Mining the epigenetic landscape of tissue polarity in search of new targets for cancer therapy

Pan-cancer analysis of m5C regulator genes reveals consistent epigenetic landscape changes in multiple cancers

BACKGROUND

5-Methylcytosine (m5C) is a reversible modification to both DNA and various cellular RNAs. However, its roles in developing human cancers are poorly understood, including the effects of mutant m5C regulators and the outcomes of modified nucleobases in RNAs.

METHODS

Based on The Cancer Genome Atlas (TCGA) database, we uncovered that mutations and copy number variations (CNVs) of m5C regulatory genes were significantly correlated across many cancer types. We then assessed the correlation between the expression of individual m5C regulators and the activity of related hallmark pathways of cancers.

RESULTS

After validating m5C regulators' expression based on their contributions to cancer development and progression, we observed their upregulation within tumor-specific processes. Notably, our research connected aberrant alterations to m5C regulatory genes with poor clinical outcomes among various tumors that may drive cancer pathogenesis and/or survival.

CONCLUSION

Our results offered strong evidence and clinical implications for the involvement of m5C regulators.

Epigenetic Alterations in Triple-Negative Breast Cancer-The Critical Role of Extracellular Matrix

Triple-negative breast cancer (TNBC) is an aggressive subgroup of breast cancer characterized by genomic complexity and therapeutic options limited to only standard chemotherapy. Although it has been suggested that stratifying TNBC patients by pathway-specific molecular alterations may predict benefit from specific therapeutic agents, application in routine clinical practice has not yet been established. There is a growing body of the literature supporting that epigenetic modifications comprised by DNA methylation, chromatin remodeling and non-coding RNAs play a fundamental role in TNBC pathogenesis. Extracellular matrix (ECM) is a highly dynamic 3D network of macromolecules with structural and cellular regulatory roles. Alterations in the expression of ECM components result in uncontrolled matrix remodeling, thus affecting its ability to regulate vital functions of cancer cells, including proliferation, migration, adhesion, invasion and epithelial-to-mesenchymal transition (EMT). Recent molecular data highlight the major role of tumor microenvironment and ECM alterations in TNBC and approaches for targeting tumor microenvironment have recently been recognized as potential therapeutic strategies. Notably, many of the ECM/EMT modifications in cancer are largely driven by epigenetic events, highlighting the pleiotropic effects of the epigenetic network in TNBC. This article presents and critically discusses the current knowledge on the epigenetic alterations correlated with TNBC pathogenesis, with emphasis on those associated with ECM/EMT modifications, their prognostic and predictive value and their use as therapeutic targets.

Epigenetic Regulation of Dlg1, via Kaiso, Alters Mitotic Spindle Polarity and Promotes Intestinal Tumorigenesis

Both alterations to the epigenome and loss of polarity have been linked to cancer initiation, progression, and metastasis. It has previously been demonstrated that loss of the epigenetic reader protein Kaiso suppresses intestinal tumorigenesis in the Apc+/min mouse model, in which altered polarity plays a key role. Thus, we investigated the link between Kaiso deficiency, polarity, and suppression of intestinal tumorigenesis. We used Kaiso-deficient mice to conditionally delete Apc within the intestinal epithelia and demonstrated upregulation of the spindle polarity genes Dlg1 and Dlgap1. To understand the role of Dlg1, we generated Villin-creApc+/minDlg1flx/flx Kaiso-/y mice to analyze gene expression, survival, tumor burden, and spindle orientation. In vivo analysis of the Dlg1-deficient intestine revealed improper orientation of mitotic spindles and a decreased rate of cellular migration. Loss of Dlg1 decreased survival in Apc+/min mice, validating its role as a tumor suppressor in the intestine. Significantly, the increased survival of Apc+/minKaisoy/- mice was shown to be dependent on Dlg1 expression. Taken together, these data indicate that maintenance of spindle polarity in the intestinal crypt requires appropriate regulation of Dlg1 expression. As Dlg1 loss leads to incorrect spindle orientation and a delay in cells transiting the intestinal crypt. We propose that the delayed exit from the crypt increase the window in which spontaneous mutations can become fixed, producing a "tumor-permissive" environment, without an increase in mutation rate. IMPLICATIONS: Loss of mitotic spindle polarity delays the exit of cells from the intestinal crypt and promotes a tumorigenic environment.