RING1 Inhibition Has a Cell-Specific Antitumoral Role by Promoting Autophagy in Endometrial Cancer Cells.

BACKGROUND/AIMS: Factors influencing gene expression through chemical modifications of histones may play an important role in the regulation of the autophagy process in cancers. RING1A or RING1B are responsible for the catalytical activity of Polycomb repressive complex 1 (PRC1) which monoubiquitylate histone H2A. The aim of the study was to determine the effect of the RING1A/B protein inhibition on the autophagy process in endometrial cancer cells and the anticancer effectiveness of RING1 inhibitor PRT4165 in combination with autophagy inhibitors. METHODS: The expression of autophagy genes and proteins were analyzed in endometrial cancer cells HEC-1A and Ishikawa grown in different glucose concentrations and treated with PRT4165. To assess the effectiveness of PRT4165 used alone or in combination with HCQ or Lys05, IC50 and the combination index (CI) were calculated. Flow cytometry method was used to estimate apoptotic cells after treatment. RESULTS: The results confirm the impact of RINGs on autophagy and apoptosis in endometrial cancer cells. PRT4165 inhibitor causes changes in the expression of ATG genes and autophagy markers and the effect depends on glucose concentration and cell types. However, the anticancer effectiveness of PRT4165 was lower when it was used in combination with autophagy inhibitors, suggesting that such a combination is not a promising anticancer strategy. CONCLUSION: The results indicate the importance of the RINGs in the process of autophagy and apoptosis. Further potentially more effective combinations of PRT4165 with autophagy modulators should be sought.

Role of O-GlcNAcylation in Breast Cancer Biology.

Breast cancer is the most common type of cancer in women. It has been extensively researched over the past decades, but the underlying mechanisms of its growth, proliferation, invasion, and metastasis require further investigation. Dysregulation of O-GlcNAcylation which is one of the most abundant post-translational modifications, impacts on the malignant features of breast cancer. O-GlcNAcylation is broadly recognized as a nutrient sensor and participates in cells' survival and death. Through its involvement in protein synthesis and energy metabolism, especially glucose metabolism, O-GlcNAcylation enables adaptation to a hostile environment. It supports the migration and invasion of cancer cells and may be crucial for breast cancer metastasis. This review summarizes the current state of knowledge about O-GlcNAcylation in breast cancer: the origins of its dysregulation, its effect on the different aspects of breast cancer biology, and the potential utility in diagnostics and therapy.

The Role of Hypoxia-Inducible Factor Isoforms in Breast Cancer and Perspectives on Their Inhibition in Therapy.

Hypoxia is a common feature associated with many types of cancer. The activity of the hypoxia-inducible factors (HIFs), the critical element of response and adaptation to hypoxia, enhances cancer hallmarks such as suppression of the immune response, altered metabolism, angiogenesis, invasion, metastasis, and more. The HIF-1α and HIF-2α isoforms show similar regulation characteristics, although they are active in different types of hypoxia and can show different or even opposite effects. Breast cancers present several unique ways of non-canonical hypoxia-inducible factors activity induction, not limited to the hypoxia itself. This review summarizes different effects of HIFs activation in breast cancer, where areas such as metabolism, evasion of the immune response, cell survival and death, angiogenesis, invasion, metastasis, cancer stem cells, and hormone receptors status have been covered. The differences between HIF-1α and HIF-2α activity and their impacts are given special attention. The paper also discusses perspectives on using hypoxia-inducible factors as targets in anticancer therapy, given current knowledge acquired in molecular studies.

Contemporary Perspectives on the Warburg Effect Inhibition in Cancer Therapy.

In the 1920s, Otto Warburg observed the phenomenon of altered glucose metabolism in cancer cells. Although the initial hypothesis suggested that the alteration resulted from mitochondrial damage, multiple studies of the subject revealed a precise, multistage process rather than a random pattern. The phenomenon of aerobic glycolysis emerges not only from mitochondrial abnormalities common in cancer cells, but also results from metabolic reprogramming beneficial for their sustenance. The Warburg effect enables metabolic adaptation of cancer cells to grow and proliferate, simultaneously enabling their survival in hypoxic conditions. Altered glucose metabolism of cancer cells includes, inter alia, qualitative and quantitative changes within glucose transporters, enzymes of the glycolytic pathway, such as hexokinases and pyruvate kinase, hypoxia-inducible factor, monocarboxylate transporters, and lactate dehydrogenase. This review summarizes the current state of knowledge regarding inhibitors of cancer glucose metabolism with a focus on their clinical potential. The altered metabolic phenotype of cancer cells allows for targeting of specific mechanisms, which might improve conventional methods in anti-cancer therapy. However, several problems such as drug bioavailability, specificity, toxicity, the plasticity of cancer cells, and heterogeneity of cells in tumors have to be overcome when designing therapies based on compounds targeted in cancer cell energy metabolism.

Mitochondrial O-GlcNAc Transferase Interacts with and Modifies Many Proteins and Its Up-Regulation Affects Mitochondrial Function and Cellular Energy Homeostasis.

O-GlcNAcylation is a cell glucose sensor. The addition of O-GlcNAc moieties to target protein is catalyzed by the O-Linked N-acetylglucosamine transferase (OGT). OGT is encoded by a single gene that yields differentially spliced OGT isoforms. One of them is targeted to mitochondria (mOGT). Although the impact of O-GlcNAcylation on cancer cells biology is well documented, mOGT's role remains poorly investigated. We performed studies using breast cancer cells with up-regulated mOGT or its catalytic inactive mutant to identify proteins specifically modified by mOGT. Proteomic approaches included isolation of mOGT protein partners and O-GlcNAcylated proteins from mitochondria-enriched fraction followed by their analysis by mass spectrometry. Moreover, we analyzed the impact of mOGT dysregulation on mitochondrial activity and cellular metabolism using a variety of biochemical assays. We found that mitochondrial OGT expression is glucose-dependent. Elevated mOGT expression affected the mitochondrial transmembrane potential and increased intramitochondrial ROS generation. Moreover, mOGT up-regulation caused a decrease in cellular ATP level. We identified many mitochondrial proteins as mOGT substrates. Most of these proteins are localized in the mitochondrial matrix and the inner mitochondrial membrane and participate in mitochondrial respiration, fatty acid metabolism, transport, translation, apoptosis, and mtDNA processes. Our findings suggest that mOGT interacts with and modifies many mitochondrial proteins, and its dysregulation affects cellular bioenergetics and mitochondria function.

Expression of voltage-dependent anion channels in endometrial cancer and its potential prognostic significance.

The exchange of metabolites between mitochondria and cytosol occurs through pores formed by voltage-dependent anion channel proteins. Voltage-dependent anion channels appear to be master regulators of mitochondrial bioenergetics and the intracellular flow of energy. Deregulation of voltage-dependent anion channels expression is thought to be related to mitochondrial dysfunction in cancer. The aim of this study was to investigate the mRNA and protein expression levels of VDAC1, VDAC2, and VDAC3 in relation to clinicopathological characteristics of endometrial cancer as well as the prognostic significance of voltage-dependent anion channels expression for overall survival. VDAC1 and VDAC3 expressions were significantly higher in cancer compared to normal tissues. Kaplan-Meier analysis indicated that high expression of all VDAC genes or high VDAC2 protein level predicted poor overall survival. Multivariate analysis identified the VDAC1 and VDAC2 mRNA levels as well as VDAC2 protein level as independent prognostic factors. Our results suggest that increased expression of voltage-dependent anion channels correlates with tumor progression and may serve as a potential prognostic biomarker in endometrial cancer.