Transglutaminase 2 Promotes Autophagy by LC3 Induction through p53 Depletion in Cancer Cell

Type 2 transglutaminase in the nucleus: the new epigenetic face of a cytoplasmic enzyme

One of the major mysteries in science is how it is possible to pack the cellular chromatin with a total length of over 1 m, into a small sphere with a diameter of 5 mm "the nucleus", and even more difficult to envisage how to make it functional. Although we know that compaction is achieved through the histones, however, the DNA needs to be accessible to the transcription machinery and this is allowed thanks to a variety of very complex epigenetic mechanisms. Either DNA (methylation) or post-translational modifications of histone proteins (acetylation, methylation, ubiquitination and sumoylation) play a crucial role in chromatin remodelling and consequently on gene expression. Recently the serotonylation and dopaminylation of the histone 3, catalyzed by the Transglutaminase type 2 (TG2), has been reported. These novel post-translational modifications catalyzed by a predominantly cytoplasmic enzyme opens a new avenue for future investigations on the enzyme function itself and for the possibility that other biological amines, substrate of TG2, can influence the genome regulation under peculiar cellular conditions. In this review we analyzed the nuclear TG2's biology by discussing both its post-translational modification of various transcription factors and the implications of its epigenetic new face. Finally, we will focus on the potential impact of these events in human diseases.

New Therapeutic Interventions for Kidney Carcinoma: Looking to the Future

Simple Summary

Renal cell carcinoma (RCC) in metastatic form is a lethal pathology difficult to treat; therefore, the research of new therapeutic options for the treatment of metastatic patients is crucial to improve quality of life and overall survival. Recently, new signaling pathways and biological processes involved in cancer development and progression by scientific research community have been identified. These components including factors affecting angiogenesis, cell migration and invasion, autophagy and ferroptosis that are dysregulated in kidney cancer represent novel possible target molecules. In this work, we discuss current and new therapies for kidney cancer treatment; in particular, agents targeting new molecules involved in renal carcinogenesis that in future might become more powerful drugs for the cure of metastatic RCC.

Abstract

Patients suffering from metastatic renal cell carcinoma (mRCC) show an overall survival rate of lower than 10% after 5 years from diagnosis. Currently, the first-line treatment for mRCC patients is based on antiangiogenic drugs that are able to inhibit tyrosine kinase receptors (TKI) in combination with immuno-oncology (IO) therapy or IO-IO treatments. Second-line therapy involves the use of other TKIs, immunotherapeutic drugs, and mTOR inhibitors. Nevertheless, many patients treated with mTOR and TK inhibitors acquire drug resistance, making the therapy ineffective. Therefore, the research of new therapeutic targets is crucial for improving the overall survival and quality of life of mRCC patients. The investigation of the molecular basis of RCC, especially in clear cell renal cell carcinoma (ccRCC), has led to the identification of different signaling pathways that are involved in renal carcinogenesis. Most of ccRCCs are associated with mutation in VHL gene, which mediates the degradation of hypoxia-inducible factors (HIFs), that, in turn, regulate the pathways related to tumorigenesis, including angiogenesis and invasion. Renal tumorigenesis is also associated with the activation of tyrosine kinases that modulate the PI3K-Akt-mTOR pathway, promoting cell proliferation and survival. In ccRCC, the abnormal activity of mTOR activates the MDM2 protein, which leads to the degradation of tumor suppressor p53 via proteasome machinery. In addition, p53 may be degraded by autophagy in a mechanism involving the enzyme transglutaminase 2 (TG2). Suppression of wild-type p53 promotes cell growth, invasion, and drug resistance. Finally, the activation of ferroptosis appears to inhibit cancer progression in RCC. In conclusion, these pathways might represent new therapeutic targets for mRCC.

