SIRT2 inhibits non-small cell lung cancer cell growth through impairing Skp2-mediated p27 degradation

Research progress on the structural and anti-colorectal malignant tumor properties of Shikonin

ABSTRACT

Colorectal cancer is the third most prevalent malignant tumor worldwide. Despite the advancements in surgical procedures and treatment options, CRC remains a considerable cause of cancer-related mortality. Shikonin is a naphthoquinone compound that exhibits multiple biological activities, including anti-inflammatory and anti-tumor effects as well as wound healing promotion. Recently, Shikonin has been increasingly used in basic research on colorectal malignant tumors. Therefore, we explored the mechanisms of action and structural improvements of Shikonin in colorectal cancer through a literature review to provide valuable insights for the advancement of research and development of related pharmaceuticals.

Targeting sirtuins for cancer therapy: epigenetics modifications and beyond

Sirtuins (SIRTs) are well-known as nicotinic adenine dinucleotide+(NAD+)-dependent histone deacetylases, which are important epigenetic enzymes consisting of seven family members (SIRT1-7). Of note, SIRT1 and SIRT2 are distributed in the nucleus and cytoplasm, while SIRT3, SIRT4 and SIRT5 are localized in the mitochondria. SIRT6 and SIRT7 are distributed in the nucleus. SIRTs catalyze the deacetylation of various substrate proteins, thereby modulating numerous biological processes, including transcription, DNA repair and genome stability, metabolism, and signal transduction. Notably, accumulating evidence has recently underscored the multi-faceted roles of SIRTs in both the suppression and progression of various types of human cancers. Crucially, SIRTs have been emerging as promising therapeutic targets for cancer therapy. Thus, in this review, we not only present an overview of the molecular structure and function of SIRTs, but elucidate their intricate associations with oncogenesis. Additionally, we discuss the current landscape of small-molecule activators and inhibitors targeting SIRTs in the contexts of cancer and further elaborate their combination therapies, especially highlighting their prospective utility for future cancer drug development.

Emerging role of sirtuins in non‑small cell lung cancer (Review)

Non‑small cell lung cancer (NSCLC) is a highly prevalent lung malignancy characterized by insidious onset, rapid progression and advanced stage at the time of diagnosis, making radical surgery impossible. Sirtuin (SIRT) is a histone deacetylase that relies on NAD+ for its function, regulating the aging process through modifications in protein activity and stability. It is intricately linked to various processes, including glycolipid metabolism, inflammation, lifespan regulation, tumor formation and stress response. An increasing number of studies indicate that SIRTs significantly contribute to the progression of NSCLC by regulating pathophysiological processes such as energy metabolism, autophagy and apoptosis in tumor cells through the deacetylation of histones or non‑histone proteins. The present review elaborates on the roles of different SIRTs and their mechanisms in NSCLC, while also summarizing novel therapeutic agents based on SIRTs. It aims to present new ideas and a theoretical basis for NSCLC treatment.

Defining the heterogeneous molecular landscape of lung cancer cell responses to epigenetic inhibition

Epigenetic inhibitors exhibit powerful antiproliferative and anticancer activities. However, cellular responses to small-molecule epigenetic inhibition are heterogenous and dependent on factors such as the genetic background, metabolic state, and on-/off-target engagement of individual small-molecule compounds. The molecular study of the extent of this heterogeneity often measures changes in a single cell line or using a small number of compounds. To more comprehensively profile the effects of small-molecule perturbations and their influence on these heterogeneous cellular responses, we present a molecular resource based on the quantification of chromatin, proteome, and transcriptome remodeling due to histone deacetylase inhibitors (HDACi) in non-isogenic cell lines. Through quantitative molecular profiling of 10,621 proteins, these data reveal coordinated molecular remodeling of HDACi treated cancer cells. HDACi-regulated proteins differ greatly across cell lines with consistent (JUN, MAP2K3, CDKN1A) and divergent (CCND3, ASF1B, BRD7) cell-state effectors. Together these data provide valuable insight into cell-type driven and heterogeneous responses that must be taken into consideration when monitoring molecular perturbations in culture models.

Acetylation of ELMO1 correlates with Rac1 activity and colorectal cancer progress

Acetylation, a critical regulator of diverse cellular processes, holds significant implications in various cancer contexts. Further understanding of the acetylation patterns of key cancer-driven proteins is crucial for advancing therapeutic strategies in cancer treatment. This study aimed to unravel the acetylation patterns of Engulfment and Cell Motility Protein 1 (ELMO1) and its relevance to the pathogenesis of colorectal cancer (CRC). Immunoprecipitation and mass spectrometry precisely identified lysine residue 505 (K505) as a central acetylation site in ELMO1. P300 emerged as the acetyltransferase for ELMO1 K505 acetylation, while SIRT2 was recognized as the deacetylase. Although K505 acetylation minimally affected ELMO1's localization and stability, it played a crucial role in mediating ELMO1-Dock180 interaction, thereby influencing Rac1 activation. Functionally, ELMO1 K505 acetylation proved to be a pivotal factor in CRC progression, exerting its influence on key cellular processes. Clinical analysis of CRC samples unveiled elevated ELMO1 acetylation in primary tumors, indicating a potential association with CRC pathologies. This work provides insights into ELMO1 acetylation and its significance in advancing potentially therapeutic interventions in CRC treatment.

