p53 SUMOylation promotes its nuclear export by facilitating its release from the nuclear export receptor CRM1

Pantothenate-encapsulated liposomes combined with exercise for effective inhibition of CRM1-mediated PKM2 translocation in Alzheimer's therapy

Alzheimer's disease (AD) is a complex neurodegenerative condition characterized by metabolic imbalances and neuroinflammation, posing a formidable challenge in medicine due to the lack of effective treatments. Despite considerable research efforts, a cure for AD remains elusive, with current therapies primarily focused on symptom management rather than addressing the disease's underlying causes. This study initially discerned, through Mendelian randomization analysis that elevating pantothenate levels significantly contributes to the prophylaxis of Alzheimer's disease. We explore the therapeutic potential of pantothenate encapsulated in liposomes (Pan@TRF@Liposome NPs), targeting the modulation of CRM1-mediated PKM2 nuclear translocation, a critical mechanism in AD pathology. Additionally, we investigate the synergistic effects of exercise, proposing a combined approach to AD treatment. Exercise-induced metabolic alterations share significant similarities with those associated with dementia, suggesting a potential complementary effect. The Pan@TRF@Liposome NPs exhibit notable biocompatibility, showing no liver or kidney toxicity in vivo, while demonstrating stability and effectiveness in modulating CRM1-mediated PKM2 nuclear translocation, thereby reducing neuroinflammation and neuronal apoptosis. The combined treatment of exercise and Pan@TRF@Liposome NP administration in an AD animal model leads to improved neurofunctional outcomes and cognitive performance. These findings highlight the nanoparticles' role as effective modulators of CRM1-mediated PKM2 nuclear translocation, with significant implications for mitigating neuroinflammation and neuronal apoptosis. Together with exercise, this dual-modality approach could offer new avenues for enhancing cognitive performance and neurofunctional outcomes in AD, marking a promising step forward in developing treatment strategies for this challenging disorder.

Unravelling the molecular interplay: SUMOylation, PML nuclear bodies and vascular cell activity in health and disease

In the seemingly well-researched field of vascular research, there are still many underestimated factors and molecular mechanisms. In recent years, SUMOylation has become increasingly important. SUMOylation is a post-translational modification in which small ubiquitin-related modifiers (SUMO) are covalently attached to target proteins. Sites where these SUMO modification processes take place in the cell nucleus are PML nuclear bodies (PML-NBs) - multiprotein complexes with their essential main component and organizer, the PML protein. PML and SUMO, either alone or as partners, influence a variety of cellular processes, including regulation of transcription, senescence, DNA damage response and defence against microorganisms, and are involved in innate immunity and inflammatory responses. They also play an important role in maintaining homeostasis in the vascular system and in pathological processes leading to the development and progression of cardiovascular diseases. This review summarizes information about the function of SUMO(ylation) and PML(-NBs) in the human vasculature from angiogenesis to disease and highlights their clinical potential as drug targets.

Working title: Molecular involvement of p53-MDM2 interactome in gastrointestinal cancers

The interaction between murine double minute 2 (MDM2) and p53, marked by transcriptional induction and feedback inhibition, orchestrates a functional loop dictating cellular fate. The functional loop comprising p53-MDM2 axis is made up of an interactome consisting of approximately 81 proteins, which are spatio-temporally regulated and involved in DNA repair mechanisms. Biochemical and genetic alterations of the interactome result in dysregulation of the p53-mdm2 axis that leads to gastrointestinal (GI) cancers. A large subset of interactome is well known and it consists of proteins that either stabilize p53 or MDM2 and proteins that target the p53-MDM2 complex for ubiquitin-mediated destruction. Upstream signaling events brought about by growth factors and chemical messengers invoke a wide variety of posttranslational modifications in p53-MDM2 axis. Biochemical changes in the transactivation domain of p53 impact the energy landscape, induce conformational switching, alter interaction potential and could change solubility of p53 to redefine its co-localization, translocation and activity. A diverse set of chemical compounds mimic physiological effectors and simulate biochemical modifications of the p53-MDM2 interactome. p53-MDM2 interactome plays a crucial role in DNA damage and repair process. Genetic aberrations in the interactome, have resulted in cancers of GI tract (pancreas, liver, colorectal, gastric, biliary, and esophageal). We present in this article a review of the overall changes in the p53-MDM2 interactors and the effectors that form an epicenter for the development of next-generation molecules for understanding and targeting GI cancers.

SUMOylation of GMFB regulates its stability and function in retinal pigment epithelial cells under hyperglycemia

BACKGROUND

Glia maturation factor beta (GMFB) is a growth and differentiation factor that acts as an intracellular regulator of signal transduction pathways. The small ubiquitin-related modifier (SUMO) modification, SUMOylation, is a posttranslational modification (PTM) that plays a key role in protein subcellular localization, stability, transcription, and enzymatic activity. Recent studies have highlighted the importance of SUMOylation in the inflammation and progression of numerous diseases. However, the relationship between GMFB and SUMOylation is unclear.

RESULTS

Here, we report for the first time that GMFB and SUMO1 are markedly increased in retinal pigment epithelial (RPE) cells at the early stage of diabetes mellitus (DM) under hyperglycemia. The GMFΒ protein could be mono-SUMOylated by SUMO1 at the K20, K35, K58 or K97 sites. SUMOylation of GMFB led to its increased protein stability and subcellular translocation. Furthermore, deSUMOylation of GMFΒ downregulates multiple signaling pathways, including the Jak-STAT signaling pathway, p38 pathway and NF-kappa B signaling pathway.

CONCLUSIONS

This work provides novel insight into the role of SUMOylated GMFB in RPE cells and provides a novel therapeutic target for diabetic retinopathy (DR).

Exercise-Induced Reduction of IGF1R Sumoylation Attenuates Neuroinflammation in APP/PS1 Transgenic Mice

INTRODUCTION

Alzheimer's Disease (AD), a progressive neurodegenerative disorder, is marked by cognitive deterioration and heightened neuroinflammation. The influence of Insulin-like Growth Factor 1 Receptor (IGF1R) and its post-translational modifications, especially sumoylation, is crucial in understanding the progression of AD and exploring novel therapeutic avenues.

OBJECTIVES

This study investigates the impact of exercise on the sumoylation of IGF1R and its role in ameliorating AD symptoms in APP/PS1 mice, with a specific focus on neuroinflammation and innovative therapeutic strategies.

METHODS

APP/PS1 mice were subjected to a regimen of moderate-intensity exercise. The investigation encompassed assessments of cognitive functions, alterations in hippocampal protein expressions, neuroinflammatory markers, and the effects of exercise on IGF1R and SUMO1 nuclear translocation. Additionally, the study evaluated the efficacy of KPT-330, a nuclear export inhibitor, as an alternative to exercise.

RESULTS

Exercise notably enhanced cognitive functions in AD mice, possibly through modulations in hippocampal proteins, including Bcl-2 and BACE1. A decrease in neuroinflammatory markers such as IL-1β, IL-6, and TNF-α was observed, indicative of reduced neuroinflammation. Exercise modulated the nuclear translocation of SUMO1 and IGF1R in the hippocampus, thereby facilitating neuronal regeneration. Mutant IGF1R (MT IGF1R), lacking SUMO1 modification sites, showed reduced SUMOylation, leading to diminished expression of pro-inflammatory cytokines and apoptosis. KPT-330 impeded the formation of the IGF1R/RanBP2/SUMO1 complex, thereby limiting IGF1R nuclear translocation, inflammation, and neuronal apoptosis, while enhancing cognitive functions and neuron proliferation.

CONCLUSION

Moderate-intensity exercise effectively mitigates AD symptoms in mice, primarily by diminishing neuroinflammation, through the reduction of IGF1R Sumoylation. KPT-330, as a potential alternative to physical exercise, enhances the neuroprotective role of IGF1R by inhibiting SUMOylation through targeting XPO1, presenting a promising therapeutic strategy for AD.

Cell fate regulation governed by p53: Friends or reversible foes in cancer therapy

Cancer is a leading cause of death worldwide. Targeted therapies aimed at key oncogenic driver mutations in combination with chemotherapy and radiotherapy as well as immunotherapy have benefited cancer patients considerably. Tumor protein p53 (TP53), a crucial tumor suppressor gene encoding p53, regulates numerous downstream genes and cellular phenotypes in response to various stressors. The affected genes are involved in diverse processes, including cell cycle arrest, DNA repair, cellular senescence, metabolic homeostasis, apoptosis, and autophagy. However, accumulating recent studies have continued to reveal novel and unexpected functions of p53 in governing the fate of tumors, for example, functions in ferroptosis, immunity, the tumor microenvironment and microbiome metabolism. Among the possibilities, the evolutionary plasticity of p53 is the most controversial, partially due to the dizzying array of biological functions that have been attributed to different regulatory mechanisms of p53 signaling. Nearly 40 years after its discovery, this key tumor suppressor remains somewhat enigmatic. The intricate and diverse functions of p53 in regulating cell fate during cancer treatment are only the tip of the iceberg with respect to its equally complicated structural biology, which has been painstakingly revealed. Additionally, TP53 mutation is one of the most significant genetic alterations in cancer, contributing to rapid cancer cell growth and tumor progression. Here, we summarized recent advances that implicate altered p53 in modulating the response to various cancer therapies, including chemotherapy, radiotherapy, and immunotherapy. Furthermore, we also discussed potential strategies for targeting p53 as a therapeutic option for cancer.

