Perturbations in the control of cellular arachidonic acid levels block cell growth and induce apoptosis in HL-60 cells

Our previous studies demonstrated that inhibitors of arachidonate-phospholi pid remodeling [i.e, the enzyme CoA-independent transacylase (CoA-IT)] decr ease cell proliferation and induce apoptosis in neoplastic cells. The goal of the current study was to elucidate the molecular events associated with arachidonate-phospholipid remodeling that influence cell proliferation and survival. Initial experiments revealed the essential nature of cellular ara chidonate to the signaling process by demonstrating that HL-60 cells deplet ed of arachidonate were more resistant to apoptosis induced by CoA-IT inhib ition. In cells treated with CoA-IT inhibitors a marked increase in free ar achidonic acid and AA-containing triglycerides were measured. TG. enrichmen t was likely due to acylation of arachidonic acid into diglycerides and tri glycerides via de novo glycerolipid biosynthesis. To determine the potentia l of free fatty acids to affect cell proliferation, HL-60 cells were incuba ted with varying concentrations of free fatty acids; exogenously provided 2 0-carbon polyunsaturated fatty acids caused a dose-dependent inhibition of cell proliferation, whereas oleic acid was without effect. Blocking 5-lipox ygenase or cyclooxygenases had no effect on the inhibition of cell prolifer ation induced by arachidonic acid or CoA-IT inhibitors. An increase in cell -associated ceramides (mainly in the 16:0-ceramide fraction) was measured i n cells exposed to free arachidonic acid or to CoA-IT inhibitors. This stud y, in conjunction with other recent studies, suggests that perturbations in the control of cellular arachidonic acid levels affect cell proliferation and survival.