Acetylation regulates gluconeogenesis by promoting PEPCK1 degradation via recruiting the UBR5 ubiquitin ligase

SZC-6, a small-molecule activator of SIRT3, attenuates cardiac hypertrophy in mice

Sirtuin3 (SIRT3), a class III histone deacetylase, is implicated in various cardiovascular diseases as a novel therapeutic target. SIRT3 has been proven to be cardioprotective in a model of Ang II-induced cardiac hypertrophy. However, a few small-molecule compounds targeting deacetylases could activate SIRT3. In this study, we generated a novel SIRT3 activator, 3-(2-bromo-4-hydroxyphenyl)-7-hydroxy-2H-chromen-2-one (SZC-6), through structural optimization of the first SIRT3 agonist C12. We demonstrated that SZC-6 directly bound to SIRT3 with Kd value of 15 μM, and increased SIRT3 deacetylation activity with EC50 value of 23.2 ± 3.3 µM. In neonatal rat cardiomyocytes (NRCMs), pretreatment with SZC-6 (10, 20, 40 µM) dose-dependently attenuated isoproterenol (ISO)-induced hypertrophic responses. Administration of SZC-6 (20, 40 and 60 mg·kg-1·d-1, s.c.) for 2 weeks starting from one week prior ISO treatment dose-dependently reversed ISO-induced impairment of diastolic and systolic cardiac function in wild-type mice, but not in SIRT3 knockdown mice. We showed that SZC-6 (10, 20, 40 µM) dose-dependently inhibited cardiac fibroblast proliferation and differentiation into myofibroblasts, which was abolished in SIRT3-knockdown mice. We further revealed that activation of SIRT3 by SZC-6 increased ATP production and rate of mitochondrial oxygen consumption, and reduced ROS, improving mitochondrial function in ISO-treated NRCMs. We also found that SZC-6 dose-dependently enhanced LKB1 phosphorylation, thereby promoting AMPK activation to inhibit Drp1-dependent mitochondrial fragmentation. Taken together, these results demonstrate that SZC-6 is a novel SIRT3 agonist with potential value in the treatment of cardiac hypertrophy partly through activation of the LKB1-AMPK pathway.

Long non-coding RNA in glioma: novel genetic players in temozolomide resistance

Glioma is the most common primary malignant brain tumor in adults and accounts for approximately 80% of brain and central nervous system tumors. In 2021, the World Health Organization (WHO) published a new taxonomy for glioma based on its histological features and molecular alterations. Isocitrate dehydrogenase (IDH) catalyzes the decarboxylation of isocitrate, a critical metabolic reaction in energy generation in cells. Mutations in the IDH genes interrupt cell differentiation and serve as molecular biomarkers that can be used to classify gliomas. For example, the mutant IDH is widely detected in low-grade gliomas, whereas the wild type is in high-grade ones, including glioblastomas. Long non-coding RNAs (lncRNAs) are epigenetically involved in gene expression and contribute to glioma development. To investigate the potential use of lncRNAs as biomarkers, we examined lncRNA dysregulation dependent on the IDH mutation status. We found that several lncRNAs, namely, AL606760.2, H19, MALAT1, PVT1 and SBF2-AS1 may function as glioma risk factors, whereas AC068643.1, AC079228.1, DGCR5, FAM13A-AS1, HAR1A and WDFY3-AS2 may have protective effects. Notably, H19, MALAT1, PVT1, and SBF2-AS1 have been associated with temozolomide resistance in glioma patients. This review study suggests that targeting glioma-associated lncRNAs might aid the treatment of glioma.

Exosomal circ_0026611 contributes to lymphangiogenesis by reducing PROX1 acetylation and ubiquitination in human lymphatic endothelial cells (HLECs)

BACKGROUND

Esophageal squamous carcinoma (ESCC) is a common malignancy that originates in the digestive tract. Lymph node metastasis (LNM) is a complicated process, and tumor lymphangiogenesis has been reported to be associated with the spread of tumor cells to lymph nodes (LNs), including in ESCC. However, little is currently known about the mechanisms involved in lymphangiogenesis in ESCC tumors. According to previous literature, we know that hsa_circ_0026611 expresses at a high level in serum exosomes of patients with ESCC and shows a close association with LNM and poor prognosis. However, details on the functions of circ_0026611 in ESCC remain unclear. We aim to explore the effects of circ_0026611 in ESCC cell-derived exosomes on lymphangiogenesis and its potential molecular mechanism.

METHODS

We firstly examined how circ_0026611 may express in ESCC cells and exosomes by quantitative reverse transcription real-time polymerase chain reaction (RT-qPCR). The potential effects circ_0026611 may exert on lymphangiogenesis in ESCC cell-derived exosomes were assessed afterward via mechanism experiments.

RESULTS

circ_0026611 high expression pattern was confirmed in ESCC cells and exosomes. ESCC cell-derived exosomes promoted lymphangiogenesis by transferring circ_0026611. Besides, circ_0026611 interacted with N-α-acetyltransferase 10 (NAA10) to inhibit NAA10-mediated prospero homeobox 1 (PROX1) acetylation with subsequent ubiquitination and degradation. Furthermore, circ_0026611 was verified to promote lymphangiogenesis in a PROX1-mediated manner.

CONCLUSIONS

Exosomal circ_0026611 inhibited PROX1 acetylation and ubiquitination to promote lymphangiogenesis in ESCC.

Implications of altered sirtuins in metabolic regulation and oral cancer

Sirtuins (SIRTs 1-7) are a group of histone deacetylase enzymes with a wide range of enzyme activities that target a range of cellular proteins in the nucleus, cytoplasm, and mitochondria for posttranslational modifications by acetylation (SIRT1, 2, 3, and 5) or ADP ribosylation (SIRT4, 6, and 7). A variety of cellular functions, including mitochondrial functions and functions in energy homeostasis, metabolism, cancer, longevity and ageing, are regulated by sirtuins. Compromised sirtuin functions and/or alterations in the expression levels of sirtuins may lead to several pathological conditions and contribute significantly to alterations in metabolic phenotypes as well as oral carcinogenesis. Here, we describe the basic characteristics of seven mammalian sirtuins. This review also emphasizes the key molecular mechanisms of sirtuins in metabolic regulation and discusses the possible relationships of sirtuins with oral cancers. This review will provide novel insight into new therapeutic approaches targeting sirtuins that may potentially lead to effective strategies for combating oral malignancies.

Angiotensin-converting enzyme inhibitor promotes angiogenesis through Sp1/Sp3-mediated inhibition of notch signaling in male mice

Angiogenesis is a critical pathophysiological process involved in organ growth and various diseases. Transcription factors Sp1/Sp3 are necessary for fetal development and tumor growth. Sp1/Sp3 proteins were downregulated in the capillaries of the gastrocnemius in patients with critical limb ischemia samples. Endothelial-specific Sp1/Sp3 knockout reduces angiogenesis in retinal, pathological, and tumor models and induced activation of the Notch1 pathway. Further, the inactivation of VEGFR2 signaling by Notch1 contributes to the delayed angiogenesis phenotype. Mechanistically, endothelial Sp1 binds to the promoter of Notch1 and inhibits its transcription, which is enhanced by Sp3. The proangiogenic effect of ACEI is abolished in Sp1/Sp3-deletion male mice. We identify USP7 as an ACEI-activated deubiquitinating enzyme that translocated into the nucleus binding to Sp1/Sp3, which are deacetylated by HDAC1. Our findings demonstrate a central role for endothelial USP7-Sp1/Sp3-Notch1 signaling in pathophysiological angiogenesis in response to ACEI treatment.

