PTEN activation through K163 acetylation by inhibiting HDAC6 contributes to tumour inhibition

SIRT7 facilitates endometrial cancer progression by regulating PTEN stability in an estrogen-dependent manner

The prognosis of metastatic endometrial carcinoma (EC), one of the most common gynecological malignancies worldwide, remains poor, and the underlying driver of metastases is poorly understood. Dysregulation in estrogen-related signaling and inactivation of tumor suppressor PTEN are two essential risk factors of EC. However, whether and how they are interconnected during EC development remains unclear. Here, we demonstrate that the deacetylase SIRT7 is upregulated in EC patients and mouse models, facilitating EC progression in vitro and in vivo. Mechanistically, in an estrogen-dependent fashion, SIRT7 mediates PTEN deacetylation at K260, promoting PTEN ubiquitination by the E3 ligase NEDD4L, accelerating PTEN degradation and, consequently, expediting EC metastasis. Additionally, SIRT7 expression strongly correlates with poor survival in EC patients with wild-type PTEN, though no significant correlation is observed in PTEN mutation patients. These results lay the foundation for the study of targeting estrogen-SIRT7-PTEN axis, to restore PTEN abundance, offering potential avenues for EC therapy.

PRMT7-Mediated PTEN Activation Enhances Bone Regeneration in Female Mice

Epigenetic regulation provides new insights into the mechanisms of osteogenic differentiation and identifies potential targets for treating bone-related diseases. However, the specific regulatory networks and mechanisms involved still need further investigation. In this study, we identify PRMT7 as a novel epigenetic regulator of mesenchymal stem cells (MSCs) osteogenic commitment. Conditional knockout of Prmt7 in mice reveals a significant impairment in osteogenesis and bone regeneration, specifically in females, affecting both femurs and mandibles, with no noticeable effect in males. Mechanistically, PRMT7 modulates MSCs osteogenic differentiation by activating PTEN. Specifically, PRMT7 enhances PTEN transcription by increasing H3R2me1 levels at the PTEN promoter. Additionally, PRMT7 interacts with the PTEN protein and stabilizes nuclear PTEN, revealing an unprecedented pathway. Notably, overexpression of PTEN alleviates the osteogenic deficits observed in Prmt7-deficient mice. This research establishes PRMT7 as a potential therapeutic target for promoting bone formation/regeneration and offers novel molecular insights into the PRMT7-PTEN regulatory axis, underscoring its significance in bone biology and regenerative medicine.

The role of acetylation and deacetylation in cancer metabolism

As a hallmark of cancer, metabolic reprogramming adjusts macromolecular synthesis, energy metabolism and redox homeostasis processes to adapt to and promote the complex biological processes of abnormal growth and proliferation. The complexity of metabolic reprogramming lies in its precise regulation by multiple levels and factors, including the interplay of multiple signalling pathways, precise regulation of transcription factors and dynamic adjustments in metabolic enzyme activity. In this complex regulatory network, acetylation and deacetylation, which are important post-translational modifications, regulate key molecules and processes related to metabolic reprogramming by affecting protein function and stability. Dysregulation of acetylation and deacetylation may alter cancer cell metabolic patterns by affecting signalling pathways, transcription factors and metabolic enzyme activity related to metabolic reprogramming, increasing the susceptibility to rapid proliferation and survival. In this review, we focus on discussing how acetylation and deacetylation regulate cancer metabolism, thereby highlighting the central role of these post-translational modifications in metabolic reprogramming, and hoping to provide strong support for the development of novel cancer treatment strategies. KEY POINTS: Protein acetylation and deacetylation are key regulators of metabolic reprogramming in tumour cells. These modifications influence signalling pathways critical for tumour metabolism. They modulate the activity of transcription factors that drive gene expression changes. Metabolic enzymes are also affected, altering cellular metabolism to support tumour growth.

Ubiquitin-specific protease 22 controls melanoma metastasis and vulnerability to ferroptosis through targeting SIRT1/PTEN/PI3K signaling

Metastasis is a major contributing factor that affects the prognosis of melanoma patients. Nevertheless, the underlying molecular mechanisms involved in melanoma metastasis are not yet entirely understood. Here, we identified ubiquitin-specific protease 22 (USP22) as a pro-oncogenic protein in melanoma through screening the survival profiles of 52 ubiquitin-specific proteases (USPs). USP22 demonstrates a strong association with poor clinical outcomes and is significantly overexpressed in melanoma. Ablation of USP22 expression remarkably attenuates melanoma migration, invasion, and epithelial-mesenchymal transition in vitro and suppresses melanoma metastasis in vivo. Mechanistically, USP22 controls melanoma metastasis through the SIRT1/PTEN/PI3K pathway. In addition, we conducted an United States Food and Drug Administration-approved drug library screening and identified topotecan as a clinically applicable USP22-targeting molecule by promoting proteasomal degradation of USP22. Finally, we found that both pharmacological and genetic silence of USP22 sensitize RSL3-induced ferroptosis through suppressing the PI3K/Akt/mTOR pathway and its downstream SCD, and ferroptosis inhibitor could partly rescued the decreased lung metastasis by topotecan in vivo. Overall, our findings reveal a prometastatic role of USP22 and identify topotecan as a potent USP22-targeting drug to limit melanoma metastasis.

Post-Translational Modification of PTEN Protein: Quantity and Activity

Post-translational modifications play crucial roles in regulating protein functions and stabilities. PTEN is a critical tumor suppressor involved in regulating cellular proliferation, survival, and migration processes. However, dysregulation of PTEN is common in various human cancers. PTEN stability and activation/suppression have been extensively studied in the context of tumorigenesis through inhibition of the PI3K/AKT signaling pathway. PTEN undergoes various post-translational modifications, primarily including phosphorylation, acetylation, ubiquitination, SUMOylation, neddylation, and oxidation, which finely tune its activity and stability. Generally, phosphorylation modulates PTEN activity through its lipid phosphatase function, leading to altered power of the signaling pathways. Acetylation influences PTEN protein stability and degradation rate. SUMOylation has been implicated in PTEN localization and interactions with other proteins, affecting its overall function. Neddylation, as a novel modification of PTEN, is a key regulatory mechanism in the loss of tumor suppressor function of PTEN. Although current therapeutic approaches focus primarily on inhibiting PI3 kinase, understanding the post-translational modifications of PTEN could help provide new therapeutic strategies that can restore PTEN's role in PIP3-dependent tumors. The present review summarizes the major recent developments in the regulation of PTEN protein level and activity. We expect that these insights will contribute to better understanding of this critical tumor suppressor and its potential implications for cancer therapy in the future.

Epigenetic-based differentiation therapy for Acute Myeloid Leukemia

Despite the development of novel therapies for acute myeloid leukemia, outcomes remain poor for most patients, and therapeutic improvements are an urgent unmet need. Although treatment regimens promoting differentiation have succeeded in the treatment of acute promyelocytic leukemia, their role in other acute myeloid leukemia subtypes needs to be explored. Here we identify and characterize two lysine deacetylase inhibitors, CM-444 and CM-1758, exhibiting the capacity to promote myeloid differentiation in all acute myeloid leukemia subtypes at low non-cytotoxic doses, unlike other commercial histone deacetylase inhibitors. Analyzing the acetylome after CM-444 and CM-1758 treatment reveals modulation of non-histone proteins involved in the enhancer-promoter chromatin regulatory complex, including bromodomain proteins. This acetylation is essential for enhancing the expression of key transcription factors directly involved in the differentiation therapy induced by CM-444/CM-1758 in acute myeloid leukemia. In summary, these compounds may represent effective differentiation-based therapeutic agents across acute myeloid leukemia subtypes with a potential mechanism for the treatment of acute myeloid leukemia.

