Are cells rescued from 'low density death' by co-operation between phospholipases C AND D?
Cells of the ciliate Tetrahymena thermophila die when transferred at low density to a lipid-free nutritionally complete medium. This death is prevented and they will start to proliferate if protein kinase C is activated and this activation is sustained. We propose that this takes place in two stages. Firstly, the phospholipase C pathway beginning with and specific for phosphatidylinositol leads to the formation of diacylglycerol and inositol tris -phosphate. Diacylglycerol activates protein kinase C, and inositol tris -phosphate via Ca(2+)phospholipase D (PLD). Secondly, the protein kinase C response can now be sustained by diacylglycerol produced by phospholipase D, using phosphatidylcholine and phosphatidylserine as substrates. Should this switching from PI-specific phospholipase C (PLC) to phospholipase D fail, then the cell will die in the course of milliseconds during the minutes following inoculation.
Rasmussen
M
M
Institute of Medical Biology, Department of Cell Biology, Odense University, Odense M, DK-5230, Denmark. m.rasmussen@winsloew.sdu.dk
Rasmussen
L
L
D000818:Animals; D016923:Cell Death; D004075:Diglycerides / Q000378:metabolism; D008954:Models, Biological; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D010739:Phospholipase D / Q000502:physiology*; D015398:Signal Transduction; D013696:Temperature; D016808:Tetrahymena thermophila / Q000201:enzymology; D013997:Time Factors; D010738:Type C Phospholipases / Q000502:physiology*
D004075:Diglycerides; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols; D010738:Type C Phospholipases; D010739:Phospholipase D