Myeloid leukemia factor 1 regulates p53 by suppressing COP1 via COP9 signalosome subunit 3

Identification of COP9 signalosome (CSN) subunits and antiviral function analysis of CSN5 in shrimp

The constitutive photomorphogenesis 9 (COP9) signalosome (CSN) typically composing of eight subunits (CSN1-8) mediates the process of deneddylation and deubiquitination. The fifth subunit of COP9 signalosome, CSN5, has special characteristics compared with the other seven subunits, and plays vital roles in the deneddylation activity and diverse cellular processes. However, the role of CSN5 in antiviral immunity is not clear. In this study, we identified 8 subunits (CSN1-8) of COP9 signalosome in shrimp Marsupenaeus japonicus. CSN1-6 were existed in all tested tissues, but CSN7-CSN8 were not detected in hepatopancreas. After WSSV challenged, the expression level of Csn1 to Csn4, and Csn6 to Csn8 were highly decreased, but the expression level of Csn5 was conspicuously increased in shrimp challenged by white spot syndrome virus (WSSV). The CSN5 was recombinantly expressed in Escherichia coli and its polyclonal antibody was prepared. The expression level of CSN5 was conspicuously increased at RNA and protein levels in the shrimp challenged by WSSV. After knockdown of Csn5 by RNA interference, the WSSV replication was obviously increased in shrimp. When injected the recombinant protein of CSN5 with the membrane penetrating peptide into shrimp, WSSV replication was inhibited and the survival rate of shrimp was significantly improved compared with control. We further analyzed the expression of antimicrobial peptides (AMPs) in Csn5-RNAi shrimp, and the results showed that the expression of several AMPs was declined significantly. These results indicate that CSN5 inhibits replication of WSSV via regulating expression of AMPs in shrimp, and the recombinant CSN5 might be used in shrimp aquaculture for the white spot syndrome disease control.

MLF2 Negatively Regulates P53 and Promotes Colorectal Carcinogenesis

Inactivation of the p53 pathway is linked to a variety of human cancers. As a critical component of the p53 pathway, ubiquitin-specific protease 7 (USP7) acts as a deubiquitinase for both p53 and its ubiquitin E3 ligase mouse double minute 2 homolog. Here, myeloid leukemia factor 2 (MLF2) is reported as a new negative regulator of p53. MLF2 interacts with both p53 and USP7. Via these interactions, MLF2 inhibits the binding of USP7 to p53 and antagonizes USP7-mediated deubiquitination of p53, thereby leading to p53 destabilization. Functionally, MLF2 plays an oncogenic role in colorectal cancer, at least partially, via the negative regulation of p53. Clinically, MLF2 is elevated in colorectal cancer and its high expression is associated with poor prognosis in patients with colorectal cancer. In wild-type-p53-containing colorectal cancer, MLF2 and p53 expressions are inversely correlated. These findings establish MLF2 as an important suppressor of p53 function. The study also reveals a critical role for the MLF2-p53 axis in promoting colorectal carcinogenesis.

New Insights into the Impact of Human Papillomavirus on Oral Cancer in Young Patients: Proteomic Approach Reveals a Novel Role for S100A8

Human papillomavirus (HPV) infection has recently been linked to a subset of cancers affecting the oral cavity. However, the molecular mechanisms underlying HPV-driven oral squamous cell carcinoma (OSCC) onset and progression are poorly understood.

METHODS

We performed MS-based proteomics profiling based on HPV status in OSCC in young patients, following biological characterization and cell assays to explore the proteome functional landscape.

RESULTS

Thirty-nine proteins are differentially abundant between HPV (+) and HPV (-) OSCC. Among them, COPS3, DYHC1, and S100A8 are unfavorable for tumor recurrence and survival, in contrast to A2M and Serpine1, low levels of which show an association with better DFS. Remarkably, S100A8 is considered an independent prognostic factor for lower survival rates, and at high levels, it alters tumor-associated immune profiling, showing a lower proportion of M1 macrophages and dendritic cells. HPV (+) OSCC also displayed the pathogen-associated patterns receptor that, when activated, triggered the S100A8 and NFκB inflammatory responses.

CONCLUSION

HPV (+) OSCC has a peculiar microenvironment pattern distinctive from HPV (-), involving the expression of pathogen-associated pattern receptors, S100A8 overexpression, and NFκB activation and responses, which has important consequences in prognosis and may guide therapeutic decisions.

Myeloid leukemia factor 1: A "double-edged sword" in health and disease

The occurrence and development of malignancies are closely related to abnormal cell cycle regulation. Myeloid leukemia factor 1 (MLF1) is a small nucleocytoplasmic shuttling protein associated with cell cycle exit, apoptosis, and certain immune functions. Therefore, it is pertinent to explore the role of MLF1 in health and diseases. Studies to date have suggested that MLF1 could act as a double-edged sword, regulating biochemical activities directly or indirectly. In hematopoietic cells, it serves as a protective factor for the development of lineages, and in malignancies, it serves as an oncogenesis factor. The diversity of its functions depends on the binding partners, including tumor inhibitors, scaffolding molecules, mitochondrial membrane proteins, and transcription factors. Emerging evidence indicates that MLF1 influences immune responses as well. This paper reviews the structure, biological function, and research progress on MLF1 in health and diseases to provide new insights for future research.

Identification of Diagnostic Biomarkers of Rape Pollen Allergy Based on MRNA Sequencing

In this study, 383 differentially expressed genes (DEGs) between the allergic group and the nonallergic group were excavated. Humoral immune response, chemokine-related biological processes, granulocyte-related biological processes, IL-17 signaling pathway, and TNF signaling pathway were found connected with DEGs. The allergic group had significantly higher enrich scores of T cells, T helper cells, TFH, and Th17 cells than the nonallergic group. We acquired 26 rape pollen allergy-associated genes by taking the intersection of key module genes from WGCNA and the DEGs. The functional enrichment results show that rape pollen allergy-associated genes are relevant to processes and pathways like regulation of inflammatory response, transcriptional regulation, lymphocyte differentiation, IL-17 signaling pathway, and MAPK signaling pathway. Then, three characteristic genes were defined by crossing the genes derived from LASSO and SVM-RFE algorithms, including MYADM, PMAIP1, and MLF1. The AUC values of these genes manifested that the three genes had a mighty discrimination power in discriminating allergic samples from nonallergic samples. In conclusion, this study revealed three characteristic genes (MYADM, PMAIP1, and MLF1) in rape pollen allergy, suggesting that they may be potential biomarkers in rape pollen allergy diagnosis and treatment.

Maternal DDB1 regulates apoptosis and lineage differentiation in porcine preimplantation embryos

CONTEXT

Maternal-effect genes (MEGs) play a critical role in modulating both cellular and molecular biology events in preimplantation embryonic development. Damage-specific DNA binding protein 1 (DDB1) is a gene that participates in meiotic resumption, ovulation, and embryonic stem cell maintenance. Its function in preimplantation development is not well-studied.

