Experimentally caused proliferation of lysosomes in cultured BHK cells involving an increase of biphosphatidic acids and triglycerides

Abstract

When cultured hamster fibroblasts (BHK 21 cells) were incubated in a synthetic serum-free medium up to 4 days, they developed signs of a progressive proliferation of lysosomes. The cells became filled with vacuoles that contained polymorphic debris and showed acid phosphatase activity. The specific activities of acid protease and acid phosphatase in the cell cultures increased three- to fourfold. The process was accompanied by a marked decrease in the contents of protein, deoxyribonucleic acid, and total phospholipids of the cultures. The concentration of lysobisphosphatidic acid increased during the incubation from about 1.5% to 3-6% of the cellular phospholipids. The concentrations of two related lipids, bisphosphatidic acid and semilysobisphosphatidic acid also increased substantially. The triglyceride content of the cells increased several fold, whereas the concentration of phosphatidylcholine decreased markedly. Lysobisphosphatidic acid did not increase upon induction of vacuolization by exogenous sucrose, nor when there was an accumulation of triglyceride due to addition of oleic acid to the growth medium. These findings suggest that the formation of the bisphosphatidic acids may be specifically linked to the autolysis of the phospholipids of the cellular membranes and the formation of triglycerides associated with this process.