Pancreatic Neuroendocrine Tumors: Signaling Pathways and Epigenetic Regulation

Pancreatic neuroendocrine tumors (PNETs) are characterized by dysregulated signaling pathways that are crucial for tumor formation and progression. The efficacy of traditional therapies is limited, particularly in the treatment of PNETs at an advanced stage. Epigenetic alterations profoundly impact the activity of signaling pathways in cancer development, offering potential opportunities for drug development. There is currently a lack of extensive research on epigenetic regulation in PNETs. To fill this gap, we first summarize major signaling events that are involved in PNET development. Then, we discuss the epigenetic regulation of these signaling pathways in the context of both PNETs and commonly occurring-and therefore more extensively studied-malignancies. Finally, we will offer a perspective on the future research direction of the PNET epigenome and its potential applications in patient care.

De novo NAD+ synthesis contributes to CD8+ T cell metabolic fitness and antitumor function

The dysfunction and clonal constriction of tumor-infiltrating CD8+ T cells are accompanied by alterations in cellular metabolism; however, how the cell-intrinsic metabolic pathway specifies intratumoral CD8+ T cell features remains elusive. Here, we show that cell-autonomous generation of nicotinamide adenine dinucleotide (NAD+) via the kynurenine pathway (KP) contributes to the maintenance of intratumoral CD8+ T cell metabolic and functional fitness. De novo NAD+ synthesis is involved in CD8+ T cell metabolism and antitumor function. KP-derived NAD+ promotes PTEN deacetylation, thereby facilitating PTEN degradation and preventing PTEN-dependent metabolic defects. Importantly, impaired cell-autonomous NAD+ synthesis limits CD8+ T cell responses in human colorectal cancer samples. Our results reveal that KP-derived NAD+ regulates the CD8+ T cell metabolic and functional state by restricting PTEN activity and suggest that modulation of de novo NAD+ synthesis could restore CD8+ T cell metabolic fitness and antitumor function.

Cancer and Autism: How PTEN Mutations Degrade Function at the Membrane and Isoform Expression in the Human Brain

Mutations causing loss of PTEN lipid phosphatase activity can promote cancer, benign tumors (PHTS), and neurodevelopmental disorders (NDDs). Exactly how they preferentially trigger distinct phenotypic outcomes has been puzzling. Here, we demonstrate that PTEN mutations differentially allosterically bias P loop dynamics and its connection to the catalytic site, affecting catalytic activity. NDD-related mutations are likely to sample conformations of the functional wild-type state, while sampled conformations for the strong, cancer-related driver mutation hotspots favor catalysis-primed conformations, suggesting that NDD mutations are likely to be weaker, and our large-scale simulations show why. Prenatal PTEN isoform expression data suggest exons 5 and 7, which harbor NDD mutations, as cancer-risk carriers. Since cancer requires more than a single mutation, our conformational and genomic analysis helps discover how same protein mutations can foster different clinical manifestations, articulates a role for co-occurring background latent driver mutations, and uncovers relationships of splicing isoform expression to life expectancy.

The Role of Histone Deacetylases in Acute Lung Injury-Friend or Foe

Acute lung injury (ALI), caused by intrapulmonary or extrapulmonary factors such as pneumonia, shock, and sepsis, eventually disrupts the alveolar-capillary barrier, resulting in diffuse pulmonary oedema and microatasis, manifested by refractory hypoxemia, and respiratory distress. Not only is ALI highly lethal, but even if a patient survives, there are also multiple sequelae. Currently, there is no better treatment than supportive care, and we urgently need to find new targets to improve ALI. Histone deacetylases (HDACs) are epigenetically important enzymes that, together with histone acetylases (HATs), regulate the acetylation levels of histones and non-histones. While HDAC inhibitors (HDACis) play a therapeutic role in cancer, inflammatory, and neurodegenerative diseases, there is also a large body of evidence suggesting the potential of HDACs as therapeutic targets in ALI. This review explores the unique mechanisms of HDACs in different cell types of ALI, including macrophages, pulmonary vascular endothelial cells (VECs), alveolar epithelial cells (AECs), and neutrophils.

Phospho PTEN mediated dephosphorylation of mitotic kinase PLK1 and Aurora Kinase A prevents aneuploidy and preserves genomic stability

PTEN, dual phosphatase tumor suppressor protein, is found to be frequently mutated in various cancers. Post-translational modification of PTEN is important for its sub-cellular localization and catalytic functions. But how these modifications affect cytological damage and aneuploidy is not studied in detail. We focus on the role of phosphatase activity along with C-terminal phosphorylation of PTEN in perspective of cytological damage like micronucleus, nuclear bud, and nuclear bridge formation. Our data suggest that wild-type PTEN, but not phospho-mutant PTEN significantly reduces cytological damage in PTEN null PC3 cells. In case of phosphatase-dead PTEN, cytological damage markers are increased during 24 h recovery after DNA damage. When we use phosphorylation and phosphatase-dead dual mutant PTEN, the extent of different cytological DNA damage parameters are similar to phosphatase-dead PTEN. We also find that both of those activities are essential for maintaining chromosome numbers. PTEN null cells exhibit significantly aberrant γ-tubulin pole formation during metaphase. Interestingly, we observed that p-PTEN localized to spindle poles along with PLK1 and Aurora Kinase A. Further depletion of phosphorylation and phosphatase activity of PTEN increases the expression of p-Aurora Kinase A (T288) and p-PLK1 (T210), compared to cells expressing wild-type PTEN. Again, wild-type PTEN but not phosphorylation-dead mutant is able to physically interact with PLK1 and Aurora Kinase A. Thus, our study suggests that the phosphorylation-dependent interaction of PTEN with PLK1 and Aurora Kinase A causes dephosphorylation of those mitotic kinases and by lowering their hyperphosphorylation status, PTEN prevents aberrant chromosome segregation in metaphase.

Curriculum vitae of HDAC6 in solid tumors

Histone deacetylase 6 (HDAC6) is the only member of the HDAC family that resides primarily in the cytoplasm with two catalytic domains and a ubiquitin-binding domain. HDAC6 is highly expressed in various solid tumors and participates in a wide range of biological activities, including hormone receptors, the p53 signaling pathway, and the kinase cascade signaling pathway due to its unique structural foundation and abundant substrate types. Additionally, HDAC6 can function as an oncogenic factor in solid tumors, boosting tumor cell proliferation, invasion and metastasis, drug resistance, stemness, and lowering tumor cell immunogenicity, so assisting in carcinogenesis. Pan-HDAC inhibitors for cancer prevention are associated with potential cardiotoxicity in clinical investigations. It's interesting that HDAC6 silencing didn't cause any significant harm to normal cells. Currently, the use of HDAC6 specific inhibitors, individually or in combination, is among the most promising therapies in solid tumors. This review's objective is to give a general overview of the structure, biological functions, and mechanism of HDAC6 in solid tumor cells and in the immunological milieu and discuss the preclinical and clinical trials of selective HDAC6 inhibitors. These endeavors highlight that targeting HDAC6 could effectively kill tumor cells and enhance patients' immunity during solid tumor therapy.