Selective inhibition of SIRT2: A disputable therapeutic approach in cancer therapy

Sirtuin 2 (SIRT2) is involved in a wide range of processes, from transcription to metabolism to genome stability. Dysregulation of SIRT2 has been associated with the pathogenesis and progression of different diseases, such as cancer and neurodegenerative disorders. In this context, targeting SIRT2 activity by small molecule inhibitors is a promising therapeutic strategy for treating related conditions, particularly cancer. This review summarizes the regulatory roles and molecular mechanisms of SIRT2 in cancer and the attempts to evaluate potential antitumor activities of SIRT2-selective inhibitors by in vitro and in vivo testing, which are expected to deepen our understanding of the role of SIRT2 in tumorigenesis and progression and may offer important clues or inspiration ideas for developing SIRT2 inhibitors with excellent affinity and selectivity.

Resveratrol analog, triacetylresveratrol, a potential immunomodulator of lung adenocarcinoma immunotherapy combination therapies

Introduction

Resveratrol, an activator for longevity regulatory genes-sirtuin family (SIRTs) and Sirtuin 2 (SIRT2) is an important factor of SIRTs which demonstrated biological function in cancers, but the underlying mechanism is unrevealed.

Methods

We investigated the mRNA and protein levels of SIRT2 in a variety of cancers and the potential role for clinical prognosis, as well as analysed the association between the gene and immune infiltration in various cancers. And an analysis of two types of lung cancer was conducted to construct a systematic prognostic landscape. Finally, putative binding site of the triacetylresveratrol bound to SIRT2 was built from homology modeling.

Results and discussion

We concluded that higher mRNA and protein levels of SIRT2 affected prognosis in various types of cancers, especially in LUAD cohorts. In addition, SIRT2 is linked with a better overall survival (OS) in LUAD patients. Further research suggested a possible explanation for this phenotype might be that SIRT2 mRNA levels are positively correlated with infiltrating status of multiple immunocytes in LU-AD but not LUSC, i.e. SIRT2 expression may contribute to the recruitment of CD8+T cell, CD4+ T cell, T cell CD4+ memory resting, Tregs, T cell NK and positively correlated to the expression of PD-1, also excluding neutrophil, T cell CD8+ naïve and B cell plasma cells in LUAD. We found that triacetyl-resveratrol demonstrated the most potent agonist efficiency to SIRT2 and the EC 50 as low as 142.79 nM. As a result, SIRT2 appears to be a promising novel biomarker for prognosis prediction in patients with LUAD and triacetylresveratrol might be a potential immunomodulator of LUAD to anti-PD-1 based immunotherapy combination therapies.

Development of a NanoBRET assay to validate dual inhibitors of Sirt2-mediated lysine deacetylation and defatty-acylation that block prostate cancer cell migration

Sirtuin2 (Sirt2) with its NAD⁺-dependent deacetylase and defatty-acylase activities plays a central role in the regulation of specific cellular functions. Dysregulation of Sirt2 activity has been associated with the pathogenesis of many diseases, thus making Sirt2 a promising target for pharmaceutical intervention. Herein, we present new high affinity Sirt2 selective Sirtuin-Rearranging Ligands (SirReals) that inhibit both Sirt2-dependent deacetylation and defatty-acylation in vitro and in cells. We show that simultaneous inhibition of both Sirt2 activities results in strongly reduced levels of the oncoprotein c-Myc and an inhibition of cancer cell migration. Furthermore, we describe the development of a NanoBRET-based assay for Sirt2, thereby providing a method to study cellular target engagement for Sirt2 in a straightforward and accurately quantifiable manner. Applying this assay, we could confirm cellular Sirt2 binding of our new Sirt2 inhibitors and correlate their anticancer effects with their cellular target engagement.

Sirt2 inhibitors that show simultaneous inhibition of Sirt2 deacetylase and defatty-acylase activity block prostate cancer cell migration and their target engagement is shown by a newly developed NanoBRET assay.

SIRT1 regulates the phosphorylation and degradation of P27 by deacetylating CDK2 to promote T-cell acute lymphoblastic leukemia progression

Background

Despite marked advances in the clinical therapies, clinical outcome of most T-cell acute lymphoblastic leukemia (T-ALL) patients remains poor, due to the high risk of relapse, even after complete remission. Previous studies suggest that the NAD-dependent deacetylase sirtuin 1 (SIRT1) has a dual role in hematologic malignancies, acting as a tumor suppressor or tumor promoter depending on the tumor type. However, little is known about the expression and functions of SIRT1 in T-ALL leukemogenesis.

Methods

Public RNA-seq data, a Notch1 driven T-ALL mouse model and γ-secretase inhibitor were used to identify SIRT1 expression in T-ALL. We knocked down SIRT1 expression with ShRNAs and assessed the impacts of SIRT1 deficiency on cell proliferation, colony formation, the cell cycle and apoptosis. Transgenic SIRT1 knockout mice were used to determine the function of SIRT1 in vivo. RT-PCR, western blot, co-immunoprecipitation and ubiquitination analyses were used to detect SIRT1, p27 and CDK2 expression and their interactions.

