The online version of this article (https://doi.org/10.1186/s12885-018-4720-z) contains supplementary material, which is available to authorized users.
Hypoxia is a hallmark of the solid tumor microenvironment and is associated with poor outcomes in cancer patients. The present study was performed to investigate mechanisms underlying the hypoxia-induced phenotypic changes using human malignant mesothelioma (HMM) cells.
Hypoxic conditions were achieved by incubating HMM cells in the air chamber. The effect of hypoxia on phenotype changes in HMM cells was investigated by performing in vitro clonogenicity, drug resistance, migration, and invasion assays. Signaling pathways and molecules involved in the more aggressive behaviors of HMM cells under hypoxia were investigated. A two-tailed unpaired Student’s t-test or one-way ANOVA with Bonferroni post-test correction was used in this study.
Hypoxic conditions upregulated hypoxia-inducible factor 1 alpha (HIF-1α) and HIF-2α in parallel with the upregulation of its target, Glut-1, in HMM cells. In vitro clonogenicity of HMM cells was significantly increased in hypoxic conditions, but the proliferation of cells at a high density in hypoxia was lower than that in normoxic conditions. The expression levels of HIF-2α and Oct4 were increased in hypoxic HMM cells. The percentage of cells with high CD44 expression was significantly higher in HMM cells cultured in hypoxia than those cultured in normoxia. Hypoxia significantly enhanced the resistance of HMM cells to cisplatin, which occurred through cytoprotection against cisplatin-induced apoptosis. While cisplatin treatment decreased the ratio of Bcl-2 to Bax in normoxic condition, hypoxia conversely increased the ratio in HMM cells treated with cisplatin. Hypoxia increased the mobility and invasiveness of HMM cells. Epithelial to mesenchymal transition was promoted, which was indicated by the repression of E-cadherin and the concomitant increase of vimentin in HMM cells.
The data illustrated that hypoxic conditions augmented the aggressive phenotypes of HMM cells at the biological and molecular levels. The present study provides valuable background information beginning to understand aggressiveness of HMM in tumor microenvironments, suggesting that a control measure for tumor hypoxia may be an effective therapeutic strategy to reduce the aggressiveness of cancer cells in HMM patients.
Additional file 1: Table S1. The list of primers used in this study. (XLSX 10 kb)12885_2018_4720_MOESM1_ESM.xlsx
Additional file 2: All dataset and their information about statistical analysis in the present are deposited in this Excel spreadsheets. (XLSX 24 kb)12885_2018_4720_MOESM2_ESM.xlsx
Additional file 3: Figure S1. The effect of hypoxia on the abundance of HMM cells with CD44 expression. The percentage of cells with high CD44 expression is significantly higher in HMM cultured in hypoxia than those cultured in normoxia. Representative histogram of CD44 expression is presented. * P value < 0.05, as calculated by Student’s t-test. (TIF 719 kb)12885_2018_4720_MOESM3_ESM.tif
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