Acetylation stabilizes the signaling protein WISP2 by preventing its degradation to suppress the progression of acute myeloid leukemia

Acute myeloid leukemia (AML) is challenging to treat due to its heterogeneity, prompting a deep understanding of its pathogenesis mechanisms, diagnosis, and treatment. Here, we found reduced expression and acetylation levels of WISP2 in bone marrow mononuclear cells from AML patients and that AML patients with lower WISP2 expression tended to have reduced survival. At the functional level, overexpression of WISP2 in leukemia cells (HL-60 and Kasumi-1) suppressed cell proliferation, induced cell apoptosis, and exerted antileukemic effects in an in vivo model of AML. Our mechanistic investigation demonstrated that WISP2 deacetylation was regulated by the deacetylase histone deacetylase (HDAC)3. In addition, we determined that crosstalk between acetylation and ubiquitination was involved in the modulation of WISP2 expression in AML. Deacetylation of WISP2 decreased the stability of the WISP2 protein by boosting its ubiquitination mediated by NEDD4 and proteasomal degradation. Moreover, pan-HDAC inhibitors (valproic acid and trichostatin A) and an HDAC3-specific inhibitor (RGFP966) induced WISP2 acetylation at lysine K6 and prevented WISP2 degradation. This regulation led to inhibition of proliferation and induction of apoptosis in AML cells. In summary, our study revealed that WISP2 contributes to tumor suppression in AML, which provided an experimental framework for WISP2 as a candidate for gene therapy of AML.

How PTEN mutations degrade function at the membrane and life expectancy of carriers of mutations in the human brain

PTEN dysfunction, caused by loss of lipid phosphatase activity or deletion, promotes pathologies, cancer, benign tumors, and neurodevelopmental disorders (NDDs). Despite efforts, exactly how the mutations trigger distinct phenotypic outcomes, cancer or NDD, has been puzzling. It has also been unclear how to distinguish between mutations harbored by isoforms, are they cancer or NDDs-related. Here we address both. We demonstrate that PTEN mutations differentially allosterically bias P-loop dynamics and its connection to the catalytic site, affecting catalytic activity. NDD-related mutations are likely to sample conformations present in the wild-type, while sampled conformations sheltering cancer-related hotspots favor catalysis-prone conformations, suggesting that NDD mutations are weaker. Analysis of isoform expression data indicates that if the transcript has NDD-related mutations, alone or in combination with cancer hotspots, there is high prenatal expression. If no mutations within the measured days, low expression levels. Cancer mutations promote stronger signaling and cell proliferation; NDDs' are weaker, influencing brain cell differentiation. Further, exon 5 is impacted by NDD or non-NDD mutations, while exon 7 is exclusively impacted by NDD mutations. Our comprehensive conformational and genomic analysis helps discover how same allele mutations can foster different clinical manifestations and uncovers correlations of splicing isoform expression to life expectancy.

Targeting PTEN Regulation by Post Translational Modifications

Phosphatidylinositol-3,4,5-triphosphate (PIP₃) is a lipidic second messenger present at very low concentrations in resting normal cells. PIP₃ levels, though, increase quickly and transiently after growth factor addition, upon activation of phosphatidylinositol 3-kinase (PI3-kinase). PIP₃ is required for the activation of intracellular signaling pathways that induce cell proliferation, cell migration, and survival. Given the critical role of this second messenger for cellular responses, PIP₃ levels must be tightly regulated. The lipid phosphatase PTEN (phosphatase and tensin-homolog in chromosome 10) is the phosphatase responsible for PIP₃ dephosphorylation to PIP₂. PTEN tumor suppressor is frequently inactivated in endometrium and prostate carcinomas, and also in glioblastoma, illustrating the contribution of elevated PIP₃ levels for cancer development. PTEN biological activity can be modulated by heterozygous gene loss, gene mutation, and epigenetic or transcriptional alterations. In addition, PTEN can also be regulated by post-translational modifications. Acetylation, oxidation, phosphorylation, sumoylation, and ubiquitination can alter PTEN stability, cellular localization, or activity, highlighting the complexity of PTEN regulation. While current strategies to treat tumors exhibiting a deregulated PI3-kinase/PTEN axis have focused on PI3-kinase inhibition, a better understanding of PTEN post-translational modifications could provide new therapeutic strategies to restore PTEN action in PIP₃-dependent tumors.

Role of Tumor Suppressor PTEN and Its Regulation in Malignant Transformation of Endometrium

Tumor-suppressive effects of PTEN are well-known, but modern evidence suggest that they are not limited to its ability to inhibit pro-oncogenic PI3K/AKT signaling pathway. Features of PTEN structure facilitate its interaction with substrates of different nature and display its activity in various ways both in the cytoplasm and in cell nuclei, which makes it possible to take a broader look at its ability to suppress tumor growth. The possible mechanisms of the loss of PTEN effects are also diverse - PTEN can be regulated at many levels, leading to change in the protein activity or its amount in the cell, while their significance for the development of malignant tumors has yet to be studied. Here we summarize the current data on the PTEN structure, its functions and changes in its regulatory mechanisms during malignant transformation of the cells, focusing on one of the most sensitive to the loss of PTEN types of malignant tumors - endometrial cancer.

Targeting the acetylation signaling pathway in cancer therapy

Acetylation represents one of the major post-translational protein modifications, which introduces an acetyl functional group into amino acids such as the lysine residue to yield an acetate ester bond, neutralizing its positive charge. Regulation of protein functions by acetylation occurs in multiple ways, such as affecting protein stability, activity, localization, and interaction with other proteins or DNA. It has been well documented that the recruitment of histone acetyltransferases (HATs) and histone deacetylases (HDACs) to the transcriptional machinery can modulate histone acetylation status, which is directly involved in the dynamic regulation of genes controlling cell proliferation and division. Dysregulation of gene expression is involved in tumorigenesis and aberrant activation of histone deacetylases has been reported in several types of cancer. Moreover, there is growing body of evidence showing that acetylation is widely involved in non-histone proteins to impact their roles in various cellular processes including tumorigenesis. As such, small molecular compounds inhibiting HAT or HDAC enzymatic activities have been developed and investigated for therapeutic purpose. Here we review the recent progress in our understanding of protein acetylation and discuss the therapeutic potential of targeting the acetylation signaling pathway in cancer.

HDAC6: A unique HDAC family member as a cancer target

BACKGROUND

HDAC6, a structurally and functionally distinct member of the HDAC family, is an integral part of multiple cellular functions such as cell proliferation, apoptosis, senescence, DNA damage and genomic stability, all of which when deregulated contribute to carcinogenesis. Among several HDAC family members known so far, HDAC6 holds a unique position. It differs from the other HDAC family members not only in terms of its subcellular localization, but also in terms of its substrate repertoire and hence cellular functions. Recent findings have considerably expanded the research related to the substrate pool, biological functions and regulation of HDAC6. Studies in HDAC6 knockout mice highlighted the importance of HDAC6 as a cell survival player in stressful situations, making it an important anticancer target. There is ample evidence stressing the importance of HDAC6 as an anti-cancer synergistic partner of many chemotherapeutic drugs. HDAC6 inhibitors have been found to enhance the effectiveness of conventional chemotherapeutic drugs such as DNA damaging agents, proteasome inhibitors and microtubule inhibitors, thereby highlighting the importance of combination therapies involving HDAC6 inhibitors and other anti-cancer agents.

CONCLUSIONS

Here, we present a review on HDAC6 with emphasis on its role as a critical regulator of specific physiological cellular pathways which when deregulated contribute to tumorigenesis, thereby highlighting the importance of HDAC6 inhibitors as important anticancer agents alone and in combination with other chemotherapeutic drugs. We also discuss the synergistic anticancer effect of combination therapies of HDAC6 inhibitors with conventional chemotherapeutic drugs.

Metabolite-derived protein modifications modulating oncogenic signaling

Malignant growth is defined by multiple aberrant cellular features, including metabolic rewiring, inactivation of tumor suppressors and the activation of oncogenes. Even though these features have been described as separate hallmarks, many studies have shown an extensive mutual regulatory relationship amongst them. On one hand, the change in expression or activity of tumor suppressors and oncogenes has extensive direct and indirect effects on cellular metabolism, activating metabolic pathways required for malignant growth. On the other hand, the tumor microenvironment and tumor intrinsic metabolic alterations result in changes in intracellular metabolite levels, which directly modulate the protein modification of oncogenes and tumor suppressors at both epigenetic and post-translational levels. In this mini-review, we summarize the crosstalk between tumor suppressors/oncogenes and metabolism-induced protein modifications at both levels and explore the impact of metabolic (micro)environments in shaping these.