Results

SIRT1 protein expression was positively correlated with the activation of Notch1. Downregulation of SIRT1 expression suppressed the proliferation and colony formation of T-ALL cell lines, which was reversed by SIRT1 overexpression. SIRT1 silencing prolonged the lifespan of T-ALL model mice. We demonstrated that p27 was involved in the downstream mechanism of cell cycle arrest induced by silencing SIRT1. SIRT1 increased the phosphorylation of p27 on Thr187 by deacetylating CDK2 and enhanced the interaction between p27 and SKP2 leading to the degradation of p27.

Conclusion

Our findings suggest that SIRT1 is a promising target in T-ALL and offer a mechanistic link between the upregulation of SIRT1 and downregulation of p27.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-02071-w.

Emerging Roles of SKP2 in Cancer Drug Resistance

More than half of all cancer patients receive chemotherapy, however, some of them easily acquire drug resistance. Resistance to chemotherapy has become a massive obstacle to achieve high rates of pathological complete response during cancer therapy. S-phase kinase-associated protein 2 (Skp2), as an E3 ligase, was found to be highly correlated with drug resistance and poor prognosis. In this review, we summarize the mechanisms that Skp2 confers to drug resistance, including the Akt-Skp2 feedback loop, Skp2-p27 pathway, cell cycle and mitosis regulation, EMT (epithelial-mesenchymal transition) property, enhanced DNA damage response and repair, etc. We also addressed novel molecules that either inhibit Skp2 expression or target Skp2-centered interactions, which might have vast potential for application in clinics and benefit cancer patients in the future.

Resveratrol's Anti-Cancer Effects through the Modulation of Tumor Glucose Metabolism

Simple Summary

The prevention and treatment of cancer is an ongoing medical challenge. In the context of personalized medicine, the well-studied polyphenol resveratrol could complement classical tumor therapy. It may affect key processes such as inflammation, angiogenesis, proliferation, metastasis, glucose metabolism, and apoptosis in various cancers because resveratrol acts as a multi-targeting agent by modulating multiple signal transduction pathways. This review article focuses on resveratrol’s ability to modify tumor glucose metabolism and its associated therapeutic capacity. Resveratrol reduces glucose uptake and glycolysis by affecting Glut1, PFK1, HIF-1α, ROS, PDH, and the CamKKB/AMPK pathway. It also inhibits cell growth, invasion, and proliferation by targeting NF-kB, Sirt1, Sirt3, LDH, PI-3K, mTOR, PKM2, R5P, G6PD, TKT, talin, and PGAM. In addition, resveratrol induces apoptosis by targeting integrin, p53, LDH, and FAK. In conclusion, resveratrol has many potentials to intervene in tumor processes if bioavailability can be increased and this natural compound can be used selectively.

Abstract

Tumor cells develop several metabolic reprogramming strategies, such as increased glucose uptake and utilization via aerobic glycolysis and fermentation of glucose to lactate; these lead to a low pH environment in which the cancer cells thrive and evade apoptosis. These characteristics of tumor cells are known as the Warburg effect. Adaptive metabolic alterations in cancer cells can be attributed to mutations in key metabolic enzymes and transcription factors. The features of the Warburg phenotype may serve as promising markers for the early detection and treatment of tumors. Besides, the glycolytic process of tumors is reversible and could represent a therapeutic target. So-called mono-target therapies are often unsafe and ineffective, and have a high prevalence of recurrence. Their success is hindered by the ability of tumor cells to simultaneously develop multiple chemoresistance pathways. Therefore, agents that modify several cellular targets, such as energy restriction to target tumor cells specifically, have therapeutic potential. Resveratrol, a natural active polyphenol found in grapes and red wine and used in many traditional medicines, is known for its ability to target multiple components of signaling pathways in tumors, leading to the suppression of cell proliferation, activation of apoptosis, and regression in tumor growth. Here, we describe current knowledge on the various mechanisms by which resveratrol modulates glucose metabolism, its potential as an imitator of caloric restriction, and its therapeutic capacity in tumors.

The Clinical Significance of SIRT2 in Malignancies: A Tumor Suppressor or an Oncogene?

Sirtuin 2 (SIRT2) is a member of the sirtuin protein family. It is a Class III histone deacetylase (HDACs) and predominantly localized to the cytosol. SIRT2 deacetylates histones and a number of non-histone proteins and plays a pivotal role in various physiologic processes. Previously, SIRT2 has been considered indispensable during carcinogenesis; however, there is now a significant controversy regarding whether SIRT2 is an oncogene or a tumor suppressor. The purpose of this review is to summarize the physiological functions of SIRT2 and its mechanisms in cancer. We will focus on five malignancies (breast cancer, non-small cell lung cancer, hepatocellular carcinoma, colorectal cancer, and glioma) to describe the current status of SIRT2 research and discuss the clinical evaluation of SIRT2 expression and the use of SIRT2 inhibitors.