A comprehensive dynamic immune acetylproteomics profiling induced by Puccinia polysora in maize

Lysine-ε-acetylation (Kac) is a reversible post-translational modification that plays important roles during plant-pathogen interactions. Some pathogens can deliver secreted effectors encoding acetyltransferases or deacetylases into host cell to directly modify acetylation of host proteins. However, the function of these acetylated host proteins in plant-pathogen defense remains to be determined. Employing high-resolution tandem mass spectrometry, we analyzed protein abundance and lysine acetylation changes in maize infected with Puccinia polysora (P. polysora) at 0 h, 12 h, 24 h, 48 h and 72 h. A total of 7412 Kac sites from 4697 proteins were identified, and 1732 Kac sites from 1006 proteins were quantified. Analyzed the features of lysine acetylation, we found that Kac is ubiquitous in cellular compartments and preferentially targets lysine residues in the -F/W/Y-X-X-K (ac)-N/S/T/P/Y/G- motif of the protein, this Kac motif contained proteins enriched in basic metabolism and defense-associated pathways during fungal infection. Further analysis of acetylproteomics data indicated that maize regulates cellular processes in response to P. polysora infection by altering Kac levels of histones and non-histones. In addition, acetylation of pathogen defense-related proteins presented converse patterns in signaling transduction, defense response, cell wall fortification, ROS scavenging, redox reaction and proteostasis. Our results provide informative resources for studying protein acetylation in plant-pathogen interactions, not only greatly extending the understanding on the roles of acetylation in vivo, but also providing a comprehensive dynamic pattern of Kac modifications in the process of plant immune response.

Acetylome reprograming participates in the establishment of fruit metabolism during polyploidization in citrus

Polyploidization leads to novel phenotypes and is a major force in evolution. However, the relationship between the evolution of new traits and variations in the post-translational modifications (PTM) of proteins during polyploidization has not been studied. Acetylation of lysine residues is a common protein PTM that plays a critical regulatory role in central metabolism. To test whether changes in metabolism in citrus fruit is associated with the reprogramming of lysine acetylation (Kac) in non-histone proteins during allotetraploidization, we performed a global acetylome analysis of fruits from a synthetic allotetraploid citrus and its diploid parents. A total of 4,175 Kac sites were identified on 1,640 proteins involved in a wide range of fruit traits. In the allotetraploid, parental dominance (i.e. resemblance to one of the two parents) in specific fruit traits, such as fruit acidity and flavonol metabolism, was highly associated with parental Kac level dominance in pertinent enzymes. This association is due to Kac-mediated regulation of enzyme activity. Moreover, protein Kac probably contributes to the discordance between the transcriptomic and proteomic variations during allotetraploidization. The acetylome reprogramming can be partially explained by the expression pattern of several lysine deacetylases (KDACs). Overexpression of silent information regulator 2 (CgSRT2) and histone deacetylase 8 (CgHDA8) diverted metabolic flux from primary metabolism to secondary metabolism and partially restored a metabolic status to the allotetraploid, which expressed attenuated levels of CgSRT2 and CgHDA8. Additionally, KDAC inhibitor treatment greatly altered metabolism in citrus fruit. Collectively, these findings reveal the important role of acetylome reprogramming in trait evolution during polyploidization.

Unraveling the structures, functions and mechanisms of epithelial membrane protein family in human cancers

Peripheral myelin protein 22 (PMP22) and epithelial membrane proteins (EMP-1, -2, and -3) belong to a small hydrophobic membrane protein subfamily, with four transmembrane structures. PMP22 and EMPs are widely expressed in various tissues and play important roles in cell growth, differentiation, programmed cell death, and metastasis. PMP22 presents its highest expression in the peripheral nerve and participates in normal physiological and pathological processes of the peripheral nervous system. The progress of molecular genetics has shown that the genetic changes of the PMP22 gene, including duplication, deletion, and point mutation, are behind various hereditary peripheral neuropathies. EMPs have different expression patterns in diverse tissues and are closely related to the risk of malignant tumor progression. In this review, we focus on the four members in this protein family which are related to disease pathogenesis and discuss gene mutations and post-translational modification of them. Further research into the interactions between structural alterations and function of PMP22 and EMPs will help understand their normal physiological function and role in diseases and might contribute to developing novel therapeutic tools.

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.

MiR-34a-5p promotes hepatic gluconeogenesis by suppressing SIRT1 expression

Elevated hepatic gluconeogenesis is a major contributor of fasting hyperglycemia in diabetes. MicroRNAs (miRNAs) are tightly linked to glucose metabolism, but their role in hepatic gluconeogenesis remains largely unkown. In this current study, miR-34a-5p expression was significantly increased in liver tissues of db/db mice. Overexpression of miR-34a-5p promoted hepatic glucose production in mouse primary hepatocytes with increased expressions of gluconeogenic genes while miR-34a-5p inhibition displayed a contrary action. MiR-34a-5p overexpression in mouse primary hepatocytes repressed SIRT1 expression. SIRT1 inhibition by EX527 blocked phosphoenolpyruvate carboxykinase (PEPCK) protein degradation and enhanced hepatic gluconeogenesis. Treatment of A485 (a CBP/p300 inhibitor) decreased miR-34a-5p and PEPCK expressions in the livers of db/db mice, but elevated SIRT1 protein expression. In mouse primary hepatocytes, A485 exhibited a similar result. Overexpression of miR-34a-5p attenuated A485-inhibited gluconeogenic gene expressions and A485-induced SIRT1 protein expression. Finally, after miR-34a-5p was inhibited in the livers of db/db mice, hepatic glucose production and gluconeogenic gene expressions were markedly lowered. Our findings highlight a critical role of miR-34a-5p in the regulation of hepatic gluconeogenesis and miR-34a-5p may be a potential target in the treatment of type 2 diabetes.

Multiple Roles of SIRT2 in Regulating Physiological and Pathological Signal Transduction

Sirtuin 2 (SIRT2), as a member of the sirtuin family, has representative features of evolutionarily highly conserved nicotinamide adenine dinucleotide (NAD+)-dependent deacetylase activity. In addition, SIRT2, as the only sirtuin protein colocalized with tubulin in the cytoplasm, has its own functions and characteristics. In recent years, studies have increasingly shown that SIRT2 can participate in the regulation of gene expression and regulate signal transduction in the metabolic pathway mainly through its post-translational modification of target genes; thus, SIRT2 has become a key centre in the metabolic pathway and participates in the pathological process of metabolic disorder-related diseases. In this paper, it is discussed that SIRT2 can regulate all aspects of gene expression, including epigenetic modification, replication, transcription and translation, and post-translational modification, which enables SIRT2 to participate in energy metabolism in life activities, and it is clarified that SIRT2 is involved in metabolic process-specific signal transduction mechanisms. Therefore, SIRT2 can be involved in metabolic disorder-related inflammation and oxidative stress, thereby triggering the occurrence of metabolic disorder-related diseases, such as neurodegenerative diseases, tumours, diabetes, and cardiovascular diseases. Currently, although the role of SIRT2 in some diseases is still controversial, given the multiple roles of SIRT2 in regulating physiological and pathological signal transduction, SIRT2 has become a key target for disease treatment. It is believed that with increasing research, the clinical application of SIRT2 will be promoted.

Will Sirtuin 2 Be a Promising Target for Neuroinflammatory Disorders?

Neuroinflammatory disorder is a general term that is associated with the progressive loss of neuronal structure or function. At present, the widely studied diseases with neuroinflammatory components are mainly divided into neurodegenerative and neuropsychiatric diseases, namely, Alzheimer’s disease, Parkinson’s disease, depression, stroke, and so on. An appropriate neuroinflammatory response can promote brain homeostasis, while excessive neuroinflammation can inhibit neuronal regeneration and damage the central nervous system. Apart from the symptomatic treatment with cholinesterase inhibitors, antidepressants/anxiolytics, and neuroprotective drugs, the treatment of neuroinflammation is a promising therapeutic method. Sirtuins are a host of class III histone deacetylases, that require nicotinamide adenine dinucleotide for their lysine residue deacetylase activity. The role of sirtuin 2 (SIRT2), one of the sirtuins, in modulating senescence, myelin formation, autophagy, and inflammation has been widely studied. SIRT2 is associated with many neuroinflammatory disorders considering it has deacetylation properties, that regulate the entire immune homeostasis. The aim of this review was to summarize the latest progress in regulating the effects of SIRT2 on immune homeostasis in neuroinflammatory disorders. The overall structure and catalytic properties of SIRT2, the selective inhibitors of SIRT2, the relationship between immune homeostasis and SIRT2, and the multitasking role of SIRT2 in several diseases with neuroinflammatory components were discussed.