XPO1 Enables Adaptive Regulation of mRNA Export Required for Genotoxic Stress Tolerance in Cancer Cells

Exportin-1 (XPO1), the main soluble nuclear export receptor in eukaryotic cells, is frequently overexpressed in diffuse large B-cell lymphoma (DLBCL). A selective XPO1 inhibitor, selinexor, received approval as single agent for relapsed or refractory (R/R) DLBCL. Elucidating the mechanisms by which XPO1 overexpression supports cancer cells could facilitate further clinical development of XPO1 inhibitors. We uncovered here that XPO1 overexpression increases tolerance to genotoxic stress, leading to a poor response to chemoimmunotherapy. Upon DNA damage induced by MYC expression or exogenous compounds, XPO1 bound and exported EIF4E and THOC4 carrying DNA damage repair mRNAs, thereby increasing synthesis of DNA damage repair proteins under conditions of increased turnover. Consequently, XPO1 inhibition decreased the capacity of lymphoma cells to repair DNA damage and ultimately resulted in increased cytotoxicity. In a phase I clinical trial conducted in R/R DLBCL, the combination of selinexor with second-line chemoimmunotherapy was tolerated with early indication of efficacy. Overall, this study reveals that XPO1 overexpression plays a critical role in the increased tolerance of cancer cells to DNA damage while providing new insights to optimize the clinical development of XPO1 inhibitors.

SIGNIFICANCE

XPO1 regulates the dynamic ribonucleoprotein nuclear export in response to genotoxic stress to support tolerance and can be targeted to enhance the sensitivity of cancer cells to endogenous and exogenous DNA damage. See related commentary by Knittel and Reinhardt, p. 3.

SUMOylation indirectly suppresses activity of the HIF-1α pathway in intestinal epithelial cells

The hypoxia-inducible factor (HIF) is a master regulator of the cellular transcriptional response to hypoxia. While the oxygen-sensitive regulation of HIF-1α subunit stability via the ubiquitin-proteasome pathway has been well described, less is known about how other oxygen-independent post-translational modifications impact the HIF pathway. SUMOylation, the attachment of SUMO (small ubiquitin-like modifier) proteins to a target protein, regulates the HIF pathway, although the impact of SUMO on HIF activity remains controversial. Here, we examined the effects of SUMOylation on the expression pattern of HIF-1α in response to pan-hydroxylase inhibitor dimethyloxalylglycine (DMOG) in intestinal epithelial cells. We evaluated the effects of SUMO-1, SUMO-2, and SUMO-3 overexpression and inhibition of SUMOylation using a novel selective inhibitor of the SUMO pathway, TAK-981, on the sensitivity of HIF-1α in Caco-2 intestinal epithelial cells. Our findings demonstrate that treatment with TAK-981 decreases global SUMO-1 and SUMO-2/3 modification and enhances HIF-1α protein levels, whereas SUMO-1 and SUMO-2/3 overexpression results in decreased HIF-1α protein levels in response to DMOG. Reporter assay analysis demonstrates reduced HIF-1α transcriptional activity in cells overexpressing SUMO-1 and SUMO-2/3, whereas pretreatment with TAK-981 increased HIF-1α transcriptional activity in response to DMOG. In addition, HIF-1α nuclear accumulation was decreased in cells overexpressing SUMO-1. Importantly, we showed that HIF-1α is not directly SUMOylated, but that SUMOylation affects HIF-1α stability and activity indirectly. Taken together, our results indicate that SUMOylation indirectly suppresses HIF-1α protein stability, transcriptional activity, and nuclear accumulation in intestinal epithelial cells.

XPO1 inhibition sensitises CLL cells to NK cell mediated cytotoxicity and overcomes HLA-E expression

The first-in-class inhibitor of exportin-1 (XPO1) selinexor is currently under clinical investigation in combination with the BTK inhibitor ibrutinib for patients with chronic lymphocytic leukaemia (CLL) or non-Hodgkin lymphoma. Selinexor induces apoptosis of tumour cells through nuclear retention of tumour suppressor proteins and has also recently been described to modulate natural killer (NK) cell and T cell cytotoxicity against lymphoma cells. Here, we demonstrate that XPO1 inhibition enhances NK cell effector function against primary CLL cells via downregulation of HLA-E and upregulation of TRAIL death receptors DR4 and DR5. Furthermore, selinexor potentiates NK cell activation against CLL cells in combination with several approved treatments; acalabrutinib, rituximab and obinutuzumab. We further demonstrate that lymph node associated signals (IL-4 + CD40L) inhibit NK cell activation against CLL cells via upregulation of HLA-E, and that inhibition of XPO1 can overcome this protective effect. These findings allow for the design of more efficacious combination strategies to harness NK cell effector functions against CLL.

DAXX drives de novo lipogenesis and contributes to tumorigenesis

Cancer cells exhibit elevated lipid synthesis. In breast and other cancer types, genes involved in lipid production are highly upregulated, but the mechanisms that control their expression remain poorly understood. Using integrated transcriptomic, lipidomic, and molecular studies, here we report that DAXX is a regulator of oncogenic lipogenesis. DAXX depletion attenuates, while its overexpression enhances, lipogenic gene expression, lipogenesis, and tumor growth. Mechanistically, DAXX interacts with SREBP1 and SREBP2 and activates SREBP-mediated transcription. DAXX associates with lipogenic gene promoters through SREBPs. Underscoring the critical roles for the DAXX-SREBP interaction for lipogenesis, SREBP2 knockdown attenuates tumor growth in cells with DAXX overexpression, and DAXX mutants unable to bind SREBP1/2 have weakened activity in promoting lipogenesis and tumor growth. Remarkably, a DAXX mutant deficient of SUMO-binding fails to activate SREBP1/2 and lipogenesis due to impaired SREBP binding and chromatin recruitment and is defective of stimulating tumorigenesis. Hence, DAXX's SUMO-binding activity is critical to oncogenic lipogenesis. Notably, a peptide corresponding to DAXX's C-terminal SUMO-interacting motif (SIM2) is cell-membrane permeable, disrupts the DAXX-SREBP1/2 interactions, and inhibits lipogenesis and tumor growth. These results establish DAXX as a regulator of lipogenesis and a potential therapeutic target for cancer therapy.

The Four Homeostasis Knights: In Balance upon Post-Translational Modifications

A cancer outcome is a multifactorial event that comes from both exogenous injuries and an endogenous predisposing background. The healthy state is guaranteed by the fine-tuning of genes controlling cell proliferation, differentiation, and development, whose alteration induces cellular behavioral changes finally leading to cancer. The function of proteins in cells and tissues is controlled at both the transcriptional and translational level, and the mechanism allowing them to carry out their functions is not only a matter of level. A major challenge to the cell is to guarantee that proteins are made, folded, assembled and delivered to function properly, like and even more than other proteins when referring to oncogenes and onco-suppressors products. Over genetic, epigenetic, transcriptional, and translational control, protein synthesis depends on additional steps of regulation. Post-translational modifications are reversible and dynamic processes that allow the cell to rapidly modulate protein amounts and function. Among them, ubiquitination and ubiquitin-like modifications modulate the stability and control the activity of most of the proteins that manage cell cycle, immune responses, apoptosis, and senescence. The crosstalk between ubiquitination and ubiquitin-like modifications and post-translational modifications is a keystone to quickly update the activation state of many proteins responsible for the orchestration of cell metabolism. In this light, the correct activity of post-translational machinery is essential to prevent the development of cancer. Here we summarize the main post-translational modifications engaged in controlling the activity of the principal oncogenes and tumor suppressors genes involved in the development of most human cancers.