SIRT2, a direct target of miR-212-5p, suppresses the proliferation and metastasis of colorectal cancer cells

The aberrant expression of human sirtuin 2 (SIRT2) has been detected in various types of cancer; however, the biological roles, underlying mechanisms and clinical significance of SIRT2 dysregulation in human colorectal cancer (CRC) remain unclear. The results of this study demonstrate that compared with paired normal tissues, SIRT2 expression is significantly decreased in CRC tissues. SIRT2 loss has been correlated with clinicopathological characteristics, including distant metastasis, lymph node metastasis and American Joint Committee on Cancer (AJCC) stage; this loss serves as an independent factor that indicates a poor prognosis for patients with CRC. Further gain‐ and loss‐of‐function analyses have demonstrated that SIRT2 suppresses CRC cell proliferation and metastasis both in vivo and in vitro. Mechanistically, miR‐212‐5p was identified to directly target the SIRT2 3′‐untranslated region (3′‐UTR), leading to SIRT2 down‐regulation. The ectopic expression of SIRT2 reverses the effect of miR‐212‐5p overexpression on CRC cell colony formation, invasion, migration and proliferation. Clinically, an inverse correlation was found between miR‐212‐5p and SIRT2 expression. High miR‐212‐5p expression has been found to result in a poor prognosis and aggressive clinicopathological characteristics in patients with CRC. Taken together, these results suggest that SIRT2, targeted by miR‐212‐5p, acts as a tumour suppressor in CRC and that the miR‐212‐5p/SIRT2 axis is a promising prognostic factor and potential therapeutic target in CRC.

The role of SIRT2 in cancer: A novel therapeutic target

Sirtuin 2 (SIRT2) belongs to the sirtuins family. It exists in many tissues and organs of the human body and regulates a wide range of biological functions. Studies have found that the abnormal expression of SIRT2 was associated with a variety of malignant tumors. SIRT2 possesses an important role in tumorigenesis, with both tumor-promoting and tumor-suppressing function. However, the mechanisms in which SIRT2 plays the roles in cancer are still controversial. This article reviews the role and molecular mechanism of SIRT2 in tumor evolution, and provides ideas for future research in this field, to guide the targeted therapy and drug development of related malignancies.

E3 Ubiquitin Ligase HRD1 Promotes Lung Tumorigenesis by Promoting Sirtuin 2 Ubiquitination and Degradation

The NAD-dependent histone deacetylase sirtuin 2 (SIRT2) plays critical roles in mitosis and cell cycle progression and recently was shown to suppress tumor growth and to be downregulated in several types of cancers. However, the underlying mechanism of SIRT2 downregulation remains unknown. In this study, using bioinformatics, gene expression profiling, protein overexpression approaches, and cell migration assays, we showed that E3 ubiquitin ligase 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase degradation 1 (HRD1) interacts with SIRT2 and promotes its ubiquitination and degradation.

The NAD-dependent histone deacetylase sirtuin 2 (SIRT2) plays critical roles in mitosis and cell cycle progression and recently was shown to suppress tumor growth and to be downregulated in several types of cancers. However, the underlying mechanism of SIRT2 downregulation remains unknown. In this study, using bioinformatics, gene expression profiling, protein overexpression approaches, and cell migration assays, we showed that E3 ubiquitin ligase 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase degradation 1 (HRD1) interacts with SIRT2 and promotes its ubiquitination and degradation. Furthermore, we found that HRD1 deficiency induces SIRT2 upregulation and inhibits the growth and tumor formation of lung cancer cells both in vitro and in vivo. Of note, we observed that SIRT2 expression is downregulated in human lung cancer and also negatively correlates with HRD1 expression in these cancers. Additionally, we found that patients with lung adenocarcinoma having lower HRD1 or higher SIRT2 expression levels tend to survive longer. On the basis of these results, we propose a mechanism of lung tumorigenesis that involves HRD1-mediated downregulation of SIRT2 and suggest that interventions targeting HRD1 activity could be a potential therapeutic strategy to treat patients with lung cancer.

Targeting epigenetic regulators for cancer therapy: mechanisms and advances in clinical trials

Epigenetic alternations concern heritable yet reversible changes in histone or DNA modifications that regulate gene activity beyond the underlying sequence. Epigenetic dysregulation is often linked to human disease, notably cancer. With the development of various drugs targeting epigenetic regulators, epigenetic-targeted therapy has been applied in the treatment of hematological malignancies and has exhibited viable therapeutic potential for solid tumors in preclinical and clinical trials. In this review, we summarize the aberrant functions of enzymes in DNA methylation, histone acetylation and histone methylation during tumor progression and highlight the development of inhibitors of or drugs targeted at epigenetic enzymes.

SIRT2: Controversy and multiple roles in disease and physiology

Sirtuin 2 (SIRT2) is an NAD+-dependent deacetylase that was under studied compared to other sirtuin family members. SIRT2 is the only sirtuin protein which is predominantly found in the cytoplasm but is also found in the mitochondria and in the nucleus. Recently, accumulating evidence has uncovered a growing number of substrates and additional detailed functions of SIRT2 in a wide range of biological processes, marking its crucial role. Here, we give a comprehensive profile of the crucial physiological functions of SIRT2 and its role in neurological diseases, cancers, and other diseases. This review summarizes the functions of SIRT2 in the nervous system, mitosis regulation, genome integrity, cell differentiation, cell homeostasis, aging, infection, inflammation, oxidative stress, and autophagy. SIRT2 inhibition rescues neurodegenerative disease symptoms and hence SIRT2 is a potential therapeutic target for neurodegenerative disease. SIRT2 is undoubtedly dysfunctional in cancers and plays a dual-faced role in different types of cancers, and although its mechanism is unresolved, SIRT2 remains a promising therapeutic target for certain cancers. In future, the continued rapid growth in SIRT2 research will help clarify its role in human health and disease, and promote the progress of this target in clinical practice.

