Stimulation of phosphatidylethanolamine synthesis during the last stages of the G1 phase in concanavalin A-activated human peripheral lymphocytes.

Phospholipid synthesis was investigated in concanavalin A-activated human peripheral lymphocytes up until 72 h following cell activation, i.e., during the G1 and S phases of the cell cycle. Using [32P]phosphate pulse experiments (5 h), striking differences were observed between phosphatidylethanolamine (PE) and phosphatidylcholine (PC) synthesis. Both the incorporation of [32P]phosphate into PE and the PE/PC incorporation ratio were greatly enhanced, 16-fold and 8-fold, respectively, after 48 h of incubation with the mitogen. This increase in PE synthesis was still observed when cell entry into the S phase was inhibited by an excess of concanavalin A; thereby it must be related to the late stages of the G1 phase. The stimulation of the incorporation into PE was the same for both [14C]ethanolamine and [32P]phosphate, therefore suggesting the involvement of the phosphoethanolamine synthesis pathway. Kinetics of continuous incorporation of [32P]phosphate into PE and PC indicated that the PE/PC net synthesis ratio was enhanced in activated cells, which corresponds to PE enrichment in lymphocyte membranes. The stimulation of PE synthesis in late G1 may be of importance for cell progression through the cell cycle by changing the membrane physical properties. Furthermore, it may serve as a test for checking lymphocyte reactivity to mitogens.