A transglutaminase 2-like gene from sea cucumber Apostichopus japonicus mediates coelomocytes autophagy

Transglutaminases (TGases) are widely known to play critical roles in innate immunity, in particular, TGase2, which involves in autophagy process to help degrade protein aggregates under stressful conditions in mammals. Nevertheless, the function of the TGase2 counterpart whether involves in invertebrate autophagy is largely unknown. In this study, a novel TGase2-like homologous gene from the sea cucumber Apostichopus japonicus (named as AjTGase2-like) was cloned using RACE technology and its biological functions were also investigated. The AjTGase2-like gene encoded a peptide of 750 amino acids with the representative domains of Transglut_N domain, TGc domain, and two Transglut_C domains, which exhibited highly conservative with vertebrate TGase2. Multiple sequence alignments and phylogenetic analysis both supported that AjTGase2-like belonged to a new member of TGase2 subfamily. AjTGase2-like was pervasively expressed in all examined tissues, with the largest transcription in muscle, followed by respiratory trees, and intestine. After immersion infection with Vibrio splendidus, the mRNA and protein levels of AjTGase2-like were both significantly induced and reached the highest levels at 24 h, indicating AjTGase2-like plays a key role in immune response. Further functional analysis showed that the ubiquitinated protein level was significantly increased by 1.65-fold (p < 0.01) after silencing of AjTGase2-like, and the protein levels of AjLC3-II/I and AjBeclin1 were both obviously decreased by 0.49-fold (p < 0.01) and 0.64-fold (p < 0.01) at the same time, while the authophagy receptor of Ajp62 was signally up-regulated by 1.40-fold (p < 0.01) under same condition. Moreover, the immunofluorescence signals of AjLC3 and Ajp62 were consistent with their protein levels, suggesting knockdown of AjTGase2-like causes a blockage in autophagy. More importantly, the AjLC3 positive signal was not increased after adding with chloroquine in the case of AjTGase2-like interference, indicating AjTGase2-like might play pivotal role in the early step of autophagosome formation. Besides, our results showed that the fluorescence signal of AjTGase2-like was largely co-localized with Ajp62 around the cytoplasm in vivo, and rAjp62 could directly combine with rAjTGase2-like in vitro, indicating AjTGase2-like interacts with Ajp62 during autophagy. Overall, our findings supported that AjTGase2-like served as a positive regulator in sea cucumber authophay.

Cryptotanshinone Inhibits the Growth of HCT116 Colorectal Cancer Cells Through Endoplasmic Reticulum Stress-Mediated Autophagy

Among cancers, colorectal cancer (CRC) has one of the highest annual incidence and death rates. Considering severe adverse reactions associated with classical chemotherapy medications, traditional Chinese medicines have become potential drug candidates. In the current study, the effects of cryptotanshinone (CPT), a major component of Salvia miltiorrhiza Bunge (Danshen) on CRC and underlying mechanism were explored. First of all, data from in vitro experiments and in vivo zebrafish models indicated that CPT selectively inhibited the growth and proliferation of HCT116 and SW620 cells while had little effect on SW480 cells. Secondly, both ER stress and autophagy were associated with CRC viability regulation. Interestingly, ER stress inhibitor and autophagy inhibitor merely alleviated cytotoxic effects on HCT116 cells in response to CPT stimulation, while have little effect on SW620 cells. The significance of apoptosis, autophagy and ER stress were verified by clinical data from CRC patients. In summary, the current study has revealed the anti-cancer effects of CPT in CRC by activating autophagy signaling mediated by ER stress. CPT is a promising drug candidate for CRC treatment.

The interaction mechanism between autophagy and apoptosis in colon cancer

Autophagy and apoptosis play crucial roles in tumorigenesis. Recent studies have shown that autophagy and apoptosis have a cross-talk relationship in anti-tumor therapy. It is well established that apoptosis is one of the main pathways of tumor cell death. While autophagy can occurs in tumors with opposite function: protective autophagy and lethal autophagy. Protective autophagy can inhibit tumor apoptosis induced by anticancer drugs, while lethal autophagy can induce tumor cell apoptosis in cooperation with anticancer drugs. Hence, autophagy and apoptosis have synergistic and antagonistic effects in tumor. Colorectal cancer is a common malignant tumor with high morbidity and mortality. In recent years, colorectal carcinoma has achieved improved clinical efficacy with drug treatment. Nonetheless, increasing drug-resistance limit the treatment efficacy, highlighting the urgency of exploring the molecular events that drive drug resistance. Researchers have found that autophagy is one of the major factors leading to drug resistance in colon cancer. Therefore, elucidating the interaction between autophagy and apoptosis is helpful to improve the efficacy of anticancer drugs in clinical treatment of colorectal cancer. This review attaches great importance to the relationship between autophagy and apoptosis and related factors in colorectal cancer.