WNT5A promotes the metastasis of esophageal squamous cell carcinoma by activating the HDAC7/SNAIL signaling pathway

Esophageal squamous cell carcinoma (ESCC) is one of the most common cancers worldwide, with high incidence and mortality rates and low survival rates. However, the detailed molecular mechanism of ESCC progression remains unclear. Here, we first showed significantly higher WNT5A and SNAIL expression in ESCC samples than in corresponding paracancerous samples. High WNT5A and SNAIL expression levels correlated positively with lymphatic metastasis and poor prognosis for patients with ESCC based on immunohistochemical (IHC) staining of 145 paired ESCC samples. Spearman's correlation analyses confirmed the strong positive correlation between WNT5A and SNAIL expression, and patients with ESCC presenting coexpression of WNT5A and SNAIL had the worst prognosis. Then, we verified that the upregulation of WNT5A promoted ESCC cell metastasis in vivo and in vitro, suggesting that WNT5A might be a promising therapeutic target for the prevention of ESCC. Furthermore, WNT5A overexpression induced the epithelial-mesenchymal transition via histone deacetylase 7 (HDAC7) upregulation, and HDAC7 silencing significantly reversed WNT5A-induced SNAIL upregulation and ESCC cell metastasis. In addition, we used HDAC7 inhibitors (SAHA and TMP269) to further confirm that HDAC7 participates in WNT5A-mediated carcinogenesis. Based on these results, HDAC7 is involved in WNT5A-mediated ESCC progression, and approaches targeting WNT5A and HDAC7 might be potential therapeutic strategies for ESCC.

Acetylation stabilizes stathmin1 and promotes its activity contributing to gallbladder cancer metastasis

Gallbladder cancer is the most common biliary tract malignant tumor with highly metastatic characters and poor prognosis. However, the underlying mechanism remains unclear. Stathmin1 is ubiquitous phosphoprotein, regulating microtubule stabilization. We identified the acetylation of stahtmin1 at lysine 9 (K9) in gallbladder cancer. K9 acetylation of stathmin1 was reversely regulated by the acetyltransferase PCAF and the deacetylases sirt2. K9 acetylation of stathmin1 inhibited the combining of stathmin1 to E3 ubiquitin ligase RLIM, thereby inhibiting its ubiquitination degradation. Moreover, K9 acetylation also promoted the activity of stahtmin1 interacting and destabilizing microtubule through the inhibition of stathmin1 phosphorylation. K9 acetylated stathmin1 significantly promoted gallbladder cancer cell migration and invasion viability in vitro and lung metastasis in vivo, and indicated poor prognosis of nude mice. IHC assay suggested the positive correlation of high levels of K9 acetylation and stathmin1 expression in gallbladder cancer. Our study revealed that K9 acetylation up-regulated stathmin1 protein stability and microtubule-destabilizing activity to promoted gallbladder cancer metastasis, which provides a potential target for gallbladder cancer therapy.

UBR5 targets tumor suppressor CDC73 proteolytically to promote aggressive breast cancer

UBR5, a HECT-domain E3 ubiquitin ligase, is an attractive therapeutic target for aggressive breast cancers. Defining the substrates of UBR5 is crucial for scientific understanding and clinical intervention. Here, we demonstrate that CDC73, a component of the RNA polymerase II-associated factor 1 complex, is a key substrate that impedes UBR5's profound tumorigenic and metastatic activities in triple-negative breast cancer (TNBC) via mechanisms of regulating the expression of β-catenin and E-cadherin, tumor cell apoptosis and CD8+ T cell infiltration. Expression of CDC73 is also negatively associated with the progression of breast cancer patients. Moreover, we show that UBR5 destabilizes CDC73 by polyubiquitination at Lys243, Lys247, and Lys257 in a non-canonical manner that is dependent on the non-phosphorylation state of CDC73 at Ser465. CDC73 could serve as a molecular switch to modulate UBR5's pro-tumor activities and may provide a potential approach to developing breast cancer therapeutic interventions.

SIRT2 Is Critical for Sheep Oocyte Maturation through Regulating Function of Surrounding Granulosa Cells

Oocyte in vitro maturation is crucial for in vitro embryo production technology, which provides oocytes resources for in vitro fertilization and somatic cell nuclear transfer. Previous studies proved that SIRT2, a member of the sirtuin family, plays a role in oocyte meiosis, but its role in sheep oocyte maturation and its regulating mechanism remains unknown. Firstly, we confirmed the role of Sirt2 in sheep oocytes maturation by supplementation of SIRT2 inhibitor and activator. To further explore the specific mechanism, we performed knockdown of Sirt2 in granulosa cells and then cocultured them with oocytes. Moreover, we determined the effects of Sirt2 on granulosa cell oxidative apoptosis, cell migration, and diffusion, and examined its effects on granulosa cell mitochondrial function, mitophagy, and steroid hormone levels. The results showed that supplementation of SIRT2 inhibitor decreased the oocytes maturation rate (69.28% ± 1.28 vs. 45.74% ± 4.74, p < 0.05), while resveratrol, a SIRT2 activator, increased its maturation rate (67.44% ± 1.68 vs. 78.52 ± 1.28, p < 0.05). Knockdown of Sirt2 in sheep granulosa cells also reduced the oocytes maturation rate (47.98% ± 1.43 vs. 33.60% ± 1.77, p < 0.05), and led to decreased cell migration and expansion ability, oxidative apoptosis, abnormal mitochondrial gene expression, decreased mitochondrial membrane potential and ATP level, and increased mitophagy level. Overexpression of Sirt2 improved mitochondrial membrane potential and ATP level and improved mitochondrial function. Furthermore, we found that Sirt2 knockdown in granulosa cells promotes the secretion of P4 through regulating p-ERK1/2. In conclusion the present study showed that SIRT2 is critical for sheep oocyte maturation through regulating the function of ovarian granulosa cells, especially affecting its mitochondrial function.

Flavonoids as Sirtuin Modulators

Sirtuins (SIRTs) are described as NAD+-dependent deacetylases, also known as class III histone deacetylases. So far, seven sirtuin genes (SIRTS 1-7) have been identified and characterized in mammals and also known to occur in bacteria and eukaryotes. SIRTs are involved in various biological processes including endocrine system, apoptosis, aging and longevity, diabetes, rheumatoid arthritis, obesity, inflammation, etc. Among them, the best characterized one is SIRT1. Actually, small molecules seem to be the most effective SIRT modulators. Flavonoids have been reported to possess many positive effects favrable for human health, while a relatively less research has been reported so far on their funcions as SIRT modulation mechanisms. In this regard, we herein aimed to focus on modulatory effects of flavonoids on SIRTs as the most common secondary metabolites in natural products. Our literature survey covering the years of 2006-2021 pointed out that flavonoids frequently interact with SIRT1 and SIRT3 followed by SIRT6. It can be also concluded that some popular flavonoid derivatives, e.g. resveratrol, quercetin, and catechin derivatives came forward in terms of SIRT modulation.

UBR5 is a novel regulator of WNK1 stability

The with no lysine (K) 1 (WNK1) protein kinase maintains cellular ion homeostasis in many tissues through actions on ion cotransporters and channels. Increased accumulation of WNK1 protein leads to pseudohypoaldosteronism type II (PHAII), a form of familial hypertension. WNK1 can be degraded via its adaptor-dependent recruitment to the Cullin3-RBX1 E3 ligase complex by the ubiquitin-proteasome system. Disruption of this process also leads to disease. To determine if this is the primary mechanism of WNK1 turnover, we examined WNK1 protein stability and degradation by measuring its rate of decay after blockade of translation. Here, we show that WNK1 protein degradation exhibits atypical kinetics in Hela cells. Consistent with this apparent complexity, we found that multiple degradative pathways can modulate cellular WNK1 protein amount. WNK1 protein is degraded not only by the proteasome, but also by the lysosome. Non-lysosomal cysteine proteases calpain and caspases also influence WNK1 degradation, as inhibitors of these proteases modestly increased WNK1 protein expression. Importantly, we discovered that the E3 ubiquitin ligase UBR5 interacts with WNK1 and its deficiency results in increased WNK1 protein. Our results further demonstrate that increased WNK1 in UBR5-depleted cells is attributable to reduced lysosomal degradation of WNK1 protein. Taken together, our findings provide insights into the multiplicity of degradative pathways involved in WNK1 turnover and uncover UBR5 as a previously unknown regulator of WNK1 protein stability that leads to lysosomal degradation of WNK1 protein.