AIMS

We aimed to explore the expression pattern, genomic heritage, and potential molecular mechanisms of DDB1 in preimplantation embryos in porcine.

METHODS

In this study, RNA interference, microinjection, RT-qPCR, immunofluorescence staining and single-cell RNA sequencing were used to explore the molecular function of DDB1 in porcine preimplantation embryos.

KEY RESULTS

DDB1 was found to be expressed in germinal vesicle (GV) and Meiosis II (MII) oocytes and in preimplantation embryos. We confirmed it is a MEG. DDB1-deficient blastocysts had a significantly reduced number of trophectoderm cells, an increased apoptotic cell number and increased apoptosis index. According to a next-generation sequencing (NGS) analysis, 236 genes (131 upregulated and 105 downregulated) significantly changed in the DDB1-deficient morula. The myeloid leukaemia factor 1 (MLF1) and yes-associated protein 1 (YAP1) expressions were significantly upregulated and downregulated respectively, in the DDB1-deficient morula. In combination with the decreased expression of TEAD4, CDX2, GATA3, OCT4, and NANOG and the increased expression of SOX2 in the blastocyst, DDB1 may play a role in determining lineage differentiation and pluripotency maintenance.

CONCLUSIONS

DDB1 is a MEG and it plays a crucial role in porcine preimplantation embryonic development.

IMPLICATIONS

This study provides a theoretical basis for further understanding the molecular mechanisms of preimplantation embryo development.

Overexpression of MLF1IP promotes colorectal cancer cell proliferation through BRCA1/AKT/p27 signaling pathway

BACKGROUND AND OBJECTIVE

MLF1IP has been correlated with the progression and prognosis of a few tumors. However, the role of MLF1IP in colorectal cancer remains unclear. Here, we examined the expression and function of MLF1IP in colorectal cancer and investigated possible molecular mechanisms.

METHODS

MLF1IP expressions in colorectal cancer tissues and cell lines were detected by quantitative real-time PCR, western blotting, and immunohistochemistry. In vitro and in vivo assays were performed to explore the function and underlying molecular mechanisms of MLF1IP in colorectal cancer.

RESULTS

The expression levels of MLF1IP were significantly up-regulated in colorectal cancer tissues and CRC cell lines (P < 0.05). High expression of MLF1IP was significantly associated with TNM stage, T classification, lymph node involvement, distant metastasis, and poor patient survival (all P < 0.05). Overexpressing MLF1IP promoted while silencing MLF1IP inhibited, the proliferation and clonogenicity of colorectal cancer cells and tumorigenicity in NOD/SCID mice (P < 0.05). In addition, we demonstrated that the pro-proliferative effect of MLF1IP on colorectal cancer cells was associated with mediating the G1-to-S phase transition. MLF1IP knockdown enhanced BRCA1 activity concomitantly with p-AKT downregulation and p27 upregulation, while overexpression of MLF1IP has the opposite effect. Moreover, upregulation of BRCA1 can partially abolish the proliferative activity of MLF1IP.

CONCLUSIONS

These findings suggest that MLF1IP may promote proliferation and tumorigenicity of colorectal cancer cells via BRCA1/AKT/p27 signaling axis, and thereby provides potential targets for colorectal cancer therapy.

RFWD2 Knockdown as a Blocker to Reverse the Oncogenic Role of TRIB2 in Lung Adenocarcinoma

RFWD2, an E3 ubiquitin ligase, is overexpressed in numerous human cancers, including leukemia, lung cancer, breast cancer, renal cell carcinoma, and colorectal cancer. The roles of RFWD2 in cancer are related to the targeting of its substrates for ubiquitination and degradation. This study aimed to investigate the role of TRIB2 in relation to the regulation of protein degradation through RFWD2. inBio Discover™ results demonstrated that TRIB2 can perform its functions by interacting with RFWD2 or other factors. TRIB2 can interact with and regulate RFWD2, which further attends the proteasome-mediated degradation of the RFWD2 substrate p-IκB-α. TRIB2 colocalizes with RFWD2-related IκB-α to form a ternary complex and further affects the IκB-α degradation by regulating its phosphorylation. Specific domain analysis showed that TRIB2 may bind to RFWD2 via its C-terminus, whereas it binds to IκB via its pseudokinase domain. TRIB2 acts as an oncogene and promotes cancer cell proliferation and migration, whereas RFWD2 knockdown reversed the role of TRIB2 in promoting cancer cell growth and colony formation in vitro and in vivo. In summary, this study reveals that TRIB2 promotes the progression of cancer by affecting the proteasome-mediated degradation of proteins through the interaction with RFWD2.

Analysis of expression profiles and prognostic value of COP9 signalosome subunits for patients with head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) has been associated with poor prognosis, due to its strong invasive ability and resistance to chemotherapy. Thus, there is an urgent requirement to identify effective biomarkers for the early diagnosis and prognostic evaluation of HNSCC. COP9 signalosome (COPS) regulates numerous cancer-associated biological processes in various malignancies. The aim of the present study was to investigate the association between COPS and HNSCC. The mRNA expression profiles of COPS in HNSCC were analyzed using UALCAN, Oncomine and UCSC Xena databases. The association between overall survival time in patients with HNSCC and the COPS genes was investigated using the Kaplan-Meier plotter database. The CERES score was obtained and evaluated to determine the importance of the COPS genes for survival of the HNSCC cell lines. Functional analysis for Gene Ontology and Gene Set Enrichment Analysis (GSEA) was performed using The Database for Annotation, Visualization and Integrated Discovery and GSEA software, respectively. After knocking down COPS5 and COPS6, cell Counting Kit-8 and wound healing assays were used to detect cell growth and migration of the CAL27 and SCC25 cell lines, respectively. Among the 10 COPS genes examined, most COPS subunits were upregulated in HNSCC samples compared with that in normal tissues, except for COPS9. Increased mRNA expression level of COPS5, COPS6, COPS7B, COPS8 and COPS9 was associated with TNM stage in patients with HNSCC. High mRNA expression level of COPS2, COPS5, COPS6, COPS7A, COPS7B, COPS8 and COPS9 had prognostic significance of patients with HNSCC. Knockdown of COPS5 and COPS6 inhibited cell growth and migration of the CAL27 and SCC25 cell lines. The results from the present study suggested that COPS subunits could be potential biomarkers in patients with HNSCC. COPS5 and COPS6 were important for cell survival and migration of the HNSCC cells.

