DNA methylation-driven EMT is a common mechanism of resistance to various therapeutic agents in cancer

Hypoxia Alters Epigenetic and N-Glycosylation Profiles of Ovarian and Breast Cancer Cell Lines in-vitro

Background: Glycosylation is one of the most fundamental post-translational modifications. Importantly, glycosylation is altered in many cancers. These alterations have been proven to impact on tumor progression and to promote tumor cell survival. From the literature, it is known that there is a clear link between chemoresistance and hypoxia, hypoxia and epigenetics and more recently glycosylation and epigenetics. Methods and Results: Our objective was to investigate these differential parameters, in an in vitro model of ovarian and breast cancer. Ovarian (A2780, A2780cis, PEO1, PEO4) and triple negative breast cancer (TNBC) (MDA-MB-231 and MDA-MB-436) cells were exposed to differential hypoxic conditions (0.5-2% O₂) and compared to normoxia (21% O₂). Results demonstrated that in hypoxic conditions some significant changes in glycosylation on the secreted N-glycans from the ovarian and breast cancer cell lines were observed. These included, alterations in oligomannosylated, bisected glycans, glycans with polylactosamine extensions, in branching, galactosylation and sialylation in all cell lines except for PEO1. In general, hypoxia exposed ovarian and TNBC cells also displayed increased epithelial to mesenchymal transition (EMT) and migration, with a greater effect seen in the 0.5% hypoxia exposed samples compared to 1 and 2% hypoxia (p ≤ 0.05). SiRNA transient knock down of GATA2/3 transcription factors resulted in a decrease in the expression of glycosyltransferases ST3GAL4 and MGAT5, which are responsible for sialylation and branching, respectively. Conclusions: These glycan changes are known to be integral to cancer cell survival and metastases, suggesting a possible mechanism of action, linking GATA2 and 3, and invasiveness of both ovarian and TNBC cells in vitro.

DNA methylation repels binding of hypoxia-inducible transcription factors to maintain tumor immunotolerance

BACKGROUND

Hypoxia is pervasive in cancer and other diseases. Cells sense and adapt to hypoxia by activating hypoxia-inducible transcription factors (HIFs), but it is still an outstanding question why cell types differ in their transcriptional response to hypoxia.

RESULTS

We report that HIFs fail to bind CpG dinucleotides that are methylated in their consensus binding sequence, both in in vitro biochemical binding assays and in vivo studies of differentially methylated isogenic cell lines. Based on in silico structural modeling, we show that 5-methylcytosine indeed causes steric hindrance in the HIF binding pocket. A model wherein cell-type-specific methylation landscapes, as laid down by the differential expression and binding of other transcription factors under normoxia, control cell-type-specific hypoxia responses is observed. We also discover ectopic HIF binding sites in repeat regions which are normally methylated. Genetic and pharmacological DNA demethylation, but also cancer-associated DNA hypomethylation, expose these binding sites, inducing HIF-dependent expression of cryptic transcripts. In line with such cryptic transcripts being more prone to cause double-stranded RNA and viral mimicry, we observe low DNA methylation and high cryptic transcript expression in tumors with high immune checkpoint expression, but not in tumors with low immune checkpoint expression, where they would compromise tumor immunotolerance. In a low-immunogenic tumor model, DNA demethylation upregulates cryptic transcript expression in a HIF-dependent manner, causing immune activation and reducing tumor growth.

CONCLUSIONS

Our data elucidate the mechanism underlying cell-type-specific responses to hypoxia and suggest DNA methylation and hypoxia to underlie tumor immunotolerance.

PTEN: What we know of the function and regulation of this onco-suppressor factor in bladder cancer?

Bladder cancer accounts for high morbidity and mortality around the world and its incidence rate is suggested to be higher in following years. A number of factors involve in bladder cancer development such as lifestyle and drugs. However, it appears that genetic factors play a significant role in bladder cancer development and progression. Phosphatase and tensin homolog (PTEN) is a cancer-related transcription factor that is corelated with reduced proliferation and invasion of cancer cells by negatively targeting PI3K/Akt/mTOR signaling pathway. In the present review, we aimed to explore the role of PTEN in bladder cancer cells and how upstream modulators affect PTEN in this life-threatening disorder. Down-regulation of PTEN is associated with poor prognosis, chemoresistance and progression of cancer cells. Besides, microRNAs, long non-coding RNAs, circular RNAs and other molecular pathways such as NF-kB are able to target PTEN in bladder cancer cells. Notably, anti-tumor drugs such as kaempferol, β-elemene and sorafenib upregulate the expression of PTEN to exert their inhibitory effects on bladder cancer cells.