The role of p53 in the alternation of vascular functions

Ageing is a risk factor for many degenerative diseases. Cardiovascular diseases (CVDs) are usually big burdens for elderly, caregivers and the health system. During the aging process, normal functions of vascular cells and tissue progressively lost and eventually develop vascular diseases. Endothelial dysfunction, reduced bioavailability of endothelium-derived nitric oxide are usual phenomena observed in patients with cardiovascular diseases. Myriad of studies have been done to investigate to delay the vascular dysfunction or improve the vascular function to prolong the aging process. Tumor suppressor gene p53, also a transcription factor, act as a gatekeeper to regulate a number of genes to maintain normal cell function including but not limited to cell proliferation, cell apoptosis. p53 also crosstalk with other key transcription factors like hypoxia-inducible factor 1 alpha that contribute to the progression of cardiovascular diseases. Therefore, in recent three decades, p53 has drawn scientists’ attention on its effects in vascular function. Though the role of tumor suppressor gene p53 is still not clear in vascular function, it is found to play regulatory roles and may involve in vascular remodeling, atherosclerosis or pulmonary hypertension. p53 may have a divergent role in endothelial and vascular muscle cells in those conditions. In this review, we describe the different effects of p53 in cardiovascular physiology. Further studies on the effects of endothelial cell-specific p53 deficiency on atherosclerotic plaque formation in common animal models are required before the therapeutic potential can be realized.

SUMO1 Promotes Mesangial Cell Proliferation Through Inhibiting Autophagy in a Cell Model of IgA Nephropathy

IgA nephropathy (IgAN) is a common form of primary glomerulonephritis and its main pathological changes are mesangial cell proliferation and matrix expansion. Autophagy inhibition may result in its mesangial cell proliferation and renal lesions. SUMOylation is a eukaryotic-reversible post-translational modification where SUMO is covalently attached to target proteins to regulate their properties. It is largely unclear whether SUMOylation contributes to the pathogenesis of IgAN. This study was designed to investigate the change of protein SUMO1 in mesangial cells of IgAN and its association with autophagy. We found the expression of SUMO1 was upregulated in IgAN, IgA mouse model, and aIgA1-stimulated mesangial cells. In aIgA1-stimulated mesangial cell model, we tested LC3II/I and p62, the autophagy-related proteins suggested the inhibition of autophagy. Inhibited SUMOylation with ginkgolic acid (GA) or silencing SUMO1 could downregulate SUMO1 and SUMO1-p53, promote autophagy, and lessen cell proliferation. In summary, in the mesangial cells stimulated with aIgA1, SUMO1 may contribute to its cell proliferation through inhibited autophagy, and SUMO1-p53 may play a role in this process.

Protein of a thousand faces: The tumor-suppressive and oncogenic responses of p53

The p53 protein is a pleiotropic regulator working as a tumor suppressor and as an oncogene. Depending on the cellular insult and the mutational status, p53 may trigger opposing activities such as cell death or survival, senescence and cell cycle arrest or proliferative signals, antioxidant or prooxidant activation, glycolysis, or oxidative phosphorylation, among others. By augmenting or repressing specific target genes or directly interacting with cellular partners, p53 accomplishes a particular set of activities. The mechanism in which p53 is activated depends on increased stability through post-translational modifications (PTMs) and the formation of higher-order structures (HOS). The intricate cell death and metabolic p53 response are reviewed in light of gaining stability via PTM and HOS formation in health and disease.

Bioinformatic reanalysis of public proteomics data reveals that nuclear proteins are recurrent in cancer secretomes

Proteins secreted by tumoral cells (cancer secretomes) have been continuously associated with cancer development and progression processes. In this context, secreted proteins contribute to the signaling mechanisms related to tumor growth and spreading and studies on tumor secretomes provide valuable clues on putative tumor biomarkers. Although the in vitro identification of intracellular proteins in cancer secretome studies has usually been associated with contamination derived from cell lysis or fetal bovine serum, accumulated evidence reports on intracellular proteins with moonlighting functions in the extracellular environment. In this study, we performed a systematic reanalysis of public proteomics data regarding different cancer secretomes, aiming to identify intracellular proteins potentially secreted by tumor cells via unconventional secretion pathways. We found a similar repertoire of unconventionally secreted proteins, including the recurrent identification of nuclear proteins secreted by different cancer cells. In addition, in some cancer types, immunohistochemical data were in line with proteomics identifications and suggested that nuclear proteins might relocate from the nucleus to the cytoplasm. Both the presence of nuclear proteins and the likely unconventional secretion of such proteins may comprise biological signatures of malignant transformation in distinct cancer types and may be targeted for further analysis aiming at the prognostic/therapeutic value of such features.

Measuring and Interpreting Nuclear Transport in Neurodegenerative Disease-The Example of C9orf72 ALS

Transport from and into the nucleus is essential to all eukaryotic life and occurs through the nuclear pore complex (NPC). There are a multitude of data supporting a role for nuclear transport in neurodegenerative diseases, but actual transport assays in disease models have provided diverse outcomes. In this review, we summarize how nuclear transport works, which transport assays are available, and what matters complicate the interpretation of their results. Taking a specific type of ALS caused by mutations in C9orf72 as an example, we illustrate these complications, and discuss how the current data do not firmly answer whether the kinetics of nucleocytoplasmic transport are altered. Answering this open question has far-reaching implications, because a positive answer would imply that widespread mislocalization of proteins occurs, far beyond the reported mislocalization of transport reporters, and specific proteins such as FUS, or TDP43, and thus presents a challenge for future research.

Deciphering the PTM codes of the tumor suppressor p53

The genome guardian p53 functions as a transcription factor that senses numerous cellular stresses and orchestrates the corresponding transcriptional events involved in determining various cellular outcomes, including cell cycle arrest, apoptosis, senescence, DNA repair, and metabolic regulation. In response to diverse stresses, p53 undergoes multiple posttranslational modifications (PTMs) that coordinate with intimate interdependencies to precisely modulate its diverse properties in given biological contexts. Notably, PTMs can recruit ‘reader’ proteins that exclusively recognize specific modifications and facilitate the functional readout of p53. Targeting PTM–reader interplay has been developing into a promising cancer therapeutic strategy. In this review, we summarize the advances in deciphering the ‘PTM codes’ of p53, focusing particularly on the mechanisms by which the specific reader proteins functionally decipher the information harbored within these PTMs of p53. We also highlight the potential applications of intervention with p53 PTM–reader interactions in cancer therapy and discuss perspectives on the ‘PTMomic’ study of p53 and other proteins.

SLX4IP promotes RAP1 SUMOylation by PIAS1 to coordinate telomere maintenance through NF-κB and Notch signaling

The maintenance of telomere length supports repetitive cell division and therefore plays a central role in cancer development and progression. Telomeres are extended by either the enzyme telomerase or the alternative lengthening of telomeres (ALT) pathway. Here, we found that the telomere-associated protein SLX4IP dictates telomere proteome composition by recruiting and activating the E3 SUMO ligase PIAS1 to the SLX4 complex. PIAS1 SUMOylated the telomere-binding protein RAP1, which disrupted its interaction with the telomere-binding protein TRF2 and facilitated its nucleocytoplasmic shuttling. In the cytosol, RAP1 bound to IκB kinase (IKK), resulting in activation of the transcription factor NF-κB and its induction of Jagged-1 expression, which promoted Notch signaling and the institution of ALT. This axis could be targeted therapeutically in ALT-driven cancers and in tumor cells that develop resistance to antitelomerase therapies. Our results illuminate the mechanisms underlying SLX4IP-dependent telomere plasticity and demonstrate the role of telomere proteins in directly coordinating intracellular signaling and telomere maintenance dynamics.

Regulation of p53 stability as a therapeutic strategy for cancer

The tumor suppressor protein p53 participates in the control of key biological functions such as cell death, metabolic homeostasis and immune function, which are closely related to various diseases such as tumors, metabolic disorders, infection and neurodegeneration. The p53 gene is also mutated in approximately 50% of human cancer cells. Mutant p53 proteins escape from the ubiquitination-dependent degradation, gain oncogenic function and promote the carcinogenesis, malignant progression, metastasis and chemoresistance. Therefore, the stability of both wild type and mutant p53 needs to be precisely regulated to maintain normal functions and targeting the p53 stability is one of the therapeutic strategies against cancer. Here, we focus on compound-induced degradation of p53 by both the ubiquitination-dependent proteasome and autophagy-lysosome degradation pathways. We also review other posttranslational modifications which control the stability of p53 and the biological functions involved in these processes. This review provides the current theoretical basis for the regulation of p53 abundance and its possible applications in different diseases.

