Phospholipase D1 and potential targets of its hydrolysis product, phosphatidic acid

Abstract

Phospholipase D (PLD) hydrolyses phosphatidylcholine into phosphatidic acid (PA) and choline. Our work aims to understand the properties of PLD1, and to identify downstream targets of PA. In one set of projects, we have focused on membrane-targeting mechanisms and have proposed a hierarchy of signals that allows PLD1 to localize to intracellular membranes. These signals involve a functional pleckstrin homology (PH) domain and its fatty acylation on two adjacent cysteine residues. A nearby Phox homology (PX) domain may modulate the function of the fatty acylated PH domain. This complex array of signals is probably necessitated by the targeting of PLD1 to multiple endocytic and secretory membranes under basal and signal-dependent conditions. In another set of projects, we have used chemically synthesized PA coupled to a solid support in order to identify proteins that interact with this phospholipid. Several proteins have emerged from this screen as potential targets. Some (e.g. ADP-ribosylation factor, coatomer β subunit) are involved in trafficking and their PA affinity can be understood in terms of their regulated cycling on and off membranes during rounds of transport. Others (sphingosine 1-phosphate kinase and PtdIns4P 5-kinase) are implicated in pathways that also involve PLD activation. Others still are novel proteins (brain-specific neurochondrin) whose affinity for PA may contribute to an understanding of their cellular function.

Ral Isoforms Are Implicated in FcγR-Mediated Phagocytosis: Activation of Phospholipase D by RalA

“…PA can be converted to other bioactive lipids (e.g., diacylglycerol) (23), or it can stimulate lipid production, as for PI(4,5)P 2 (41), both of which are implicated in the phagocytotic process. Alternatively, PA may activate or recruit regulators of the actin cytoskeleton and membrane trafficking (42). In the case of focal exocytosis, PA could participate directly in the fusion process because membrane domains of PA (due to its small polar head) promote negative membrane curvatures favoring membrane hemifusion (43) or, indirectly, by serving as a lipid anchor for proteins involved in the fusion process [e.g., 11FIP, located on recycling endosomes (44) or syntaxin, one of the SNARE proteins (45)].…”

Bacterial protein toxins and lipids: role in toxin targeting and activity

“…Both molecules can play various roles in cell signalling (Cook and Wakelam, 1991;Cuadrado et al, 1993;English, 1996;Ktistakis et al, 2003). Ymt (Yersinia pestis murine toxin) is now recognized as a PLD superfamily member (Figure 2).…”

Neurochondrin Negatively Regulates CaMKII Phosphorylation, and Nervous System-specific Gene Disruption Results in Epileptic Seizure

“…These facts demonstrate its possible involvement in bone metabolism. The finding that neurochondrin protein associates with semaphorin4C (a transmembrane-type semaphorin) and phosphatidic acid (a possible second messenger) indicates its role as a signal molecule (4,5). Besides all these conceivable functions, our previous trial in disclosing its in vivo role by conventional loss of function strategy in mice failed because of its lethality in utero (6).…”