Homocysteine induces cell cycle G1 arrest in endothelial cells through the PI3K/Akt/FOXO signaling pathway.
OBJECTIVE
High levels of homocysteine (Hcy) induce a sustained injury on arterial endothelial cells, which accelerates the development of thrombosis and atherosclerosis. Hcy specifically inhibits the growth of endothelial cells. The present study investigated the signaling pathways underlying this cell-cycle effect.


METHODS
Human umbilical venous endothelial cells were treated with Hcy, and/or LY294002, okadaic acid, peroxovanadate (PV), antisense Akt, phosphorylation of Akt and FKHRL1 proteins. p27(kip1) protein levels were measured with Western blotting, and Akt kinase activity and cell cycle were measured with immunoprecipitation and flow cytometry, respectively.


RESULTS
We demonstrate that Hcy induces dephosphorylation of Akt and FKHRL1 and upregulates the cyclin-dependent kinase inhibitors p27(kip1) in a time- and dose-dependent manner. Phosphatidylinositol-3 kinase (PI3K) activator PV and phosphatase 2A inhibitor okadaic acid could reverse it, which suggests it was dependent on PI3K activity. Moreover, Hcy induces cell cycle G1 phase arrest prevented by pretreatment with PV and okadaic acid. Transfection with specific antisense oligonucleotides to Akt further proves the observations.


CONCLUSIONS
The studies implied that a novel signaling pathway, PI3K/Akt/FOXO, might play an important role in mediating cell cycle G1 arrest in endothelial cells.
Zhang
Hong-Sheng
HS
Institute of Biophysics, Academia Sinica, Beijing, China.
Cao
En-Hua
EH
Qin
Jing-Fen
JF
D015153:Blotting, Western; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism*; D042783:Endothelial Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D000071161:Forkhead Box Protein O1; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D016193:G1 Phase / Q000187:drug effects*; D006710:Homocysteine / Q000737:chemistry / Q000494:pharmacology*; D006801:Humans; D047468:Immunoprecipitation; D007536:Isomerism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction / Q000187:drug effects; D014157:Transcription Factors / Q000378:metabolism*
D004268:DNA-Binding Proteins; D000071161:Forkhead Box Protein O1; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D006710:Homocysteine; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D014157:Transcription Factors; C085126:FOXO1 protein, human; C499517:FOXO3 protein, human; C494918:AKT1 protein, human