Dietary flavonoid fisetin binds human SUMO1 and blocks sumoylation of p53

Flavonoids are plant-derived compounds that occur abundantly in fruits and vegetables and have been shown to possess potent anti-cancer, antioxidant, and anti-inflammatory properties. However, their direct targets and molecular mechanism of action are not well characterized, hampering exploitation of the beneficial properties of flavonoids for drug development. Small ubiquitin-related modifier 1 (SUMO1) is attached to target proteins as part of a post-translational modification system implicated in a myriad of cellular processes from nuclear trafficking to transcriptional regulation. Using a combination of surface plasmon resonance, differential scanning fluorimetry and fluorescence quenching studies, we provide evidence for direct binding of the dietary flavonoid fisetin to human SUMO1. Our NMR chemical shift perturbation analyses reveal that binding to fisetin involves four conserved amino acid residues (L65, F66, E67, M82) previously shown to be important for conjugation of SUMO1 to target proteins. In vitro sumoylation experiments indicate that fisetin blocks sumoylation of tumor suppressor p53, consistent with fisetin negatively affecting post-translational modification and thus the biological activity of p53. A series of differential scanning fluorimetry experiments suggest that high concentrations of fisetin result in destabilization and unfolding of SUMO1, presenting a molecular mechanism by which flavonoid binding affects its activity. Overall, our data establish a novel direct interaction between fisetin and SUMO1, providing a mechanistic explanation for the ability of fisetin to modulate multiple key signaling pathways inside cells.

Regulating tumor suppressor genes: post-translational modifications

Tumor suppressor genes cooperate with each other in tumors. Three important tumor suppressor proteins, retinoblastoma (Rb), p53, phosphatase, and tensin homolog deleted on chromosome ten (PTEN) are functionally associated and they regulated by post-translational modification (PTMs) as well. PTMs include phosphorylation, SUMOylation, acetylation, and other novel modifications becoming growing appreciated. Because most of PTMs are reversible, normal cells use them as a switch to control the state of cells being the resting or proliferating, and PTMs also involve in cell survival and cell cycle, which may lead to abnormal proliferation and tumorigenesis. Although a lot of studies focus on the importance of each kind of PTM, further discoveries shows that tumor suppressor genes (TSGs) form a complex "network" by the interaction of modification. Recently, there are several promising strategies for TSGs for they change more frequently than carcinogenic genes in cancers. We here review the necessity, characteristics, and mechanisms of each kind of post-translational modification on Rb, p53, PTEN, and its influence on the precise and selective function. We also discuss the current antitumoral therapies of Rb, p53 and PTEN as predictive, prognostic, and therapeutic target in cancer.

Small Molecule Inhibitors of CRM1

The transport through the nuclear pore complex is used by cancer cells to evade tumor-suppressive mechanisms. Several tumor-suppressors have been shown to be excluded from the cell nucleus in cancer cells by the nuclear export receptor CRM1 and abnormal expression of CRM1 is oncogenic. Inhibition of CRM1 has long been postulated as potential approach for the treatment of cancer and to overcome therapy resistance. Furthermore, the nuclear export of viral components mediated by the CRM1 is crucial in various stages of the viral lifecycle and assembly of many viruses from diverse families, including coronavirus. However, the first nuclear export inhibitors failed or never entered into clinical trials. More recently CRM1 reemerged as a cancer target and a successful proof of concept was achieved with the clinical approval of Selinexor. The chemical complexity of natural products is a promising perspective for the discovery of new nuclear export inhibitors with a favorable toxicity profile. Several screening campaigns have been performed and several natural product-based nuclear export inhibitors have been identified. With this review we give an overview over the role of CRM1-mediated nuclear export in cancer and the effort made to identify and develop nuclear export inhibitors in particular from natural sources.

SUMO3 modification by PIAS1 modulates androgen receptor cellular distribution and stability

Background

Abnormal reactivation of androgen receptor (AR) signaling in castration-resistant prostate cancer (CRPC) mainly results from overexpression and down-regulation of AR. Sumoylation of AR can influence its function. However, regulation of AR sumoylation by SUMO E3 ligases PIASs to modify AR distribution and stability are not well understood.

Methods

We assessed the potential effect of SUMO3 modification on AR intracellular localization by immunostaining in AR-negative prostate cancer DU145 cells, and detected the effect of PIAS1/SUMO3 overexpression on AR sumoylation related degradation. Then we characterized AR sumoylation sites involved modified by SUMO3, and the key residue of PIAS1 involved in itself sumoylation and further mediated AR sumoylation (sumo3-conjugated), translocation and degradation. Finally we detected the recognition of PIAS1 (sumoylation ligase) to MDM2, a ubiquin ligase mediated AR degradation.

Results

We demonstrate that SUMO E3 ligase PIAS1, along with SUMO3, mediates AR cytosolic translocation and subsequent degradation via a ubiquitin-proteasome pathway. Although AR sumoylation occurs prior to ubiquitination, the SUMO-acceptor lysine 386 on AR, together with ubiquitin-acceptor lysine 845, contribute to PIAS1/SUMO3-induced AR nuclear export, ubiquitination and subsequent degradation. Moreover, PIAS1 itself is modified by SUMO3 overexpression, and mutation of SUMO-acceptor lysine 117 on PIAS1 can impair AR cytoplasmic distribution, demonstrating the essential role of sumoylated PIAS1 in AR translocation. We further determine that sumoylated PIAS1 interacts with AR lysine 386 and 845 to form a binary complex. Consistent with the effect on AR distribution, SUMO3 modification of PIAS1 is also required for AR ubiquitination and degradation by recruiting ubiquitin E3 ligase MDM2.

Conclusion

Taken together, SUMO3 modification of PIAS1 modulates AR cellular distribution and stability. Our study provided the evidence the crosstalk between AR sumoylation and ubquitination mediated by PIAS1 and SUMO3.

The Role of Protein SUMOylation in the Pathogenesis of Atherosclerosis

Atherosclerosis is a progressive, inflammatory cardiovascular disorder characterized by the development of lipid-filled plaques within arteries. Endothelial cell dysfunction in the walls of blood vessels results in an increase in vascular permeability, alteration of the components of the extracellular matrix, and retention of LDL in the sub-endothelial space, thereby accelerating plaque formation. Epigenetic modification by SUMOylation can influence the surface interactions of target proteins and affect cellular functionality, thereby regulating multiple cellular processes. Small ubiquitin-like modifier (SUMO) can modulate NFκB and other proteins such as p53, KLF, and ERK5, which have critical roles in atherogenesis. Furthermore, SUMO regulates leukocyte recruitment and cytokine release and the expression of adherence molecules. In this review, we discuss the regulation by SUMO and SUMOylation modifications of proteins and pathways involved in atherosclerosis.

Taking a holistic view of PEST-containing nuclear protein (PCNP) in cancer biology

Polypeptide sequences enriched with proline (P), glutamic acid (E), aspartic acid (D) and serine (S)/ threonine (T) (PEST) have been reported to be the most abundant and frequently distributed at the cellular level. There is growing evidence that PEST sequences act as proteolytic recognition signals for degradation of residual proteins which is critical for activation or deactivation of regulatory proteins involved in cellular signaling pathways of cell growth, differentiation, stress responses and physiological death. A PEST containing nuclear protein (PCNP) was demonstrated as a tumor suppressor in a neuroblastoma cancer model and tumor promoter in lung adenocarcinoma cancer model. Its unique properties like ubiquitination by NIRF, co‐localization with NIRF in nucleus and tumor progression attract the attention of researchers. PCNP was reported to be ubiquitinated by ring finger protein NIRF in E3 ligase manner and as modulator of MAPK and PI3K/AKT/mTOR signaling pathways. In this review, we summarize PCNP linked DNA damage response, Post translational modifications, and transportation to address initiation, prognosis, and resistance of tumor cells in terms of cell cycle regulation, transcription and apoptosis. Hence, we demonstrate PCNP as a novel target in cancer diagnosis and treatment.