Bisphenol A drives di(2-ethylhexyl) phthalate promoting thyroid tumorigenesis via regulating HDAC6/PTEN and c-MYC signaling

Bisphenol A (BPA) and di-(2-ethylhcxyl) phthalate (DEHP) are exist widespread in the environment and produce adverse effect to human as environmental disruptors (EDCs). Epidemiological studies have found that the exposure of DEHP and BPA could increase the susceptibility to thyroid diseases including thyroid cancer and benign thyroid nodules. Due to the existence of multiple pollutants in our daily life, the mixed toxic effects of exposure and their interrelationships may distinguish from the exposure to a single chemical, so it is of great significance to explore the mixed toxic effect of DEHP and BPA co-exposure. Thyroid, as one of the target organs of EDCs, is prone to tumor occurrence, however, whether the mixture of BPA and DEHP will affect the occurrence of thyroid cancer is still obscure. We aim to investigate the effect of single or combined exposure to BPA and DEHP on the occurrence of thyroid cancer. An animal model of exposure to BPA and DEHP was firstly established to evaluate their effect on DMD-induced thyroid cancer. Additionally, human thyroid cancer cells BCPAP and thyroid cells Nthy-ori3-1 were used to further clarify some possible mechanisms of BPA and MEHP, the main metabolite of DEHP. Consequently, we found that BPA alone could increase the incidence of thyroid tumors in female rats compared with DEHP, and DEHP enhanced the effect of BPA on cancer promotion. BPA alone and in combination with DEHP mainly induced the expression of HDAC6, inhibited tumor suppressor gene PTEN upregulated the expression of oncogene c-MYC, and eventually elevate the susceptibility to thyroid tumors. Mechanistically, BPA alone and in combination with MEHP could significantly induce the proliferation of BCPAP cells depending on HDAC6, which could modulate H3K9ac to inhibit PTEN, activate AKT signaling pathway, and simultaneously upregulate the expression of c-MYC. Interestingly, we found that BPA alone and in combination with MEHP could significantly induce the proliferation of Nthy-ori3-1 cells independent on HDAC6 via activating ERK signaling pathway. Taken together, these findings not only provide new evidence of the promoting effect of BPA and DEHP on thyroid cancer but also discusses some possible mechanisms underlying these effects.

The synergistic anticancer effect of the bromodomain inhibitor OTX015 and histone deacetylase 6 inhibitor WT-161 in osteosarcoma

Background

Osteosarcoma (OS) is a tumour with a high malignancy level and a poor prognosis. First-line chemotherapy for OS has not been improved for many decades. Bromodomain and extraterminal domain (BET) and histone deacetylases (HDACs) regulate histone acetylation in tandem, and BET and HDACs have emerged as potential cancer therapeutic targets.

Methods

Cell proliferation, migration, invasion, colony formation, and sphere-forming assays were performed with the two inhibitors alone or in combination to evaluate their suppressive effect on the malignant properties of OS cells. Apoptosis and the cell cycle profile were measured by flow cytometry. The synergistic inhibitory effect of OTX015/WT-161 on tumours was also examined in a nude mouse xenograft model.

Results

The combined therapy of OTX015/WT-161 synergistically inhibited growth, migration, and invasion and induced apoptosis, resulting in G1/S arrest of OS cells. Additionally, OTX015/WT-161 inhibited the self-renewal ability of OS stem cells (OSCs) in a synergistic manner. Further mechanistic exploration revealed that the synergistic downregulation of β-catenin by OTX015-mediated suppression of FZD2 and WT-161-mediated upregulation of PTEN may be critical for the synergistic effect. Finally, the results of an in vivo assay showed that tumour xenografts were significantly decreased after treatment with the OTX015/WT-161 combination compared with OTX015 or WT-161 alone.

Conclusions

Our findings in this study demonstrated that OTX015 and WT-161 had synergistic anticancer efficacy against OS, and their combination might be a promising therapeutic strategy for OS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-022-02443-y.

Histone deacetylase inhibitors inhibit cervical cancer growth through Parkin acetylation-mediated mitophagy

Parkin, an E3 ubiquitin ligase, plays a role in maintaining mitochondrial homeostasis through targeting damaged mitochondria for mitophagy. Accumulating evidence suggests that the acetylation modification of the key mitophagy machinery influences mitophagy level, but the underlying mechanism is poorly understood. Here, our study demonstrated that inhibition of histone deacetylase (HDAC) by treatment of HDACis activates mitophagy through mediating Parkin acetylation, leading to inhibition of cervical cancer cell proliferation. Bioinformatics analysis shows that Parkin expression is inversely correlated with HDAC2 expression in human cervical cancer, indicating the low acetylation level of Parkin. Using mass spectrometry, Parkin is identified to interact with two upstream molecules, acetylase acetyl-CoA acetyltransferase 1 (ACAT1) and deacetylase HDAC2. Under treatment of suberoylanilide hydroxamic acid (SAHA), Parkin is acetylated at lysine residues 129, 220 and 349, located in different domains of Parkin protein. In in vitro experiments, combined mutation of Parkin largely attenuate the interaction of Parkin with PTEN induced putative kinase 1 (PINK1) and the function of Parkin in mitophagy induction and tumor suppression. In tumor xenografts, the expression of mutant Parkin impairs the tumor suppressive effect of Parkin and decreases the anticancer activity of SAHA. Our results reveal an acetylation-dependent regulatory mechanism governing Parkin in mitophagy and cervical carcinogenesis, which offers a new mitophagy modulation strategy for cancer therapy.

The Potential of Natural Products in the Treatment of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a subtype of breast cancer that lacks receptors for targeted therapy. Consequently, chemotherapy is currently the mainstay of systemic treatment options. However, the enrichment of cancer stem cells (CSC, a subpopulation with stem-cell characteristics and tumor-initiating propensity) promotes chemo-resistance and tumorigenesis, resulting in cancer recurrence and relapse. Furthermore, toxic side effects of chemotherapeutics reduce patient wellbeing. Natural products, specifically compounds derived from plants, have the potential to treat TNBC and target CSCs by inhibiting CSC signaling pathways. Literature evidence from six promising compounds were reviewed, including sulforaphane, curcumin, genistein, resveratrol, lycopene, and epigallocatechin-3-gallate. These compounds have been shown to promote cell cycle arrest and apoptosis in TNBC cells. They also could inhibit the epithelial-mesenchymal transition (EMT) that plays an important role in metastasis. In addition, those natural compounds have been found to inhibit pathways important for CSCs, such as NF-κB, PI3K/Akt/mTOR, Notch 1, Wnt/β-catenin, and YAP. Clinicals trials conducted on these compounds have shown varying degrees of effectiveness. Epidemiological case-control studies for the compounds commonly consumed in certain human populations have also been summarized. While in vivo and in vitro data are promising, further basic and clinical investigations are required. Likely, natural products in combination with other drugs may hold great potential to improve TNBC treatment efficacy and patient outcomes.