Protein post-translational modifications in the regulation of cancer hallmarks

Posttranslational modifications (PTMs) of proteins, the major mechanism of protein function regulation, play important roles in regulating a variety of cellular physiological and pathological processes. Although the classical PTMs, such as phosphorylation, acetylation, ubiquitination and methylation, have been well studied, the emergence of many new modifications, such as succinylation, hydroxybutyrylation, and lactylation, introduces a new layer to protein regulation, leaving much more to be explored and wide application prospects. In this review, we will provide a broad overview of the significant roles of PTMs in regulating human cancer hallmarks through selecting a diverse set of examples, and update the current advances in the therapeutic implications of these PTMs in human cancer.

The Role of Palmitoleic Acid in Regulating Hepatic Gluconeogenesis through SIRT3 in Obese Mice

Hepatic gluconeogenesis is a crucial process to maintain glucose level during starvation. However, unabated glucose production in diabetic patients is a major contributor to hyperglycemia. Palmitoleic acid is a monounsaturated fatty acid (16:1n7) that is available from dietary sources. Palmitoleic acid exhibits health beneficial effects on diabetes, insulin resistance, inflammation, and metabolic syndrome. However, the mechanism by which palmitoleate reduces blood glucose is still unclear. SIRT3 is a key metabolism-regulating NAD⁺-dependent protein deacetylase. It is known that fasting elevates the expression of SIRT3 in the liver and it regulates many aspects of liver’s response to nutrient deprivation, such as fatty acid oxidation and ketone body formation. However, it is unknown whether SIRT3 also regulates gluconeogenesis. Our study revealed that palmitoleic acid reduced hepatic gluconeogenesis and the expression of SIRT3 under high-fat diet conditions. Overexpression of SIRT3 in the liver and hepatocytes enhanced gluconeogenesis. Further study revealed that SIRT3 played a role in enhancing the activities of gluconeogenic enzymes, such as PEPCK, PC, and MDH2. Therefore, our study indicated that under a high-fat diet, palmitoleic acid decreased gluconeogenesis by reducing enzymatic activities of PEPCK, PC, and MDH2 by down-regulating the expression of SIRT3.

PCK1 dysregulation in cancer: Metabolic reprogramming, oncogenic activation, and therapeutic opportunities

The last few decades have witnessed an advancement in our understanding of multiple cancer cell pathways related to metabolic reprogramming. One of the most important cancer hallmarks, including aerobic glycolysis (the Warburg effect), the central carbon pathway, and multiple-branch metabolic pathway remodeling, enables tumor growth, progression, and metastasis. Phosphoenolpyruvate carboxykinase 1 (PCK1), a key rate-limiting enzyme in gluconeogenesis, catalyzes the conversion of oxaloacetate to phosphoenolpyruvate. PCK1 expression in gluconeogenic tissues is tightly regulated during fasting. In tumor cells, PCK1 is regulated in a cell-autonomous manner rather than by hormones or nutrients in the extracellular environment. Interestingly, PCK1 has an anti-oncogenic role in gluconeogenic organs (the liver and kidneys), but a tumor-promoting role in cancers arising from non-gluconeogenic organs. Recent studies have revealed that PCK1 has metabolic and non-metabolic roles in multiple signaling networks linking metabolic and oncogenic pathways. Aberrant PCK1 expression results in the activation of oncogenic pathways, accompanied by metabolic reprogramming, to maintain tumorigenesis. In this review, we summarize the mechanisms underlying PCK1 expression and regulation, and clarify the crosstalk between aberrant PCK1 expression, metabolic rewiring, and signaling pathway activation. In addition, we highlight the clinical relevance of PCK1 and its value as a putative cancer therapeutic target.

Deferoxamine Inhibits Acute Lymphoblastic Leukemia Progression through Repression of ROS/HIF-1α, Wnt/β-Catenin, and p38MAPK/ERK Pathways

Acute lymphoblastic leukemia (ALL) is the most common type of childhood cancer, with a feature of easy to induce multidrug resistance and relapse. Abundant studies have proved that iron overload strengthens the growth and metastasis of tumor cells. Herein, we found that deferoxamine (DFO) effectively decreased the concentration of intracellular iron in ALL cells. DFO inhibited proliferation, induced apoptosis, and obstructed cell cycle of ALL cells, whereas DFO and dextriferron (Dex) used in combination significantly decreased the sensitivity of ALL cells to DFO. Reactive oxygen species (ROS) level was reduced in ALL cells treated with DFO, and the combination of DFO and Dex reversed the effects of DFO. In vivo, DFO inhibited mouse tumor growth. Besides, cyclinD1, β-catenin, c-Myc, hypoxia inducible factor 1 (HIF-1), p-p38MAPK, and p-ERK1/2 protein levels were significantly downregulated, and the levels of prolyl hydroxylase-2 (PHD-2) were upregulated after treated with DFO, whereas Dex treatment reversed those in vivo and in vitro. In conclusion, DFO inhibited the proliferation and ALL xenograft tumor growth, obstructed the cell cycle, and induced apoptosis of ALL cells, probably via inactivating the ROS/HIF-1α, Wnt/β-catenin, and p38MAPK/ERK signaling.

Involvement of HECT-type E3 ubiquitin ligase genes in salt chemotaxis learning in Caenorhabditis elegans

The ubiquitin-proteasome system is associated with various phenomena including learning and memory. In this study, we report that E3 ubiquitin ligase homologs and proteasome function are involved in taste avoidance learning, a type of associative learning between starvation and salt concentrations, in Caenorhabditis elegans. Pharmacological inhibition of proteasome function using bortezomib causes severe defects in taste avoidance learning. Among 9 HECT-type ubiquitin ligase genes, loss-of-function mutations of 6 ubiquitin ligase genes cause significant abnormalities in taste avoidance learning. Double mutations of those genes cause lethality or enhanced defects in taste avoidance learning, suggesting that the HECT-type ubiquitin ligases act in multiple pathways in the processes of learning. Furthermore, mutations of the ubiquitin ligase genes cause additive effects on taste avoidance learning defects of the insulin-like signaling mutants. Our findings unveil the consequences of aberrant functions of the proteasome and ubiquitin systems in learning behavior of Caenorhabditis elegans.

The modulation of PD-L1 induced by the oncogenic HBXIP for breast cancer growth

Programmed death ligand-1 (PD-L1)/PD-1 checkpoint extensively serves as a central mediator of immunosuppression. A tumor-promoting role for abundant PD-L1 in several cancers is revealed. However, the importance of PD-L1 and how the PD-L1 expression is controlled in breast cancer remains obscure. Here, the mechanisms of controlling PD-L1 at the transcription and protein acetylation levels in promoting breast cancer growth are presented. Overexpressed PD-L1 accelerates breast cancer growth in vitro and in vivo. RNA-seq uncovers that PD-L1 can induce some target genes affecting many cellular processes, especially cancer development. In clinical breast cancer tissues and cells, PD-L1 and HBXIP are both increased, and their expressions are positively correlated. Mechanistic exploration identifies that HBXIP stimulates the transcription of PD-L1 through co-activating ETS2. Specifically, HBXIP induces PD-L1 acetylation at K270 site through interacting with acetyltransferase p300, leading to the stability of PD-L1 protein. Functionally, depletion of HBXIP attenuates PD-L1-accelerated breast tumor growth. Aspirin alleviates breast cancer via targeting PD-L1 and HBXIP. Collectively, the findings display new light into the mechanisms of controlling tumor PD-L1 and broaden the utility for PD-L1 as a target in breast cancer therapy.