Stabilization of fatty acid synthesis enzyme acetyl-CoA carboxylase 1 suppresses acute myeloid leukemia development

Cancer cells reprogram lipid metabolism during their malignant progression, but limited information is currently available on the involvement of alterations in fatty acid synthesis in cancer development. We herein demonstrate that acetyl-CoA carboxylase 1 (ACC1), a rate-limiting enzyme for fatty acid synthesis, plays a critical role in regulating the growth and differentiation of leukemia-initiating cells. The Trib1-COP1 complex is an E3 ubiquitin ligase that targets C/EBPA, a transcription factor regulating myeloid differentiation, for degradation, and its overexpression specifically induces acute myeloid leukemia (AML). We identified ACC1 as a target of the Trib1-COP1 complex and found that an ACC1 mutant resistant to degradation because of the lack of a Trib1-binding site attenuated complex-driven leukemogenesis. Stable ACC1 protein expression suppressed the growth-promoting activity and increased ROS levels with the consumption of NADPH in a primary bone marrow culture, and delayed the onset of AML with increases in mature myeloid cells in mouse models. ACC1 promoted the terminal differentiation of Trib1-COP1-expressing cells and eradicated leukemia-initiating cells in the early phase of leukemic progression. These results indicate that ACC1 is a natural inhibitor of AML development. The upregulated expression of the ACC1 protein has potential as an effective strategy for cancer therapy.

The Proteomics and Metabolomics Analysis for Screening the Molecular Targets of Action of β-Eudesmol in Cholangiocarcinoma

OBJECTIVE

β-eudesmol is the active compound isolated from Atractylodes lancea (Thunb) D.C. The actions of this compound against cholangiocarcinoma (CCA) cells include anti-angiogenesis and anti-cell proliferation and growth. For more understanding of the molecular targets of action of β-eudesmol, the CCA cells (CL-6) were exposed to β-eudesmol for 24 and 48 hours.

METHODS

Proteins and metabolites from the intra- and extra-cellular components of the CL-6 cells were extracted and identified by LC-MS/MS.  Protein analysis was performed using the Venn diagram (protein grouping), PANTHER (gene ontology), and STITCH software (protein-protein interaction). Metabolite analysis including their interactions with proteins, was performed using MetaboAnalyst software.

RESULTS

The analysis showed that the actions of β-eudesmol were associated with various biological processes particularly apoptosis and cell cycle. These included blood coagulation, wound healing, DNA repair, PI3K-Akt signaling pathway, immune system process, MAPK cascade, urea cycle, purine metabolism, ammonia recycling, and methionine metabolism.

CONCLUSION

Possible molecular targets of action of β-eudesmol against CL-6 for cell apoptosis induction were TNFRSf6, cytochrome C, BAX3, DHCR24, CD29, and ATP.  On the other hand, possible targets for cell cycle arrest induction were CDKN2B, MLF1, TFDP2, CDK11-p110, and nicotinamide.

Transcriptomic Changes in Endothelial Cells Triggered by Na,K-ATPase Inhibition: A Search for Upstream Na+i/K+i Sensitive Genes

Stimulus-dependent elevation of intracellular Ca²⁺ affects gene expression via well-documented calmodulin-mediated signaling pathways. Recently, we found that the addition of extra- and intracellular Ca²⁺ chelators increased, rather than decreased, the number of genes expressed, and that this is affected by the elevation of [Na⁺]_i/[K⁺]_i-ratio. This assumes the existence of a novel Na⁺_i/K⁺_i-mediated Ca²⁺_i-independent mechanism of excitation-transcription coupling. To identify upstream Na⁺_i/K⁺_i-sensitive genes, we examined the kinetics of transcriptomic changes in human umbilical vein endothelial cells (HUVEC) subjected to Na,K-ATPase inhibition by ouabain or K⁺-free medium. According to our data, microRNAs, transcription factors, and proteins involved in immune response and inflammation might be considered as key components of Na⁺_i/K⁺_i-mediated excitation-transcription coupling. Special attention was focused on the FOS gene and the possible mechanism of transcription regulation via G-quadruplexes, non-canonical secondary structures of nucleic acids, whose stability depends on [Na⁺]_i/[K⁺]_i-ratio. Verification of the [Na⁺]_i/[K⁺]_i-sensitive transcription regulation mechanism should be continued in forthcoming studies.

-Omic Analysis of the Sepia officinalis White Body: New Insights into Multifunctionality and Haematopoiesis Regulation

Cephalopods, like other protostomes, lack an adaptive immune system and only rely on an innate immune system. The main immune cells are haemocytes (Hcts), which are able to respond to pathogens and external attacks. First reports based on morphological observations revealed that the white body (WB) located in the optic sinuses of cuttlefish was the origin of Hcts. Combining transcriptomic and proteomic analyses, we identified several factors known to be involved in haematopoiesis in vertebrate species in cuttlefish WB. Among these factors, members of the JAK-STAT signaling pathway were identified, some of them for the first time in a molluscan transcriptome and proteome. Immune factors, such as members of the Toll/NF-κB signaling pathway, pattern recognition proteins and receptors, and members of the oxidative stress responses, were also identified, and support an immune role of the WB. Both transcriptome and proteome analyses revealed that the WB harbors an intense metabolism concurrent with the haematopoietic function. Finally, a comparative analysis of the WB and Hct proteomes revealed many proteins in common, confirming previous morphological studies on the origin of Hcts in cuttlefish. This molecular work demonstrates that the WB is multifunctional and provides bases for haematopoiesis regulation in cuttlefish.

Curcumin Derivatives Verify the Essentiality of ROS Upregulation in Tumor Suppression

Background: Curcumin has been shown to exert pleiotropic biological effects, including anti-tumorigenic activity. We previously showed that curcumin controls reactive oxygen species (ROS) levels through the ROS metabolic enzymes, to prevent tumor cell growth. In this study, we synthesized 39 novel curcumin derivatives and examined their anti-proliferative and anti-tumorigenic properties. Methods and Results: Thirty-nine derivatives exhibited anti-proliferative activity toward human cancer cell lines, including CML-derived K562 leukemic cells, in a manner sensitive to an antioxidant, N-acetyl-cysteine (NAC). Some compounds exhibited lower GI₅₀ values than curcumin, some efficiently induced cell senescence, and others markedly increased ROS levels, efficiently induced cell death and suppressed tumor formation in a xenograft mouse model, without any detectable side effects. A clustering analysis of the selected compounds and their measurement variables revealed that anti-tumorigenic activity was most well-correlated with an increase in ROS levels. Pulldown assays and a molecular docking analysis showed that curcumin derivatives competed with co-enzymes to bind to the respective ROS metabolic enzymes and inhibited their enzymatic activities. Conclusions: The analysis of novel curcumin derivatives established the importance of ROS upregulation in suppression of tumorigenesis, and these compounds are potentially useful for the development of an anti-cancer drug with few side effects.

Pentagamavunon-1 (PGV-1) inhibits ROS metabolic enzymes and suppresses tumor cell growth by inducing M phase (prometaphase) arrest and cell senescence

We previously showed that curcumin, a phytopolyphenol found in turmeric (Curcuma longa), targets a series of enzymes in the ROS metabolic pathway, induces irreversible growth arrest, and causes apoptosis. In this study, we tested Pentagamavunon-1 (PGV-1), a molecule related to curcumin, for its inhibitory activity on tumor cells in vitro and in vivo. PGV-1 exhibited 60 times lower GI₅₀ compared to that of curcumin in K562 cells, and inhibited the proliferation of cell lines derived from leukemia, breast adenocarcinoma, cervical cancer, uterine cancer, and pancreatic cancer. The inhibition of growth by PGV-1 remained after its removal from the medium, which suggests that PGV-1 irreversibly prevents proliferation. PGV-1 specifically induced prometaphase arrest in the M phase of the cell cycle, and efficiently induced cell senescence and cell death by increasing intracellular ROS levels through inhibition of ROS-metabolic enzymes. In a xenograft mouse model, PGV-1 had marked anti-tumor activity with little side effects by oral administration, whereas curcumin rarely inhibited tumor formation by this administration. Therefore, PGV-1 is a potential therapeutic to induce tumor cell apoptosis with few side effects and low risk of relapse.