Enhancing Therapeutic Approaches for Melanoma Patients Targeting Epigenetic Modifiers

Melanoma is the least common but deadliest type of skin cancer. Melanomagenesis is driven by a series of mutations and epigenetic alterations in oncogenes and tumor suppressor genes that allow melanomas to grow, evolve, and metastasize. Epigenetic alterations can also lead to immune evasion and development of resistance to therapies. Although the standard of care for melanoma patients includes surgery, targeted therapies, and immune checkpoint blockade, other therapeutic approaches like radiation therapy, chemotherapy, and immune cell-based therapies are used for patients with advanced disease or unresponsive to the conventional first-line therapies. Targeted therapies such as the use of BRAF and MEK inhibitors and immune checkpoint inhibitors such as anti-PD-1 and anti-CTLA4 only improve the survival of a small subset of patients. Thus, there is an urgent need to identify alternative standalone or combinatorial therapies. Epigenetic modifiers have gained attention as therapeutic targets as they modulate multiple cellular and immune-related processes. Due to melanoma's susceptibility to extrinsic factors and reversible nature, epigenetic drugs are investigated as a therapeutic avenue and as adjuvants for targeted therapies and immune checkpoint inhibitors, as they can sensitize and/or reverse resistance to these therapies, thus enhancing their therapeutic efficacy. This review gives an overview of the role of epigenetic changes in melanoma progression and resistance. In addition, we evaluate the latest advances in preclinical and clinical research studying combinatorial therapies and discuss the use of epigenetic drugs such as HDAC and DNMT inhibitors as potential adjuvants for melanoma patients.

Upregulation of ERK-EGR1-heparanase axis by HDAC inhibitors provides targets for rational therapeutic intervention in synovial sarcoma

BACKGROUND

Synovial sarcoma (SS) is an aggressive soft tissue tumor with limited therapeutic options in advanced stage. SS18-SSX fusion oncogenes, which are the hallmarks of SS, cause epigenetic rewiring involving histone deacetylases (HDACs). Promising preclinical studies supporting HDAC targeting for SS treatment were not reflected in clinical trials with HDAC inhibitor (HDACi) monotherapies. We investigated pathways implicated in SS cell response to HDACi to identify vulnerabilities exploitable in combination treatments and improve the therapeutic efficacy of HDACi-based regimens.

METHODS

Antiproliferative and proapoptotic effects of the HDACi SAHA and FK228 were examined in SS cell lines in parallel with biochemical and molecular analyses to bring out cytoprotective pathways. Treatments combining HDACi with drugs targeting HDACi-activated prosurvival pathways were tested in functional assays in vitro and in a SS orthotopic xenograft model. Molecular mechanisms underlying synergisms were investigated in SS cells through pharmacological and gene silencing approaches and validated by qRT-PCR and Western blotting.

RESULTS

SS cell response to HDACi was consistently characterized by activation of a cytoprotective and auto-sustaining axis involving ERKs, EGR1, and the β-endoglycosidase heparanase, a well recognized pleiotropic player in tumorigenesis and disease progression. HDAC inhibition was shown to upregulate heparanase by inducing expression of the positive regulator EGR1 and by hampering negative regulation by p53 through its acetylation. Interception of HDACi-induced ERK-EGR1-heparanase pathway by cell co-treatment with a MEK inhibitor (trametinib) or a heparanase inhibitor (SST0001/roneparstat) enhanced antiproliferative and pro-apoptotic effects. HDAC and heparanase inhibitors had opposite effects on histone acetylation and nuclear heparanase levels. The combination of SAHA with SST0001 prevented the upregulation of ERK-EGR1-heparanase induced by the HDACi and promoted caspase-dependent cell death. In vivo, the combined treatment with SAHA and SST0001 potentiated the antitumor efficacy against the CME-1 orthotopic SS model as compared to single agent administration.

CONCLUSIONS

The present study provides preclinical rationale and mechanistic insights into drug combinatory strategies based on the use of ERK pathway and heparanase inhibitors to improve the efficacy of HDACi-based antitumor therapies in SS. The involvement of classes of agents already clinically available, or under clinical evaluation, indicates the transferability potential of the proposed approaches.

A global map of associations between types of protein posttranslational modifications and human genetic diseases

There are >200 types of protein posttranslational modifications (PTMs) described in eukaryotes, each with unique proteome coverage and functions. We hypothesized that some genetic diseases may be caused by the removal of a specific type of PTMs by genomic variants and the consequent deregulation of particular functions. We collected >320,000 human PTMs representing 59 types and crossed them with >4M nonsynonymous DNA variants annotated with predicted pathogenicity and disease associations. We report >1.74M PTM-variant co-occurrences that an enrichment analysis distributed into 215 pairwise associations between 18 PTM types and 148 genetic diseases. Of them, 42% were not previously described. Removal of lysine acetylation exerts the most pronounced effect, and less studied PTM types such as S-glutathionylation or S-nitrosylation show relevance. Using pathogenicity predictions, we identified PTM sites that may produce particular diseases if prevented. Our results provide evidence of a substantial impact of PTM-specific removal on the pathogenesis of genetic diseases and phenotypes.

•

There is an enrichment of disease-associated nsSNVs preventing certain types of PTMs

•

We report 215 pairwise associations between 18 PTM types and 148 genetic diseases

•

The removal of lysine acetylation exerts the most pronounced effect

•

We report a set of PTM sites that may produce particular diseases if prevented

Epigenetic Regulation of Breast Cancer Stem Cells Contributing to Carcinogenesis and Therapeutic Implications

Globally, breast cancer has remained the most commonly diagnosed cancer and the leading cause of cancer death among women. Breast cancer is a highly heterogeneous and phenotypically diverse group of diseases, which require different selection of treatments. Breast cancer stem cells (BCSCs), a small subset of cancer cells with stem cell-like properties, play essential roles in breast cancer progression, recurrence, metastasis, chemoresistance and treatments. Epigenetics is defined as inheritable changes in gene expression without alteration in DNA sequence. Epigenetic regulation includes DNA methylation and demethylation, as well as histone modifications. Aberrant epigenetic regulation results in carcinogenesis. In this review, the mechanism of epigenetic regulation involved in carcinogenesis, therapeutic resistance and metastasis of BCSCs will be discussed, and finally, the therapies targeting these biomarkers will be presented.

Phosphatase and Tensin Homolog in Non-neoplastic Digestive Disease: More Than Just Tumor Suppressor

The Phosphatase and tensin homolog (PTEN) gene is one of the most important tumor suppressor genes, which acts through its unique protein phosphatase and lipid phosphatase activity. PTEN protein is widely distributed and exhibits complex biological functions and regulatory modes. It is involved in the regulation of cell morphology, proliferation, differentiation, adhesion, and migration through a variety of signaling pathways. The role of PTEN in malignant tumors of the digestive system is well documented. Recent studies have indicated that PTEN may be closely related to many other benign processes in digestive organs. Emerging evidence suggests that PTEN is a potential therapeutic target in the context of several non-neoplastic diseases of the digestive tract. The recent discovery of PTEN isoforms is expected to help unravel more biological effects of PTEN in non-neoplastic digestive diseases.

Conditional Generative Adversarial Networks for Individualized Treatment Effect Estimation and Treatment Selection

Treatment response is heterogeneous. However, the classical methods treat the treatment response as homogeneous and estimate the average treatment effects. The traditional methods are difficult to apply to precision oncology. Artificial intelligence (AI) is a powerful tool for precision oncology. It can accurately estimate the individualized treatment effects and learn optimal treatment choices. Therefore, the AI approach can substantially improve progress and treatment outcomes of patients. One AI approach, conditional generative adversarial nets for inference of individualized treatment effects (GANITE) has been developed. However, GANITE can only deal with binary treatment and does not provide a tool for optimal treatment selection. To overcome these limitations, we modify conditional generative adversarial networks (MCGANs) to allow estimation of individualized effects of any types of treatments including binary, categorical and continuous treatments. We propose to use sparse techniques for selection of biomarkers that predict the best treatment for each patient. Simulations show that MCGANs outperform seven other state-of-the-art methods: linear regression (LR), Bayesian linear ridge regression (BLR), k-Nearest Neighbor (KNN), random forest classification [RF (C)], random forest regression [RF (R)], logistic regression (LogR), and support vector machine (SVM). To illustrate their applications, the proposed MCGANs were applied to 256 patients with newly diagnosed acute myeloid leukemia (AML) who were treated with high dose ara-C (HDAC), Idarubicin (IDA) and both of these two treatments (HDAC+IDA) at M. D. Anderson Cancer Center. Our results showed that MCGAN can more accurately and robustly estimate the individualized treatment effects than other state-of-the art methods. Several biomarkers such as GSK3, BILIRUBIN, SMAC are identified and a total of 30 biomarkers can explain 36.8% of treatment effect variation.