Sirtuin function and metabolism: Role in pancreas, liver, and adipose tissue and their crosstalk impacting bone homeostasis

Mammalian sirtuins (SIRT1-7) are members of the nicotine adenine dinucleotide (NAD+)-dependent family of enzymes critical for histone deacetylation and posttranslational modification of proteins. Sirtuin family members regulate a wide spectrum of biological processes and are best known for maintaining longevity. Sirtuins are well characterized in metabolic tissues such as the pancreas, liver and adipose tissue (AT). They are regulated by a diverse range of stimuli, including nutrients and metabolic changes within the organism. Indeed, nutrient-associated conditions, such as obesity and anorexia nervosa (AN), were found to be associated with bone fragility development in osteoporosis. Interestingly, it has also been demonstrated that sirtuins, more specifically SIRT1, can regulate bone activity. Various studies have demonstrated the importance of sirtuins in bone in the regulation of bone homeostasis and maintenance of the balance between bone resorption and bone formation. However, to understand the molecular mechanisms involved in the negative regulation of bone homeostasis during overnutrition (obesity) or undernutrition, it is crucial to examine a wider picture and to determine the pancreatic, liver and adipose tissue pathway crosstalk responsible for bone loss. Particularly, under AN conditions, sirtuin family members are highly expressed in metabolic tissue, but this phenomenon is reversed in bone, and severe bone loss has been observed in human subjects. AN-associated bone loss may be connected to SIRT1 deficiency; however, additional factors may interfere with bone homeostasis. Thus, in this review, we focus on sirtuin activity in the pancreas, liver and AT in cases of over- and undernutrition, especially the regulation of their secretome by sirtuins. Furthermore, we examine how the secretome of the pancreas, liver and AT affects bone homeostasis, focusing on undernutrition. This review aims to lead to a better understanding of the crosstalk between sirtuins, metabolic organs and bone. In long term prospective it should contribute to promote improvement of therapeutic strategies for the prevention of metabolic diseases and the development of osteoporosis.

Role of the Histone Acetyl Transferase MOF and the Histone Deacetylase Sirtuins in Regulation of H4K16ac During DNA Damage Repair and Metabolic Programming: Implications in Cancer and Aging

The accurate repair of genomic damage mediated by ionizing radiation (IR), chemo- or radiomimetic drugs, or other exogenous agents, is necessary for maintenance of genome integrity, preservation of cellular viability and prevention of oncogenic transformation. Eukaryotes have conserved mechanisms designed to perceive and repair the damaged DNA quite efficiently. Among the different types of DNA damage, double strand breaks (DSB) are the most detrimental. The cellular DNA DSB response is a hierarchical signaling network that integrates damage sensing and repair with chromatin structural changes that involve a range of pre-existing and induced covalent modifications. Recent studies have revealed that pre-existing histone modifications are important contributors within this signaling/repair network. This chapter discusses the role of a critical histone acetyl transferase (HAT) known as MOF (males absent on the first) and the histone deacetylases (HDACs) Sirtuins on histone H4K16 acetylation (H4K16ac) and DNA damage repair. We also discuss the role of this important histone modification in light of metabolic rewiring and its role in regulating human pathophysiologic states.

Deubiquitinase OTUB2 exacerbates the progression of colorectal cancer by promoting PKM2 activity and glycolysis

Aberrant regulation of ubiquitination often leads to metabolic reprogramming in tumor cells. However, the underlying mechanisms are not fully understood. Here we demonstrate that OTUB2, an OTU deubiquitinase, is upregulated in colorectal cancer (CRC) and exacerbates the progression of CRC through modulating the aerobic glycolysis. Mechanistically, OTUB2 directly interacts with pyruvate kinase M2 (PKM2) and inhibits its ubiquitination by blocking the interaction between PKM2 and its ubiquitin E3 ligase Parkin, thereby enhancing PKM2 activity and promoting glycolysis. In response to glucose starvation stress, the effect of OTUB2 on PKM2 is enhanced, which confers metabolic advantage to CRC cells. Moreover, OTUB2 depletion reduces glucose consumption, lactate production, and cellular ATP production. OTUB2-knockout CRC cells exhibit attenuated proliferation and migration, as well as an elevated level of apoptosis and increased sensitivity to chemotherapy drugs. Furthermore, in vivo assays show that knockout of OTUB2 inhibits tumor growth in mice. Taken together, these findings reveal the critical role of OTUB2 in the regulation of glycolysis and illustrate the molecular mechanism underlying its role as a negative regulator of PKM2 ubiquitination in CRC, establishing a bridge between OTUB2-regulated PKM2 ubiquitination and altered metabolic patterns in CRC and suggesting that OTUB2 is a promising target for CRC treatment.

Protein acetylation effects on enzyme activity and metabolic pathway fluxes

Acetylation of proteins seems a widespread process found in the three domains of life. Several studies have shown that besides histones, acetylation of lysine residues also occurs in non-nuclear proteins. Hence, it has been suggested that this covalent modification is a mechanism that might regulate diverse metabolic pathways by modulating enzyme activity, stability, and/or subcellular localization or interaction with other proteins. However, protein acetylation levels seem to have low correlation with modification of enzyme activity and pathway fluxes. In addition, the results obtained with mutant enzymes that presumably mimic acetylation have frequently been over-interpreted. Moreover, there is a generalized lack of rigorous enzyme kinetic analysis in parallel to acetylation level determinations. The purpose of this review is to analyze the current findings on the impact of acetylation on metabolic enzymes and its repercussion on metabolic pathways function/regulation.

Sirtuin Oxidative Post-translational Modifications

Increased sirtuin deacylase activity is correlated with increased lifespan and healthspan in eukaryotes. Conversely, decreased sirtuin deacylase activity is correlated with increased susceptibility to aging-related diseases. However, the mechanisms leading to decreased sirtuin activity during aging are poorly understood. Recent work has shown that oxidative post-translational modification by reactive oxygen (ROS) or nitrogen (RNS) species results in inhibition of sirtuin deacylase activity through cysteine nitrosation, glutathionylation, sulfenylation, and sulfhydration as well as tyrosine nitration. The prevalence of ROS/RNS (e.g., nitric oxide, S-nitrosoglutathione, hydrogen peroxide, oxidized glutathione, and peroxynitrite) is increased during inflammation and as a result of electron transport chain dysfunction. With age, cellular production of ROS/RNS increases; thus, cellular oxidants may serve as a causal link between loss of sirtuin activity and aging-related disease development. Therefore, the prevention of inhibitory oxidative modification may represent a novel means to increase sirtuin activity during aging. In this review, we explore the role of cellular oxidants in inhibiting individual sirtuin human isoform deacylase activity and clarify the relevance of ROS/RNS as regulatory molecules of sirtuin deacylase activity in the context of health and disease.

SL010110, a lead compound, inhibits gluconeogenesis via SIRT2-p300-mediated PEPCK1 degradation and improves glucose homeostasis in diabetic mice

Suppression of excessive hepatic gluconeogenesis is an effective strategy for controlling hyperglycemia in type 2 diabetes (T2D). In the present study, we screened our compounds library to discover the active molecules inhibiting gluconeogenesis in primary mouse hepatocytes. We found that SL010110 (5-((4-allyl-2-methoxyphenoxy) methyl) furan-2-carboxylic acid) potently inhibited gluconeogenesis with 3 μM and 10 μM leading to a reduction of 45.5% and 67.5%, respectively. Moreover, SL010110 caused suppression of gluconeogenesis resulted from downregulating the protein level of phosphoenolpyruvate carboxykinase 1 (PEPCK1), but not from affecting the gene expressions of PEPCK, glucose-6-phosphatase, and fructose-1,6-bisphosphatase. Furthermore, SL010110 increased PEPCK1 acetylation, and promoted PEPCK1 ubiquitination and degradation. SL010110 activated p300 acetyltransferase activity in primary mouse hepatocytes. The enhanced PEPCK1 acetylation and suppressed gluconeogenesis caused by SL010110 were blocked by C646, a histone acetyltransferase p300 inhibitor, suggested that SL010110 inhibited gluconeogenesis by activating p300. SL010110 decreased NAD+/NADH ratio, inhibited SIRT2 activity, and further promoted p300 acetyltransferase activation and PEPCK1 acetylation. These effects were blocked by NMN, an NAD+ precursor, suggested that SL010110 inhibited gluconeogenesis by inhibiting SIRT2, activating p300, and subsequently promoting PEPCK1 acetylation. In type 2 diabetic ob/ob mice, single oral dose of SL010110 (100 mg/kg) suppressed gluconeogenesis accompanied by the suppressed hepatic SIRT2 activity, increased p300 activity, enhanced PEPCK1 acetylation and degradation. Chronic oral administration of SL010110 (15 or 50 mg/kg) significantly reduced the blood glucose levels in ob/ob and db/db mice. This study reveals that SL010110 is a lead compound with a distinct mechanism of suppressing gluconeogenesis via SIRT2-p300-mediated PEPCK1 degradation and potent anti-hyperglycemic activity for the treatment of T2D.