CRISPR-Cas9 Screening of Kaposi's Sarcoma-Associated Herpesvirus-Transformed Cells Identifies XPO1 as a Vulnerable Target of Cancer Cells

The abnormal proliferation of cancer cells is driven by deregulated oncogenes or tumor suppressors, among which the cancer-vulnerable genes are attractive therapeutic targets. Targeting mislocalization of oncogenes and tumor suppressors resulting from aberrant nuclear export is effective for inhibiting growth transformation of cancer cells. We performed a clustered regularly interspaced short palindromic repeat (CRISPR)-associated (Cas) screening in a unique model of matched primary and oncogenic Kaposi's sarcoma-associated herpesvirus (KSHV)-transformed cells and identified genes that were growth promoting and growth suppressive for both types of cells, among which exportin XPO1 was demonstrated to be critical for the survival of transformed cells. Using XPO1 inhibitor KPT-8602 and by small interfering RNA (siRNA) knockdown, we confirmed the essential role of XPO1 in cell proliferation and growth transformation of KSHV-transformed cells and in cell lines of other cancers, including gastric cancer and liver cancer. XPO1 inhibition induced cell cycle arrest through p53 activation, but the mechanisms of p53 activation differed among the different types of cancer cells. p53 activation depended on the formation of promyelocytic leukemia (PML) nuclear bodies in gastric cancer and liver cancer cells. Mechanistically, XPO1 inhibition induced relocalization of autophagy adaptor protein p62 (SQSTM1), recruiting p53 for activation in PML nuclear bodies. Taken the data together, we have identified novel growth-promoting and growth-suppressive genes of primary and cancer cells and have demonstrated that XPO1 is a vulnerable target of cancer cells. XPO1 inhibition induces cell arrest through a novel PML- and p62-dependent mechanism of p53 activation in some types of cancer cells.IMPORTANCE Using a model of oncogenic virus KSHV-driven cellular transformation of primary cells, we have performed a genome-wide CRISPR-Cas9 screening to identify vulnerable genes of cancer cells. This screening is unique in that this virus-induced oncogenesis model does not depend on any cellular genetic alterations and has matched primary and KSHV-transformed cells, which are not available for similar screenings in other types of cancer. We have identified genes that are both growth promoting and growth suppressive in primary and transformed cells, some of which could represent novel proto-oncogenes and tumor suppressors. In particular, we have demonstrated that the exportin XPO1 is a critical factor for the survival of transformed cells. Using a XPO1 inhibitor (KPT-8602) and siRNA-mediated knockdown, we have confirmed the essential role of XPO1 in cell proliferation and in growth transformation of KSHV-transformed cells, as well as of gastric and liver cancer cells. XPO1 inhibition induces cell cycle arrest by activating p53, but the mechanisms of p53 activation differed among different types of cancer cells. p53 activation is dependent on the formation of PML nuclear bodies in gastric and liver cancer cells. Mechanistically, XPO1 inhibition induces relocalization of autophagy adaptor protein p62 (SQSTM1), recruiting p53 for activation in PML nuclear bodies. These results illustrate that XPO1 is a vulnerable target of cancer cells and reveal a novel mechanism for blocking cancer cell proliferation by XPO1 inhibition as well as a novel PML- and p62-mediated mechanism of p53 activation in some types of cancer cells.

Crm1 knockdown by specific small interfering RNA reduces cell proliferation and induces apoptosis in head and neck cancer cell lines

Head and neck squamous cell carcinoma (HNSCC) is the most common and most aggressive type of head and neck cancer. Current approaches for the treatment of HNSCC are not sufficient to increase the patient survival or to reduce the high recurrence rate. Consequently, there is a need to explore the molecular characteristics of this cancer in order to discover potential therapeutic target molecules. The overexpression of chromosome region maintenance 1 (Crm1), responsible for the transport of different classes of macromolecules from the nuclear membrane to the cytoplasm, in various cancer cells has made it an attractive target molecule in cancer research. It has been reported that transcription factors, which are the target cargo proteins of Crm1, have critical roles in regulating intracellular processes via their expression levels and functions, which in turn are regulated by the cell cycle and signaling proteins. Previous findings show that head and neck cancer cells overexpress Crm1 and that these cells become highly dependent on Crm1 function. The results of this study show that after decreasing Crm1 expression levels in HNSCC cells through either treatment with specific Crm1 RNA interference (siRNA) or the selective Crm1 inhibitor leptomycin B (LMB), cell viability, proliferation, migration, and wound-healing abilities decreased, suppressing tumorigenic properties through the induction of apoptosis. Crm1 is a powerful diagnostic biomarker because of its central role in cancerogenesis, and it has a high potential for the development of targeted Crm1 molecules or synthetic agents, such as LMB, as well as for the improvement of the clinical features in head and neck cancer.

Inhibition of androgen receptor transactivation function by adenovirus type 12 E1A undermines prostate cancer cell survival

BACKGROUND

Mutations or truncation of the ligand-binding domain (LBD) of androgen receptor (AR) underlie treatment resistance for prostate cancer (PCa). Thus, targeting the AR N-terminal domain (NTD) could overcome such resistance.

METHODS

Luciferase reporter assays after transient transfection of various DNA constructs were used to assess effects of E1A proteins on AR-mediated transcription. Immunofluorescence microscopy and subcellular fractionation were applied to assess intracellular protein localization. Immunoprecipitation and mammalian two-hybrid assays were used to detect protein-protein interactions. qRT-PCR was employed to determine RNA levels. Western blotting was used to detect protein expression in cells. Effects of adenoviruses on prostate cancer cell survival were evaluated with CellTiter-Glo assays.

RESULTS

Adenovirus 12 E1A (E1A12) binds specifically to the AR. Interestingly, the full-length E1A12 (266 aa) preferentially binds to full-length AR, while the small E1A12 variant (235 aa) interacts more strongly with AR-V7. E1A12 promotes AR nuclear translocation, likely through mediating intramolecular AR NTD-LBD interactions. In the nucleus, AR and E1A12 co-expression in AR-null PCa cells results in E1A12 redistribution from nuclear foci containing CBX4 (also known as Pc2), suggesting a preferential AR-E1A12 interaction over other E1A12 interactors. E1A12 represses AR-mediated transcription in reporter gene assays and endogenous AR target genes such as ATAD2 and MYC in AR-expressing PCa cells. AR-expressing PCa cells are more sensitive to death induced by a recombinant adenovirus expressing E1A12 (Ad-E1A12) than AR-deficient PCa cells, which could be attributed to the increased viral replication promoted by androgen stimulation. Targeting the AR by E1A12 promotes apoptosis in PCa cells that express the full-length AR or C-terminally truncated AR variants. Importantly, inhibition of mTOR signaling that blocks the expression of anti-apoptotic proteins markedly augments Ad-E1A12-induced apoptosis of AR-expressing cells. Mechanistically, Ad-E1A12 infection triggers apoptotic response while activating the PI3K-AKT-mTOR signaling axis; thus, mTOR inhibition enhances apoptosis in AR-expressing PCa cells infected by Ad-E1A12.

CONCLUSION

Ad12 E1A inhibits AR-mediated transcription and suppresses PCa cell survival, suggesting that targeting the AR by E1A12 might have therapeutic potential for treating advanced PCa with heightened AR signaling.

SENP3 maintains the stability and function of regulatory T cells via BACH2 deSUMOylation

Regulatory T (Treg) cells are essential for maintaining immune homeostasis and tolerance, but the mechanisms regulating the stability and function of Treg cells have not been fully elucidated. Here we show SUMO-specific protease 3 (SENP3) is a pivotal regulator of Treg cells that functions by controlling the SUMOylation and nuclear localization of BACH2. Treg cell-specific deletion of Senp3 results in T cell activation, autoimmune symptoms and enhanced antitumor T cell responses. SENP3-mediated BACH2 deSUMOylation prevents the nuclear export of BACH2, thereby repressing the genes associated with CD4+ T effector cell differentiation and stabilizing Treg cell-specific gene signatures. Notably, SENP3 accumulation triggered by reactive oxygen species (ROS) is involved in Treg cell-mediated tumor immunosuppression. Our results not only establish the role of SENP3 in the maintenance of Treg cell stability and function via BACH2 deSUMOylation but also clarify the function of SENP3 in the regulation of ROS-induced immune tolerance.

The effect of aberrant expression and genetic polymorphisms of Rad21 on cervical cancer biology

The therapeutic challenge of advanced, recurrent, and refractory cervical cancer (CC) needs to develop new molecularly targeted drugs. Rad21 is an important regulatory gene that maintains the correct dissociation of sister chromatids during cell mitosis. The aim of this study was to investigate the effect of Rad21 on CC. Rad21 expression in CC and cervical intraepithelial neoplasia III was significantly increased. Women with the rs2289937 C genotype (CC+CT) of rs4570 and rs4579555 genotypes and haplotype 1 (TTTCAGGCGC) were significantly associated with CC risk, while women with low frequencies of haplotype 6 (TTTTAGGCGC) also increased the risk of CC.Rad21‐specific shRNA decreased cancerous cell proliferation, migration, and invasion and increased the proportion of cells in G2/M phase as well as sensitivity to radiation. The Rad21 influenced the expression of XPO1, CyclinB1, CDK1, P21, P27, and P53 through up‐and downregulating the Rad21 expression. The TCGA database of CC also showed that Rad21 expression was associated with poor disease survival and XPO1 expression. Moreover, the KEGG pathway indicated that Rad21 is broadly involved in the cell cycle and RNA transportation via XPO1. This suggests that Rad21 involves the development of cervical cancer possibly by participating in the regulation of cell cycle and the nuclear output of the tumor suppressor gene via XPO1.