Pre-operative progesterone benefits operable breast cancer patients by modulating surgical stress

PURPOSE

We have reported a survival benefit of single injection of hydroxyprogesterone prior to surgery for primary tumour in patients with node-positive operable breast cancer. Hydroxyprogesterone was meant to recapitulate the luteal phase of menstrual cycle in these women. We wanted to understand the molecular basis of action of hydroxyprogesterone on primary breast tumours in a peri-operative setting.

METHODS

We performed whole transcriptome sequencing (RNA-Seq) of primary breast tumour samples collected from patients before and after hydroxyprogesterone exposure and controls. Paired breast cancer samples were obtained from patients who were given hydroxyprogesterone before surgery and a group of patients who were subjected to only surgery.

RESULTS

A test of significance between the two groups revealed 207 significantly altered genes, after correction for multiple hypothesis testing. We found significantly contrasting gene expression patterns in exposed versus unexposed groups; 142 genes were up-regulated post-surgery among exposed patients, and down-regulated post-surgery among unexposed patients. Significantly enriched pathways included genes that respond to progesterone, cellular stress, nonsense-mediated decay of proteins and negative regulation of inflammatory response. These results suggest that cellular stress is modulated by hydroxyprogesterone. Network analysis revealed that UBC, a mediator of stress response, to be a major node to which many of the significantly altered genes connect.

CONCLUSIONS

Our study suggests that pre-operative exposure to progesterone favourably modulates the effect of surgical stress, and this might underlie its beneficial effect when administered prior to surgery.

MLF1 protein is a potential therapy target for lung adenocarcinoma

Myeloid leukemia factor 1 (MLF1) is a protein involved in myeloid cell differentiation which regulates the cell cycle and the expression of numerous genes. The role of MLF1 in hematologic cancers is well established; however, its role in lung adenocarcinoma is unknown. Here, we investigated the role of MLF1 in lung adenocarcinoma using a variety of cell lines along with patient samples to determine whether MLF1 plays a significant role in this devastating disease. Lung cancer cell lines (A549, H1975, HCC827, and NCI-H460) and primary lung tissue were used to assess the relative levels of MLF1 in lung adenocarcinoma. The lung adenocarcinoma cell line A549 was infected with a lentivirus to knockdown MLF1, and successful knockdown was confirmed by a real-time polymerase chain reaction (qPCR). Cell proliferation was assessed through fluorescence imaging and MTT assays. Cell cycle analysis was performed utilizing flow cytometry and formation of cell colonies evaluated microscopically. Proliferation of A549 cells was significantly inhibited in cells where MLF1 was silenced compared to controls. Cell cycle analysis indicated that cell cycle phases were not significantly changed upon the silencing of MLF1 in lung adenocarcinoma cells. A significant increase in apoptosis was observed in MLF1-knockdown cells, while a significant decrease in the number of cell colonies formed was observed in MLF1-knockdown cells compared to controls. In most, but not all, human lung adenocarcinoma tissue samples, MLF1 was upregulated. The results show that MLF1 promotes the proliferation and colony forming abilities of lung adenocarcinoma cells and significantly decreases apoptosis while having no impact on the cell cycle. Further studies with larger sample sizes are needed 1) to conclude whether human lung adenocarcinoma upregulates MLF1, 2) to reveal the mechanism of action for MLF1 in lung carcinogenesis and 3) to investigate MLF1 gene therapy for the treatment of lung adenocarcinoma.

Genetic susceptibility to neuroblastoma: current knowledge and future directions

Neuroblastoma, a malignancy of the developing peripheral nervous system that affects infants and young children, is a complex genetic disease. Over the past two decades, significant progress has been made toward understanding the genetic determinants that predispose to this often lethal childhood cancer. Approximately 1-2% of neuroblastomas are inherited in an autosomal dominant fashion and a combination of co-morbidity and linkage studies has led to the identification of germline mutations in PHOX2B and ALK as the major genetic contributors to this familial neuroblastoma subset. The genetic basis of "sporadic" neuroblastoma is being studied through a large genome-wide association study (GWAS). These efforts have led to the discovery of many common susceptibility alleles, each with modest effect size, associated with the development and progression of sporadic neuroblastoma. More recently, next-generation sequencing efforts have expanded the list of potential neuroblastoma-predisposing mutations to include rare germline variants with a predicted larger effect size. The evolving characterization of neuroblastoma's genetic basis has led to a deeper understanding of the molecular events driving tumorigenesis, more precise risk stratification and prognostics and novel therapeutic strategies. This review details the contemporary understanding of neuroblastoma's genetic predisposition, including recent advances and discusses ongoing efforts to address gaps in our knowledge regarding this malignancy's complex genetic underpinnings.

A phase 2 study of vorinostat in locally advanced, recurrent, or metastatic adenoid cystic carcinoma

Purpose

Vorinostat is a histone deacetylase inhibitor (HDACi). Based on a confirmed partial response (PR) in an adenoid cystic carcinoma (ACC) patient treated with vorinostat in a prior phase 1 trial, we initiated this phase 2 trial. Methods: Vorinostat was administered orally 400 mg daily, 28 day cycles. The primary objective was to evaluate response rate (RR). Exploratory studies included whole exome sequencing (WES) of selected patients.

Results

Thirty patients were enrolled. Median age of patients was 53 years (range 21–73). Median number of cycles was 5 (range 1-66). Lymphopenia (n = 5), hypertension (n = 3), oral pain (n = 2), thromboembolic events (n = 2) and fatigue (n = 2) were the only grade 3 adverse events (AEs) that occurred in more than 1 patient. Eleven patients were dose reduced secondary to drug-related AEs. Two patients had a partial response (PR), with response durations of 53 and 7.2 months. One patient had a minor response with a decrease in ascites (for 19 cycles). Stable disease was the best response in 27 patients. Targeted and WES of 8 patients in this trial identified mutations in chromatin remodeling genes highlighting the role of the epigenome in ACC. Conclusion: Vorinostat demonstrated efficacy in patients with ACC supporting the inclusion of HDACi in future studies to treat ACC.

