Characterization of cellular and extracellular plasma membrane vesicles from a non-metastasizing lymphoma (Eb) and its metastasizing variant (ESb)

Abstract

Plasma membrane fragments from two variants of a murine lymphoma, Eb and ESb, with different metastatic capacity were investigated. Plasma membranes were isolated from tumor cells recovered from the peritoneal cavity. They differed in their lipid composition, indicating a more fluid state of the plasma membranes derived from the highly metastatic tumor line ESb. Extracellular membrane vesicles could be isolated from the ascites of the tumor-bearing mice. The shedding capacity of ESb cells was much higher than that of Eb cells. The extracellular membranes by chemical analysis and the measurement of marker enzymes proved to be derived from the plasma membranes. However, they differed from the plasma membranes from which they were derived in several aspects: (i) the lipid to protein ratio was diminished; (ii) the activities of some plasma membrane-associated enzymes were lower while other were identical in plasma membranes and extracellular membranes; (iii) the content of saturated fatty acids in phopholipids was enhanced in extracellular membranes. These effects were more pronounced in the highly metastasizing tumor line ESb. It is thus concluded that shedding of extracellular membranes is not a random process. The biochemical differences found in the plasma membranes and the extracellular membranes of the two tumor lines are discussed with respect to the different metastatic capacity of the tumors.