Desumoylase SENP6 maintains osteochondroprogenitor homeostasis by suppressing the p53 pathway

The development, growth, and renewal of skeletal tissues rely on the function of osteochondroprogenitors (OCPs). Protein sumoylation/desumoylation has emerged as a pivotal mechanism for stem cell/progenitor homeostasis, and excessive sumoylation has been associated with cell senescence and tissue aging, but its role in regulating OCP function is unclear. Here we show that postnatal loss of the desumoylase SUMO1/sentrin-specific peptidase 6 (SENP6) causes premature aging. OCP-specific SENP6 knockout mice exhibit smaller skeletons, with elevated apoptosis and cell senescence in OCPs and chondrocytes. In Senp6 ^‒/‒ cells, the two most significantly elevated pathways are p53 signaling and senescence-associated secreted phenotypes (SASP), and Trp53 loss partially rescues the skeletal and cellular phenotypes caused by Senp6 loss. Furthermore, SENP6 interacts with, desumoylates, and stabilizes TRIM28, suppressing p53 activity. Our data reveals a crucial role of the SENP6-p53 axis in maintaining OCP homeostasis during skeletal development.

Pharmacological treatment with inhibitors of nuclear export enhances the antitumor activity of docetaxel in human prostate cancer

Background and aims

Docetaxel (DTX) modestly increases patient survival of metastatic castration-resistant prostate cancer (mCRPC) due to insurgence of pharmacological resistance. Deregulation of Chromosome Region Maintenance (CRM-1)/ exportin-1 (XPO-1)-mediated nuclear export may play a crucial role in this phenomenon.

Material and methods

Here, we evaluated the effects of two Selective Inhibitor of Nuclear Export (SINE) compounds, selinexor (KPT-330) and KPT-251, in association with DTX by using 22rv1, PC3 and DU145 cell lines with their. DTX resistant derivatives.

Results and conclusions

We show that DTX resistance may involve overexpression of β-III tubulin (TUBB3) and P-glycoprotein as well as increased cytoplasmic accumulation of Foxo3a. Increased levels of XPO-1 were also observed in DTX resistant cells suggesting that SINE compounds may modulate DTX effectiveness in sensitive cells as well as restore the sensitivity to DTX in resistant ones. Pretreatment with SINE compounds, indeed, sensitized to DTX through increased tumor shrinkage and apoptosis by preventing DTX-induced cell cycle arrest. Basally SINE compounds induce FOXO3a activation and nuclear accumulation increasing the expression of FOXO-responsive genes including p21, p27 and Bim causing cell cycle arrest. SINE compounds-catenin and survivin supporting apoptosis. βdown-regulated Cyclin D1, c-myc, Nuclear sequestration of p-Foxo3a was able to reduce ABCB1 and TUBB3 H2AX levels, prolonged γ expression. Selinexor treatment increased DTX-mediated double strand breaks (DSB), and reduced the levels of DNA repairing proteins including DNA PKc and Topo2A. Our results provide supportive evidence for the therapeutic use of SINE compounds in combination with DTX suggesting their clinical use in mCRPC patients.

SUMO1 modification of KHSRP regulates tumorigenesis by preventing the TL-G-Rich miRNA biogenesis

Background

MicroRNAs (miRNAs) are important regulators involved in diverse physiological and pathological processes including cancer. SUMO (small ubiquitin-like modifier) is a reversible protein modifier. We recently found that SUMOylation of TARBP2 and DGCR8 is involved in the regulation of the miRNA pathway. KHSRP is a single stranded nucleic acid binding protein with roles in transcription and mRNA decay, and it is also a component of the Drosha-DGCR8 complex promoting the miRNA biogenesis.

Methods

The in vivo SUMOylation assay using the Ni²⁺-NTA affinity pulldown or immunoprecipitation (IP) and the in vitro E.coli-based SUMOylation assay were used to analyze SUMOylation of KHSRP. Nuclear/Cytosol fractionation assay and immunofluorescent staining were used to observe the localization of KHSRP. High-throughput miRNA sequencing, quantantive RT-PCR and RNA immunoprecipitation assay (RIP) were employed to determine the effects of KHSRP SUMO1 modification on the miRNA biogenesis. The soft-agar colony formation, migration, vasculogenic mimicry (VM) and three-dimensional (3D) cell culture assays were performed to detect the phenotypes of tumor cells in vitro, and the xenograft tumor model in mice was conducted to verify that SUMO1 modification of KHSRP regulated tumorigenesis in vivo.

Results

KHSRP is modified by SUMO1 at the major site K87, and this modification can be increased upon the microenvironmental hypoxia while reduced by the treatment with growth factors. SUMO1 modification of KHSRP inhibits its interaction with the pri-miRNA/Drosha-DGCR8 complex and probably increases its translocation from the nucleus to the cytoplasm. Consequently, SUMO1 modification of KHSRP impairs the processing step of pre-miRNAs from pri-miRNAs which especially harbor short G-rich stretches in their terminal loops (TL), resulting in the downregulation of a subset of TL-G-Rich miRNAs such as let-7 family and consequential tumorigenesis.

Conclusions

Our data demonstrate how the miRNA biogenesis pathway is connected to tumorigenesis and cancer progression through the reversible SUMO1 modification of KHSRP.

Electronic supplementary material

The online version of this article (10.1186/s12943-017-0724-6) contains supplementary material, which is available to authorized users.

SUMOylation regulates nuclear accumulation and signaling activity of the soluble intracellular domain of the ErbB4 receptor tyrosine kinase

Erb-B2 receptor tyrosine kinase 4 (ErbB4) is a kinase that can signal via a proteolytically released intracellular domain (ICD) in addition to classical receptor tyrosine kinase-activated signaling cascades. Previously, we have demonstrated that ErbB4 ICD is posttranslationally modified by the small ubiquitin-like modifier (SUMO) and functionally interacts with the PIAS3 SUMO E3 ligase. However, direct evidence of SUMO modification in ErbB4 signaling has remained elusive. Here, we report that the conserved lysine residue 714 in the ErbB4 ICD undergoes SUMO modification, which was reversed by sentrin-specific proteases (SENPs) 1, 2, and 5. Although ErbB4 kinase activity was not necessary for the SUMOylation, the SUMOylated ErbB4 ICD was tyrosine phosphorylated to a higher extent than unmodified ErbB4 ICD. Mutation of the SUMOylation site compromised neither ErbB4-induced phosphorylation of the canonical signaling pathway effectors Erk1/2, Akt, or STAT5 nor ErbB4 stability. In contrast, SUMOylation was required for nuclear accumulation of the ErbB4 ICD. We also found that Lys-714 was located within a leucine-rich stretch, which resembles a nuclear export signal, and could be inactivated by site-directed mutagenesis. Furthermore, SUMOylation modulated the interaction of ErbB4 with chromosomal region maintenance 1 (CRM1), the major nuclear export receptor for proteins. Finally, the SUMO acceptor lysine was functionally required for ErbB4 ICD-mediated inhibition of mammary epithelial cell differentiation in a three-dimensional cell culture model. Our findings indicate that a SUMOylation-mediated mechanism regulates nuclear localization and function of the ICD of ErbB4 receptor tyrosine kinase.

Sumoylation in p27kip1 via RanBP2 promotes cancer cell growth in cholangiocarcinoma cell line QBC939

BACKGROUND

Cholangiocarcinoma is one of the deadly disease with poor 5-year survival and poor response to conventional therapies. Previously, we found that p27kip1 nuclear-cytoplasmic translocation confers proliferation potential to cholangiocarcinoma cell line QBC939 and this process is mediated by crm-1. However, no other post-transcriptional regulation was found in this process including sumoylation in cholangiocarcinoma.

RESULTS

In this study, we explored the role of sumoylation in the nuclear-cytoplasmic translocation of p27kip1 and its involvement of QBC939 cells' proliferation. First, we identified K73 as the sumoylation site in p27kip1. By utilizing plasmid flag-p27kip1, HA-RanBP2, GST-RanBP2 and His-p27kip1 and immunoprecipitation assay, we validated that p27kip1 can serve as the sumoylation target of RanBP2 in QBC939. Furthermore, we confirmed crm-1's role in promoting nuclear-cytoplasmic translocation of p27kip1 and found that RanBP2's function relies on crm-1. However, K73R mutated p27kip1 can't be identified by crm-1 or RanBP2 in p27kip1 translocation process, suggesting sumoylation of p27kip1 via K73 site is necessary in this process by RanBP2 and crm-1. Phenotypically, the overexpression of either RanBP2 or crm-1 can partially rescue the anti-proliferative effect brought by p27kip1 overexpression in both the MTS and EdU assay. For the first time, we identified and validated the K73 sumoylation site in p27kip1, which is critical to RanBP2 and crm-1 in p27kip1 nuclear-cytoplasmic translocation process.