The COP9 Signalosome regulates seed germination by facilitating protein degradation of RGL2 and ABI5

The control of seed germination and seed dormancy are critical for the successful propagation of plant species, and are important agricultural traits. Seed germination is tightly controlled by the balance of gibberellin (GA) and abscisic acid (ABA), and is influenced by environmental factors. The COP9 Signalosome (CSN) is a conserved multi-subunit protein complex that is best known as a regulator of the Cullin-RING family of ubiquitin E3 ligases (CRLs). Multiple viable mutants of the CSN showed poor germination, except for csn5b-1. Detailed analyses showed that csn1-10 has a stronger seed dormancy, while csn5a-1 mutants exhibit retarded seed germination in addition to hyperdormancy. Both csn5a-1 and csn1-10 plants show defects in the timely removal of the germination inhibitors: RGL2, a repressor of GA signaling, and ABI5, an effector of ABA responses. We provide genetic evidence to demonstrate that the germination phenotype of csn1-10 is caused by over-accumulation of RGL2, a substrate of the SCF (CRL1) ubiquitin E3 ligase, while the csn5a-1 phenotype is caused by over-accumulation of RGL2 as well as ABI5. The genetic data are consistent with the hypothesis that CSN5A regulates ABI5 by a mechanism that may not involve CSN1. Transcriptome analyses suggest that CSN1 has a more prominent role than CSN5A during seed maturation, but CSN5A plays a more important role than CSN1 during seed germination, further supporting the functional distinction of these two CSN genes. Our study delineates the molecular targets of the CSN complex in seed germination, and reveals that CSN5 has additional functions in regulating ABI5, thus the ABA signaling pathway.

The control of seed germination and seed dormancy are critical for successful propagation of plant species, and manipulation of these processes is important for agriculture. The COP9 Signalosome (CSN) is a multi-subunit protein complex that regulates proteasome-mediated protein degradation in part as a regulator of SCF ubiquitin E3 ligases. The CSN is important for timely germination of seeds, but its molecular targets in this process is unclear. In this study, we demonstrate that the CSN regulates protein stabilities of two different targets from two antagonistic hormonal pathways, RGL2 of the GA pathway and ABI5 of the ABA pathway. Our genetic and transcriptome analyses showed that, although csn1-10 and csn5a-1 exhibit similar defects in timely germination, the mechanisms of how the mutations affect seed germination differ. Since RGL2 is known to be targeted by SCF during germination, the defect in the timely degradation of RGL2 in csn1-10 and csn5a-1 is consistent with the role of CSN as a regulator of the SCF. In addition, we show that CSN5A, but not CSN1, has an additional function in regulating ABI5, a downstream inhibitor of germination.

Curcumin targets multiple enzymes involved in the ROS metabolic pathway to suppress tumor cell growth

Curcumin has been reported to exhibit anti-tumorigenic activity; however, since its precise actions remain unclear, its effects are considered to be deceptive. In the present study, we confirmed the anti-tumorigenic effects of curcumin on CML-derived leukemic cells in a xenograft model and in vitro culture system. In vitro pull-down and mass analyses revealed a series of enzymes (carbonyl reductase, glutathione-S-transferase, glyoxalase, etc.) that function in a reactive oxygen species (ROS) metabolic pathway as curcumin-binding targets, the expression of which was up-regulated in human leukemia. Curcumin increased ROS levels over the threshold in leukemic cells, and the antioxidant, glutathione (GSH) and overexpression of curcumin-binding enzymes partially mitigated the up-regulation of ROS and growth inhibition caused by curcumin. These results show that curcumin specifically inhibits tumor growth by increasing ROS levels over the threshold through the miscellaneous inhibition of ROS metabolic enzymes. Curcumin has potential in therapy to regulate ROS levels in tumor cells, thereby controlling tumor growth.

Corrected and Republished from: The COP9 Signalosome Interacts with and Regulates Interferon Regulatory Factor 5 Protein Stability

The transcription factor interferon regulatory factor 5 (IRF5) exerts crucial functions in the regulation of host immunity against extracellular pathogens, DNA damage-induced apoptosis, death receptor signaling, and macrophage polarization. Tight regulation of IRF5 is thus warranted for an efficient response to extracellular stressors and for limiting autoimmune and inflammatory responses. Here we report that the COP9 signalosome (CSN), a general modulator of diverse cellular and developmental processes, associates constitutively with IRF5 and promotes its protein stability. The constitutive CSN/IRF5 interaction was identified using proteomics and confirmed by endogenous immunoprecipitations. The CSN/IRF5 interaction occurred on the carboxyl and amino termini of IRF5; a single internal deletion (Δ455-466) was found to significantly reduce IRF5 protein stability. CSN3 was identified as a direct interacting partner of IRF5, and knockdown of this subunit with small interfering RNAs (siRNAs) resulted in enhanced degradation. Degradation was further augmented by knockdown of CSN1 and CSN3 together. The ubiquitin E1 inhibitor UBEI-41 or the proteasome inhibitor MG132 prevented IRF5 degradation, supporting that its stability is regulated by the ubiquitin-proteasome system. Importantly, activation of IRF5 by the death receptor ligand tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) resulted in enhanced degradation via loss of the CSN/IRF5 interaction. This study defines the CSN as a new interacting partner of IRF5 that controls its stability.

Myeloid leukemia factor functions in anti-WSSV immune reaction of kuruma shrimp, Marsupenaeus japonicus

Myeloid leukemia factor (MLF) plays an important role in development, cell cycle, myeloid differentiation, and regulates the RUNX transcription factors. However, the function of MLF in immunity is still unclear. In this study, an MLF was identified and characterized in kuruma shrimp Marsupenaeus japonicus, and named as MjMLF. The full-length cDNA of MjMLF contained 1111 nucleotides, which had an opening reading frame of 816 bp encoding a protein of 272 amino acids with an MLF1-interacting protein domain. MjMLF could be ubiquitously detected in different tissues of shrimp at the transcriptional level. The expression pattern analysis showed that MjMLF could be upregulated in shrimp hemocytes and hepatopancreas after white spot syndrome virus challenge. The RNA interference and protein injection assay showed that MjMLF could inhibit WSSV replication in vivo. Flow cytometry assay showed that MjMLF could induce hemocytes apoptosis which functioned in the shrimp antiviral reaction. All the results suggested that MjMLF played an important role in the antiviral immune reaction of kuruma shrimp. The research indicated that MjMLF might function as a novel regulator to inhibit WSSV replication in shrimp.

Myeloid leukemia factor 1 stabilizes tumor suppressor C/EBPα to prevent Trib1-driven acute myeloid leukemia

C/EBPα is a key transcription factor regulating myeloid differentiation and leukemogenesis. The Trib1-COP1 complex is an E3 ubiquitin ligase that targets C/EBPα for degradation, and its overexpression specifically induces acute myeloid leukemia (AML). Here we show that myeloid leukemia factor 1 (MLF1) stabilizes C/EBPα protein levels by inhibiting the ligase activity of the Trib1-COP1 complex. MLF1 directly interacts with COP1 in the nucleus and interferes with the formation of the Trib1-COP1 complex, thereby blocking its ability to polyubiquitinate C/EBPα for degradation. MLF1 overexpression suppressed the Trib1-induced growth advantage in a murine bone marrow (BM) culture and Trib1-induced AML development in BM-transplanted mouse models. MLF1 was expressed in hematopoietic stem cells and myeloid progenitors (common myeloid progenitors and granulocyte-macrophage progenitors) in normal hematopoiesis, which is consistent with the distribution of C/EBPα. An MLF1 deficiency conferred a more immature phenotype on Trib1-induced AML development. A higher expression ratio of Trib1 to MLF1 was a key determinant for AML development in mouse models, which was also confirmed in human patient samples with acute leukemia. These results indicate that MLF1 is a positive regulator that is critical for C/EBPα stability in the early phases of hematopoiesis and leukemogenesis.

