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Differential responses of choroidal melanocytes and uveal melanoma cells to low oxygen conditions

ABSTRACT: PURPOSE: Tissue culture is traditionally performed at atmospheric oxygen concentration (21%), which induces hyperoxic stress, as endogenous physiologic oxygen tension found in tissues varies between 2% and 9%. This discrepancy may lead to misinterpretation of results and may explain why effects observed in vitro cannot always be reproduced in vivo and vice versa. Only a few studies have been conducted in low physiologic oxygen conditions to understand the development and differentiation of cells from the eye. METHODS: The aim of this study was to investigate the growth and gene expression profile of melanocytes from the choroid permanently exposed to 21% (hyperoxic) or 3% (physiologic) oxygen with proliferation assays and DNA microarray. The cellular behavior of the melanocytes was then compared to that of cancer cells. RESULTS: The gross morphology and melanin content of choroidal melanocytes changed slightly when they were exposed to 3% O2, and the doubling time was statistically significantly faster. There was an increase in the percentage of choroidal melanocytes in the active phases of the cell cycle as observed by using the proliferation marker Ki67. The caveolin-1 senescence marker was not increased in choroidal melanocytes or uveal melanoma cells grown in hyperoxia. In comparison, the morphology of the uveal melanoma cells was similar between the two oxygen levels, and the doubling time was slower at 3% O2. Surprisingly, gene expression profiling of the choroidal melanocytes did not reveal a large list of transcripts considerably dysregulated between the two oxygen concentrations; only the lactate transporter monocarboxylate transporter (MCT4) was statistically significantly upregulated at 3% O2. CONCLUSIONS: This study showed that the oxygen concentration must be tightly controlled in experimental settings, because it influences the subsequent cellular behavior of human choroidal melanocytes.

ORGANISM(S): Homo sapiens

PROVIDER: GSE86789 | GEO | 2016/09/10

SECONDARY ACCESSION(S): PRJNA342500

REPOSITORIES: GEO

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Project description:Preclinical studies of primary cancer cells are always done after tumors are removed from patients or animals at ambient atmospheric oxygen (O2, ~21%). However, O2 concentrations in organs are in the ~3-10% range, with most tumors in an hypoxic or 1-2% O2 environment in vivo. Although effects of O2 tension on tumor cell characteristics in vitro have been studied, these studies are done only after tumors are first collected and processed in ambient air. Similarly, sensitivity of primary cancer cells to anti-cancer agents is routinely examined at ambient O2. Here, using both mouse models and human cancers, we demonstrate that tumors collected, processed and propagated at physiologic (physioxia) O2 compared to ambient air display very distinct differences in key signaling networks including Lgr5/Wnt, Yap, and Nrf2/Keap1, nuclear reactive oxygen species levels, alternative splicing, and sensitivity to several targeted therapies including PIK3CAalpha-specific and EGFR inhibitors. Significance: Extra-physiologic oxygen shock/stress (EPHOSS), as noted in cells collected/processed under ambient air, has been demonstrated to have significant impact on numbers and engrafting ability of hematopoietic stem cells. We report deleterious effects of EPHOSS on cancer cell behavior and EPHOSS-mediated effects on cancer cells give misleading information on signaling pathway activation that could severely impact the relevance of these findings. Cancer cells under EPHOSS show higher proliferation rate compared to cells under physioxia and thus are sensitive to anti-proliferative agents. Thus, drugs that show effectiveness on cancer cells collected in ambient air and subjected to EPHOSS may not be effective or as relevant in vivo, results that could partially explain the limited clinical translation of laboratory findings. Evaluating cell signaling and effects of drugs on cancer cells under physiologic O2 prior to in vivo studies could substantially reduce cost and aid in drug discovery relevant to the actual physioxia/pathological status of the tumor cells in vivo.

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Differential responses of choroidal melanocytes and uveal melanoma cells to low oxygen conditions

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