ABSTRACT
PURPOSE: Lapatinib is a candidate drug for treatment of trastuzumab-resistant, human epidermal growth factor receptor 2 (HER2)–positive gastric cancer (GC). Unfortunately, lapatinib resistance renders this drug ineffective. The present study investigated the implication of forkhead box O1 (FOXO1) signaling in the acquired lapatinib resistance in HER2-positive GC cells. MATERIALS AND METHODS: Lapatinib-resistant GC cell lines (SNU-216 LR2-8) were generated in vitro by chronic exposure of lapatinib-sensitive, HER2-positive SNU-216 cells to lapatinib. SNU-216 LR cells with FOXO1 overexpression were generated by stable transfection of a constitutively active FOXO1 mutant (FOXO1A3). HER2 and MET in SNU-216 LR cells were downregulated using RNA interference. The sensitivity of GC cells to lapatinib and/or cisplatin was determined by crystal violet assay. In addition, Western blot analysis, luciferase reporter assay and reverse transcription–polymerase chain reaction were performed. RESULTS: SNU-216 LR cells showed upregulations of HER2 and MET, but downregulation of FOXO1 compared to parental SNU-216 cells. FOXO1 overexpression in SNU-216 LR cells significantly suppressed resistance to lapatinib and/or cisplatin. In addition, FOXO1 negatively controlled HER2 and MET at the transcriptional level and was negatively controlled by these molecules at the post-transcriptional level. A positive crosstalk was shown between HER2 and MET, each of which increased resistance to lapatinib and/or cisplatin. CONCLUSION: FOXO1 serves as an important linker between HER2 and MET signaling pathways through negative crosstalks and is a key regulator of the acquired lapatinib resistance in HER2-positive GC cells. These findings provide a rationale for establishing a novel treatment strategy to overcome lapatinib resistance in a subtype of GC patients.
Subject(s)
Humans , Blotting, Western , Cell Line , Cisplatin , Down-Regulation , Drug Resistance , Gentian Violet , In Vitro Techniques , Luciferases , Parents , ErbB Receptors , Receptor, ErbB-2 , RNA Interference , Stomach Neoplasms , Transfection , Up-RegulationABSTRACT
PURPOSE: We previously reported that forkhead transcription factors of the O class 1 (FOXO1) expression in gastric cancer (GC) was associated with angiogenesis-related molecules. However, there is little experimental evidence for the direct role of FOXO1 in GC. In the present study, we investigated the effect of FOXO1 on the tumorigenesis and angiogenesis in GC and its relationship with SIRT1. MATERIALS AND METHODS: Stable GC cell lines (SNU-638 and SNU-601) infected with a lentivirus containing FOXO1 shRNA were established for animal studies as well as cell culture experiments. We used xenograft tumors in nude mice to evaluate the effect of FOXO1 silencing on tumor growth and angiogenesis. In addition, we examined the association between FOXO1 and SIRT1 by immunohistochemical tissue array analysis of 471 human GC specimens and Western blot analysis of xenografted tumor tissues. RESULTS: In cell culture, FOXO1 silencing enhanced hypoxia inducible factor-1alpha (HIF-1alpha) expression and GC cell growth under hypoxic conditions, but not under normoxic conditions. The xenograft study showed that FOXO1 downregulation enhanced tumor growth, microvessel areas, HIF-1alpha activation and vascular endothelial growth factor (VEGF) expression. In addition, inactivated FOXO1 expression was associated with SIRT1 expression in human GC tissues and xenograft tumor tissues. CONCLUSION: Our results indicate that FOXO1 inhibits GC growth and angiogenesis under hypoxic conditions via inactivation of the HIF-1alpha-VEGF pathway, possibly in association with SIRT1. Thus, development of treatment modalities aiming at this pathway might be useful for treating GC.
Subject(s)
Animals , Humans , Mice , Angiogenesis Modulating Agents , Hypoxia , Blotting, Western , Carcinogenesis , Cell Culture Techniques , Cell Line , Down-Regulation , Forkhead Transcription Factors , Heterografts , Lentivirus , Mice, Nude , Microvessels , RNA, Small Interfering , Stomach Neoplasms , Tissue Array Analysis , Transcription Factors , Vascular Endothelial Growth Factor AABSTRACT
Objective:Investigate the relation between the phosphorylation of FOXO1 and the apoptosis and the proliferation of lymphoma cells and to clarify its specific mechanism.Methods:The lymphoma cells Namalwa and Jurkat were treated with PI3K inhibitor wort mannin or etoposide or Wortmannin plus etoposide for different times-pan and at different concentration.The inhibition rates for cell growth of lymphoma cells were examined by XTT assay.Apoptosis were detected by flow cytometry.The expressions of p-Akt,p-FOXO1,FOXO1 and Bim were determined by Western blot analysis.Results:Wortmannin induced apoptosis of Jurkat cells and Namalwa cells and inhibited their survival effectively.The growth inhibition rate and the apoptosis rate of lymphoma cells induced by Wortmannin plus etoposide were higher than those induced by etoposide alone.After treated with Wortmannin,phosphorylation of FOXO1 remarkably reduced and bim markedly increased.Conclusion:The dephosphorylation of FOXO1 inhibits proliferation of Jurkat cells and Namalwa cells,promotes their apoptosis and enhanced the sensitivity of Non-Hodgkin lymphoma cells to etoposide.Bim activated by FOXO1 promotes cell apoptosis.