Hypoxia-inducible factors regulate pluripotency factor expression by ZNF217- and ALKBH5-mediated modulation of RNA methylation in breast cancer cells

Abstract

Exposure of breast cancer cells to hypoxia increases the percentage of breast cancer stem cells (BCSCs), which are required for tumor initiation and metastasis, and this response is dependent on the activity of hypoxia-inducible factors (HIFs). We previously reported that exposure of breast cancer cells to hypoxia induces the ALKBH5-mediated demethylation of N6-methyladenosine (m6A) in NANOG mRNA leading to increased expression of NANOG, which is a pluripotency factor that promotes BCSC specification. Here we report that exposure of breast cancer cells to hypoxia also induces ZNF217-dependent inhibition of m6A methylation of mRNAs encoding NANOG and KLF4, which is another pluripotency factor that mediates BCSC specification. Although hypoxia induced the BCSC phenotype in all breast-cancer cell lines analyzed, it did so through variable induction of pluripotency factors and ALKBH5 or ZNF217. However, in every breast cancer line, the hypoxic induction of pluripotency factor and ALKBH5 or ZNF217 expression was HIF-dependent. Immunohistochemistry revealed that expression of HIF-1α and ALKBH5 was concordant in all human breast cancer biopsies analyzed. ALKBH5 knockdown in MDA-MB-231 breast cancer cells significantly decreased metastasis from breast to lungs in immunodeficient mice. Thus, HIFs stimulate pluripotency factor expression and BCSC specification by negative regulation of RNA methylation.

SUMOylation of the m6A-RNA methyltransferase METTL3 modulates its function

“…Most recently, a growing number of studies have reported that methylases and demethylases of m 6 A are correlated with cancer (8,30,38,39). As METTL3 is the core component of m 6 A the methyltransferase complex, we wondered whether SUMOylation of METTL3 is connected with tumorigenesis.…”

“…Growing evidences have also revealed that key enzymes for m 6 A demethylation such as ALKBH5 (8,39) and FTO (38) have important regulatory roles in tumorigenesis. In this study, we found that the SUMO-site mutant METTL3-4KR repressed the anchor-independent growth and xenograft tumor growth in H1299 cells (Figure 5), possibly resulting from higher abundance of m 6 A methylation in mRNAs, when compared to those of METTL3-WT (Figures 4E, G and 6A–C).…”

The Role of Hypoxia-Inducible Factors in Cancer Resistance

“…Importantly, they showed that this response is dependent on the activity of hypoxia-inducible factors (HIFs) which induce the increase in cancer stem cell markers expression. They found that NANOG, SOX2, and OCT4 expression increased in all human breast cancer cells they analyzed in response to chemotherapy or hypoxia [77].…”

“…A growing body of experimental evidence has indicated that cancerand metastasis-initiating cells with stem cell-like features typically display a higher resistance than the bulk mass of differentiated cancer cells to radiation therapy and chemotherapy, and thereby they can be responsible for disease relapse [76,77]. Cancer stem cells (CSC) are a small subpopulation of cells within various tumor types, which have the dual properties of self-renewal and differentiation by giving rise to both daughter cancer stem cells and bulk (non-stem) cancer cells, It has been demonstrated that CSCs are involved in initiating and sustaining tumor growth in many cancer types.…”

“…Many recent studies have shown that hypoxia inhibits differentiation of embryonic stem cells, progenitor cells [78], and mesenchymal stem/progenitor cells [79]. Under hypoxic conditions, tumor cells show increased clonogenic potential and Semenza's group in 2016 [77], demonstrated that the exposure of breast cancer cells to hypoxia increases the percentage of breast cancer stem cells, which are required for tumor initiation and metastasis. Importantly, they showed that this response is dependent on the activity of hypoxia-inducible factors (HIFs) which induce the increase in cancer stem cell markers expression.…”