The sirtuin family in cancer

Sirtuins are a family of protein deacylases and ADP-ribosyl-transferases, homologs to the yeast SIR2 protein. Seven sirtuin paralogs have been described in mammals, with different subcellular locations, targets, enzymatic activities, and regulatory mechanisms. All sirtuins share NAD+ as substrate, placing them as central metabolic hubs with strong relevance in lifespan, metabolism, and cancer development. Much effort has been devoted to studying the roles of sirtuins in cancer, providing a wealth of data on sirtuins roles in mouse models and humans. Also, extensive data are available on the effects of pharmacological modulation of sirtuins in cancer development. Here, we present a comprehensive and organized resume of all the existing evidence linking every sirtuin with cancer development. From our analysis, we conclude that sirtuin modulation after tumor initiation results in unpredictable outcomes in most tumor types. On the contrary, all genetic and pharmacological models indicate that sirtuins activation prior to tumor initiation can constitute a powerful preventive strategy.

Upregulated tumor sirtuin 2 expression correlates with reduced TNM stage and better overall survival in surgical breast cancer patients

BACKGROUND

This study is aimed at exploring the correlation of sirtuin 2 (SIRT2) with clinical characteristics as well as overall survival (OS) in breast cancer patients.

METHODS

Totally, 296 primary breast cancer patients who underwent surgical resection were retrospectively reviewed in this study, and SIRT2 expression in tumor and adjacent tissues was determined by immunohistochemistry (IHC) and scored by semiquantitative scoring (0-12). Clinicopathological features were retrieved, and OS was calculated.

RESULTS

Both SIRT2 IHC semiquantitative score and percentage of SIRT2 high expression by IHC score > 3 were lower in tumor tissues compared with adjacent tissues. Additionally, tumor SIRT2 high expression was associated with lower T stage, decreased N stage, and reduced TNM stage. Kaplan-Meier curves displayed that tumor SIRT2 high expression predicted longer OS. Univariate Cox's regression analysis showed that tumor SIRT2 high expression was associated with prolonged OS, while multivariate Cox's regression analysis displayed that tumor SIRT2 high expression was not an independent predictive factor for OS, which implied that tumor SIRT2 might predict OS indirectly through the interaction of tumor features (such as TNM stage) in breast cancer patients.

CONCLUSION

SIRT2 expression is lower in tumor tissues compared with adjacent tissues, and tumor SIRT2 high expression correlates with lower T stage, decreased N stage, reduced TNM stage, and longer OS in breast cancer patients.

CD74 knockout attenuates alcohol intake-induced cardiac dysfunction through AMPK-Skp2-mediated regulation of autophagy

CD74, a non-polymorphic type II transmembrane glycoprotein and MHC class II chaperone, is the cell surface receptor for the inflammatory cytokine macrophage migration inhibitory factor (MIF) and participates in inflammatory signaling regulation. This study examined the potential role of CD74 in binge drinking-induced cardiac contractile dysfunction. WT and CD74 knockout mice were exposed to ethanol (3 g/kg/d, i.p., for 3 days). Echocardiography, cardiomyocyte function, histological staining and autophagy signaling including AMPK, mTOR, and AMPK downstream signals Skp2 and Sirt1 were evaluated. Our results revealed that ethanol challenge overtly compromised echocardiographic, cardiomyocyte contractile, intracellular Ca²⁺ and ultrastructural properties along with overt apoptosis, inflammation (elevated MIF, IL-1β and IL-6) and mitochondrial O₂^- production (p < 0.01), the effect of which was reconciled by CD74 ablation (p < 0.01 vs. ethanol group) with the exception of MIF expression. Ethanol challenge upregulated autophagy (p < 0.001), promoted AMPK phosphorylation and Sirt1 levels (p < 0.003) while suppressing mTOR phosphorylation and Skp2 levels (p < 0.02). These effects were reversed by CD74 ablation. In vitro studies demonstrated that short-term ethanol challenge compromised cardiomyocyte contractile function and facilitated GFP-Puncta formation, which were mitigated by CD74 knockout (p < 0.0001). Moreover, the CD74 ablation-offered beneficial effects against ethanol-induced cardiomyocyte dysfunction, and GFP-Puncta formation were nullified by the AMPK activator AICAR, the Skp2 inhibitor C1 or the Sirt1 activator SRT1720 (p < 0.0001). Taken together, our data revealed that CD74 ablation counteracts acute ethanol challenge-induced myocardial dysfunction, inflammation and apoptosis possibly through an AMPK-mTOR-Skp2-mediated regulation of autophagy.

SIRT6 drives epithelial-to-mesenchymal transition and metastasis in non-small cell lung cancer via snail-dependent transrepression of KLF4

BACKGROUND

Epithelial-to-mesenchymal transition (EMT) contributes to the invasion and metastasis of epithelial tumors. Sirtuin 6 (SIRT6), an NAD-dependent deacetylase, is known to promote metastasis of non-small cell lung cancer (NSCLC).

