Differential subcellular distribution of four phospholipase C isoforms and secretion of GPI-PLC activity.
Phospholipase C (PLC) is an important enzyme of signal transduction pathways by generation of second messengers from membrane lipids. PLCs are also indicated to cleave glycosylphosphatidylinositol (GPI)-anchors of surface proteins thus releasing these into the environment. However, it remains unknown whether this enzymatic activity on the surface is due to distinct PLC isoforms in higher eukaryotes. Ciliates have, in contrast to other unicellular eukaryotes, multiple PLC isoforms as mammals do. Thus, Paramecium represents a perfect model to study subcellular distribution and potential surface activity of PLC isoforms. We have identified distinct subcellular localizations of four PLC isoforms indicating functional specialization. The association with different calcium release channels (CRCs) argues for distinct subcellular functions. They may serve as PI-PLCs in microdomains for local second messenger responses rather than free floating IP3. In addition, all isoforms can be found on the cell surface and they are found together with GPI-cleaved surface proteins in salt/ethanol washes of cells. We can moreover show them in medium supernatants of living cells where they have access to GPI-anchored surface proteins. Among the isoforms we cannot assign GPI-PLC activity to specific PLC isoforms; rather each PLC is potentially responsible for the release of GPI-anchored proteins from the surface.
Saarland University, Molecular Cell Dynamics, Centre for Human and Molecular Biology, Campus A2 4, 66123 Saarbrücken, Germany; University of Kaiserslautern, Department of Biology, Erwin-Schrödinger Straße, Building Nr. 14, 67663 Kaiserslautern, Germany.
Emanuel
E
Staudt
Saarland University, Molecular Cell Dynamics, Centre for Human and Molecular Biology, Campus A2 4, 66123 Saarbrücken, Germany.
Pathmanaban
P
Ramasamy
University of Konstanz, Senior Research Group for Cell Biology and Ultrastructure Research, Department of Biology, 78457 Konstanz, Germany.
Helmut
H
Plattner
Saarland University, Molecular Cell Dynamics, Centre for Human and Molecular Biology, Campus A2 4, 66123 Saarbrücken, Germany. Electronic address: martin.simon@uni-saarland.de.
Martin
M
Simon
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000201:enzymology; D002923:Cilia / Q000201:enzymology; D019084:Fluorescent Antibody Technique, Indirect; D017261:Glycosylphosphatidylinositols / Q000378:metabolism*; D007527:Isoenzymes / Q000032:analysis; D008958:Models, Molecular; D011817:Rabbits; D010738:Type C Phospholipases / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism
D017261:Glycosylphosphatidylinositols; D007527:Isoenzymes; D010738:Type C Phospholipases; D002118:Calcium
GPI-PLC; GPI-anchor; GPI-release; Glycosylphosphatidylinositol; PI-PLC; Phospholipase C