Exogenous phospholipase D generates lysophosphatidic acid and activates Ras, Rho and Ca2+ signaling pathways.
BACKGROUND
Phospholipase D (PLD) hydrolyzes phospholipids to generate phosphatidic acid (PA) and a free headgroup. PLDs occur as both intracellular and secreted forms; the latter can act as potent virulence factors. Exogenous PLD has growth-factor-like properties, in that it induces proto-oncogene transcription, mitogenesis and cytoskeletal changes in target cells. The underlying mechanism is unknown, although it is generally assumed that PLD action is mediated by PA serving as a putative second messenger.


RESULTS
In quiescent fibroblasts, exogenous PLD (from Streptomyces chromofuscus) stimulated accumulation of the GTP-bound form of Ras, activation of mitogen-activated protein (MAP) kinase and DNA synthesis, through the pertussis-toxin-sensitive inhibitory G protein Gi. Furthermore, PLD mimicked bioactive lysophospholipids (but not PA) in inducing Ca2+ mobilization, membrane depolarization and Rho-mediated neurite retraction. PLD action was mediated by Iysophosphatidic acid (LPA) derived from Iysophosphatidylcholine acting on cognate G-protein-coupled LPA receptor(s). There was no evidence for the involvement of PA in mediating the effects of exogenous PLD.


CONCLUSIONS
Our results provide a molecular explanation for the multiple cellular responses to exogenous PLDs. These PLDs generate bioactive LPA from pre-existing Iysophosphatidylcholine in the outer membrane leaflet, resulting in activation of G-protein-coupled LPA receptors and consequent activation of Ras, Rho and Ca2+ signaling pathways. Unscheduled activation of LPA receptors may underlie, at least in part, the known pathogenic effects of exogenous PLDs.
van Dijk
M C
MC
Division of Cellular Biochemistry The Netherlands Cancer Institute Plesmanlaan 121, 1066CX, Amsterdam, The Netherlands.
Postma
F
F
Hilkmann
H
H
Jalink
K
K
van Blitterswijk
W J
WJ
Moolenaar
W H
WH
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D003599:Cytoskeleton / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000378:metabolism*; D008244:Lysophosphatidylcholines / Q000378:metabolism / Q000494:pharmacology; D008246:Lysophospholipids / Q000096:biosynthesis*; D008565:Membrane Proteins / Q000378:metabolism*; D010739:Phospholipase D / Q000378:metabolism / Q000494:pharmacology*; D051381:Rats; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled; D049368:Receptors, Lysophosphatidic Acid; D015398:Signal Transduction / Q000187:drug effects; D018631:ras Proteins / Q000378:metabolism*; D020743:rhoB GTP-Binding Protein
D008244:Lysophosphatidylcholines; D008246:Lysophospholipids; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D049368:Receptors, Lysophosphatidic Acid; D010739:Phospholipase D; D019204:GTP-Binding Proteins; D018631:ras Proteins; D020743:rhoB GTP-Binding Protein; D002118:Calcium