Insulin-like growth factor-1-induced phosphorylation of transcription factor FKHRL1 is mediated by phosphatidylinositol 3-kinase/Akt kinase and role of this pathway in insulin-like growth factor-1-induced survival of cultured hippocampal neurons.
Insulin-like growth factor-1 (IGF-1) is a trophic factor promoting cell survival by activating phosphatidylinositol 3-kinase (PI3K)/Akt kinase pathway. FKHRL1, a member of the Forkhead family of transcription factors possibly involved in cell cycle and apoptosis, is a downstream target of Akt in fibroblasts. However, very little information is available concerning neurons. We report herein that IGF-1 rapidly induced the phosphorylation of endogenous FKHRL1 in hippocampal neurons. The PI3K/Akt kinase pathway mediates this action, as evidenced by the use of different kinase inhibitors, the expression of constitutively active Akt, and in vitro kinase assay. IGF-1 blocked the nuclear translocation of FKHRL1 in hippocampal neurons and promoted survival in parallel to the phosphorylation of Akt and FKHRL1. Similarly, the expression of constitutively active Akt in PC-12 cells increased the phosphorylation of FKHRL1 and promoted survival, whereas the expression of kinase dead Akt attenuated IGF-1-mediated survival of PC-12 cells. Moreover, the overexpression of wild-type FKHRL1 and its nonphosphorylated mutant induced apoptosis in cultured hippocampal neurons. Interestingly, IGF-1 and PI3-kinase inhibitors have no significant effect on the cell cycle inhibitor p27kip1 in hippocampal neurons. This finding suggests that in contrast to fibroblasts, FKHRL1 is unlikely to be involved in cell cycle in neurons. Taken together, these data reveal that endogenous FKHRL1 is a downstream substrate of PI3K/Akt in IGF-1 receptor signaling in hippocampal neurons and suggest that the phosphorylation of this transcription factor may play an important role in the neuronal survival properties of IGF-1.
Zheng
Wen-Hua
WH
Department of Psychiatry, Douglas Hospital Research Center, McGill University, Montreal, Quebec, Canada.
Kar
Satyabrata
S
Quirion
Rémi
R
D021581:Active Transport, Cell Nucleus; D000818:Animals; D017209:Apoptosis; D002470:Cell Survival / Q000502:physiology; D002478:Cells, Cultured; D016895:Culture Media, Serum-Free; D004268:DNA-Binding Proteins / Q000378:metabolism*; D053222:Fas Ligand Protein; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D006624:Hippocampus / Q000166:cytology; D007334:Insulin-Like Growth Factor I / Q000378:metabolism* / Q000502:physiology; D008562:Membrane Glycoproteins / Q000235:genetics; D009419:Nerve Tissue Proteins; D009474:Neurons / Q000201:enzymology* / Q000378:metabolism; D009584:Nitrogen; D016716:PC12 Cells; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics; D051381:Rats; D017526:Receptor, IGF Type 1 / Q000502:physiology; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D013912:Threonine / Q000378:metabolism; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D000071161:Forkhead Box Protein O1
D016895:Culture Media, Serum-Free; D004268:DNA-Binding Proteins; D053222:Fas Ligand Protein; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D007334:Insulin-Like Growth Factor I; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D009584:Nitrogen; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2; D017526:Receptor, IGF Type 1; D012694:Serine; D013912:Threonine; D014157:Transcription Factors; C499515:FOXO3 protein, rat; C505662:Faslg protein, rat; C074639:Foxo1 protein, rat; D000071161:Forkhead Box Protein O1; C494920:Akt1 protein, rat