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Intermittent hypoxia confers pro-metastatic gene expression selectively through NF-kB in inflammatory breast cancer cells

ABSTRACT: Inflammatory breast cancer (IBC) is the most aggressive form of breast cancer. Treatment options are limited and the mechanisms underlying its aggressiveness are poorly understood. Intermittent hypoxia (IH) causes oxidative stress and is emerging as important regulator of tumor metastasis. Vessels in IBC tumors were shown to be immature, which is a primary cause of IH. We therefore investigated the relevance of IH for the modulation of gene expression in IBC cells in order to assess IH as potential regulator of IBC aggressiveness. Gene array analysis of IBC cells following chronic IH (45-60 days) demonstrated increased expression of pro-metastatic genes of the extracellular matrix, such as tenascin-C (TNC; an essential factor of the metastatic niche) and matrix metalloproteinase 9 (MMP9), and of pro-inflammatory processes, such as cyclooxygenase-2 (COX-2). Investigating the oxidative stress-dependent regulation of TNC, we found a gradual sensitivity on mRNA and protein levels. Oxidative stress activated NF-E2-related factor 2 (Nrf2), c-Jun N-terminal kinase (JNK), c-Jun and nuclear factor κB (NF-κB), but TNC upregulation was only dependent on NF-κB activation. Pharmacological inhibition of inhibitor of NF-κB α (IκBα) phosphorylation as well as overexpression of IκBα prevented TNC, MMP9 and COX-2 induction, whereas the pro-inflammatory cytokine interleukin-1β (IL-1β) increased their expression levels. Analysis of the gene array data showed NF-κB binding sites for 64% of all upregulated genes, linking NF-κB and IH-dependent regulation of pro-metastatic gene expression in IBC cells. Our results provide a first link between intermittent hypoxia and pro-metastatic gene expression in IBC cells, revealing a putative novel mechanism for the high metastatic potential of IBC.

ORGANISM(S): Homo sapiens

PROVIDER: GSE81416 | GEO | 2016/10/06

SECONDARY ACCESSION(S): PRJNA321509

REPOSITORIES: GEO

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Project description:The long-term effects of neonatal intermittent hypoxia (IH), an accepted model of apnea-induced hypoxia, are unclear. We have previously shown lasting âprogrammingâ effects on the HPA axis in adult rats exposed to neonatal IH. We hypothesized that neonatal rat exposure to IH will subsequently result in a heightened inflammatory state in the adult. Rat pups were exposed to normoxia (control) or six cycles of 5% IH or 10% IH over one hour daily from postnatal day 2 â 6. Plasma samples from blood obtained at 114 days of age were analyzed by assessing the capacity to induce transcription in a healthy peripheral blood mononuclear cell (PBMC) population and read using a high-density microarray. The analysis of plasma from adult rats previously exposed to neonatal 5% IH vs. 10% IH resulted in 2,579 significantly regulated genes including increased expression of Cxcl1, Cxcl2, Ccl3, Il1a, and Il1b. We conclude that neonatal exposure to intermittent hypoxia elicits a long-lasting programming effect in the adult resulting in an upregulation of inflammatory-related genes. Apnea is the most common cause of neonatal hypoxia affecting about 50% of preterm births (30 Ã¢ÂÂ 31 weeks), usually due to immature respiratory development. Upregulation of inflammatory genes and pathways in children 7 Ã¢ÂÂ 10 years of age has been shown, and there is a known increased risk of insulin resistance in adulthood when the fetus is exposed to maternal hypoxia, but the mechanism is unclear. The long-term metabolic, endocrine, and immunological effects of neonatal intermittent hypoxia (IH) exposure, an accepted model of apnea-induced hypoxia, have not been thoroughly evaluated. Recent studies in rats have shown that perinatal IH exposure can result in oxidative stress, causing a permanent immune response subsequently resulting in features of diabetes mellitus. We have previously examined adult rats exposed to neonatal intermittent hypoxia and perinatal continuous hypoxia, and have found lasting Ã¢ÂÂprogrammingÃ¢ÂÂ effects on the HPA axis. We now assess the long term effects of an accepted model of apnea-induced hypoxia using a validated transcriptional bioassay to study the extracellular milieu of adult rats exposed to neonatal intermittent hypoxia. We hypothesize that exposure to neonatal intermittent hypoxia will result in an increased inflammatory state in the adult as a result of long-lasting programming. Sprague-Dawley (SD) rat pups were treated with neonatal normoxia (21% O2, control), 5% intermittent hypoxia (IH), or 10% IH on postnatal days (PD) 2-6, daily over 1 hr. They were reared normally by birth dams and weaned at PD22. Males were allowed to mature and sacrificed at age PD114 after an overnight fast. Whole blood collected by decapitation into tubes with EDTA, and plasma saved for further analysis. Two adult (~180 day) male Brown Norway (BN) rats served as PBMC donors. Cells were incubated with 20% plasma that was either autologous BN (self-control), or one of 3 pools: a) SD normoxic N=8, b) SD 5% IH treated N=5, and c) SD 10% IH N=3.

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Intermittent hypoxia confers pro-metastatic gene expression selectively through NF-kB in inflammatory breast cancer cells

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