Sirtuins as Interesting Players in the Course of HIV Infection and Comorbidities

The sirtuins (SIRTs) are a family of enzymes from the group of NAD⁺-dependent deacetylases. Through the reaction of splitting the acetyl group of various transcription factors and histones they regulate many processes in the organism. The activity of sirtuins is linked to metabolic control, oxidative stress, inflammation and apoptosis, and they also affect the course of viral infections. For this reason, they may participate in the pathogenesis and development of many diseases, but little is known about their role in the course of human immunodeficiency virus (HIV) infection, which is the subject of this review. In the course of HIV infection, comorbidities such as: neurodegenerative disorders, obesity, insulin resistance and diabetes, lipid disorders and cardiovascular diseases, renal and bone diseases developed more frequently and faster compared to the general population. The role of sirtuins in the development of accompanying diseases in the course of HIV infection may also be interesting. There is still a lack of detailed information on this subject. The role of sirtuins, especially SIRT1, SIRT3, SIRT6, are indicated to be of great importance in the course of HIV infection and the development of the abovementioned comorbidities.

SIRT2-mediated deacetylation and deubiquitination of C/EBPβ prevents ethanol-induced liver injury

Protein acetylation has emerged to play pivotal roles in alcoholic liver disease (ALD). Sirutin 2 (SIRT2) is a nicotinamide adenine dinucleotide (NAD+)-dependent deacetylase involved in the regulation of aging, metabolism, and stress. However, the role of SIRT2 in ALD remains unclear. Here, we report that the SIRT2-mediated deacetylation-deubiquitination switch of CCAAT/enhancer-binding protein beta (C/EBPβ) prevents ALD. Our results showed that hepatic SIRT2 protein expression was negatively correlated with the severity of alcoholic liver injury in ALD patients. Liver-specific SIRT2 deficiency sensitized mice to ALD, whereas transgenic SIRT2 overexpression in hepatocytes significantly prevented ethanol-induced liver injury via normalization of hepatic steatosis, lipid peroxidation, and hepatocyte apoptosis. Mechanistically, we identified C/EBPβ as a critical substrate of SIRT2 implicated in ALD. SIRT2-mediated deacetylation at lysines 102 and 211 decreased C/EBPβ ubiquitination, resulting in enhanced protein stability and subsequently increased transcription of C/EBPβ-target gene LCN2. Importantly, hepatic deacetylated C/EBPβ and LCN2 compensation reversed SIRT2 deletion-induced ALD aggravation in mice. Furthermore, C/EBPβ protein expression was positively correlated with SIRT2 and LCN2 expression in the livers of ALD patients and was inversely correlated with ALD development. Therefore, activating SIRT2-C/EBPβ-LCN2 signaling pathway is a potential therapy for ALD.

Emerging roles of Sirtuin 2 in cardiovascular diseases

Sirtuins are a family of NAD⁺ -dependent deacetylases implicated in a wide variety of age-associated pathologies, including cardiovascular disorders. Among the seven mammalian sirtuins, SIRT2 modulates various cellular processes through the deacetylation or deacylation of their target proteins. Notably, the levels of SIRT2 in the heart decline with age and other pathological conditions, leading to cardiovascular dysfunction. In the present review, we discuss the emerging roles of SIRT2 in cardiovascular dysfunction and heart failure associated with factors like age, hypertension, oxidative stress, and diabetes. We also discuss the potential of using inhibitors to study the unexplored role of SIRT2 in the heart. While SIRT2 undoubtedly plays a crucial role in the cardiovascular system, its functions are only beginning to be understood, making it an attractive candidate for further research in the field.

Combined intermittent fasting and ERK inhibition enhance the anti-tumor effects of chemotherapy via the GSK3β-SIRT7 axis

Dietary interventions such as intermittent fasting (IF) have emerged as an attractive strategy for cancer therapies; therefore, understanding the underlying molecular mechanisms is pivotal. Here, we find SIRT7 decline markedly attenuates the anti-tumor effect of IF. Mechanistically, AMP-activated protein kinase (AMPK) phosphorylating SIRT7 at T263 triggers further phosphorylation at T255/S259 by glycogen synthase kinase 3β (GSK3β), which stabilizes SIRT7 by decoupling E3 ligase UBR5. SIRT7 hyperphosphorylation achieves anti-tumor activity by disrupting the SKP2-SCF E3 ligase, thus preventing SKP2-mediated K63-linked AKT polyubiquitination and subsequent activation. In contrast, GSK3β-SIRT7 axis is inhibited by EGF/ERK2 signaling, with ERK2 inactivating GSK3β, thus accelerating SIRT7 degradation. Unfavorably, glucose deprivation or chemotherapy hijacks the GSK3β-SIRT7 axis via ERK2, thus activating AKT and ensuring survival. Notably, Trametinib, an FDA-approved MEK inhibitor, enhances the efficacy of combination therapy with doxorubicin and IF. Overall, we have revealed the GSK3β-SIRT7 axis that must be fine-tuned in the face of the energetic and oncogenic stresses in malignancy.

The combination of intermittent fasting and chemotherapy can improve the response to treatment. Here, the authors show that SIRT7 activation is required to inactivate Akt during intermittent fasting and that the combination of intermittent fasting and inhibitors that block the Erk pathway can improve efficacy of treatment.

Protein acetylation and deacetylation in plant-pathogen interactions

Protein acetylation and deacetylation catalysed by lysine acetyltransferases (KATs) and deacetylases (KDACs), respectively, are major mechanisms regulating various cellular processes. During the fight between microbial pathogens and host plants, both apply a set of measures, including acetylation interference, to strengthen themselves while suppressing the other. In this review, we first summarize KATs and KDACs in plants and their pathogens. Next, we introduce diverse acetylation and deacetylation mechanisms affecting protein functions, including the regulation of enzyme activity and specificity, protein-protein or protein-DNA interactions, subcellular localization and protein stability. We then focus on the current understanding of acetylation and deacetylation in plant-pathogen interactions. Additionally, we also discuss potential acetylation-related approaches for controlling plant diseases.

Ins and Outs of the TCA Cycle: The Central Role of Anaplerosis

The reactions of the tricarboxylic acid (TCA) cycle allow the controlled combustion of fat and carbohydrate. In principle, TCA cycle intermediates are regenerated on every turn and can facilitate the oxidation of an infinite number of nutrient molecules. However, TCA cycle intermediates can be lost to cataplerotic pathways that provide precursors for biosynthesis, and they must be replaced by anaplerotic pathways that regenerate these intermediates. Together, anaplerosis and cataplerosis help regulate rates of biosynthesis by dictating precursor supply, and they play underappreciated roles in catabolism and cellular energy status. They facilitate recycling pathways and nitrogen trafficking necessary for catabolism, and they influence redox state and oxidative capacity by altering TCA cycle intermediate concentrations. These functions vary widely by tissue and play emerging roles in disease. This article reviews the roles of anaplerosis and cataplerosis in various tissues and discusses how they alter carbon transitions, and highlights their contribution to mechanisms of disease. Expected final online publication date for the Annual Review of Nutrition, Volume 41 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

A comprehensive review of Sirtuins: With a major focus on redox homeostasis and metabolism

Sirtuins are Class III protein deacetylases with seven conserved isoforms. In general, Sirtuins are highly activated under cellular stress conditions in which NAD⁺ levels are increased. Nevertheless, regulation of Sirtuins extends far beyond the influences of cellular NAD⁺/NADH ratio and a rapidly expanding body of evidence currently suggests that their expression and catalytic activity are highly kept under control at multiple levels by various factors and processes. Owing to their intrinsic ability to enzymatically target various intracellular proteins, Sirtuins are prominently involved in the regulation of fundamental biological processes including inflammation, metabolism, redox homeostasis, DNA repair and cell proliferation and senescence. In fact, Sirtuins are well established to regulate and reprogram different redox and metabolic pathways under both pathological and physiological conditions. Therefore, alterations in Sirtuin levels can be a pivotal intermediary step in the pathogenesis of several disorders. This review first highlights the mechanisms involved in the regulation of Sirtuins and further summarizes the current findings on the major functions of Sirtuins in cellular redox homeostasis and bioenergetics (glucose and lipid metabolism).

