Plasma membrane properties of cultured local LM cell tumors and metastases from athymic (nude) mice

Abstract

Some cell surface membrane properties of tumors may depend upon the host tissue site. Therefore, local tumors and lung metastases were excised from athymic (nude) mice injected subcutaneously with LM fibroblasts. The excised local tumors and lung metastases were cultured in chemically-defined, serum-free medium to characterize their plasma membrane properties without complicating factors such as site of growth, presence of host inflammatory cells, and variation in nutrition. Plasma membranes were isolated from the cultured local tumor cells and cultured metastatic cells. The specific activities of (N +, K +)-ATPase and 5′-nucleotidase were elevated and decreased, respectively, in plasma membranes from metastatic cells as compared to local tumor cells, a finding consistent with data from directly excised local tumors and lung metastases. Plasma membranes of metastatic cells had a lower ratio of sterol/phospholipid, higher ratio of phosphatidylcholine/phosphatidylethanolamine, and no differences in phospholipid unsaturated/saturated fatty acid ratio compared to plasma membranes from the locally-derived tumor cells. Plasma membranes of metastatic cells were more fluid (lower limiting anisotropy) than those of local tumor cells as indicated by multifrequency phase and modulation fluorometry and the fluorescence probe molecule, 1,6-diphenyl-1,3,5-hexatriene. Thus, the higher fluidity of metastatic as compared to local tumor plasma membranes was not due to differences in site of growth, host cell contamination, and/or nutrition.