METHODS

In this work, we determined the role of SIRT6 in the EMT of NSCLC cells and identified the key EMT-related genes involved in the oncogenic activity of SIRT6.

RESULTS

We report that depletion of SIRT6 inhibits transforming growth factor-β1 (TGF-β1)-induced EMT in A549 and H1299 NSCLC cells, which is rescued by ectopic expression of SIRT6. Knockdown of SIRT6 leads to a reduction in Snail protein without affecting the mRNA level. Immunoprecipitation experiments demonstrate a physical association between SIRT6 and Snail. SIRT6 deacetylates Snail and prevents its proteasomal degradation. Silencing of Snail blunts SIRT6-induced NSCLC cell migration and invasion, while overexpression of Snail restores the invasion and EMT in SIRT6-depleted NSCLC cells. SIRT6 depletion leads to an upregulation of kruppel-like factor 4 (KLF4) and reduced Snail binding to the promoter of Klf4 in NSCLC cells. Knockdown of KLF4 rescues the invasive capacity in SIRT6-depleted NSCLC cells. Conversely, co-expression of KLF4 impairs SIRT6-induced aggressive behavior. In vivo data further demonstrate that SIRT6-induced NSCLC metastasis is antagonized by overexpression of KLF4.

CONCLUSIONS

These findings provide mechanistic insights into the pro-metastatic activity of SIRT6 and highlight the role of the SIRT6/Snail/KLF4 axis in regulating EMT and invasion of NSCLC cells.

Associations of sirtuins with clinicopathological parameters and prognosis in non-small cell lung cancer

BACKGROUND

Lung cancer is the leading cause of cancer-related death worldwide and it is critical to discover specific biomarkers to provide better individualized treatment and subsequently better prognosis. The sirtuins (SIRT1-7) have been reported to be involved in cancers including non-small cell lung cancer (NCSLC), however, the results are not consistent and not all the seven sirtuins are explored and compared.

METHODS

TCGA data was downloaded and used to investigate and compare the associations of sirtuins mRNA levels with clinicopathological parameters and prognosis in NSCLC.

RESULTS

Our results suggested SIRT1, SIRT3, SIRT4, and SIRT7 were highly expressed in adeno-carcinoma (ADC) patients and female patients while SIRT5 were highly expressed in squamous cell carcinoma (SCC) patients and male patients. Associations of high SIRT7 with younger onset age, high SIRT1 with distant metastasis and low T stage, and high SIRT4 with high T stage and TNM stage were also found. Kaplan-Meier plot curves and univariate Cox proportional regression analyses indicated that high SIRT2, SIRT4, and SIRT6 expressions were associated with longer overall survival (OS) time. Multivariate analyses indicated that SIRT2 and SIRT6 were still associated with OS. For recurrence-free survival (RFS), high SIRT1 expression was significantly associated with shorter RFS time while high SIRT2-3 and SIRT5-7 expressions were associated with longer RFS time in univariate analyses. After adjusting the confounding factors, significant associations were still found in SIRT1-2 and SIRT5-7 but not in SIRT3. We also stratified the patients by combining SIRT1 and SIRT2 and revealed that the combination of SIRT1 and SIRT2 was a better prediction model for RFS in NSCLC. To preliminarily understand the potential mechanisms of sirtuins in NSCLC carcinogenesis, the genes co-expressed with sirtuins were analyzed and annotated.

CONCLUSION

sirtuins might be the potential therapy targets and prognostic biomarkers in NSCLC.

A variant in SIRT2 gene 3'-UTR is associated with susceptibility to colorectal cancer

SIRT2 is a member of sirtuin family and is associated with cell growth in various cancers. In this study, we searched for variants in functional region of SIRT2 gene and identify rs2015 and rs2241703 in the 3'UTR with minor allele frequency >0.05 in Chinese Han Beijing population from 1000 Genomes Project. We then genotyped these two variants in 842 colorectal cancer (CRC) patients and 1,718 healthy controls using Taqman genotyping assay. Association between variants and risk of CRC is calculated using logistic regression adjusted for sex and age. We found that rs2015C was significantly associated with increased risk of CRC. Compared with CC genotype carriers, CA genotype and AA genotype carriers were associated with CRC susceptibility with OR being 0.79 (95% CI: 0.65-0.96, P = 0.019) and 0.73 (95% CI: 0.58-0.92, P = 0.009), respectively. When stratified by sex and age, significant associations were observed only in males (OR = 0.82, 95% CI: 0.71-0.96, P = 0.010) for rs2015, but not females (OR = 0.90, 95% CI: 0.73-1.10, P = 0.287). It is suggested that the sequence including rs2015C allele lies within a binding site for the full seed region of hsa-miR-376a-5p. Through a systematic interrogate of variants in the functional region of SIRT2 gene, we identified rs2015 was significantly associated with CRC susceptibility, providing new insights into the carcinogenesis of CRC.