Transglutaminase 2-Mediated p53 Depletion Promotes Angiogenesis by Increasing HIF-1α-p300 Binding in Renal Cell Carcinoma

Angiogenesis and the expression of vascular endothelial growth factor (VEGF) are increased in renal cell carcinoma (RCC). Transglutaminase 2 (TGase 2), which promotes angiogenesis in endothelial cells during wound healing, is upregulated in RCC. Tumor angiogenesis involves three domains: cancer cells, the extracellular matrix, and endothelial cells. TGase 2 stabilizes VEGF in the extracellular matrix and promotes VEGFR-2 nuclear translocation in endothelial cells. However, the role of TGase 2 in angiogenesis in the cancer cell domain remains unclear. Hypoxia-inducible factor (HIF)-1α-mediated VEGF production underlies the induction of angiogenesis in cancer cells. In this study, we show that p53 downregulated HIF-1α in RCC, and p53 overexpression decreased VEGF production. Increased TGase 2 promoted angiogenesis by inducing p53 degradation, leading to the activation of HIF-1α. The interaction of HIF-1α and p53 with the cofactor p300 is required for stable transcriptional activation. We found that TGase 2-mediated p53 depletion increased the availability of p300 for HIF-1α-p300 binding. A preclinical xenograft model suggested that TGase 2 inhibition can reverse angiogenesis in RCC.

The Gαh/phospholipase C-δ1 interaction promotes autophagosome degradation by activating the Akt/mTORC1 pathway in metastatic triple-negative breast cancer

Lung metastasis (LM) is commonly found in triple-negative breast cancer (TNBC); however, the molecular mechanism underlying TNBC metastasis to lungs remains largely unknown. We thus aimed to uncover a possible mechanism for the LM of TNBC. Here we show that the phosphorylation of Akt and mTORC1 was positively but the autophagy activity was negatively correlated with endogenous Gαh levels and cell invasion ability in TNBC cell lines. Whereas the knockdown of Gαh, as well as blocking its binding with PLC-δ1 by a synthetic peptide inhibitor, in the highly invasive MDA-MB231 cells dramatically suppressed Akt/mTORC1 phosphorylation and blocked autophagosome degradation, the overexpression of Gαh in the poorly invasive HCC1806 cells enhanced Akt/mTORC1 phosphorylation but promoted autophagosome degradation. The pharmaceutical inhibition of autophagy initiation by 3-methyladenine was found to rescue the cell invasion ability and LM potential of Gαh-silenced MDA-MB231 cells. In contrast, the inhibition of mTORC1 activity by rapamycin suppressed autophagosome degradation but mitigated the cell invasion ability and LM potential of Gαh-overexpressing HCC1806 cells. These findings demonstrate that the induction of autophagy activity or the inhibition of Akt-mTORC1 axis provides a useful strategy to combat the Gαh/PLC-δ1-driven LM of TNBC.

Inhibition of Transglutaminase 2 but Not of MDM2 Has a Significant Therapeutic Effect on Renal Cell Carcinoma

More than 50% of human cancers harbor TP53 mutations and increased expression of Mouse double minute 2 homolog(MDM2), which contribute to cancer progression and drug resistance. Renal cell carcinoma (RCC) has an unusually high incidence of wild-type p53, with a mutation rate of less than 4%. MDM2 is master regulator of apoptosis in cancer cells, which is triggered through proteasomal degradation of wild-type p53. Recently, we found that p53 protein levels in RCC are regulated by autophagic degradation. Transglutaminase 2 (TGase 2) was responsible for p53 degradation through this pathway. Knocking down TGase 2 increased p53-mediated apoptosis in RCC. Therefore, we asked whether depleting p53 from RCC cells occurs via MDM2-mediated proteasomal degradation or via TGase 2-mediated autophagic degradation. In vitro gene knockdown experiments revealed that stability of p53 in RCC was inversely related to levels of both MDM2 and TGase 2 protein. Therefore, we examined the therapeutic efficacy of inhibitors of TGase 2 and MDM2 in an in vivo model of RCC. The results showed that inhibiting TGase 2 but not MDM2 had efficient anticancer effects.

