Phosphorylation of p53 at threonine 155 is required for Jab1-mediated nuclear export of p53

Cyclic AMP (cAMP)-dependent proteolysis of GATA6 by proteasome: Zinc-finger domain of GATA6 has signals for nuclear export and proteolysis, both of which are responsive to cAMP

Transcription factor GATA6 stably expressed in Chinese hamster ovary (CHO)-K1 cells is exported from the nucleus to the cytoplasm and degraded there by proteasome upon treatment with dibutylyl-cyclic AMP (dbcAMP), which is a membrane-permeable cyclic AMP (cAMP) analogue. The cAMP-dependent proteolysis of GATA6 was characterized by dissection of the GATA6 protein into a zinc-finger domain (Zf) and the surrounding region (ΔZf). These segments were separately expressed in CHO-K1 cells stably, and followed by treatment with dbcAMP. The nuclear localized Zf was degraded by proteasome similarly to the full-length GATA6. Site-directed mutants of nuclear localizing signal (NLS) (³⁴⁵RKRKPK³⁵⁰ → AAAAPK and AAAAPA) and closely related GATA4 showed the same behavior. Although nuclear-localized ΔZf was degraded by proteasome, the cytoplasmic-located ΔZf was resistant to proteolysis in contrast to the NLS mutants. We also searched for a potential NLS and nuclear export signal (NES) with computational prediction programs and compared the results with ours. All these results suggest that the amino acid sequence(s) of the Zf of GATA6 is responsive to cAMP-dependent nuclear export and proteolysis.

Structural and functional characterisation of HepTH1-5 peptide as a potential hepcidin replacement

Hepcidin is a principal regulator of iron homeostasis and its dysregulation has been recognised as a causative factor in cancers and iron disorders. The strategy of manipulating the presence of hepcidin peptide has been used for cancer treatment. However, this has demonstrated poor efficiency and has been short-lived in patients. Many studies reported using minihepcidin therapy as an alternative way to treat hepcidin dysregulation, but this was only applied to non-cancer patients. Highly conserved fish hepcidin protein, HepTH1-5, was investigated to determine its potential use in developing a hepcidin replacement for human hepcidin (Hepc25) and as a therapeutic agent by targeting the tumour suppressor protein, p53, through structure-function analysis. The authors found that HepTH1-5 is stably bound to ferroportin, compared to Hepc25, by triggering the ferroportin internalisation via Lys42 and Lys270 ubiquitination, in a similar manner to the Hepc25 activity. Moreover, the residues Ile24 and Gly24, along with copper and zinc ligands, interacted with similar residues, Lys24 and Asp1 of Hepc25, respectively, showing that those molecules are crucial to the hepcidin replacement strategy. HepTH1-5 interacts with p53 and activates its function through phosphorylation. This finding shows that HepTH1-5 might be involved in the apoptosis signalling pathway upon a DNA damage response. This study will be very helpful for understanding the mechanism of the hepcidin replacement and providing insights into the HepTH1-5 peptide as a new target for hepcidin and cancer therapeutics.Communicated by Ramaswamy H. Sarma.

LncRNA PVT1 promotes tumorigenesis of glioblastoma by recruiting COPS5 to deubiquitinate and stabilize TRIM24

LncRNA PVT1 has been implicated in numerous pathophysiological processes and diseases, especially cancers. However, the role and mechanism of PVT1 in the tumorigenesis of glioblastoma remain unclear. We investigated the alteration of PVT1 and its key functions in glioblastoma. PVT1 was upregulated and associated with poor prognosis in glioblastoma. We demonstrated that PVT1 silencing suppressed cell proliferation, colony formation, and orthotopic xenograft tumor growth. Mechanistic investigations found that PVT1 interacted with TRIM24 directly and increased its protein stability. PVT1 recruited COPS5 to deubiquitinate TRIM24; reciprocally, PVT1 depletion impaired the interaction between COPS5 and TRIM24, resulting in decreased expression of TRIM24. PVT1, TRIM24, and COPS5 coordinately contributed to the activation of STAT3 signaling and malignant phenotype of glioblastoma. Collectively, this study elucidates the essential role of PVT1 in the tumorigenesis of glioblastoma, which provides candidacy therapeutic target for glioblastoma treatment.

