Regulation of Eukaryotic Phosphatidylinositol-Specific Phospholipase C and Phospholipase D

Abstract

This review focuses on two phospholipase activities involved in eukaryotic signal transduction. The action of the phosphatidylinositol-specific phospholipase C enzymes produces two well-characterized second messengers, inositol 1,4,5-trisphosphate and diacylglycerol. This discussion emphasizes recent advances in elucidation of the mechanisms of regulation and catalysis of the various isoforms of these enzymes. These are especially related to structural information now available for a phospholipase C delta isozyme. Phospholipase D hydrolyzes phospholipids to produce phosphatidic acid and the respective head group. A perspective of selected past studies is related to emerging molecular characterization of purified and cloned phospholipases D. Evidence for various stimulatory agents (two small G protein families, protein kinase C, and phosphoinositides) suggests complex regulatory mechanisms, and some studies suggest a role for this enzyme activity in intracellular membrane traffic.

Phosphoinositides in Constitutive Membrane Traffic

“…Phosphatidic acid (PA) has been shown to stimulate these enzymes (164,243), and all three of the PIP5Ks are activated ϳ10-fold by this lipid (158). A major source of PA is through the hydrolysis of phosphatidylcholine by phospholipases D 1 and D 2 , enzymes that are themselves activated by PtdIns(4,5)P 2 (326). In vitro the PIP5KIs can phosphorylate phosphoinositides other than PtdIns(4)P and will convert PtdIns(3,4)P 2 to PtdIns(3,4,5)P 3 and PtdIns(3)P to both PtdIns(3,5)P 2 and PtdIns(3,4,5)P 3 (106,356,409).…”

“…Interest in a possible role for PtdIns(4,5)P 2 on the Golgi arose when it was discovered that nucleotide exchange on the important regulator of Golgi membrane traffic, Arf1, was increased by membranes containing PtdIns(4,5)P 2 (354) and that Arf is an activator of PLD (29). PLD produces PA, which is a potent activator of all of the PIP5KI enzymes, and PLD is itself potently stimulated by PtdIns(4,5)P 2 (326). Thus the possibility that secretory events on the Golgi might be regulated through PtdIns(4,5)P 2 acting in positive and negative feedback mechanisms affecting Arf1 activity has received much attention.…”

Differential roles of Ras and Rap1 in growth factor-dependent activation of phospholipase Cε

“…Phosphoinositide-specific phospholipase C (PLC) catalyzes the hydrolysis of phosphatidylinositol 4,5-biphosphate, yielding two intracellular second messengers, diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP 3 ), which direct protein kinase C activity and calcium mobilization, respectively (Singer et al, 1997). Thus, PLC plays a pivotal role in a diverse array of signal transduction pathways that regulate cell growth, differentiation and development.…”

Phosphorylation of phospholipase D1 and the modulation of its interaction with RhoA by cAMP-dependent protein kinase

“…Most PLD enzymes are membrane-associated proteins, although cytosolic PLD has been reported in certain cells (Siddiqi et al, 1995;Singer et al, 1997) and the membrane-bound active form of RhoA was extractable by PKA-mediated phosphorylation (Lang et al, 1996;Kwak and Uhlinger, 2000;Forget et al, 2002). We examined whether cAMP-induced phosphorylation could affect the association of PLD with the membrane.…”

“…PA can be further metabolized by PA phosphohydrolase to form diacylglycerol and by phospholipase A2 to form lysophosphatidic acid. Moreover, PA and its metabolites act as second messengers in the regulation of secretion, mitogenesis, and cytoskeletal reorganization (Exton, 1999;Liscovitch et al, 2000) PLD is tightly regulated by a variety of hormones, growth factors, cytokines, and other agonists (Singer et al, 1997;Frohman et al, 1999). Two types of PLD have been cloned, PLD1 (~120 kDa) and PLD2 (~105 kDa), which differ both in activation mechanism and subcellular localization (Hammond et al, 1995;Colley et al, 1997).…”