Multitarget Inhibition of Histone Deacetylase (HDAC) and Phosphatidylinositol-3-kinase (PI3K): Current and Future Prospects

The discovery of histone deacetylase (HDAC) inhibitors is a hot topic in the medicinal chemistry community regarding cancer research. This is related primarily to two factors: success in the clinic, e. g., the four FDA-approved HDAC inhibitors, and strong versatility to combine their pharmacophoric features to design new hybrid compounds with multitarget profiles. Thus, the selection of adequate pharmacophores to combine, i. e., combining targets that can result in a synergistic effect, is desirable, as it increases the probability of discovering a new useful therapeutic strategy. In this work, we highlight the design of multitarget HDAC/PI3K inhibitors. Although this approach is still in its early stages, many significant works have described the design and pharmacological evaluation of this new promising class of multitarget inhibitors, where compound CUDC-907, which is already in clinical trials, stands out. Therefore, the question emerges of whether there still space for the design and evaluation of new multitarget HDAC/PI3K inhibitors. When considering the selectivity profile of the described multitarget compounds, the answer appears to be in the affirmative, especially since the first examples of compounds with a certain selectivity profile only recently appeared in 2020.

PTEN as a Guardian of the Genome: Pathways and Targets

Faithful transmission of genetic information is only possible with the structural and functional integrity of the genome. PTEN has been recognized as a guardian of the genome since the identification of its noncanonical localization and function in the nucleus. Yet, the role of PTEN in guarding the genome relies on integration of diverse mechanisms elicited by its canonical activity in antagonizing PI3K as well as emerging noncanonical functions. In the nucleus, PTEN maintains the structural integrity of chromosomes and the architecture of heterochromatin by physically interacting with chromosomal and nucleosomal components. PTEN also controls the functional integrity of key genetic transmission machineries by promoting proper assembly of the replisome and mitotic spindles. Deregulation of PTEN signaling impairs genome integrity, leading to spontaneous replication/mitotic stress and subsequent stress tolerance. Identification of novel targets of PTEN signaling and illumination of the interplay of diverse PTEN pathways in genome maintenance will help us better understand mechanisms underlying tumor evolution and therapeutic resistance.

Posttranslational Regulation and Conformational Plasticity of PTEN

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a tumor suppressor that is frequently down-modulated in human cancer. PTEN inhibits the phosphatidylinositol 3-phosphate kinase (PI3K)/AKT pathway through its lipid phosphatase activity. Multiple PI3K/AKT-independent actions of PTEN, protein-phosphatase activities and functions within the nucleus have also been described. PTEN, therefore, regulates many cellular processes including cell proliferation, survival, genomic integrity, polarity, migration, and invasion. Even a modest decrease in the functional dose of PTEN may promote cancer development. Understanding the molecular and cellular mechanisms that regulate PTEN protein levels and function, and how these may go awry in cancer contexts, is, therefore, key to fully understanding the role of PTEN in tumorigenesis. Here, we discuss current knowledge on posttranslational control and conformational plasticity of PTEN, as well as therapeutic possibilities toward reestablishment of PTEN tumor-suppressor activity in cancer.

Entinostat is a novel therapeutic agent to treat oral squamous cell carcinoma

INTRODUCTION

Alterations of the epigenome may influence cancer initiation and progression. At the cellular level, histones are key regulators of chromatin accessibility and gene transcription; thus, the inhibition of histone deacetylase enzymes (HDACs) constitutes an attractive target for therapy. In this study, we investigated the effects of the HDAC inhibitor entinostat on oral squamous cell carcinoma (OSCC).

MATERIALS AND METHODS

We tested the effects of entinostat on OSCC cell lines. Cell viability and growth were analyzed using MTT assay. Cell cycle analysis, cell apoptosis, cancer stem cell (CSC) content, and the concentration of reactive oxygen species (ROS) in OSCC tumor cells were assessed using flow cytometry. The expression of histones and cell cycle regulatory proteins was examined by Western blot.

RESULTS

The administration of entinostat resulted in reduced proliferation of OSCC cells, followed by cell cycle arrest at the G0/G1 phase, as well as substantial tumor apoptosis. We found an increase in ROS production and significant reductions in CSCs. We also found that entinostat caused increased acetylation histone H3 and histone H4, and changes in the expression of cell cycle-associated proteins such as p21.

CONCLUSION

This study indicates that entinostat is a potential novel therapeutic agent for OSCC by halting tumor proliferation, inducing cytotoxicity and intracellular ROS, and attacking the CSCs.

YY1-mediated PTEN dephosphorylation antagonizes IR-induced DNA repair contributing to tongue squamous cell carcinoma radiosensitization

Ionizing radiation (IR) confers a survival advantage in tongue squamous cell carcinoma (TSCC), however, IR resistance limits its efficacy. Although Yin Yang 1 (YY1) has been reported to play a role in genotoxic drug resistance by accelerating DNA repair, its role in TSCC radioresistance remains unclear. In this study, we examined YY1 mRNA and protein expression in human tongue cancer samples using qRT-PCR and western blotting, respectively. DNA array data identified YY1 mRNA expression in IR sensitivity or resistance cell lines and tissues. Tongue carcinoma primary cells and CAL27 cells with YY1 stably overexpressed or knocked-down were exposed to IR and evaluated for cell proliferation and apoptosis by CCK8-assay and caspase-3 assay, respectively. We also examined DNA damage- or repair-related indicators, such as YY1, p-H2AX, nuclear PTEN, p-PTEN, and Rad51 through Western blot analysis. Additionally, we explored the mechanism of IR-induced PTEN nuclear translocation by introducing a series of PTEN phosphorylation site mutations and co-IP assay. We observed that YY1 mRNA and protein are highly expressed in TSCC tissues, which was correlated with worse overall survival. Moreover, higher expression of YY1 and Rad51 was observed in radioresistant cells and tissues, overexpression of YY1 led to IR resistance in TSCC cells, whereas YY1 knockdown sensitized TSCC cells to IR. The underlying mechanism showed that the overexpression of YY1 upregulated nuclear PTEN and Rad51 expression, which is essential for DNA repair. IR upregulated YY1, nuclear PTEN, and Rad51; thus, knockdown of YY1 completely blocked IR-induced upregulation of nuclear PTEN/Rad51. IR upregulated PTEN phosphorylation, and mutation of the phosphorylation site of Ser380 nearly completely blocked IR-induced PTEN nuclear translocation. Furthermore, the phosphatase PP2A negatively regulated pS380-PTEN, and knockdown of YY1 completely blocked IR-induced pS380-PTEN through PP2A. In conclusion, knockdown of YY1 enhanced TSCC radiosensitivity through PP2A-mediated dephosphorylation of PTEN Ser380; thus, antagonizing the IR-induced nuclear PTEN/Rad51 axis and targeting YY1 may reverse IR resistance in TSCC.