C-phycoerythrin from Phormidium persicinum Prevents Acute Kidney Injury by Attenuating Oxidative and Endoplasmic Reticulum Stress

C-phycoerythrin (C-PE) is a phycobiliprotein that prevents oxidative stress and cell damage. The aim of this study was to evaluate whether C-PE also counteracts endoplasmic reticulum (ER) stress as a mechanism contributing to its nephroprotective activity. After C-PE was purified from Phormidium persicinum by using size exclusion chromatography, it was characterized by spectrometry and fluorometry. A mouse model of HgCl₂-induced acute kidney injury (AKI) was used to assess the effect of C-PE treatment (at 25, 50, or 100 mg/kg of body weight) on oxidative stress, the redox environment, and renal damage. ER stress was examined with the same model and C-PE treatment at 100 mg/kg. C-PE diminished oxidative stress and cell damage in a dose-dependent manner by impeding the decrease in expression of nephrin and podocin normally caused by mercury intoxication. It reduced ER stress by preventing the activation of the inositol-requiring enzyme-1α (IRE1α) pathway and avoiding caspase-mediated cell death, while leaving the expression of protein kinase RNA-like ER kinase (PERK) and activating transcription factor 6α (ATF6α) pathways unmodified. Hence, C-PE exhibited a nephroprotective effect on HgCl₂-induced AKI by reducing oxidative stress and ER stress.

Targeting Nuclear Export Proteins in Multiple Myeloma Therapy

Multiple myeloma (MM) is an incurable malignancy of plasma cells with a clinical course characterized by multiple relapses and treatment refractoriness. While recent treatment advancements have extended overall survival (OS), refractory MM has a poor prognosis, with a median OS of between 4 and 6 months. Nuclear export inhibition, specifically inhibition of CRM1/XPO1, is an emerging novel treatment modality that has shown promise in treatment-refractory MM. Initially discovered in yeast in 1983, early clinical applications were met with significant toxicities that limited their utility. The creation of small molecule inhibitors of nuclear export (SINE) has improved on toxicity limitations and has led to investigation in a number of malignancies at the preclinical and clinical stages. Preclinical studies of SINEs in MM have shown that these molecules are cytotoxic to myeloma cells, play a role in therapy resensitization, and suggest a role in limiting bone disease progression. In July 2019, selinexor became the first nuclear export inhibitor approved for use in relapsed/refractory MM based on the STORM trial. As of May 2020, there were eight ongoing trials combining selinexor with standard treatment regimens in relapsed/refractory MM. Eltanexor, a second-generation SINE, is also under investigation and has shown preliminary signs of efficacy in an early clinical trial while potentially having an improved toxicity profile compared with selinexor. Results in ongoing trials will help further define the role of SINEs in MM.

Ubiquitin-conjugating enzyme E2T(UBE2T) promotes colorectal cancer progression by facilitating ubiquitination and degradation of p53

OBJECTIVES

The expression level of Ubiquitin-conjugating enzyme E2T (UBE2T) is upregulated in various types of human tumors. We explored the correlation and regulatory mechanism of UBE2T in the development of colorectal cancer (CRC).

METHODS

Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was used to examine the expression of UBE2T in the CRC tissues and cell lines. Immunohistochemical staining, spearman correlation analysis, and Kaplan Meier-survival analysis were used to demonstrate the correlation between UBE2T high expression level and the clinical characteristics of malignant patients and the overall survival. The proliferation, apoptosis, migration and invasion of CRC cells were analyzed by cell transfection, MTT, colony formation, scratch assay, transwell, and flow cytometry. Furthermore, the expression of cell proliferation and apoptosis related proteins and ubiquitination of p53 were detected by western blot.