CONCLUSION

Taken together, targeted inhibition of sumoylation of p27kip1 may serve as a potentially potent therapeutic target in the eradication of cholangiocarcinoma development and relapses.

Androgen induces G3BP2 and SUMO-mediated p53 nuclear export in prostate cancer

The androgen receptor (AR) has a central role in prostate cancer progression, particularly treatment-resistance disease including castration-resistant prostate cancer. Loss of the p53 tumor suppressor, a nuclear transcription factor, is also known to contribute to prostate malignancy. Here we report that p53 is translocated to the cytoplasm by androgen-mediated induction of G3BP2, a newly described direct target gene of AR. G3BP2 induces both cell cycle progression and blocks apoptosis. Translocation of p53 is regulated by androgen-dependent sumoylation mediated by the G3BP2-interacting SUMO-E3 ligase, RanBP2. G3BP2 knockdown results in reduced tumor growth and increased nuclear p53 accumulation in mouse xenograft models of prostate cancer with or without long-term androgen deprivation. Moreover, strong cytoplasmic p53 localization is correlated clinically with elevated G3BP2 expression and predicts poor prognosis and disease progression to the hormone-refractory state. Our findings reveal a new AR-mediated mechanism of p53 inhibition that promotes treatment-resistant prostate cancer.

Profiling Cell Lines Nuclear Sub-proteome

Proteins are very dynamic within the cell and their localization and trafficking between subcellular compartments are critical for their correct function. Indeed, the abnormal localization of a protein might lead to the pathogenesis of several diseases. The association of cell fractionation methods and mass spectrometry based proteomic methods allow both the localization and quantification of proteins in different sub-compartments. Here we present a detailed protocol for enrichment, identification, and quantitation of the nuclear proteome in cell lines combining nuclear subproteome enrichment by differential centrifugation and high-throughput proteomics.

Molecular Imaging Biosensor Monitors p53 Sumoylation in Cells and Living Mice

Small molecule mediated stabilization of p53 tumor suppressor protein through sumoylation is a promising new strategy for improving cancer chemotherapy. A molecular tool that monitors p53 sumoylation status and expedites screening for drugs that enhance p53 sumoylation would be beneficial. We report a molecularly engineered reporter fragment complementation biosensor based on optical imaging of Firefly luciferase (FLuc), to quantitatively image p53 sumoylation and desumoylation in cells and living mice. We initially characterized this biosensor by successfully imaging sumoylation of several target proteins, achieving significant FLuc complementation for ERα (p < 0.01), p53 (p < 0.005), FKBP12 (p < 0.03), ID (p < 0.03), and HDAC1 (p < 0.002). We then rigorously tested the sensitivity and specificity of the biosensor using several variants of p53 and SUMO1, including deletion mutants, and those with modified sequences containing the SUMO-acceptor site of target proteins. Next we evaluated the performance of the biosensor in HepG2 cells by treatment with ginkgolic acid, a drug that reduces p53 sumoylation, as well as trichostatin A, a potential inducer of p53 sumoylation by enhancement of its nuclear export. Lastly, we demonstrated the in vivo utility of this biosensor in monitoring and quantifying the effects of these drugs on p53 sumoylation in living mice using bioluminescence imaging. Adoption of this biosensor in future high throughput drug screening has the important potential to help identify new and repurposed small molecules that alter p53 sumoylation, and to preclinically evaluate candidate anticancer drugs in living animals.

Methionine adenosyltransferase α2 sumoylation positively regulate Bcl-2 expression in human colon and liver cancer cells

Ubiquitin-conjugating enzyme 9 (Ubc9) is required for sumoylation and inhibits apoptosis via Bcl-2 by unknown mechanism. Methionine adenosyltransferase 2A (MAT2A) encodes for MATα2, the catalytic subunit of the MATII isoenzyme that synthesizes S-adenosylmethionine (SAMe). Ubc9, Bcl-2 and MAT2A expression are up-regulated in several malignancies. Exogenous SAMe decreases Ubc9 and MAT2A expression and is pro-apoptotic in liver and colon cancer cells. Here we investigated whether there is interplay between Ubc9, MAT2A and Bcl-2. We used human colon and liver cancer cell lines RKO and HepG2, respectively, and confirmed key finding in colon cancer specimens. We found MATα2 can regulate Bcl-2 expression at multiple levels. MATα2 binds to Bcl-2 promoter to activate its transcription. This effect is independent of SAMe as MATα2 catalytic mutant was also effective. MATα2 also directly interacts with Bcl-2 to enhance its protein stability. MATα2's effect on Bcl-2 requires Ubc9 as MATα2's stability is influenced by sumoylation at K340, K372 and K394. Overexpressing wild type (but not less stable MATα2 sumoylation mutants) protected from 5-fluorouracil-induced apoptosis in both colon and liver cancer cells. Colon cancer have higher levels of sumoylated MATα2, total MATα2, Ubc9 and Bcl-2 and higher MATα2 binding to the Bcl-2 P2 promoter. Taken together, Ubc9's protective effect on apoptosis may be mediated at least in part by sumoylating and stabilizing MATα2 protein, which in turn positively maintains Bcl-2 expression. These interactions feed forward to further enhance growth and survival of the cancer cell.

Disturbed Flow-Induced Endothelial Proatherogenic Signaling Via Regulating Post-Translational Modifications and Epigenetic Events

SIGNIFICANCE

Hemodynamic shear stress, the frictional force exerted onto the vascular endothelial cell (EC) surface, influences vascular EC functions. Atherosclerotic plaque formation in the endothelium is known to be site specific: disturbed blood flow (d-flow) formed at the lesser curvature of the aortic arch and branch points promotes plaque formation, and steady laminar flow (s-flow) at the greater curvature is atheroprotective.

RECENT ADVANCES

Post-translational modifications (PTMs), including phosphorylation and SUMOylation, and epigenetic events, including DNA methylation and histone modifications, provide a new perspective on the pathogenesis of atherosclerosis, elucidating how gene expression is altered by d-flow. Activation of PKCζ and p90RSK, SUMOylation of ERK5 and p53, and DNA hypermethylation are uniquely induced by d-flow, but not by s-flow.

CRITICAL ISSUES

Extensive cross talk has been observed among the phosphorylation, SUMOylation, acetylation, and methylation PTMs, as well as among epigenetic events along the cascade of d-flow-induced signaling, from the top (mechanosensory systems) to the bottom (epigenetic events). In addition, PKCζ activation plays a role in regulating SUMOylation-related enzymes of PIAS4, p90RSK activation plays a role in regulating SUMOylation-related enzymes of Sentrin/SUMO-specific protease (SENP)2, and DNA methyltransferase SUMOylation may play a role in d-flow signaling.

FUTURE DIRECTIONS

Although possible contributions of DNA events such as histone modification and the epigenetic and cytosolic events of PTMs in d-flow signaling have become clearer, determining the interplay of each PTM and epigenetic event will provide a new paradigm to elucidate the difference between d-flow and s-flow and lead to novel therapeutic interventions to inhibit plaque formation. Antioxid. Redox Signal. 25, 435-450.

NADPH oxidases: key modulators in aging and age-related cardiovascular diseases?

Reactive oxygen species (ROS) and oxidative stress have long been linked to aging and diseases prominent in the elderly such as hypertension, atherosclerosis, diabetes and atrial fibrillation (AF). NADPH oxidases (Nox) are a major source of ROS in the vasculature and are key players in mediating redox signalling under physiological and pathophysiological conditions. In this review, we focus on the Nox-mediated ROS signalling pathways involved in the regulation of 'longevity genes' and recapitulate their role in age-associated vascular changes and in the development of age-related cardiovascular diseases (CVDs). This review is predicated on burgeoning knowledge that Nox-derived ROS propagate tightly regulated yet varied signalling pathways, which, at the cellular level, may lead to diminished repair, the aging process and predisposition to CVDs. In addition, we briefly describe emerging Nox therapies and their potential in improving the health of the elderly population.

Hypoxia regulates sumoylation pathways in intervertebral disc cells: implications for hypoxic adaptations

OBJECTIVE

To explore the hypoxic regulation of sumoylation pathways and cell viability in nucleus pulposus (NP) and annulus fibrosus (AF) cells.

DESIGN

Expression of small ubiquitin-like modifier (SUMO) molecules, SUMO E1 activating enzymes SAE1 and SAE2, SUMO E2 conjugating enzyme UBC9, and de-sumoylation enzyme sentrin/SUMO-specific proteases (SENP)1 was immunolocalized in rat intervertebral disc (IVD) cells. NP and AF cells were cultured in hypoxia and cell viability was evaluated by quantifying cell proliferation, cellular senescence, apoptosis, and cell cycle distribution. Hypoxic regulation of sumoylation pathways was studied by analyzing the transcription and expression of SUMO molecules and sumoylation enzymes. Loss of function study using SENP1 siRNA was performed to investigate the regulatory role of sumoylation on the function of hypoxia inducible factor 1α (HIF-1α) and the hypoxic tolerance of IVD cells.

