Available evidence suggests the involvement of phospholipase D (PLD) in cell proliferation and survival. Phosphoinositide 3-kinase (PI 3-kinase)/Akt and extracellular signal-regulated kinases (ERKs) are signalling molecules that have essential roles in cell proliferation and survival. We previously demonstrated that sphingosine 1-phosphate (S1P)-induced PLD activation via the G-protein-coupled receptor endothelial differentiation gene (EDG) 3/S1P3 was involved in S1P-induced stimulation of PI 3-kinase and Akt. In the present study, we examined the involvement of two PLD isozymes, PLD1 and PLD2, in insulin-like growth factor (IGF)-I receptor tyrosine kinase-mediated stimulation of PI 3-kinase/Akt and ERKs. IGF-I and to a lesser degree S1P stimulated PI 3-kinase activity in Chinese hamster ovary cells overexpressing EDG3/S1P3. IGF-I-induced ERK phosphorylation was suppressed by butan-1-ol, but not butan-2-ol, whereas no effect of butanol was observed in IGF-I-induced Akt activation in S1P3-overexpressing Chinese hamster ovary cells. Overexpression of wild-type PLD1 and PLD2 substantially potentiated S1P-, but not IGF-I-, induced activation of PI 3-kinase and Akt, whereas overexpression of the catalytically inactive mutant of PLD1 or PLD2 did not affect the responses to either agonist. On the other hand, overexpression of wild-type PLD1 and PLD2 potentiated IGF-I- and, to much smaller extents, S1P-induced ERK stimulation. ERK activation by IGF-I as well as S1P was dependent on Ras, but Akt activation by IGF-I was not dependent on Ras. These results suggest that PLDs are involved in growth factor regulation of at least two signalling pathways, PI 3-kinase/Akt and ERKs, depending on the class of cell-surface receptors.
- CHO-K1 cells
- extracellular signal-regulated kinase (ERK)
- insulin-like growth factor-I (IGF-I)
- phosphoinositide 3-kinase (PI 3-kinase)
- sphingosine 1-phosphate
Abbreviations used: CHO, Chinese hamster ovary; EDG, endothelial differentiation gene; ERK, extracellular signal-regulated kinase; GPCR, G-protein-coupled receptor; IGF, insulin-like growth factor; PBut, phosphatidylbutanol; PI 3-kinase, phosphoinositide 3-kinase; PLD, phospholipase D; PLD1KR, K898R mutant of PLD1; PLD2KR, K758R mutant of PLD; PLD1WT and PLD2WT, wild-type PLD1 and PLD2 respectively; S1P, sphingosine 1-phosphate.
- The Biochemical Society, London ©2003