RESULTS

UBE2T was up-regulated in CRC tissues and cell lines, and high expression level of UBE2T was correlated with the clinical characteristics of malignant of CRC patients (P<0.05), and patients with high expression level of UBE2T had lower overall survival (P=0.0455). In addition, UBE2T could promote the growth, proliferation, invasion and metastasis of CRC cells and inhibit the apoptosis. At the same time, knockdown of UBE2T inhibited the growth of transplanted tumor in mice of subcutaneous CRC model. Moreover, our experimental results proved that UBE2T regulated the expression of downstream related proteins through ubiquitination of p53 protein to promote the occurrence and development of CRC.

CONCLUSION

Our study elucidated that high expression of UBE2T would enhance the development of CRC, and then further explored its molecular mechanism both in vitro and in vivo. The results indicated that UBE2T facilitated ubiquitination and degradation of p53, which predicts the possibility of UBE2T as one of molecular diagnosis markers, prognostic indicators and therapeutic drug targets of CRC patients.

Litopenaeus vannamei Notch interacts with COP9 signalosome complex subunit 1 (CNS1) to negatively regulate the NF-κB pathway

Notch signaling pathway is a highly evolutionary conserved signaling pathway, which modulates many biological processes such as cell differentiation, tissue development and immune response. Our previous study revealed that Litopenaeus vannamei Notch (LvNotch) was involved in immune response by regulating reactive oxygen species (ROS) production in hemocytes. However, the immune regulatory networks mediated by LvNotch remain unclear in shrimp. In this study, 21 proteins that potentially interact with LvNotch were identified by GST pull-down and liquid chromatography tandem mass spectrometry (LC-MS/MS) analyses. Among these proteins, COP9 signalosome complex subunit 1 (CSN1) was chosen for further studies due to its putative role in immune response. The interaction between LvNotch and LvCSN1 was confirmed by Far-Western blot and GST pull-down analyses. In vivo knockdown of LvNotch resulted in an increase in LvCSN1 expression in hemocytes, which suggest that the COP9 signalosome complex might be negatively regulated by LvNotch. In addition, in vivo silencing of LvNotch upregulated the expression of LvDorsal, LvTNFSF and LvCrustin2 (NF-κB pathway related-genes), while their expression decreased after LvCSN1 depletion. Collectively, the current results indicate that LvNotch negatively regulates the NF-κB pathway by modulating LvCSN1 in shrimp. SIGNIFICANCE: Although the Notch signaling pathway has been implicated in the regulation of immune response in vertebrates and invertebrates, the functions and immune-related interacting networks of Notch in shrimp immune response remain unknown. In this study, twenty-one proteins including COP9 signalosome complex subunit 1 (CSN1) were identified as potential interacting partners of LvNotch. Further analysis revealed that LvNotch negatively regulates the NF-κB pathway by binding to CSN1 and modulating its expression. These findings for the first time suggest that the Notch signaling pathway has cross-talk with the NF-κB pathway in shrimp as part of the immune response.

Multifaceted behavior of PEST sequence enriched nuclear proteins in cancer biology and role in gene therapy

The amino acid sequence enriched with proline (P), glutamic acid (E), serine (S), and threonine (T) (PEST) is a signal-transducing agent providing unique features to its substrate nuclear proteins (PEST-NPs). The PEST motif is responsible for particular posttranslational modifications (PTMs). These PTMs impart distinct properties to PEST-NPs that are responsible for their activation/inhibition, intracellular localization, and stability/degradation. PEST-NPs participate in cancer metabolism, immunity, and protein transcription as oncogenes or as tumor suppressors. Gene-based therapeutics are getting the attention of researchers because of their cell specificity. PEST-NPs are good targets to explore as cancer therapeutics. Insights into PTMs of PEST-NPs demonstrate that these proteins not only interact with each other but also recruit other proteins to/from their active site to promote/inhibit tumors. Thus, the role of PEST-NPs in cancer biology is multivariate. It is hard to obtain therapeutic objectives with single gene therapy. An especially designed combination gene therapy might be a promising strategy in cancer treatment. This review highlights the multifaceted behavior of PEST-NPs in cancer biology. We have summarized a number of studies to address the influence of structure and PEST-mediated PTMs on activation, localization, stability, and protein-protein interactions of PEST-NPs. We also recommend researchers to adopt a pragmatic approach in gene-based cancer therapy.

