Rapid turnover of arachidonyl-phosphatidylinositol in L cells stimulated by antibody

Abstract

Binding of anti-L cell antibody (3 × 10 6 IgG molecules/cell) produced a stimulated incorporation of phosphate (1.5 nmols/l × 10 6 cells/hr) in tumorigenic L cells and a stimulated incorporation ( 32P)orthophosphate (1,420 cpm/μg/hr, P < 0.0008) into isolated cell membrane phosphatidylinositol measured at 1 hour. At the same time there was a rapid increased incorporation of [ 14C]arachidonic acid into certain cell membrane phospholipid fractions isolated by two dimensional thin layer chromatography: phosphatidylinositol (2,318 cpm/μg/hr, P < 0.0104), phosphatidylcholine (473 cpm/μg/hr, P < 0.0030), phosphatidylethanolamine (320 cpm/μg/hr, P < 0.0383). Thus, the increased turnover of arachidonic acid in phosphatidylinositol was 4.6-fold and 7.2-fold greater than those with phosphatidylcholine and phosphatidylethanolamine, respectively. Since there was no simultaneous enhancement in the incorporation of [ 3H]glycerol, it appeared that these increases were not due to de novo synthesis but, rather, to turnover phenomena possibly via deacylation and reacylation reactions. Since arachidonic acid is an important metabolic precursor of prostaglandins which exert control of cell growth, its rapid turnover especially in the phosphatidylinositol fraction of membrane phospholipids may be an important initial event in the antibody-mediated immunological enhancement of tumor cell growth.