A Precision Strategy to Cure Renal Cell Carcinoma by Targeting Transglutaminase 2

In a recent report, no significance of transglutaminase 2 (TGase 2) was noted in the analyses of expression differences between normal and clear cell renal cell carcinoma (ccRCC), although we found that knock down of TGase 2 induced significant p53-mediated cell death in ccRCC. Generally, to find effective therapeutic targets, we need to identify targets that belong specifically to a cancer phenotype that can be differentiated from a normal phenotype. Here, we offer precise reasons why TGase 2 may be the first therapeutic target for ccRCC, according to several lines of evidence. TGase 2 is negatively regulated by von Hippel-Lindau tumor suppressor protein (pVHL) and positively regulated by hypoxia-inducible factor 1-α (HIF-1α) in renal cell carcinoma (RCC). Therefore, most of ccRCC presents high level expression of TGase 2 because over 90% of ccRCC showed VHL inactivity through mutation and methylation. Cell death, angiogenesis and drug resistance were specifically regulated by TGase 2 through p53 depletion in ccRCC because over 90% of ccRCC express wild type p53, which is a cell death inducer as well as a HIF-1α suppressor. Although there have been no detailed studies of the physiological role of TGase 2 in multi-omics analyses of ccRCC, a life-long study of the physiological roles of TGase 2 led to the discovery of the first target as well as the first therapeutic treatment for ccRCC in the clinical field.

Advancing the Role of Gamma-Tocotrienol as Proteasomes Inhibitor: A Quantitative Proteomic Analysis of MDA-MB-231 Human Breast Cancer Cells

Tocotrienol, an analogue of vitamin E has been known for its numerous health benefits and anti-cancer effects. Of the four isoforms of tocotrienols, gamma-tocotrienol (γT3) has been frequently reported for their superior anti-tumorigenic activity in both in vitro and in vivo studies, when compared to its counterparts. In this study, the effect of γT3 treatment in the cytoplasmic and nuclear fraction of MDA-MB-231 human breast cancer cells were assessed using the label-free quantitative proteomics analysis. The cytoplasmic proteome results revealed the ability of γT3 to inhibit a group of proteasome proteins such as PSMA, PSMB, PSMD, and PSME. The inhibition of proteasome proteins is known to induce apoptosis in cancer cells. As such, the findings from this study suggest γT3 as a potential proteasome inhibitor that can overcome deficiencies in growth-inhibitory or pro-apoptotic molecules in breast cancer cells. The nuclear proteome results revealed the involvement of important nuclear protein complexes which hardwire the anti-tumorigenesis mechanism in breast cancer following γT3 treatment. In conclusion, this study uncovered the advancing roles of γT3 as potential proteasomes inhibitor that can be used for the treatment of breast cancer.

The role of transglutaminase 2 in mediating glial cell function and pathophysiology in the central nervous system

The ubiquitously expressed transglutaminase 2 (TG2) has diverse functions in virtually all cell types, with its role depending not only on cell type, but also on specific subcellular localization. In the central nervous system (CNS) different types of glial cells, such as astrocytes, microglia, and oligodendrocytes and their precursor cells (OPCs), play pivotal supportive functions. This review is focused on what is currently known about the role of TG2 in each type of glial cell, in the context of normal function and pathophysiology. For example, astrocytic TG2 facilitates their migration and proliferation, but hinders their ability to protect neurons after CNS injury. The review also examines the interactions between glial cell types, and how TG2 in one cell type may affect another, as well as implications for specific TG2 populations as therapeutic targets in CNS pathology.

The Role of Tissue Transglutaminase in Cancer Cell Initiation, Survival and Progression

Tissue transglutaminase (transglutaminase type 2; TG2) is the most ubiquitously expressed member of the transglutaminase family (EC 2.3.2.13) that catalyzes specific post-translational modifications of proteins through a calcium-dependent acyl-transfer reaction (transamidation). In addition, this enzyme displays multiple additional enzymatic activities, such as guanine nucleotide binding and hydrolysis, protein kinase, disulfide isomerase activities, and is involved in cell adhesion. Transglutaminase 2 has been reported as one of key enzymes that is involved in all stages of carcinogenesis; the molecular mechanisms of action and physiopathological effects depend on its expression or activities, cellular localization, and specific cancer model. Since it has been reported as both a potential tumor suppressor and a tumor-promoting factor, the role of this enzyme in cancer is still controversial. Indeed, TG2 overexpression has been frequently associated with cancer stem cells’ survival, inflammation, metastatic spread, and drug resistance. On the other hand, the use of inducers of TG2 transamidating activity seems to inhibit tumor cell plasticity and invasion. This review covers the extensive and rapidly growing field of the role of TG2 in cancer stem cells survival and epithelial–mesenchymal transition, apoptosis and differentiation, and formation of aggressive metastatic phenotypes.