Absence of Sirtuin 1 impairs the testicular development in cattleyak by inactivating SF-1

Cattleyak, which are interspecific hybrids between cattle and yak, display much higher growth performances than yak. However, F1 male cattleyak are infertile due to defective testicular development. Sirtuin 1 (SIRT1) is a histone deacetylase that is essential for various biological processes, while the roles of testicular SIRT1 in yak and cattleyak are still poorly understood. Here, we found that SIRT1 was localized in various kinds of yak testicular cells except elongated spermatids while it was deficient in cattleyak testis. Further studies indicated that cattleyak testis exhibited decreased histone acetylation levels on H3 and H4. One of SIRT1 co-factors, steroidogenic factor-1 (SF-1), was lost in cattleyak testis at protein level. Expressions of several SF-1 target genes responsible for Sertoli cell development and steroidogenesis, including STAR, CYP11A1, CYP26B1, FDX1 and HSD3B, decreased significantly in cattleyak testis. In addition, SIRT1-mediated P53 acetylation was not responsible for the cell apoptosis in cattleyak testis. Taken together, our results suggested the deficiency of SIRT1 in yak testis caused inactivation of SF-1 and the impairment of testicular development. This research provides theoretical bases for understanding the mechanism of cattleyak sterility and gives new insights in revealing the roles of SIRT1 in regulating yak testicular development.

Understanding p53 functions through p53 antibodies

TP53 is the most frequently mutated gene across all cancer types. Our understanding of its functions has evolved since its discovery four decades ago. Initially thought to be an oncogene, it was later realized to be a critical tumour suppressor. A significant amount of our knowledge about p53 functions have come from the use of antibodies against its various forms. The early anti-p53 antibodies contributed to the recognition of p53 accumulation as a common feature of cancer cells and to our understanding of p53 DNA-binding and transcription activities. They led to the concept that conformational changes can facilitate p53’s activity as a growth inhibitory protein. The ensuing p53 conformational-specific antibodies further underlined p53’s conformational flexibility, collectively forming the basis for current efforts to generate therapeutic molecules capable of altering the conformation of mutant p53. A subsequent barrage of antibodies against post-translational modifications on p53 has clarified p53’s roles further, especially with respect to the mechanistic details and context-dependence of its activity. More recently, the generation of p53 mutation-specific antibodies have highlighted the possibility to go beyond the general framework of our comprehension of mutant p53—and promises to provide insights into the specific properties of individual p53 mutants. This review summarizes our current knowledge of p53 functions derived through the major classes of anti-p53 antibodies, which could be a paradigm for understanding other molecular events in health and disease.

IDH1-dependent α-KG regulates brown fat differentiation and function by modulating histone methylation

OBJECTIVE

Brown adipocytes play important roles in the regulation of energy homeostasis by uncoupling protein 1-mediated non-shivering thermogenesis. Recent studies suggest that brown adipocytes as novel therapeutic targets for combating obesity and associated diseases, such as type II diabetes. However, the molecular mechanisms underlying brown adipocyte differentiation and function are not fully understood.

METHODS

We employed previous findings obtained through proteomic studies performed to assess proteins displaying altered levels during brown adipocyte differentiation. Here, we performed assays to determine the functional significance of their altered levels during brown adipogenesis and development.