Control of RUNX-induced repression of Notch signaling by MLF and its partner DnaJ-1 during Drosophila hematopoiesis

A tight regulation of transcription factor activity is critical for proper development. For instance, modifications of RUNX transcription factors dosage are associated with several diseases, including hematopoietic malignancies. In Drosophila, Myeloid Leukemia Factor (MLF) has been shown to control blood cell development by stabilizing the RUNX transcription factor Lozenge (Lz). However, the mechanism of action of this conserved family of proteins involved in leukemia remains largely unknown. Here we further characterized MLF's mode of action in Drosophila blood cells using proteomic, transcriptomic and genetic approaches. Our results show that MLF and the Hsp40 co-chaperone family member DnaJ-1 interact through conserved domains and we demonstrate that both proteins bind and stabilize Lz in cell culture, suggesting that MLF and DnaJ-1 form a chaperone complex that directly regulates Lz activity. Importantly, dnaj-1 loss causes an increase in Lz+ blood cell number and size similarly as in mlf mutant larvae. Moreover we find that dnaj-1 genetically interacts with mlf to control Lz level and Lz+ blood cell development in vivo. In addition, we show that mlf and dnaj-1 loss alters Lz+ cell differentiation and that the increase in Lz+ blood cell number and size observed in these mutants is caused by an overactivation of the Notch signaling pathway. Finally, using different conditions to manipulate Lz activity, we show that high levels of Lz are required to repress Notch transcription and signaling. All together, our data indicate that the MLF/DnaJ-1-dependent increase in Lz level allows the repression of Notch expression and signaling to prevent aberrant blood cell development. Thus our findings establish a functional link between MLF and the co-chaperone DnaJ-1 to control RUNX transcription factor activity and Notch signaling during blood cell development in vivo.

Knockdown of subunit 3 of the COP9 signalosome inhibits C2C12 myoblast differentiation via NF-KappaB signaling pathway

Background

The COP9 signalosome (CSN) is a conserved protein complex composed of 8 subunits designated CSN1-CSN8. CSN3 represents the third subunit of the CSN and maintains the integrity of the complex. CSN3 binds to the striated muscle-specific β1D integrin tail, and its subcellular localization is altered in differentiated skeletal muscle cells. However, the role of CSN3 in skeletal muscle differentiation is unknown. The main goal of this study was to identify whether CSN3 participates in myoblast differentiation and the signalling mechanisms involved using C2C12 cells as a skeletal muscle cell model.

Methods

Small-hairpin (shRNA) was used to knockdown CSN3 in C2C12 cells. Differentiation was evaluated by immunostaining and confocal microscopy. Markers of differentiation, NF-κB signaling and CSN subunits expression, were assessed by immunoblotting and/or immunostaining. Cell proliferation was analysed by cell counting, flow cytometry and a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Data were analyzed by one or two-way analysis of variance (ANOVA) followed by post-hoc testing.

Results

Transduction of C2C12 cells with two distinct CSN3 shRNAs led to the production of two cells lines expressing 7% of CSN3 protein (shCSN3-Low) and 43% of CSN3 protein (CSN3-Med) compared to controls. Knockdown of CSN3 was accompanied by destabilization of several CSN subunits and increased nuclear NF-κB localization. shCSN3-Med cells expressed less myogenin and formed shorter and thinner myotubes. In contrast, the shCSN3-Low cells expressed higher levels of myogenin prior and during the differentiation and remained mononucleated throughout the differentiation period. Both CSN3 knockdown cell lines failed to express sarcomeric myosin heavy chain (MHC) protein during differentiation. The fusion index was significantly higher in control cells than in shCSN3-Med cells, whereas shCSN3-Low cells showed no cell fusion. Interestingly, CSN3 knockdown cells exhibited a significantly slower growth rate relative to the control cells. Cell cycle analysis revealed that CSN3 knockdowns delayed in S phase and had increased levels of nuclear p21/Cip1 and p27/Kip1.

Conclusions

This study clarifies the first step toward unrevealing the CSN3/CSN-mediated pathways that controls C2C12 differentiation and proliferation. Further in vivo characterization of CSN/CSN3 may lead to the discovery of novel therapeutic target of skeletal muscle diseases such as muscular dystrophies.

MLF1 is a proapoptotic antagonist of HOP complex-mediated survival

In the HAX1/HtrA2-OMI/PARL (HOP) mitochondrial protein complex, anti-apoptotic signals are generated by cleavage and activation of the serine protease HtrA2/OMI by the rhomboid protease PARL upon recruitment of both proteases to inner mitochondrial membrane protein HAX1 (HS1-associated protein X-1). Here we report the negative regulation of the HOP complex by human leukemia-associated myeloid leukemia factor 1 (MLF1). We demonstrate that MLF1 physically and functionally associates with HAX1 and HtrA2. Increased interaction of MLF1 with HAX1 and HtrA2 displaces HtrA2 from the HOP complex and inhibits HtrA2 cleavage and activation, resulting in the apoptotic cell death. Conversely, over-expressed HAX1 neutralizes MLF1's effect and inhibits MLF1-induced apoptosis. Importantly, Mlf1 deletion reverses B- and T-cell lymphopenia and significantly ameliorates the progressive striatal and cerebellar neurodegeneration observed in Hax1^-/- mice, with a doubling of the lifespan of Mlf1^-/-/Hax1^-/- animals compared to Hax1^-/- animals. Collectively, these data indicate that MLF1 serves as a proapoptotic antagonist that interacts with the HOP mitochondrial complex to modulate cell survival.

Myeloid leukemia factor-1 is a novel modulator of neonatal rat cardiomyocyte proliferation

The present study focuses on the identification of the gene expression profile of neonatal rat cardiomyocytes (NRVCMs) after dynamic mechanical stretch through microarrays of RNA isolated from cells stretched for 2, 6 or 24h. In this analysis, myeloid leukemia factor-1 (MLF1) was found to be significantly downregulated during the course of stretch. We found that MLF1 is highly expressed in the heart, however, its cardiac function is unknown yet. In line with microarray data, MLF1 was profoundly downregulated in in vivo mouse models of cardiomyopathy, and also significantly reduced in the hearts of human patients with dilated cardiomyopathy. Our data indicates that the overexpression of MLF1 in NRVCMs inhibited cell proliferation while augmenting apoptosis. Conversely, knockdown of MLF1 protected NRVCMs from apoptosis and promoted cell proliferation. Moreover, we found that knockdown of MLF1 protected NRVCMs from hypoxia-induced cell death. The observed accelerated apoptosis is attributed to the activation of caspase-3/-7/PARP-dependent apoptotic signaling and upregulation of p53. Most interestingly, MLF1 knockdown significantly upregulated the expression of D cyclins suggesting its possible role in cyclin-dependent cell proliferation. Taken together, we, for the first time, identified an important role for MLF1 in NRVCM proliferation.

