title: Phosphorylation of FOXO3a by PI3K/Akt pathway in HK-2 renal proximal tubular epithelial cells exposed to cadmium.
abstract: We examined the effects of cadmium chloride (CdCl2) exposure on the phosphorylation and function of the forkhead box class O (FOXO) transcription factor FOXO3a in HK-2 human renal proximal tubular cells. Phosphorylation of FOXO3a (at Thr32 and Ser253) and its upstream kinase, Akt (at Thr308 and Ser473) were markedly increased following exposure to 10 or 20 μM CdCl2. Treatment with wortmannin (500 nM), an inhibitor of phosphoinositide-3-kinase (PI3K), suppressed CdCl2-induced phosphorylation of Akt and FOXO3a at their Akt phosphorylation sites. CdCl2-induced phosphorylation of FOXO3a was markedly suppressed by the epidermal growth factor receptor inhibitor, AG1478 (1 μM), the Ca(2+)/calmodulin-dependent kinase II inhibitor, KN-93 (10 μM), and the Src inhibitor, PP2 (10 μM), but only partially suppressed by the insulin-like growth factor-1 receptor inhibitor, PPP (2.5 μM). Furthermore, the p38 inhibitor, SB203580 (20 μM), suppressed CdCl2-induced phosphorylation of Akt and FOXO3a, suggesting possible cross-talk between p38 mitogen-activated protein kinase and Akt. Although phosphorylation of FOXO3a was associated with reduced levels of nuclear FOXO3a, this change in cellular localization was transient. Silencing of FOXO3a expression using short interfering RNA suppressed CdCl2-induced cellular damage and accumulation of cytoplasmic nucleosomes in HK-2 cells. These results show that cadmium exposure induces phosphorylation of FOXO3a through the PI3K/Akt signaling pathway and suggest that FOXO3a phosphorylation (inactivation) transiently promotes survival of HK-2 cells. Phosphorylation of FOXO3a by the PI3K/Akt pathway may regulate cell fate in proximal tubules exposed to cadmium.
authors.affiliation: Department of Hygiene and Public Health I, Tokyo Women's Medical University, Tokyo, 162-8666, Japan.
authors.forename: Kota
authors.initials: K
authors.lastname: Fujiki
authors.forename: Hisako
authors.initials: H
authors.lastname: Inamura
authors.forename: Masato
authors.initials: M
authors.lastname: Matsuoka
mesh_terms: D015153:Blotting, Western; D019256:Cadmium Chloride / Q000633:toxicity*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism; D002452:Cell Count; D002460:Cell Line; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D066246:ErbB Receptors / Q000378:metabolism; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000378:metabolism*; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009707:Nucleosomes / Q000187:drug effects; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering; D017526:Receptor, IGF Type 1 / Q000235:genetics / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: C499517:FOXO3 protein, human; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D009707:Nucleosomes; D034741:RNA, Small Interfering; D019869:Phosphatidylinositol 3-Kinases; D066246:ErbB Receptors; D017526:Receptor, IGF Type 1; D051057:Proto-Oncogene Proteins c-akt; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D019256:Cadmium Chloride