RESULTS

Sumoylation pathways were expressed in IVD cells and localized predominantly in nuclei. Both NP and AF cells maintained viability under hypoxia and upregulated the expression of SENP1. In NP cells hypoxia transiently increased the expression of SUMO-1, SUMO-2/3, SAE2, and UBC9, whereas SUMO-1 was elevated while SUMO-2/3, SAE1, SAE2, and UBC9 were reduced by low oxygen tensions in AF cells. Although downregulation of SENP1 decreased the transcriptional activity of HIF-1α, the viability of disc cells showed no significant loss under hypoxia.

CONCLUSIONS

NP and AF cells equally tolerate oxygen deficiency, but differently regulate the sumoylation pathways under hypoxia. The distinct sumoylation dynamics may help extend our understanding of the cell-specific regulation of the molecular basis that promotes cell survival in the hypoxic IVD.

Chromosome region maintenance 1 expression and its association with clinical pathological features in primary carcinoma of the liver

Liver cancer is the third leading cause of cancer-associated mortality worldwide. Recurrence and metastasis are the major factors affecting the prognosis; thus, investigation of the underlying molecular mechanisms of invasion and metastasis, and detection of novel drug target may improve the mortality rate of liver cancer patients. Chromosome region maintenance 1 (CRM1) recognizes specific leucine-rich nuclear export signal sequences, and its overexpression is associated with tumor-suppressor gene inactivation, proliferation, invasion and resistance to chemotherapy. The aim of the present study was to examine the association of CRM1 expression with the clinical and pathological features of primary liver cancer. In total, 152 cases diagnosed with liver cancer were included. CRM1 expression was detected in cancer tissues and adjacent normal tissues by immunohistochemical assay. No statistically significant difference was found between the CRM1 expression levels in tumor and adjacent normal tissues (P=0.106). However, CRM1 expression in adjacent normal tissues was higher compared with that in tumor tissues in the negative hepatitis B envelope antigen (HBeAg; P=0.029) and low differentiation (P=0.004) groups. In tumor tissues, CRM1 expression was significantly correlated with differentiation (P=0.045), whereas in adjacent normal tissues, CRM1 expression was significantly correlated with the tumor diameter (P=0.004). Therefore, it can be concluded that CRM1 is highly expressed in both tumor and adjacent normal tissues. Furthermore, CRM1 expression is associated with the tumor differentiation degree and diameter. Lower differentiation and larger tumor diameter resulted in higher CRM1 expression in adjacent normal tissues, and higher tendency for invasion and metastasis. In addition, the risk of invasion and metastasis remains in chronic hepatitis B patients with negative HBeAg.

Serial interactome capture of the human cell nucleus

Novel RNA-guided cellular functions are paralleled by an increasing number of RNA-binding proteins (RBPs). Here we present 'serial RNA interactome capture' (serIC), a multiple purification procedure of ultraviolet-crosslinked poly(A)-RNA-protein complexes that enables global RBP detection with high specificity. We apply serIC to the nuclei of proliferating K562 cells to obtain the first human nuclear RNA interactome. The domain composition of the 382 identified nuclear RBPs markedly differs from previous IC experiments, including few factors without known RNA-binding domains that are in good agreement with computationally predicted RNA binding. serIC extends the number of DNA-RNA-binding proteins (DRBPs), and reveals a network of RBPs involved in p53 signalling and double-strand break repair. serIC is an effective tool to couple global RBP capture with additional selection or labelling steps for specific detection of highly purified RBPs.

Putative role of SUMOylation in controlling the activity of deubiquitinating enzymes in cancer

Deubiquitinating enzymes (DUBs) are specialized proteins that can recognize ubiquitinated proteins, and after direct interaction, deconjugate monomeric or polymeric ubiquitin chains, thus changing the fate of the substrates. This process is instrumental in mediating or changing downstream signaling pathways. Beside mutations and alterations in their expression levels, the activity and stability of deubiquitinating enzymes is vital for their function. SUMOylations consist of the conjugation of the small peptide SUMO to protein substrates which is very similar to ubiquitination in the mechanistic and machinery required. In this review, we will focus on how SUMOylation can regulate DUB enzymatic activity, stability or DUB interaction with partners and substrates, in cancer. Furthermore, we will discuss the impact of these recent findings in the identification of new potential tools for efficient anticancer treatment strategies.

Analysis of CRM1-Dependent Nuclear Export in Permeabilized Cells

Nuclear protein import and export assays in permeabilized cells have been instrumental for the identification of transport factors and for the molecular characterization of nucleocytoplasmic transport pathways. Our original assay to quantitatively analyze CRM1-dependent export was based on stably transfected cells expressing GFP-NFAT. We now present a simplified version of the assay using transiently transfected cells expressing GFP-NFAT or GFP-snurportin1 as a fluorescent export cargo and mCherry-emerin as a marker protein for transfected cells. CRM1- and Ran-dependent export is recapitulated in digitonin-permeabilized cells and quantified by flow cytometry. The assay should be applicable to other combinations of cargo and marker proteins.

KPT-330, a potent and selective exportin-1 (XPO-1) inhibitor, shows antitumor effects modulating the expression of cyclin D1 and survivin [corrected] in prostate cancer models

BACKGROUND AND AIMS

Increased expression of Chromosome Region Maintenance (CRM-1)/exportin-1 (XPO-1) has been correlated with poor prognosis in several aggressive tumors, making it an interesting therapeutic target. Selective Inhibitor of Nuclear Export (SINE) compounds bind to XPO-1 and block its ability to export cargo proteins. Here, we investigated the effects of a new class of SINE compounds in models of prostate cancer.

MATERIAL AND METHODS

We evaluated the expression of XPO-1 in human prostate cancer tissues and cell lines. Next, six SINE (KPT-127, KPT-185, KPT-205, KPT-225, KPT-251 and KPT-330) compounds having different potency with broad-spectrum, tumor-selective cytotoxicity, tolerability and pharmacokinetic profiles were tested in a panel of prostate cancer cells representing distinct differentiation/progression states of disease and genotypes. Two SINE candidates for clinical trials (KPT-251 and KPT-330) were also tested in vivo in three cell models of aggressive prostate cancer engrafted in male nude mice.

RESULTS AND CONCLUSIONS

XPO-1 is overexpressed in prostate cancer compared to normal or hyperplastic tissues. Increased XPO-1 expression, mainly in the nuclear compartment, was associated with increased Gleason score and bone metastatic potential supporting the use of SINEs in advanced prostate cancer. SINE compounds inhibited proliferation and promoted apoptosis of tumor cells, but did not affect immortalized non-transformed prostate epithelial cells. Nuclei from SINE treated cells showed increased protein localization of XPO-1, survivin and cyclin D1 followed by degradation of these proteins leading to cell cycle arrest and apoptosis. Oral administration of KPT-251 and KPT-330 in PC3, DU145 and 22rv1 tumor-bearing nude mice reduced tumor cell proliferation, angiogenesis and induced apoptosis. Our results provide supportive evidence for the therapeutic use of SINE compounds in advanced/castration resistant prostate cancers and warrants further clinical investigation.

Oncogenic role of p21 in hepatocarcinogenesis suggests a new treatment strategy

A well-known tumor suppressor, p21, acts paradoxically by promoting tumor growth in some cellular conditions. These conflicting functions have been demonstrated in association with the HBx gene and in hepatocarcinogenesis. The molecular behavior of p21 depends on its subcellular localization. Nuclear p21 may inhibit cell proliferation and be proapoptotic, while cytoplasmic p21 may have oncogenic and anti-apoptotic functions. Because most typical tumor suppressive proteins also have different effects according to subcellular localization, elucidating the regulatory mechanisms underlying nucleo-cytoplasmic transport of these proteins would be significant and may lead to a new strategy for anti-hepatocellular carcinoma (HCC) therapy. Chromosome region maintenance 1 (CRM1) is a major nuclear export receptor involved in transport of tumor suppressors from nucleus to cytoplasm. Expression of CRM1 is enhanced in a variety of malignancies and in vitro studies have shown the efficacy of specific inhibition of CRM1 against cancer cell lines. Interestingly, interferon may keep p21 in the nucleus; this is one of the mechanisms of its anti-hepatocarcinogenic function. Here we review the oncogenic property of p21, which depends on its subcellular localization, and discuss the rationale underlying a new strategy for HCC treatment and prevention.