Roles of Multifunctional COP9 Signalosome Complex in Cell Fate and Implications for Drug Discovery

The eight subunits containing COP9 signalosome (CSN) complex, is highly conserved among eukaryotes. CSN, identified as a negative regulator of photomorphogenesis, has also been demonstrated to be important in proteolysis, cellular signal transduction and cell cycle regulation in various eukaryotic organisms. This review mainly summarizes the roles of CSN in cell cycle regulation, signal transduction and apoptosis, and its potential as diagnostic biomarkers, drug targets for cancer and infectious diseases. J. Cell. Physiol. 232: 1246-1253, 2017. © 2016 Wiley Periodicals, Inc.

Constitutive photomorphogenesis protein 1 (COP1) and COP9 signalosome, evolutionarily conserved photomorphogenic proteins as possible targets of melatonin

The ubiquitin proteasome system has been proposed as a possible mechanism involved in the multiple actions of melatonin. COP1 (constitutive photomorphogenesis protein 1), a RING finger-type ubiquitin E3 ligase formerly identified in Arabidopsis, is a central switch for the transition from plant growth underground in darkness (etiolation) to growth under light exposure (photomorphogenesis). In darkness, COP1 binds to photomorphogenic transcription factors driving its degradation via the 26S proteasome; blue light, detected by cryptochromes, and red and far-red light detected by phytochromes, negatively regulate COP1. Homologues of plant COP1 containing all the structural features present in Arabidopsis as well as E3 ubiquitin ligase activity have been identified in mice and humans. Substrates for mammalian (m) COP1 include p53, AP-1 and c-Jun, p27(Kip1) , ETV1, MVP, 14-3-3σ, C/EBPα, MTA1, PEA3, ACC, TORC2 and FOXO1. This mCOP1 target suggests functions related to tumorigenesis, gluconeogenesis, and lipid metabolism. The role of mCOP1 in tumorigenesis (either as a tumor promoter or tumor suppressor), as well as in glucose metabolism (inhibition of gluconeogenesis) and lipid metabolism (inhibition of fatty acid synthesis), has been previously demonstrated. COP1, along with numerous other ubiquitin ligases, is regulated by the COP9 signalosome; this protein complex is associated with the oxidative stress sensor Keap1 and the deubiquitinase USP15. The objective of this review was to provide new information on the possible role of COP1 and COP9 as melatonin targets. The hypothesis is based on common functional aspects of melatonin and COP1 and COP9, including their dependence on light, regulation of the metabolism, and their control of tumor growth.

Genetic factors conferring metastasis in osteosarcoma

Osteosarcoma (OS) is a deadly bone malignancy affecting mostly children and adolescents. OS has outstandingly complex genetic alterations likely due to p53-independent genomic instability. Based on analysis of recent published research we claim existence of various genetic mechanisms of osteosarcomagenesis conferring great variability to different OS properties including metastatic potential. We also propose a model explaining how diverse genetic mechanisms occur and providing a framework for future research. P53-independent preexisting genomic instability, which precedes and frequently causes TP53 genetic alterations, is central in our model. In addition, our analyses reveal a possible cooperation between aberrantly activated HIF-1α and AP-1 genetic pathways in OS metastasis. We also review the involvement of noncoding RNA genes in OS metastasis.

Distinctive genotypes in infants with T-cell acute lymphoblastic leukaemia

Infant T‐cell acute lymphoblastic leukaemia (iT‐ALL) is a very rare and poorly defined entity with a poor prognosis. We assembled a unique series of 13 infants with T‐ALL, which allowed us to identify genotypic abnormalities and to investigate prenatal origins. Matched samples (diagnosis/remission) were analysed by single nucleotide polymorphism‐array to identify genomic losses and gains. In three cases, we identified a recurrent somatic deletion on chromosome 3. These losses result in the complete deletion of MLF1 and have not previously been described in T‐ALL. We observed two cases with an 11p13 deletion (LMO2‐related), one of which also harboured a deletion of RB1. Another case presented a large 11q14·1‐11q23·2 deletion that included ATM and only five patients (38%) showed deletions of CDKN2A/B. Four cases showed NOTCH1 mutations; in one case FBXW7 was the sole mutation and three cases showed alterations in PTEN. KMT2A rearrangements (KMT2A‐r) were detected in three out of 13 cases. For three patients, mutations and copy number alterations (including deletion of PTEN) could be backtracked to birth using neonatal blood spot DNA, demonstrating an in utero origin. Overall, our data indicates that iT‐ALL has a diverse but distinctive profile of genotypic abnormalities when compared to T‐ALL in older children and adults.

Moonlighting and pleiotropy within two regulators of the degradation machinery: the proteasome lid and the CSN

The distinction between pleiotrotic and moonlighting roles of proteins is challenging; however, this distinction may be clearer when it comes to multiprotein complexes. Two examples are the proteasome lid and the COP9 signalosome (CSN), which are twin enzymes with 1:1 paralogy between subunits. In each complex, one out of eight subunits harbours a JAMM/MPN⁺ metalloprotease motif. This motif contributes the canonical activity of each complex: hydrolysis of covalently attached ubiquitin by Rpn11 in the proteasome lid and hydrolysis of ubiquitin-related 1 (Rub1/Nedd8) from Cullins by Csn5 in the CSN. In both complexes, executing this activity suggests pleiotropic effects and requires an assembled full complex. However, beyond canonical functions, both Rpn11 and Csn5 are involved in additional unique, complex-independent functions, herein referred to as moonlighting activities.

Exome analysis reveals differentially mutated gene signatures of stage, grade and subtype in breast cancers

Breast cancers exhibit highly heterogeneous molecular profiles. Although gene expression profiles have been used to predict the risks and prognostic outcomes of breast cancers, the high variability of gene expression limits its clinical application. In contrast, genetic mutation profiles would be more advantageous than gene expression profiles because genetic mutations can be stably detected and the mutational heterogeneity widely exists in breast cancer genomes. We analyzed 98 breast cancer whole exome samples that were sorted into three subtypes, two grades and two stages. The sum deleterious effect of all mutations in each gene was scored to identify differentially mutated genes (DMGs) for this case-control study. DMGs were corroborated using extensive published knowledge. Functional consequences of deleterious SNVs on protein structure and function were also investigated. Genes such as ERBB2, ESP8, PPP2R4, KIAA0922, SP4, CENPJ, PRCP and SELP that have been experimentally or clinically verified to be tightly associated with breast cancer prognosis are among the DMGs identified in this study. We also identified some genes such as ARL6IP5, RAET1E, and ANO7 that could be crucial for breast cancer development and prognosis. Further, SNVs such as rs1058808, rs2480452, rs61751507, rs79167802, rs11540666, and rs2229437 that potentially influence protein functions are observed at significantly different frequencies in different comparison groups. Protein structure modeling revealed that many non-synonymous SNVs have a deleterious effect on protein stability, structure and function. Mutational profiling at gene- and SNV-level revealed differential patterns within each breast cancer comparison group, and the gene signatures correlate with expected prognostic characteristics of breast cancer classes. Some of the genes and SNVs identified in this study show high promise and are worthy of further investigation by experimental studies.

