Hypoxia Drives Breast Tumor Malignancy through a TET–TNFα–p38–MAPK Signaling Axis

Abstract

Hypoxia is a hallmark of solid tumors that drives malignant progression by altering epigenetic controls. In breast tumors, aberrant DNA methylation is a prevalent epigenetic feature associated with increased risk of metastasis and poor prognosis. However, the mechanism by which hypoxia alters DNA methylation or other epigenetic controls that promote breast malignancy remains poorly understood. We discovered that hypoxia deregulates TET1 and TET3, the enzymes that catalyze conversion of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), thereby leading to breast tumor-initiating cell (BTIC) properties. TET1/3 and 5hmC levels were closely associated with tumor hypoxia, tumor malignancy, and poor prognosis in breast cancer patients. Mechanistic investigations showed that hypoxia leads to genome-wide changes in DNA hydroxymethylation associated with upregulation of TNFa expression and activation of its downstream p38-MAPK effector pathway. Coordinate functions of TET1 and TET3 were also required to activate TNFa-p38-MAPK signaling as a response to hypoxia. Our results reveal how signal transduction through the TET-TNFa-p38-MAPK signaling axis is required for the acquisition of BTIC characteristics and tumorigenicity in vitro and in vivo, with potential implications for how to eradicate BTIC as a therapeutic strategy. Cancer Res; 75(18); 3912-24. Ó2015 AACR.

Hypoxia activates Wnt/β-catenin signaling by regulating the expression of BCL9 in human hepatocellular carcinoma

“…Knowing that hypoxia is a common characteristic of the microenvironment of solid tumors including HCC1828, we subjected HepG2 and smmc-7721 cells to hypoxia treatment (0.1% O 2 ) to see whether hypoxia could modulate the expression of BCL9 in human HCC. The effective induction of hypoxia in cells was confirmed by the increased expression of vascular endothelial growth factor (VEGF), a hypoxia-responsive gene, at mRNA levels (Fig.…”

Hypoxia induces the breast cancer stem cell phenotype by HIF-dependent and ALKBH5-mediated m 6 A-demethylation of NANOG mRNA

“…Finally, it should be noted that, in addition to activating transcription of the RNA demethylase ALKBH5, HIFs also regulate the expression of two other O 2 -dependent dioxygenases that play key roles in breast cancer metastasis and stem cell maintenance (43,44): JMJD2C, which mediates demethylation of histones (45), and TET1, which mediates hydroxymethylation of DNA (46). It is interesting that, in the absence of HIFs, the activity of these dioxygenases should decline under hypoxic conditions as a result of reduced substrate (i.e., O 2 ) availability.…”

Regulation and Functional Significance of 5-Hydroxymethylcytosine in Cancer

“…Several studies that have identified such loci describe the basis of 5hmC mediated gene regulation and also identify potential and novel regions that can be involved in regulation across the genome. Loss of 5hmC has been observed in Homeobox A Cluster (HOXA) genes, mir-200 and Leucine Zipper Tumor Suppressor 1 (LZTS1), leading to hypermethylation in those regions and promoting breast tumor progression and metastasis and in contrast, 5hmC gain at regions of (Tumor Necrosis Factor-Alpha) TNFA enable cell survival and stemness in breast tumor initiating cells (BTICs) under hypoxia [40][41][42][43]. Superoxide Dismutase 3 (SOD3), which is frequently downregulated in squamous cell carcinomas and adenocarcinomas, is also less expressed in lung (A549), breast (ZR75-1) and prostate (PC3) cancer cell lines as it incurs loss of 5hmC at its promoter region [44].…”

“…The global increase of 5hmC in proneural glioblastoma promotes expression of oncogenes by increased TET1 expression [49]. High levels of 5hmC due to high TET1 & 3 expression in hypoxic BTIC predicts poor disease-free and overall survival in breast cancer [41]. Interestingly, Wang et al showed a significant correlation between high 5hmC and cervical nodal metastasis in oral squamous cell carcinoma (OSCC) that is associated with poor overall survival [50].…”

“…Tumor hypoxia is observed to increase TET expression through Hypoxia Inducible Factor (HIF)-mediated transcriptional activation [41,84]. Apparently, TET enzymes assist hypoxia response program (HRP) by oxidizing repressive cytosine methylation of hypoxia-inducible genes (HIGs), since silencing TET1 reduced the 5hmC marks of HIGs in neuroblastoma cells [85].…”