RESULTS

We identified isocitrate dehydrogenase 1 (IDH1) as upregulated during brown adipocyte differentiation, with subsequent investigations revealing that ectopic expression of IDH1 inhibited brown adipogenesis, whereas suppression of IDH1 levels promoted differentiation of brown adipocytes. Additionally, Idh1 overexpression resulted in increased levels of intracellular α-ketoglutarate (α-KG) and inhibited the expression of genes involved in brown adipogenesis. Exogenous treatment with α-KG reduced brown adipogenesis during the early phase of differentiation, and ChIP analysis revealed that IDH1-mediated α-KG reduced trimethylation of histone H3 lysine 4 in the promoters of genes associated with brown adipogenesis. Furthermore, administration of α-KG decreased adipogenic gene expression by modulating histone methylation in brown adipose tissues of mice.

CONCLUSION

These results suggested that the IDH1-α-KG axis plays an important role in regulating brown adipocyte differentiation and might represent a therapeutic target for treating metabolic diseases.

Quantitative proteomic analyses reveal that GPX4 downregulation during myocardial infarction contributes to ferroptosis in cardiomyocytes

Ischaemic heart disease (IHD) is the leading cause of death worldwide. Although myocardial cell death plays a significant role in myocardial infarction (MI), its underlying mechanism remains to be elucidated. To understand the progression of MI and identify potential therapeutic targets, we performed tandem mass tag (TMT)-based quantitative proteomic analysis using an MI mouse model. Gene ontology (GO) analysis and gene set enrichment analysis (GSEA) revealed that the glutathione metabolic pathway and reactive oxygen species (ROS) pathway were significantly downregulated during MI. In particular, glutathione peroxidase 4 (GPX4), which protects cells from ferroptosis (an iron-dependent programme of regulated necrosis), was downregulated in the early and middle stages of MI. RNA-seq and qRT-PCR analyses suggested that GPX4 downregulation occurred at the transcriptional level. Depletion or inhibition of GPX4 using specific siRNA or the chemical inhibitor RSL3, respectively, resulted in the accumulation of lipid peroxide, leading to cell death by ferroptosis in H9c2 cardiomyoblasts. Although neonatal rat ventricular myocytes (NRVMs) were less sensitive to GPX4 inhibition than H9c2 cells, NRVMs rapidly underwent ferroptosis in response to GPX4 inhibition under cysteine deprivation. Our study suggests that downregulation of GPX4 during MI contributes to ferroptotic cell death in cardiomyocytes upon metabolic stress such as cysteine deprivation.

p53 modifications: exquisite decorations of the powerful guardian

The last 40 years have witnessed how p53 rose from a viral binding protein to a central factor in both stress responses and tumor suppression. The exquisite regulation of p53 functions is of vital importance for cell fate decisions. Among the multiple layers of mechanisms controlling p53 function, posttranslational modifications (PTMs) represent an efficient and precise way. Major p53 PTMs include phosphorylation, ubiquitination, acetylation, and methylation. Meanwhile, other PTMs like sumoylation, neddylation, O-GlcNAcylation, adenosine diphosphate (ADP)-ribosylation, hydroxylation, and β-hydroxybutyrylation are also shown to play various roles in p53 regulation. By independent action or interaction, PTMs affect p53 stability, conformation, localization, and binding partners. Deregulation of the PTM-related pathway is among the major causes of p53-associated developmental disorders or diseases, especially in cancers. This review focuses on the roles of different p53 modification types and shows how these modifications are orchestrated to produce various outcomes by modulating p53 activities or targeted to treat different diseases caused by p53 dysregulation.

