Chemotherapy triggers HIF-1–dependent glutathione synthesis and copper chelation that induces the breast cancer stem cell phenotype

Abstract

Triple negative breast cancer (TNBC) accounts for 10-15% of all breast cancer but is responsible for a disproportionate share of morbidity and mortality because of its aggressive characteristics and lack of targeted therapies. Chemotherapy induces enrichment of breast cancer stem cells (BCSCs), which are responsible for tumor recurrence and metastasis. Here, we demonstrate that chemotherapy induces the expression of the cystine transporter xCT and the regulatory subunit of glutamate-cysteine ligase (GCLM) in a hypoxia-inducible factor (HIF)-1-dependent manner, leading to increased intracellular glutathione levels, which inhibit mitogenactivated protein kinase kinase (MEK) activity through copper chelation. Loss of MEK-ERK signaling causes FoxO3 nuclear translocation and transcriptional activation of the gene encoding the pluripotency factor Nanog, which is required for enrichment of BCSCs. Inhibition of xCT, GCLM, FoxO3, or Nanog blocks chemotherapy-induced enrichment of BCSCs and impairs tumor initiation. These results suggest that, in combination with chemotherapy, targeting BCSCs by inhibiting HIF-1-regulated glutathione synthesis may improve outcome in TNBC.hypoxia-inducible factor | paclitaxel | pluripotency factors | chemotherapy resistance | tumor-initiating cells

HIF-1 regulates CD47 expression in breast cancer cells to promote evasion of phagocytosis and maintenance of cancer stem cells

“…We have recently demonstrated that exposure of breast cancer cells to hypoxia or chemotherapy induces the breast CSC phenotype through multiple HIF-dependent molecular pathways (18,20,54). Induction of CD47 expression provides another mechanism by which hypoxia induces the CSC phenotype.…”

“…Human breast cell lines MCF10A, MCF7, HCC1954, SUM159, MDA-MB-231, and MDA-MB-435 were cultured as previously described (18,20,21,54). All cells were maintained at 37°C in a 5% CO 2 and 95% air (20% O 2 ) incubator.…”

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

“…depletion of BCSCs (23). High NANOG mRNA (23) or protein (41) expression in primary human breast cancers is significantly associated with increased patient mortality.…”

“…High NANOG mRNA (23) or protein (41) expression in primary human breast cancers is significantly associated with increased patient mortality. Other groups have implicated HIFs in the direct transcriptional activation of NANOG and other genes encoding pluripotency factors, both in human ESCs (42) and human cancer cells (17).…”

“…In hypoxic breast cancer cells, HIFs activate the transcription of target genes that play important roles in tumor growth, angiogenesis, metabolic reprogramming, motility, invasion, metastasis, and resistance to chemotherapy (15,16). Recent studies have demonstrated that HIFs are required for the specification and/or maintenance of BCSCs in response to hypoxia (17)(18)(19)(20)(21) or chemotherapy (22,23), leading to direct or indirect transcriptional regulation of genes encoding the pluripotency factors NANOG, SOX2, and KLF4. In addition, HIF-1α is required for hypoxia-induced epithelial-mesenchymal transition (24), which is also linked to the BCSC phenotype (25).…”