Phospholipase D: enzymology, mechanisms of regulation, and function

Abstract

Phospholipase D exists in various forms that differ in their regulation but predominantly hydrolyze phosphatidylcholine. The Ca(2+)-dependent isozymes of protein kinase C regulate phospholipase D in vitro and play a major role in its control by growth factors and G protein-linked agonists in vivo. Recent studies have demonstrated that small G proteins of the ADP-ribosylation factor (ARF) and Rho families activate the enzyme in vitro, and evidence is accumulating that they also are involved in its control in vivo. Both types of G protein play important roles in cellular function, and the possible mechanisms by which they are activated by agonists are discussed. There is also emerging evidence of the control of phospholipase D and Rho proteins by soluble tyrosine kinases and novel serine/threonine kinases. The possible role of these kinases in agonist regulation of phospholipase D is discussed. The function of phospholipase D in cells is still poorly defined. Postulated roles of phosphatidic acid produced by phospholipase D action include the activation of Ca(2+)-independent isoforms of protein kinase C, the regulation of growth and the cytoskeleton in fibroblasts, and control of the respiratory burst in neutrophils. Another important function of phosphatidic acid is to act as a substrate for a specific phospholipase A2 to generate lysophosphatidic acid, which is becoming increasingly recognized as a major intercellular messenger. Finally, it is possible that the phospholipid changes induced in various cellular membranes by phospholipase D may per se play an important role in vesicle trafficking and other membrane-associated events.

Dexamethasone enhances phospholipase D activity in M-1 cells

“…The effect of ATP on [ 3 H]PEth formation in cultured cells with dexamethasone was greater than in control untreated cells. It is well known that Ca 2+ has a role in the activation of PLD, since Ca 2+ ionophores stimulate PLD (Exton, 1997). However, ionomycin did not stimulate PLD activity significantly in M-1 cells.…”

“…As shown in Figure 1, mean basal PLD activity was higher in cells that were cultured in the presence of dexamethasone than in untreated cells (1.53 ± 0.05% vs 0.74 ± 0.1%). Phorbol 12-myristate 13-acetate (PMA) treatment has been previously shown to activate PLD activity in various cell systems (Exton, 1997). However, no stimulation was observed with 100 nM PMA for up to 1 h in M-1 cells obtained from both culture conditions ( Figure 1).…”

“…Mammalian phospholipase D (PLD) activity is very low and becomes up-regulated transiently when cells are stimulated by a variety of hormones, growth factors, and other extracellular signals (Exton, 1997). PLD hydrolyses phosphatidylcholine (PC), the major component of membrane phospholipid to phosphatidic acid (PA) and choline (Bocckino et al, 1987).…”

ATP Stimulates Human Macrophages to Kill Intracellular Virulent Mycobacterium tuberculosis Via Calcium-Dependent Phagosome-Lysosome Fusion

“…Ethanol (and other short-chain primary alcohols) inhibit PLDmediated generation of phosphatidic acid by substituting for water as the attacking nucleophile, yielding the metabolically inert alternate product, phosphatidylethanol (PEt) (17,41). Thus, ethanol inhibits PLD-dependent responses without blocking enzyme turnover, providing a complementary method of PLD inhibition that is mechanistically distinct from that of 2,3-DPG.…”

Phospholipase D is involved in oxidative stress-induced migration of vascular smooth muscle cells via tyrosine phosphorylation and protein kinase C

“…PA is generally recognized as the signaling product of PLD and functions as an effector in multiple physiological processes. Although the precise physiological function of PLD in cells is poorly understood, receptor-stimulated PLD activity has been implicated in a broad range of physiological response such as rapid response (secretion and superoxide generation) and long-term responses (proliferation, differentiation, and immune response) (Exton, 1997;Exton, 1999;Liscovitch et al, 2000;Kim et al, 2003). To date, two PLD isoforms have been cloned and characterized (Hammond et al, 1995;Colley et al, 1997;Hammond et al, 1997).…”