Transformation of cells by rous sarcoma virus: cytoplasmic vacuolization

Chick embryo cells transformed by the Bryan "high titer" strain of Rous sarcoma virus (RSV-BH) are heavily vacuolated. A variety of microscopic techniques have been used demonstrating that the vacuoles are cytoplasmic, bounded by membrane, and are composed largely of water. Proteins, lipids, glycoproteins, glycolipids, glycosaminoglycans, glycogen, and nucleic acids were undetectable in the vacuoles. Physiological requirements for development of the vacuoles, and reversal of vacuolization, were examined in cells infected with a virus mutant, RSV-BH-Ta, which induces reversible temperature-dependent transformation. Na+ was the only component of the cell culture medium found essential for both the development and reversal of vacuoles. Glucose depletion or dinitrophenol treatment inhibited vacuolization, suggesting a possible energy requirement in the vacuolization process. Ouabain, an inhibitor of Na+-K+ ATPase, enhanced vacuolization, but a variety of other substances affecting cell surface components were in active. Two sugars, glucosamine and mannosamine, prevented the disappearance of vacuoles. The observations suggest that cellular vacuolization may be a normal physiological response to an increase in water and Na+, and, in the specific case of transformation by RSV-BH, may be relevant to the physiological basis for malignancy.