Plasma Membrane and Intracellular Lipid Synthesis in Tumor Cells Rendered Resistant to Humoral Immune Killing After Treatment With Hormones23

Abstract

Line-10 hepatoma cells from Sewall Wright guinea pigs are sensitive to killing by antibody plus human complement. Hormones that decrease the sensitivity of the cells to antibody-complement-mediated killing (insulin and hydrocortisone) were examined for their effects on the ability of the cells to synthesize and incorporate specific lipids into plasma membrane and intracellular membrane fractions. Cells that had been rendered resistant to antibody-complement-mediated killing following incubation for 1 hour with either of the hormones were enhanced in their incorporation of newly synthesized L-alpha-phosphatidyl serine, L-alpha-phosphatidyl choline, and triglycerides into the plasma membrane as well as L-alpha-phosphatidyl choline, L-alpha-phosphatidyl serine, and cholesteryl ester into mitochondria, endoplasmic reticulum, nuclear membrane, or microsomes; these cells were inhibited in cardiolipin synthesis. Cells cultured for 4 hours with hormone regained their sensitivity to antibody-complement-mediated killing and reverted to control levels in their ability to synthesize and incorporate lipids into plasma and intracellular membranes. These data suggest that agents that increase the resistance of the tumor cells to humoral immune killing stimulate the synthesis and incorporation of specific complex lipids into plasma membrane and intracellular organelles; these effects are generally opposite those observed after treatment with agents that increase the sensitivity of the cells to antibody-complement-mediated killing (metabolic inhibitors).