Direct Activation of PLC Epsilon via Free Fatty Acids and Cross Talk with PLD and PLA2

Abstract

The cellular lipidome is large and diverse comprising over 1000 different lipids. Increasingly, new roles for lipids in maintaining cellular homeostasis and roles as contributors to human disease such as obesity, cancer and Alzheimer’s are being recognized. Many investigators believe that lipid effects are mediated via an indirect and non-specific manner. We have used phospholipase C epsilon as a model to demonstrate that lipids can act as ligands to bind to specific motifs and regulate protein activity via allosteric effects. Phospholipids such as phosphatidic acid and free fatty acids such as arachidonate are potent activators of PLC epsilon, increasing the rate of PI hydrolysis by 8 and 50 fold respectively. The mechanism appears to be reduction of Km, as the substrate dependence curve is shifted to the left and Km reduced 10 fold. The regulation of PLC epsilon by lipids appears to be physiologic, as reconstitution or co-transfection of either cPLA2 or PLD with PLC epsilon leads to activation of phosphodiesterase activity. Additionally, TSA-201 cells transfected with PLC epsilon and fed arachidonic acid complexed with BSA had markedly increased (4–5 fold) hydrolysis of polyphosphoinositides. This study demonstrates the ability of lipids to act as potent and direct mediators of protein function and identifies cross talk between different classes of phospholipase (PLD and PLA2 with PLC) mediated via lipid products.