Loss of p27kip1 expression is associated with poor prognosis in patients with taxane-treated breast cancer

PURPOSE

Decreased expression of p27^kip1 and p57^kip2 is considered as a prognostic indicator in patients with breast cancer receiving adjuvant chemotherapy. Previous in vitro studies have reported that reduced expression of p27^kip1 and p57^kip2 is associated with resistance to taxane, which is one of the most effective chemotherapeutic agents. In this study, we investigated the association of low p27^kip1 and p57^kip2 expression with outcomes in patients with breast cancer.

METHODS

We investigated 226 cases of breast cancer from Kangbuk SMC between 2000 and 2005. Levels of p27^kip1 and p57^kip2 expression were evaluated using immunohistochemical staining of tumor tissue microarray specimens. The relationships between the expression levels of the markers and patients' outcomes were analyzed using the Kaplan-Meier method and Cox proportional hazard model.

RESULTS

Low p57^kip2 expression was only associated with negative progesterone receptor status (p = 0.034), whereas p27^kip1 expression was associated with poor prognosis of patients receiving adjuvant chemotherapy (p = 0.005). More detailed analysis revealed that low p27^kip1 expression affects the overall survival rate of patients receiving adjuvant chemotherapy including taxane (p = 0.026), but not that of patients receiving chemotherapy without taxane.

CONCLUSIONS

Low p27^kip1 expression may be useful to predict overall survival in patients with breast cancer who are treated with taxane. Evaluation of p27^kip1 expression may provide further prognostic information beyond traditional prognostic biomarkers and an understanding of the mechanisms that impart resistance against chemotherapy.

SIRT6 delays cellular senescence by promoting p27Kip1 ubiquitin-proteasome degradation

Sirtuin6(SIRT6) has been implicated as a key factor in aging and aging-related diseases. However, the role of SIRT6 in cellular senescence has not been fully understood. Here, we show that SIRT6 repressed the expression of p27^Kip1 (p27) in cellular senescence. The expression of SIRT6 was reduced during cellular senescence, whereas enforced SIRT6 expression promoted cell proliferation and antagonized cellular senescence. In addition, we demonstrated that SIRT6 promoted p27 degradation by proteasome and SIRT6 decreased the acetylation level and protein half-life of p27. p27 acetylation increased its protein stability. Furthermore, SIRT6 directly interacted with p27. Importantly, p27 was strongly acetylated and had a prolonged protein half-life with the reduction of SIRT6 when cells were senescent, compared with those young cells. Finally, SIRT6 markedly rescued senescence induced by p27. Our findings indicate that SIRT6 decreases p27 acetylation, leading to its degradation via ubiquitin-proteasome pathway and then delays cellular senescence.

S-phase kinase-associated protein 2 promotes cell growth and motility in osteosarcoma cells

Skp2 (S-phase kinase-associated protein 2) plays an oncogenic role in a variety of human cancers. However, the function of Skp2 in osteosarcoma (OS) is elusive. Therefore, in the current study, we explore whether Skp2 exerts its oncogenic function in OS. The cell growth, apoptosis, invasion and cell cycle were measured in OS cells after Skp2 overexpression. We found that overexpression of Skp2 enhanced cell growth, and inhibited cell apoptosis in OS cells. Moreover, we observed that upregulation of Skp2 accelerated cell cycle progression in OS cells. Furthermore, the ability of migration and invasion was enhanced in Skp2 overexpressing OS cells. Mechanically, our Western blotting data suggested that Skp2 decreased the expression of E-cadherin, Foxo1, p21, and p57, but increased MMP-9 in OS cells. In conclusion, our study demonstrated that Skp2 exhibited an oncogenic function in OS cells, suggesting that inhibition of Skp2 may be a novel approach for the treatment of OS.

Sirtuin 2 mutations in human cancers impair its function in genome maintenance

mutations in genome maintenance and tumor suppression.

Egg antigen p40 of Schistosoma japonicum promotes senescence in activated hepatic stellate cells via SKP2/P27 signaling pathway

Schistosomiasis is characterized by egg deposition, granulomatous inflammatory reaction and then subsequent hepatic fibrosis formation. Activated HSCs are regarded as the main effector cells in the progression of liver fibrosis and induction of senescence in hepatic stellate cells (HSCs) is vital to the reversion of hepatic fibrosis. Our previous work has showed that S. japonicum egg antigen p40 (Sjp40) could promote HSCs senescence via a STAT3/p53/p21 mechanism. In this paper, the major aim was to explore whether there are other signaling pathways in the process of Sjp40-induced HSCs aging and the underlying effect of SKP2/P27 signal pathway in this procedure. We observed the Sjp40-induced decrease of α-SMA and the senescence of LX-2 cells, and Sjp40 could upregulate P27 and downregulate the protein level of SKP2. The senescence induced by Sjp40 might be reversed in LX-2 cells that treated with P27-specific siRNA or with SKP2-special over-expression plasmid. In addition, we also demonstrated that the decreased expression of P-Rb and α-SMA induced by Sjp40 were partly restored by SKP2-overexpression. These data suggest that Sjp40 might inhibit HSCs activation by promoting cellular senescence via SKP2/P27 signaling pathway, which put forward novel mechanism in the treatment of liver fibrosis.