Acetylation-induced PCK isoenzyme transition promotes metabolic adaption of liver cancer to systemic therapy

Sorafenib and lenvatinib are approved first-line targeted therapies for advanced liver cancer, but most patients develop acquired resistance. Herein, we found that sorafenib induced extensive acetylation changes towards a more energetic metabolic phenotype. Metabolic adaptation was mediated via acetylation of the Lys-491 (K491) residue of phosphoenolpyruvate carboxykinase isoform 2 (PCK2) (PCK2-K491) and Lys-473 (K473) residue of PCK1 (PCK1-K473) by the lysine acetyltransferase 8 (KAT8), resulting in isoenzyme transition from cytoplasmic PCK1 to mitochondrial PCK2. KAT8-catalyzed PCK2 acetylation at K491 impeded lysosomal degradation to increase the level of PCK2 in resistant cells. PCK2 inhibition in sorafenib-resistant cells significantly reversed drug resistance in vitro and in vivo. High levels of PCK2 predicted a shorter progression-free survival time in patients who received sorafenib treatment. Therefore, acetylation-induced isoenzyme transition from PCK1 to PCK2 contributes to resistance to systemic therapeutic drugs in liver cancer. PCK2 may be an emerging target for delaying tumor recurrence.

Histone deacetylases control lysine acetylation of ribosomal proteins in rice

Lysine acetylation (Kac) is well known to occur in histones for chromatin function and epigenetic regulation. In addition to histones, Kac is also detected in a large number of proteins with diverse biological functions. However, Kac function and regulatory mechanism for most proteins are unclear. In this work, we studied mutation effects of rice genes encoding cytoplasm-localized histone deacetylases (HDAC) on protein acetylome and found that the HDAC protein HDA714 was a major deacetylase of the rice non-histone proteins including many ribosomal proteins (r-proteins) and translation factors that were extensively acetylated. HDA714 loss-of-function mutations increased Kac levels but reduced abundance of r-proteins. In vitro and in vivo experiments showed that HDA714 interacted with r-proteins and reduced their Kac. Substitutions of lysine by arginine (depleting Kac) in several r-proteins enhance, while mutations of lysine to glutamine (mimicking Kac) decrease their stability in transient expression system. Ribo-seq analysis revealed that the hda714 mutations resulted in increased ribosome stalling frequency. Collectively, the results uncover Kac as a functional posttranslational modification of r-proteins which is controlled by histone deacetylases, extending the role of Kac in gene expression to protein translational regulation.

Metabolic reprogramming and epigenetic modifications on the path to cancer

Metabolic rewiring and epigenetic remodeling, which are closely linked and reciprocally regulate each other, are among the well-known cancer hallmarks. Recent evidence suggests that many metabolites serve as substrates or cofactors of chromatin-modifying enzymes as a consequence of the translocation or spatial regionalization of enzymes or metabolites. Various metabolic alterations and epigenetic modifications also reportedly drive immune escape or impede immunosurveillance within certain contexts, playing important roles in tumor progression. In this review, we focus on how metabolic reprogramming of tumor cells and immune cells reshapes epigenetic alterations, in particular the acetylation and methylation of histone proteins and DNA. We also discuss other eminent metabolic modifications such as, succinylation, hydroxybutyrylation, and lactylation, and update the current advances in metabolism- and epigenetic modification-based therapeutic prospects in cancer.

Acetylation Stabilizes Phosphoglycerate Dehydrogenase by Disrupting the Interaction of E3 Ligase RNF5 to Promote Breast Tumorigenesis

Phosphoglycerate dehydrogenase (PHGDH) is the first enzyme in the serine synthesis pathway in which it is also the rate-limiting enzyme. It is significantly upregulated in many cancers, especially breast cancer. However, the posttranslational mechanism of PHGDH upregulation in breast cancer is unknown. In this study, we find that RNF5, an E3 ubiquitin ligase, is essential for the degradation of PHGDH protein. PHGDH is degraded by RNF5 to prevent the proliferation of breast cancer cells. The acetylation of PHGDH at K58 is able to disrupt the interaction of RNF5-PHGDH and promote the proliferation of breast cancer cells. Tip60 and SIRT2 regulate the reversible acetylation modification of PHGDH in response to glucose alteration. Moreover, PHGDH is significantly upregulated in samples of human breast cancer and is associated with decreased RNF5 expression. This implies a potential therapeutic target through the interference interaction of PHGDH-RNF5 to degrade PHGDH in breast cancer.

The role of SIRT2 in vascular-related and heart-related diseases: A review

At present, cardiovascular disease is one of the important factors of human death, and there are many kinds of proteins involved. Sirtuins family proteins are involved in various physiological and pathological activities of the human body. Among them, there are more and more studies on the relationship between sirtuin2 (SIRT2) protein and cardiovascular diseases. SIRT2 can effectively inhibit pathological cardiac hypertrophy. The effect of SIRT2 on ischaemia‐reperfusion injury has different effects under different conditions. SIRT2 can reduce the level of reactive oxygen species (ROS), which may help to reduce the severity of diabetic cardiomyopathy. SIRT2 can affect a variety of cardiovascular diseases, energy metabolism and the ageing of cardiomyocytes, thereby affecting heart failure. SIRT2 also plays an important role in vascular disease. For endothelial cell damage used by oxidative stress, the role of SIRT2 is bidirectional, which is related to the degree of oxidative stress stimulation. When the degree of stimulation is small, SIRT2 plays a protective role, and when the degree of stimulation increases to a certain level, SIRT2 plays a negative role. In addition, SIRT2 is also involved in the remodelling of blood vessels and the repair of skin damage.

Generation of the short TRIM32 isoform is regulated by Lys 247 acetylation and a PEST sequence

TRIM32 is an E3 ligase implicated in diverse biological pathways and pathologies such as muscular dystrophy and cancer. TRIM32 are expressed both as full-length proteins, and as a truncated protein. The mechanisms for regulating these isoforms are poorly understood. Here we identify a PEST sequence in TRIM32 located in the unstructured region between the RING-BBox-CoiledCoil domains and the NHL repeats. The PEST sequence directs cleavage of TRIM32, generating a truncated protein similarly to the short isoform. We map three lysine residues that regulate PEST mediated cleavage and auto-ubiquitylation activity of TRIM32. Mimicking acetylation of lysine K247 completely inhibits TRIM32 cleavage, while the lysines K50 and K401 are implicated in auto-ubiquitylation activity. We show that the short isoform of TRIM32 is catalytic inactive, suggesting a dominant negative role. These findings uncover that TRIM32 is regulated by post-translational modifications of three lysine residues, and a conserved PEST sequence.

Effect of oxymatrine on liver gluconeogenesis is associated with the regulation of PEPCK and G6Pase expression and AKT phosphorylation

An increase in liver gluconeogenesis is an important pathological phenomenon in type 2 diabetes mellitus (T2DM) and oxymatrine is an effective natural drug used for T2DM treatment. The present study aimed to explore the effect of oxymatrine on gluconeogenesis and elucidate the underlying mechanism. Male Sprague-Dawley rats were treated with a high-fat diet and streptozotocin for 4 weeks to induce T2DM, and HepG2 cells were treated with 55 mM glucose to simulate T2DM in vitro. T2DM rats were treated with oxymatrine (10 or 20 mg/kg weight) or metformin for 4 weeks, and HepG2 cells were treated with oxymatrine (0.1 or 1 µM), metformin (0.1 µM), or oxymatrine combined with MK-2206 (AKT inhibitor) for 24 h. Fasting blood glucose and insulin sensitivity of rats were measured to evaluate insulin resistance. Glucose production and uptake ability were measured to evaluate gluconeogenesis in HepG2 cells, and the expression of related genes was detected to explore the molecular mechanism. Additionally, the body weight, liver weight and liver index were measured and hematoxylin and eosin staining was performed to evaluate the effects of the disease. The fasting glucose levels of T2DM rats was 16.5 mmol/l, whereas in the control rats, it was 6.1 mmol/l. Decreased insulin sensitivity (K-value, 0.2), body weight loss (weight, 300 g), liver weight gain, liver index increase (value, 48) and morphological changes were observed in T2DM rats, accompanied by reduced AKT phosphorylation, and upregulated expression of phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase). High-glucose treatment significantly increased glucose production and decreased glucose uptake in HepG2 cells, concomitant with a decrease in AKT phosphorylation and increase of PEPCK and G6Pase expression. In vivo, oxymatrine dose-dependently increased the sensitivity of T2DM rats to insulin, increased AKT phosphorylation and decreased PEPCK and G6Pase expression in the liver, and reversed the liver morphological changes. In vitro, oxymatrine dose-dependently increased AKT phosphorylation and glucose uptake of HepG2 cells subjected to high-glucose treatment, which was accompanied by inhibition of the expression of the gluconeogenesis-related genes, PEPCK and G6Pase. MK-2206 significantly inhibited the protective effects of oxymatrine in high-glucose-treated cells. These data indicated that oxymatrine can effectively prevent insulin resistance and gluconeogenesis, and its mechanism may be at least partly associated with the regulation of PEPCK and G6Pase expression and AKT phosphorylation in the liver.

