity, while concomitantly being THE JOURNAL OF CELL BIOLOGY VOLUME 99 OCTOBER 1984 1282-1288 © The Rockefeller University Press • 0021-9525/84/10/1282/07 $I .00 on A ril 3, 2017 D ow nladed fom Published October 1, 1984