Generation and characterization of a monoclonal antibody against MERS-CoV targeting the spike protein using a synthetic peptide epitope-CpG-DNA-liposome complex

Middle East respiratory syndrome coronavirus (MERS-CoV) uses the spike (S) glycoprotein to recognize and enter target cells. In this study, we selected two epitope peptide sequences within the receptor binding domain (RBD) of the MERS-CoV S protein. We used a complex consisting of the epitope peptide of the MERS-CoV S protein and CpG-DNA encapsulated in liposome complex to immunize mice, and produced the monoclonal antibodies 506-2G10G5 and 492-1G10E4E2. The western blotting data showed that both monoclonal antibodies detected the S protein and immunoprecipitated the native form of the S protein. Indirect immunofluorescence and confocal analysis suggested strong reactivity of the antibodies towards the S protein of MERS-CoV virus infected Vero cells. Furthermore, the 506-2G10G5 monoclonal antibody significantly reduced plaque formation in MERS-CoV infected Vero cells compared to normal mouse IgG and 492-1G10E4E2. Thus, we successfully produced a monoclonal antibody directed against the RBD domain of the S protein which could be used in the development of diagnostics and therapeutic applications in the future.

Generation and characterization of a monoclonal antibody against MERS-CoV targeting the spike protein using a synthetic peptide epitope-CpG-DNA-liposome complex

Middle East respiratory syndrome coronavirus (MERS-CoV) uses the spike (S) glycoprotein to recognize and enter target cells. In this study, we selected two epitope peptide sequences within the receptor binding domain (RBD) of the MERS-CoV S protein. We used a complex consisting of the epitope peptide of the MERS-CoV S protein and CpG-DNA encapsulated in liposome complex to immunize mice, and produced the monoclonal antibodies 506-2G10G5 and 492-1G10E4E2. The western blotting data showed that both monoclonal antibodies detected the S protein and immunoprecipitated the native form of the S protein. Indirect immunofluorescence and confocal analysis suggested strong reactivity of the antibodies towards the S protein of MERS-CoV virus infected Vero cells. Furthermore, the 506-2G10G5 monoclonal antibody significantly reduced plaque formation in MERS-CoV infected Vero cells compared to normal mouse IgG and 492-1G10E4E2. Thus, we successfully produced a monoclonal antibody directed against the RBD domain of the S protein which could be used in the development of diagnostics and therapeutic applications in the future. [BMB Reports 2019; 52(6): 397-402].

COP9 signalosome subunit CSN5, but not CSN6, is upregulated in lung adenocarcinoma and predicts poor prognosis

Background

The COP9 signalosome (CSN) is an evolutionarily conserved complex composed of eight subunits (CSN1-CSN8). Among the CSN subunits, CSN5 and its dimerization partner CSN6 are the only two MPN (Mpr1-Pad1-N-terminal) domain-containing subunits. These two subunits play essential roles in a variety of biological processes, such as cell cycle progression, protein stability and signal transduction. However, their expression patterns and clinical significance in lung cancer are not completely clear.

Methods

We examined the expressions of both CSN5 and CSN6 in lung adenocarcinoma (LUAD) patients (n=59) using immunohistochemistry analysis, and correlated their expressions with clinicopathological characteristics. MTT cell proliferation assay was performed to determine the effect of CSN5 silencing or overexpression on the growth of lung cancer cells. Knock down or overexpression of CSN5 was confirmed by western blotting.

Results

CSN5 expression was elevated in tumor cells, compared to the stromal compartment and adjacent normal epithelial cells. Interestingly, CSN5 was also expressed in the macrophages and lymphocytes adjacent to the tumors. Surprisingly, CSN6 was barely detected in the tumor cells of LUAD patients. Furthermore, we also demonstrated that higher levels of CSN5 were correlated with high tumor-node-metastasis (TNM) stage and worse clinical outcomes. Multivariate Cox regression analysis revealed CSN5 was an independently prognostic factor for LUAD patients. Additionally, in cellular model, depletion of CSN5 expression significantly suppressed the growth of lung cancer cells.

Conclusions

COP9 signalosome subunit CSN5, but not CSN6, is upregulated in LUAD. Moreover, CSN5 is a critical regulator for the growth of lung cancer and represents an independent prognostic factor and a promising therapeutic target for LUAD patients.