Gluconeogenic enzyme PCK1 deficiency promotes CHK2 O-GlcNAcylation and hepatocellular carcinoma growth upon glucose deprivation

Although cancer cells are frequently faced with a nutrient- and oxygen-poor microenvironment, elevated hexosamine-biosynthesis pathway (HBP) activity and protein O-GlcNAcylation (a nutrient sensor) contribute to rapid growth of tumor and are emerging hallmarks of cancer. Inhibiting O-GlcNAcylation could be a promising anticancer strategy. The gluconeogenic enzyme phosphoenolpyruvate carboxykinase 1 (PCK1) is downregulated in hepatocellular carcinoma (HCC). However, little is known about the potential role of PCK1 in enhanced HBP activity and HCC carcinogenesis under glucose-limited conditions. In this study, PCK1 knockout markedly enhanced the global O-GlcNAcylation levels under low-glucose conditions. Mechanistically, metabolic reprogramming in PCK1-loss hepatoma cells led to oxaloacetate accumulation and increased de novo uridine triphosphate synthesis contributing to uridine diphosphate-N-acetylglucosamine (UDP-GlcNAc) biosynthesis. Meanwhile, deletion of PCK1 also resulted in AMPK-GFAT1 axis inactivation, promoting UDP-GlcNAc synthesis for elevated O-GlcNAcylation. Notably, lower expression of PCK1 promoted CHK2 threonine 378 O-GlcNAcylation, counteracting its stability and dimer formation, increasing CHK2-dependent Rb phosphorylation and HCC cell proliferation. Moreover, aminooxyacetic acid hemihydrochloride and 6-diazo-5-oxo-L-norleucine blocked HBP-mediated O-GlcNAcylation and suppressed tumor progression in liver-specific Pck1-knockout mice. We reveal a link between PCK1 depletion and hyper-O-GlcNAcylation that underlies HCC oncogenesis and suggest therapeutic targets for HCC that act by inhibiting O-GlcNAcylation.

Understanding the Function of Mammalian Sirtuins and Protein Lysine Acylation

Protein lysine acetylation is an important posttranslational modification that regulates numerous biological processes. Targeting lysine acetylation regulatory factors, such as acetyltransferases, deacetylases, and acetyl-lysine recognition domains, has been shown to have potential for treating human diseases, including cancer and neurological diseases. Over the past decade, many other acyl-lysine modifications, such as succinylation, crotonylation, and long-chain fatty acylation, have also been investigated and shown to have interesting biological functions. Here, we provide an overview of the functions of different acyl-lysine modifications in mammals. We focus on lysine acetylation as it is well characterized, and principles learned from acetylation are useful for understanding the functions of other lysine acylations. We pay special attention to the sirtuins, given that the study of sirtuins has provided a great deal of information about the functions of lysine acylation. We emphasize the regulation of sirtuins to illustrate that their regulation enables cells to respond to various signals and stresses.

UBR5 inhibits the radiosensitivity of non-small cell lung cancer cells via the activation of the PI3K/AKT pathway

Ubiquitin protein ligase E3 component n-recognin 5 (UBR5) has been identified as an oncogene in diverse cancers; however, whether its expression was associated with radiosensitivities of non-small cell lung cancer (NSCLC) cells remains unclear. Expression levels of UBR5 in NSCLC tissues and cell lines were examined by immunohistochemical staining and western blotting. Colony formation assay, CCK-8 cell viability assay, flow cytometry, and caspase-3 activity assay were performed to evaluate the radiosensitization of UBR5 knockdown in NSCLC cells, and the underlying mechanism in vitro was also investigated. UBR5 was highly expressed in NSCLC tissues, and its high expression was associated with the poor prognosis in 50 patients with NSCLC. After X-ray irradiation, the protein expression levels of UBR5 were also increased in NSCLC cells. UBR5 inhibition enhanced the radiosensitivity of NSCLC cells by inhibiting the cell viability and inducing apoptosis. Further investigation indicated that UBR5 knockdown-mediated radiosensitization involved the phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway. Knockdown of UBR5 radiosensitizes NSCLC cells via the inactivation of the PI3K/AKT signal, which provided a novel therapeutic target for NSCLC radiosensitization.

Acetylation of ELF5 suppresses breast cancer progression by promoting its degradation and targeting CCND1

E74-like ETS transcription factor 5 (ELF5) is involved in a wide spectrum of biological processes, e.g., mammogenesis and tumor progression. We have identified a list of p300-interacting proteins in human breast cancer cells. Among these, ELF5 was found to interact with p300 via acetylation, and the potential acetylation sites were identified as K130, K134, K143, K197, K228, and K245. Furthermore, an ELF5-specific deacetylase, SIRT6, was also identified. Acetylation of ELF5 promoted its ubiquitination and degradation, but was also essential for its antiproliferative effect against breast cancer, as overexpression of wild-type ELF5 and sustained acetylation-mimicking ELF5 mutant could inhibit the expression of its target gene CCND1. Taken together, the results demonstrated a novel regulation of ELF5 as well as shedding light on its important role in modulation of breast cancer progression.

SIRT2 ablation inhibits glucose-stimulated insulin secretion through decreasing glycolytic flux

Rationale: Sirtuins are NAD⁺-dependent protein deacylases known to have protective effects against age-related diseases such as diabetes, cancer, and neurodegenerative disease. SIRT2 is the only primarily cytoplasmic isoform and its overall role in glucose homeostasis remains uncertain.

Methods: SIRT2-knockout (KO) rats were constructed to evaluate the role of SIRT2 in glucose homeostasis. The effect of SIRT2 on β-cell function was detected by investigating the morphology, insulin secretion, and metabolomic state of islets. The deacetylation and stabilization of GKRP in β-cells by SIRT2 were determined by western blot, adenoviral infection, and immunoprecipitation.

Results: SIRT2-KO rats exhibited impaired glucose tolerance and glucose-stimulated insulin secretion (GSIS), without change in insulin sensitivity. SIRT2 deficiency or inhibition by AGK2 decreased GSIS in isolated rat islets, with lowered oxygen consumption rate. Adenovirus-mediated overexpression of SIRT2 enhanced insulin secretion from rat islets. Metabolomics analysis revealed a decrease in metabolites of glycolysis and tricarboxylic acid cycle in SIRT2-KO islets compared with control islets. Our study further demonstrated that glucokinase regulatory protein (GKRP), an endogenous inhibitor of glucokinase (GCK), was expressed in rat islets. SIRT2 overexpression deacetylated GKRP in INS-1 β-cells. SIRT2 knockout or inhibition elevated GKRP protein stability in islet β-cells, leading to an increase in the interaction of GKRP and GCK. On the contrary, SIRT2 inhibition promoted the protein degradation of ALDOA, a glycolytic enzyme.

Conclusions: SIRT2 ablation inhibits GSIS through blocking GKRP protein degradation and promoting ALDOA protein degradation, resulting in a decrease in glycolytic flux.

Sirtuins: Enzymes with multidirectional catalytic activity

Sirtuins (SIRT) are NAD+-dependent histone deacetylases that play an important role in the functioning of the human body. They participate in numerous processes taking place in cells, including in the post-translational modification of proteins, silencing gene transcription, inducing repair processes, as well as in the regulation of metabolic processes. Sirtuins have also been shown to play an important role in reducing the level of reactive oxygen species as well as in stimulating cell growth, aging and death. Such a wide range of processes, which are affected by sirtuins, have recently made sirtuins the object of many studies aimed at a detailed understanding of the mechanisms of their action and the role they play. The aim of our study was to collect and systematize information on sirtuins, mainly from the last 10 years, both regarding the human body and based on the results of research on animal models or cell lines. The article discusses the structure, function and biological role of sirtuins in cellular processes.