Forkhead box proteins O1 (FOXO1) is a multifunctional transcription factor of the forkhead family. However the cell cycle was not markedly affected by FOXO1 siRNA. Furthermore Bim a downstream target of the Akt/FOXO1 signaling pathway was downregulated at both mRNA and protein levels in cells transfected with FOXO1 siRNA. Collectively these results indicate that FOXO1 may play an important role in inhibiting PTC development by regulating cellular proliferation growth and apoptosis. FOXO1 expression is usually a potentially useful biomarker for human PTC. Furthermore tumorigenesis of PTC may be connected with repression from the Akt/FOXO1/Bim signaling pathway. Keywords: siRNA FOXO1 Akt/FOXO1/Bim pathway papillary thyroid carcinoma proliferation apoptosis Launch Thyroid tumor can be an endocrine malignancy categorized into four main types: papillary thyroid carcinoma (PTC) follicular thyroid tumor medullary thyroid tumor and undifferentiated anaplastic thyroid tumor. Among these four types PTC may be the most common malignant thyroid tumor in the countries with enough iodine diet plans and comprises up to 80% of most thyroid malignancies.1 An epidemiologic research indicated the fact that incidence of thyroid tumor has nearly tripled from 1975 to 2009 and an upsurge in PTC may be the biggest contributor regarding to Security Epidemiology and FINAL RESULTS registry data.2 The complexities and pathogenesis of PTC are understood poorly. Exploring the root molecular mechanisms managing the advancement and development of PTC might provide us brand-new healing insights into this disease. The transcription aspect forkhead box proteins O1 (FOXO1) a founding person in the FOXO family members participates in diverse functions involving cell proliferation cell cycle control apoptosis differentiation metabolism and DNA damage repair.3-5 Increasing evidence suggests that the human FOXO1 protein is likely involved in carcinogenesis diabetes and Tmem26 other human diseases 4 because FOXO1 is downregulated in many human malignancies including breast cancer 6 prostate cancer Ginsenoside Rf 7 endometrial cancer Ginsenoside Rf 8 and Hodgkin’s lymphoma.9 Phosphatidyl inositol 3-kinase (PI3-K) and Akt signaling appear to play an important role in the progression of both papillary and follicular thyroid cancers.10 FOXO1 activity is negatively regulated by PI3-K/Akt which phosphorylates FOXO1 at multiple sites and forces FOXO1 into the cytoplasm thus decreasing its transcriptional activity.11-15 Bim a downstream target of Akt/FOXO1 signaling is a proapoptotic BH3 domain-only member of the Bcl-2 family. It has been reported that Bim is usually involved in the regulation of apoptosis in several different cell types 16 and has been Ginsenoside Rf shown to play a key role in depsipeptide-induced apoptosis in some human lung cancer cell lines.15 Although FOXO1 has been recognized as a novel tumor suppressor in different kinds of cancer its role in PTC has not been well established. Therefore the role of FOXO1 in PTC cells was validated by transfecting TPC1 and K1 cells with siRNA oligonucleotides targeting FOXO1. After transfection with siRNA mRNA and protein expression levels of FOXO1 and Bim were clearly downregulated. Downregulation of FOXO1 was Ginsenoside Rf associated with increased PTC cell proliferation and inhibition of apoptosis. FOXO1 may thus act as an anti-oncogene in PTC via the Akt/FOXO1/Bim pathway. Materials and methods Papillary thyroid carcinoma cell lines and culture conditions The PTC cell lines TPC1 and Ginsenoside Rf K1 were purchased from the cell bank of the Chinese Academy of Science (Shanghai People’s Republic of China). K1 and TPC1 cells were cultured in Dulbecco’s Modified Eagle’s Medium (DMEM; Thermo Fisher Scientific Waltham MA USA) and RPMI1640 medium (RPMI1640; Thermo Fisher Scientific) respectively supplemented with 100 Ginsenoside Rf U/mL penicillin 100 μg/mL streptomycin (Enpromise Hangzhou People’s Republic of China) and 10% fetal bovine serum (FBS Thermo Fisher Scientific) at 37°C in a humidified atmosphere containing 5% CO2. To maintain cells in viable condition cells were passaged using trypsin/ethylenediaminetetraacetic acid solution (saline made up of 0.05% trypsin 0.01 M sodium phosphate and 0.53 μM ethylene-diaminetetraacetic acid pH 7.4) when the cell density reached 80%-90% confluency. No ethics statement was required from the institutional review board for the use of these cell lines. Cell transfection FOXO1 small interfering RNA (siRNA) and siRNA unfavorable control.