Thienopyrimidinone Based Sirtuin-2 (SIRT2)-Selective Inhibitors Bind in the Ligand Induced Selectivity Pocket

Sirtuins (SIRTs) are NAD-dependent deacylases, known to be involved in a variety of pathophysiological processes and thus remain promising therapeutic targets for further validation. Previously, we reported a novel thienopyrimidinone SIRT2 inhibitor with good potency and excellent selectivity for SIRT2. Herein, we report an extensive SAR study of this chemical series and identify the key pharmacophoric elements and physiochemical properties that underpin the excellent activity observed. New analogues have been identified with submicromolar SIRT2 inhibtory activity and good to excellent SIRT2 subtype-selectivity. Importantly, we report a cocrystal structure of one of our compounds (29c) bound to SIRT2. This reveals our series to induce the formation of a previously reported selectivity pocket but to bind in an inverted fashion to what might be intuitively expected. We believe these findings will contribute significantly to an understanding of the mechanism of action of SIRT2 inhibitors and to the identification of refined, second generation inhibitors.

SIRT2 mediated antitumor effects of shikonin on metastatic colorectal cancer

SIRT2 is involved in the development of a variety of cancers. Shikonin is a natural compound that is known to have antitumor effects. This study aims to assess the effects of shikonin on the development and metastatic progression of colorectal cancer (CRC) through regulation of SIRT2 expression and whether this effect is related to the phosphorylation of extracellular signal-regulated kinases (ERKs). The results demonstrated that SIRT2 is downregulated in CRC biopsy samples (n=31) compared with the adjacent non-cancerous tissues (ANCT, n=26). Furthermore, CRC metastases were positive for SIRT2 despite a lack of expression in the primary tumor. In addition, data from an in vitro assay revealed that overexpression of SIRT2 inhibited the proliferation and metastatic progression of SW480 cells while blocking of SIRT2 expression induced the proliferation and metastatic progression of HT29 cells. Shikonin inhibited the viability, migration and invasion of SW480 cells and it also inhibited the tumor growth in the nude mice model; while AGK2 (a specific inhibitor of SIRT2) reversed these effects. Epidermal growth factor (EGF, an activator of ERK) and ERK-overexpression inhibited the effects of shikonin on SIRT2 expression, proliferation and metastasis in SW480 cells. However, this proliferative effect of EGF was reversed by SIRT2 overexpression. In conclusion, these results suggest that SIRT2 is a new therapeutic target for the treatment of CRC. The antitumor effects of shikonin on CRC seem to be mediated by SIRT2 upregulation via phospho-ERK inhibition.

Soluble Egg Antigens of Schistosoma japonicum Induce Senescence of Activated Hepatic Stellate Cells by Activation of the FoxO3a/SKP2/P27 Pathway

BACKGROUND

Liver fibrosis was viewed as a reversible process. The activation of hepatic stellate cells (HSCs) is a key event in the process of liver fibrosis. The induction of senescence of HSCs would accelerate the clearance of the activated HSCs. Previously, we demonstrated that soluble egg antigens (SEA) of Schistosoma japonicum promoted the senescence of HSCs via STAT3/P53/P21 pathway. In this paper, our study was aimed to explore whether there are other signaling pathways in the process of SEA-induced HSCs aging and the underlying effect of SKP2/P27 signal on senescent HSCs.

METHODOLOGY/PRINCIPAL FINDINGS

Human hepatic stellate cell line, LX-2 cells, were cultured and stimulated with SEA. Western blot and cellular immunofluorescence analysis were performed to determine the expression of senescence-associated protein, such as P27, SKP2 and FoxO3a. Besides, RNA interfering was applied to knockdown the expression of related protein. The senescence of HSCs was determined by senescence-associated β-gal staining. We found that SEA increased the expression of P27 protein, whereas it inhibited the expression of SKP2 and FoxO3a. Knockdown of P27 as well as overexpression of SKP2 both suppressed the SEA-induced senescence of HSCs. In addition, the nuclear translocation of FoxO3a from the nucleus to the cytoplasm was induced by SEA stimulation.

CONCLUSIONS/SIGNIFICANCE

The present study demonstrates that SEA promotes HSCs senescence through the FoxO3a/SKP2/P27 pathway.

Functional characterization of AMP-activated protein kinase signaling in tumorigenesis

AMP-activated protein kinase (AMPK) is a ubiquitously expressed metabolic sensor among various species. Specifically, cellular AMPK is phosphorylated and activated under certain stressful conditions, such as energy deprivation, in turn to activate diversified downstream substrates to modulate the adaptive changes and maintain metabolic homeostasis. Recently, emerging evidences have implicated the potential roles of AMPK signaling in tumor initiation and progression. Nevertheless, a comprehensive description on such topic is still in scarcity, especially in combination of its biochemical features with mouse modeling results to elucidate the physiological role of AMPK signaling in tumorigenesis. Hence, we performed this thorough review by summarizing the tumorigenic role of each component along the AMPK signaling, comprising of both its upstream and downstream effectors. Moreover, their functional interplay with the AMPK heterotrimer and exclusive efficacies in carcinogenesis were chiefly explained among genetically altered mice models. Importantly, the pharmaceutical investigations of AMPK relevant medications have also been highlighted. In summary, in this review, we not only elucidate the potential functions of AMPK signaling pathway in governing tumorigenesis, but also potentiate the future targeted strategy aiming for better treatment of aberrant metabolism-associated diseases, including cancer.