Precise Immunodetection of PTEN Protein in Human Neoplasia

PTEN is a major tumor-suppressor protein whose expression and biological activity are frequently diminished in sporadic or inherited cancers. PTEN gene deletion or loss-of-function mutations favor tumor cell growth and are commonly found in clinical practice. In addition, diminished PTEN protein expression is also frequently observed in tumor samples from cancer patients in the absence of PTEN gene alterations. This makes PTEN protein levels a potential biomarker parameter in clinical oncology, which can guide therapeutic decisions. The specific detection of PTEN protein can be achieved by using highly defined anti-PTEN monoclonal antibodies (mAbs), characterized with precision in terms of sensitivity for the detection technique, specificity for PTEN binding, and constraints of epitope recognition. This is especially relevant taking into consideration that PTEN is highly targeted by mutations and posttranslational modifications, and different PTEN protein isoforms exist. The precise characterization of anti-PTEN mAb reactivity is an important step in the validation of these reagents as diagnostic and prognostic tools in clinical oncology, including their routine use in analytical immunohistochemistry (IHC). Here, we review the current status on the use of well-defined anti-PTEN mAbs for PTEN immunodetection in the clinical context and discuss their potential usefulness and limitations for a more precise cancer diagnosis and patient benefit.

Emerging roles of histone modifications and HDACs in RNA splicing

Histone modifications and RNA splicing, two seemingly unrelated gene regulatory processes, greatly increase proteome diversity and profoundly influence normal as well as pathological eukaryotic cellular functions. Like many histone modifying enzymes, histone deacetylases (HDACs) play critical roles in governing cellular behaviors and are indispensable in numerous biological processes. While the association between RNA splicing and histone modifications is beginning to be recognized, a lack of knowledge exists regarding the role of HDACs in splicing. Recent studies however, reveal that HDACs interact with spliceosomal and ribonucleoprotein complexes, actively control the acetylation states of splicing-associated histone marks and splicing factors, and thereby unexpectedly could modulate splicing. Here, we review the role of histone/protein modifications and HDACs in RNA splicing and discuss the convergence of two parallel fields, which supports the argument that HDACs, and perhaps most histone modifying enzymes, are much more versatile and far more complicated than their initially proposed functions. Analogously, an HDAC-RNA splicing connection suggests that splicing is regulated by additional upstream factors and pathways yet to be defined or not fully characterized. Some human diseases share common underlying causes of aberrant HDACs and dysregulated RNA splicing and, thus, further support the potential link between HDACs and RNA splicing.

The Mechanisms Underlying PTEN Loss in Human Tumors Suggest Potential Therapeutic Opportunities

In this review, we will first briefly describe the diverse molecular mechanisms associated with PTEN loss of function in cancer. We will then proceed to discuss the molecular mechanisms linking PTEN loss to PI3K activation and demonstrate how these mechanisms suggest possible therapeutic approaches for patients with PTEN-null tumors.

Silencing of HDAC6 as a therapeutic target in chronic lymphocytic leukemia

Although the treatment paradigm for chronic lymphocytic leukemia (CLL) is rapidly changing, the disease remains incurable, except with allogeneic bone marrow transplantation, and resistance, relapsed disease, and partial responses persist as significant challenges. Recent studies have uncovered roles for epigenetic modification in the regulation of mechanisms contributing to malignant progression of CLL B cells. However, the extent to which epigenetic modifiers can be targeted for therapeutic benefit in CLL patients remains poorly explored. We report for the first time that expression of epigenetic modifier histone deacetylase 6 (HDAC6) is upregulated in CLL patient samples, cell lines, and euTCL1 transgenic mouse models compared with HDAC6 in normal controls. Genetic silencing of HDAC6 conferred survival benefit in euTCL1 mice. Administration of isoform-specific HDAC6 inhibitor ACY738 in the euTCL1 aging and adoptive transfer models deterred proliferation of CLL B cells, delayed disease onset via disruption of B-cell receptor signaling, and sensitized CLL B cells to apoptosis. Furthermore, coadministration of ACY738 and ibrutinib displayed synergistic cell kill against CLL cell lines and improved overall survival compared with either single agent in vivo. These results demonstrate for the first time the therapeutic efficacy of selective HDAC6 inhibition in preclinical CLL models and suggest a rationale for the clinical development of HDAC6 inhibitors for CLL treatment, either alone or in combination with Bruton tyrosine kinase inhibition.

Histone deacetylase 6 inhibitor tubastatin A attenuates angiotensin II-induced hypertension by preventing cystathionine γ-lyase protein degradation

Cystathionine γ-lyase (CSEγ) is a hydrogen sulfide (H₂S)-producing enzyme. Endothelial H₂S production can mediate vasodilatory effects, contributing to the alleviation of hypertension (high blood pressure). Recent studies have suggested a role of histone deacetylase 6 (HDAC6) in hypertension, although its underlying mechanisms are poorly understood. Here, we addressed the potential regulation of CSEγ by HDAC6 in angiotensin II (AngII)-induced hypertension and its molecular details focusing on CSEγ posttranslational modification. Treatment of mice with a selective HDAC6 inhibitor tubastatin A (TubA) alleviated high blood pressure and vasoconstriction induced by AngII. Cotreatment of the aorta and human aortic endothelial cells with TubA recovered AngII-mediated decreased H₂S levels. AngII treatment upregulated HDAC6 mRNA and protein expression, but conversely downregulated CSEγ protein. Notably, potent HDAC6 inhibitors and HDAC6 siRNA as well as a proteasomal inhibitor increased CSEγ protein levels and blocked the downregulatory effect of AngII on CSEγ. In contrast, other HDAC isoforms-specific inhibitors and siRNAs did not show such blocking effects. Transfected CSEγ protein levels were also reciprocally regulated by AngII and TubA, and were reduced by wild-type, but not by deacetylase-deficient, HDAC6. Moreover, TubA significantly increased both protein stability and K73 acetylation level of CSEγ. Consistent with these results, AngII induced CSEγ ubiquitination and degradation, which was inhibited by TubA. Our results indicate that AngII promoted HDAC6-dependent deacetylation of CSEγ at K73 residue, leading to its ubiquitin-mediated proteolysis, which underlies AngII-induced hypertension. Overall, this study suggests that upregulation of CSEγ and H₂S through HDAC6 inhibition may be considered as a valid strategy for preventing the progression of hypertension.

Immunoepigenetics Combination Therapies: An Overview of the Role of HDACs in Cancer Immunotherapy

Long-standing efforts to identify the multifaceted roles of histone deacetylase inhibitors (HDACis) have positioned these agents as promising drug candidates in combatting cancer, autoimmune, neurodegenerative, and infectious diseases. The same has also encouraged the evaluation of multiple HDACi candidates in preclinical studies in cancer and other diseases as well as the FDA-approval towards clinical use for specific agents. In this review, we have discussed how the efficacy of immunotherapy can be leveraged by combining it with HDACis. We have also included a brief overview of the classification of HDACis as well as their various roles in physiological and pathophysiological scenarios to target key cellular processes promoting the initiation, establishment, and progression of cancer. Given the critical role of the tumor microenvironment (TME) towards the outcome of anticancer therapies, we have also discussed the effect of HDACis on different components of the TME. We then have gradually progressed into examples of specific pan-HDACis, class I HDACi, and selective HDACis that either have been incorporated into clinical trials or show promising preclinical effects for future consideration. Finally, we have included examples of ongoing trials for each of the above categories of HDACis as standalone agents or in combination with immunotherapeutic approaches.

