Cytokine-mediated FOXO3a phosphorylation suppresses FasL expression in hemopoietic cell lines: investigations of the role of Fas in apoptosis due to cytokine starvation.
We have investigated phosphatidylinositol 3-kinase (PI3K)-dependent survival signalling pathways using several cytokines in three different hemopoietic cell lines, MC/9, FDC-P1, and TF-1. Cytokines caused PI3K- and PKB-dependent phosphorylation of FOXO3a (previously known as FKHRL1) at three distinct sites. Following cytokine withdrawal or PI3K inhibition, both of which are known to lead to apoptosis, there was a loss of FOXO3a phosphorylation, and a resulting increase in forkhead transcriptional activity, along with increased expression of Fas Ligand (FasL), which could be detected at the cell surface. Concurrently, an increase in cell surface expression of Fas was also detected. Despite the presence of both FasL and Fas, there was no detectable evidence that activation of Fas-mediated apoptotic events was contributing to apoptosis resulting from cytokine starvation or inhibition of PI3K activity. Thus, inhibition of FOXO3a activity is mediated by the PI3K-PKB pathway, but regulation of FasL is not the primary means by which cell survival is regulated in cytokine-dependent hemopoietic cells. We were also able to confirm increased expression of known FOXO3a targets, Bim and p27kip1. Together, these results support the conclusion that mitochondrial-mediated signals play the major role in apoptosis of hemopoietic cells due to loss of cytokine signalling.
Behzad
Hayedeh
H
Department of Medicine, University of British Columbia and Vancouver Coastal Health Research Institute, Jack Bell Research Centre, 2660 Oak Street, Vancouver, BC, Canada V6H 3Z6.
Jamil
Sarwat
S
Denny
Trisha A
TA
Duronio
Vincent
V
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D045744:Cell Line, Tumor; D016207:Cytokines / Q000172:deficiency / Q000502:physiology*; D015536:Down-Regulation / Q000502:physiology*; D053222:Fas Ligand Protein / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics*; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000502:physiology*; D006410:Hematopoiesis / Q000502:physiology*; D006801:Humans; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology; D019014:fas Receptor / Q000502:physiology*
D016207:Cytokines; D053222:Fas Ligand Protein; C491899:Fas protein, mouse; C505658:Fasl protein, mouse; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; C474033:FoxO3 protein, mouse; D019014:fas Receptor; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt