title: Selenite-induced survival of HuH7 hepatoma cells involves activation of focal adhesion kinase-phosphatidylinositol 3-kinase-Akt pathway and Rac1.
abstract: Selenium has been shown to sustain the growth of selected human hepatocellular carcinoma cell lines under serum-free conditions, but the detailed mechanism remained undetermined. In the present study, the molecular mechanism(s) involving sodium selenite (Na2SO3, Se) as a survival agent were determined. Selenite not only protects HuH7 cells from serum deprivation-induced apoptosis, it also supports its long-term growth in sodium selenite (10(-7)m) supplemented serum-free medium. The anti-apoptotic effect correlates with activation of focal adhesion kinase and the phosphatidylinositol 3-kinase (PI3K)-Akt kinase pathway. Using HuH7 cells stably transfected with a constitutively active Akt kinase and PI3K inhibitor LY294002, selenite-induced cell survival was shown to be PI3K-Akt-dependent. Parallel changes included a significant reduction in the intracellular reactive oxygen species content, the reversal of DNA fragmentation, and the suppression of caspase and apoptosis signal-regulating kinase 1 activities. HuH7 cells stably expressing a Rac1 mutant N17 (Rac1N17-HuH7) are refractory to selenite treatment. In these cells selenite supplement neither triggers Akt activation nor supports cell proliferation. Participation of Rac1 activation in this event is supported by the fact that selenite treatment drastically enhanced activation of Rac1. The exact link between selenite treatment, Rac1 activation, and activation of the focal adhesion kinase-PI 3-kinase, however, remains to be characterized. The mitogenic signaling mediated by selenite may involve unconventional growth stimuli including higher glutathione peroxidase 1 activity and higher transcription levels of selenoprotein P. The selenium-HuH7 system we have established thus provides a unique tool that will allow the biological role of selenite in growth regulation of hepatocytes to be studied in detail.
authors.affiliation: Institute of Genetics, School of Life Sciences, National Yang-Ming University, Shih-Pai, Taipei 112, Taiwan, Republic of China.
authors.forename: Yu-Chi
authors.initials: YC
authors.lastname: Lee
authors.forename: Yun-Chi
authors.initials: YC
authors.lastname: Tang
authors.forename: Yi-Hsien
authors.initials: YH
authors.lastname: Chen
authors.forename: Chiuan-Mei
authors.initials: CM
authors.lastname: Wong
authors.forename: Ann-Ping
authors.initials: AP
authors.lastname: Tsou
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D006528:Carcinoma, Hepatocellular / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D016895:Culture Media, Serum-Free; D004789:Enzyme Activation / Q000187:drug effects; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D015870:Gene Expression / Q000187:drug effects; D005979:Glutathione Peroxidase / Q000235:genetics; D006801:Humans; D018384:Oxidative Stress; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011506:Proteins / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D051149:Selenoprotein P; D051140:Selenoproteins; D015398:Signal Transduction / Q000187:drug effects; D018038:Sodium Selenite / Q000494:pharmacology*; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*; D000094765:Glutathione Peroxidase GPX1
chemical_list: D016895:Culture Media, Serum-Free; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D005979:Glutathione Peroxidase; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases; D011506:Proteins; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D051149:Selenoprotein P; D051140:Selenoproteins; D018038:Sodium Selenite; D020830:rac1 GTP-Binding Protein; D000094765:Glutathione Peroxidase GPX1; C496050:PTK2 protein, human; C494918:AKT1 protein, human; C000722067:GPX1 protein, human