Selective HDAC6 inhibitors improve anti-PD-1 immune checkpoint blockade therapy by decreasing the anti-inflammatory phenotype of macrophages and down-regulation of immunosuppressive proteins in tumor cells

Histone deacetylases (HDACs) are involved in diverse cellular regulatory mechanisms including non-canonical functions outside the chromatin environment. Several publications have demonstrated that selective HDAC inhibitors (HDACi) can influence tumor immunogenicity and the functional activity of specific immune cells. In particular, the selective inhibition of HDAC6 has been reported to decrease tumor growth in several malignancies. However, there is still no clarity about the cellular components mediating this effect. In this study, we evaluated the HDAC6i Nexturastat A as a priming agent to facilitate the transition of the tumor microenvironment from “cold” to “hot”, and potentially augment immune check-point blockade therapies. This combination modality demonstrated to significantly reduce tumor growth in syngeneic melanoma tumor models. Additionally, we observed a complete neutralization of the up-regulation of PD-L1 and other immunosuppressive pathways induced by the treatment with anti-PD-1 blockade. This combination also showed profound changes in the tumor microenvironment such as enhanced infiltration of immune cells, increased central and effector T cell memory, and a significant reduction of pro-tumorigenic M2 macrophages. The evaluation of individual components of the tumor microenvironment suggested that the in vivo anti-tumor activity of HDAC6i is mediated by its effect on tumor cells and tumor-associated macrophages, and not directly over T cells. Overall, our results indicate that selective HDAC6i could be used as immunological priming agents to sensitize immunologically “cold” tumors and subsequently improve ongoing immune check-point blockade therapies.

PTEN arginine methylation by PRMT6 suppresses PI3K-AKT signaling and modulates pre-mRNA splicing

Arginine methylation is a ubiquitous posttranslational modification that regulates critical cellular processes including signal transduction and pre-mRNA splicing. Here, we report that the tumor-suppressor PTEN is methylated by protein arginine methyltransferase 6 (PRMT6). Mass-spectrometry analysis reveals that PTEN is dimethylated at arginine 159 (R159). We found that PTEN is mutated at R159 in cancers, and the PTEN mutant R159K loses its capability to inhibit the PI3K-AKT cascade. Furthermore, PRMT6 is physically associated with PTEN, promotes asymmetrical dimethylation of PTEN, and regulates the PI3K-AKT cascade through PTEN R159 methylation. In addition, using transcriptome analyses, we found that PTEN R159 methylation is involved in modulation of pre-mRNA alternative splicing. Our results demonstrate that PTEN is functionally regulated by arginine methylation. We propose that PTEN arginine methylation modulates pre-mRNA alternative splicing and influences diverse physiologic processes.

HDAC6 inhibitor TST strengthens the antiproliferative effects of PI3K/mTOR inhibitor BEZ235 in breast cancer cells via suppressing RTK activation

NVP-BEZ235 (BEZ235), an available dual PI3K/mTOR inhibitor, showed antitumor effect and provided a therapy strategy in carcinomas. However, the acquired upregulation of multiple receptor tyrosine kinases (RTKs) by NVP-BEZ235 in tumors limits its clinical efficacy. HDAC6, a class II histone deacetylase, is associated with expressions of multiple RTKs. The aim of this study was to detect whether co-treatment with HDAC6 inhibitor Tubastatin A (TST) would enhance the anticancer effects of BEZ235 in breast cancer cells. In this study, we described that treatment of breast cancer cell lines (T47D, BT474, and MDA-MB-468) with BEZ235 significantly triggered PI3K/mTOR signaling inactivation and increased multiple RTK expression, including EGFR, HER2, HER3, IGF-1 receptor, insulin receptor, and their phosphorylation levels. The adding of TST destabilized these RTKs in those breast cancer cells. Co-treatment with BEZ235 and TST reduced cell proliferative rate by strengthening Akt inactivation. In addition, the combination of these two drugs also cooperatively arrested cell cycle and DNA synthesis. In conclusion, the co-treatment with PI3K/mTOR inhibitor BEZ235 and HDAC6 inhibitor TST displayed additive antiproliferative effects on breast cancer cells through inactivating RTKs and established a rationable combination therapy to treat breast cancer.

BMI1 and PTEN are key determinants of breast cancer therapy: A plausible therapeutic target in breast cancer

BMI-1 (B-lymphoma Mo-MLV insertion region 1) is a key protein partner in polycomb repressive complex 1 (PRC1) that helps in maintaining the integrity of the complex. It is also a key player in ubiquitination of histone H2A which affects gene expression pattern involved in various cellular processes such as cell proliferation, growth, DNA repair, apoptosis and senescence. In many cancers, Overexpression of BMI1correlates with advanced stages of disease, aggressive clinicopathological behavior, poor prognosis resistance to radiation and chemotherapy. BMI1 is emerging as a key player in EMT, chemo-resistance and cancer stemness. Overexpression is observed in various cancer types such as breast, primary hepatocellular carcinoma (HCC), gastric, ovarian, head and neck, pancreatic and lung cancer. Studies have shown that experimental reduction of BMI protein level in tumor cells results in inhibition of cell proliferation, induction of apoptosis and/or senescence, and increases susceptibility to cytotoxic agents and radiation therapy. Thus, inhibition of BMI1 expression particularly in breast cancer stem cells can be used as a potential strategy for the complete elimination of tumor and to prevent disease relapse. On other hand PTEN is known to be an important tumor suppressor next to p53. In many cancers particularly in breast cancer, p53 and PTEN undergo mutations. Studies have indicated the functional and mechanistic link between the BMI-1oncoprotein and tumor suppressor PTEN in the development and progression of cancer. The current review focuses on recent findings of how oncogenicity and chemo-resistance are caused by BMI1. It also highlights the transcriptional regulation between BMI1 and PTEN that dictates the therapeutic outcome in cancers where the functional p53 is absent. Herein, we have clearly demonstrated the regulation of transcription at genomic loci of BMI1 and PTEN in cancerous tissue or cells and the possible epigenetic regulation by histone deacetylase inhibitors (HDACi) at BMI1 and PTEN loci that may provide some clue for the possible therapy against TNBC in near future.

Protein Chemical Approaches to Understanding PTEN Lipid Phosphatase Regulation

Since the discovery of C-tail phosphorylation of PTEN almost 20 years ago, much progress has been made in understanding its regulatory influences on the cellular function of PTEN. Phosphorylation of Ser380, Thr382, Thr383, and Ser385 drives a PTEN conformational change from an open to closed state where catalytic function is impaired, plasma membrane binding is reduced, and cellular stability is enhanced. Despite these advances, a detailed structural and mechanistic model of how these phosphorylations impact PTEN function is lacking. We discuss here several recent approaches to analyzing PTEN phosphorylation and highlight several insights that have come from this work. We also discuss remaining challenges for the PTEN regulation field and potential directions for future research.

Mutually exclusive acetylation and ubiquitylation of the splicing factor SRSF5 control tumor growth

Most tumor cells take up more glucose than normal cells. Splicing dysregulation is one of the molecular hallmarks of cancer. However, the role of splicing factor in glucose metabolism and tumor development remains poorly defined. Here, we show that upon glucose intake, the splicing factor SRSF5 is specifically induced through Tip60-mediated acetylation on K125, which antagonizes Smurf1-mediated ubiquitylation. SRSF5 promotes the alternative splicing of CCAR1 to produce CCAR1S proteins, which promote tumor growth by enhancing glucose consumption and acetyl-CoA production. Conversely, upon glucose starvation, SRSF5 is deacetylated by HDAC1, and ubiquitylated by Smurf1 on the same lysine, resulting in proteasomal degradation of SRSF5. The CCAR1L proteins accumulate to promote apoptosis. Importantly, SRSF5 is hyperacetylated and upregulated in human lung cancers, which correlates with increased CCAR1S expression and tumor progression. Thus, SRSF5 responds to high glucose to promote cancer development, and SRSF5-CCAR1 axis may be valuable targets for cancer therapeutics.