The COP9 signalosome and vascular function: intriguing possibilities?

Disorders of vascular function contribute importantly to cardiovascular disease which represents a substantial cause of morbidity and mortality worldwide. An emerging paradigm in the study of cardiovascular diseases is that protein ubiquitination and turnover represent key pathological mechanisms. Our understanding of these processes in the vasculature is growing but remains incomplete. Since protein ubiquitination and turnover can represent a terminal event in the life of a given protein, entry into these pathways must be highly regulated. However, at present understanding of these regulatory mechanisms, particularly in the vasculature, is fragmentary. The COP9 (constitutive photomorphogenic mutant 9) signalosome (CSN) is a heteromeric protein complex implicated in the control of protein degradation. The CSN participates critically in the control of Cullin Ring Ligases (CRLs), at least in part via the detachment of a small protein, Nedd8 (deneddylation). CRLs are one of the largest groups of ubiquitin ligases, which represent the most selective control point for protein ubiquitination. Thus, the CSN by virtue of its ability to control the CRLs ubiquitin ligase activity is ideally positioned to effect selective modulation of protein turnover. This review surveys currently available data regarding the potential role of the CSN in control of vascular function. Data potentially linking the CSN to control of regulatory proteins involved in vascular smooth muscle proliferation and to vascular smooth muscle contraction are presented with the intent of providing potentially intriguing possibilities for future investigation.

Sperm and spermatids contain different proteins and bind distinct egg factors

Spermatozoa are more efficient at supporting normal embryonic development than spermatids, their immature, immediate precursors. This suggests that the sperm acquires the ability to support embryonic development during spermiogenesis (spermatid to sperm maturation). Here, using Xenopus laevis as a model organism, we performed 2-D Fluorescence Difference Gel Electrophoresis (2D-DIGE) and mass spectrometry analysis of differentially expressed proteins between sperm and spermatids in order to identify factors that could be responsible for the efficiency of the sperm to support embryonic development. Furthermore, benefiting from the availability of egg extracts in Xenopus, we also tested whether the chromatin of sperm could attract different egg factors compared to the chromatin of spermatids. Our analysis identified: (1) several proteins which were present exclusively in sperm; but not in spermatid nuclei and (2) numerous egg proteins binding to the sperm (but not to the spermatid chromatin) after incubation in egg extracts. Amongst these factors we identified many chromatin-associated proteins and transcriptional repressors. Presence of transcriptional repressors binding specifically to sperm chromatin could suggest its preparation for the early embryonic cell cycles, during which no transcription is observed and suggests that sperm chromatin has a unique protein composition, which facilitates the recruitment of egg chromatin remodelling factors. It is therefore likely that the acquisition of these sperm-specific factors during spermiogenesis makes the sperm chromatin suitable to interact with the maternal factors and, as a consequence, to support efficient embryonic development.

Drosophila myeloid leukemia factor acts with DREF to activate the JNK signaling pathway

Drosophila myelodysplasia/myeloid leukemia factor (dMLF), a homolog of human MLF1, oncogene was first identified by yeast two-hybrid screen using the DNA replication-related element-binding factor (DREF) as bait. DREF is a transcription factor that regulates proliferation-related genes in Drosophila. It is known that overexpression of dMLF in the wing imaginal discs through the engrailed-GAL4 driver causes an atrophied wing phenotype associated with the induction of apoptosis. However, the precise mechanisms involved have yet to be clarified. Here, we found the atrophied phenotype to be suppressed by loss-of-function mutation of Drosophila Jun N-terminal kinase (JNK), basket (bsk). Overexpression of dMLF induced ectopic JNK activation in the wing disc monitored with the puckered-lacZ reporter line, resulting in induction of apoptosis. The DREF-binding consensus DRE sequence could be shown to exist in the bsk promoter. Chromatin immunoprecipitation assays in S2 cells with anti-dMLF IgG and quantitative real-time PCR revealed that dMLF binds specifically to the bsk promoter region containing the DRE sequence. Furthermore, using a transient luciferase expression assay, we provide evidence that knockdown of dMLF reduced bsk gene promoter activity in S2 cells. Finally, we show that dMLF interacts with DREF in vivo. Altogether, these data indicate that dMLF acts with DREF to stimulate the bsk promoter and consequently activates the JNK pathway to promote apoptosis.

Emerging roles of Jab1/CSN5 in DNA damage response, DNA repair, and cancer

Jab1/CSN5 is a multifunctional protein that plays an important role in integrin signaling, cell proliferation, apoptosis, and the regulation of genomic instability and DNA repair. Dysregulation of Jab1/CSN5 activity has been shown to contribute to oncogenesis by functionally inactivating several key negative regulatory proteins and tumor suppressors. In this review, we discuss our current understanding of the relationship between Jab1/CSN5 and DNA damage and summarize recent findings regarding opportunities for and challenges to therapeutic intervention.

Nuclear receptor-binding protein 1: a novel tumour suppressor and pseudokinase

Pseudokinases are a class of kinases which are structurally designated as lacking kinase activity. Despite the lack of kinase domain sequence conservation, there is increasing evidence that a number of pseudokinases retain kinase activity and/or have critical cellular functions, casting aside previous notions that pseudokinases simply exist as redundant kinases. Moreover, a number of recent studies have implicated pseudokinases as critical components in cancer formation and progression. The present review discusses the interactions and potential functions that nuclear receptor-binding protein 1, a pseudokinase recently described to have a tumour-suppressive role in cancer, may play in cellular homoeostasis and protein regulation. The recent findings highlighted in the present review emphasize the requirement to fully determine the function of pseudokinases in vitro and in vivo, the understanding of which may ultimately uncover new directions for drug discovery.

COP1 targets C/EBPα for degradation and induces acute myeloid leukemia via Trib1

The ubiquitin ligase constitutively photomorphogenic 1 (COP1) is involved in many biological responses in mammalian cells, but its role in tumorigenesis remains unclear. Here we show that COP1 is a ubiquitin ligase for the tumor suppressor CCAAT/enhancer-binding protein (C/EBPα) and promotes its degradation in vivo, thereby blocking myeloid differentiation of hematopoietic cells for tumorigenesis. In this process, mammalian homolog of Tribbles, Trib1, which contains a COP1-binding motif, is essential for down-regulation of C/EBPα expression. Murine bone marrow transplantation experiments showed that coexpression of COP1 accelerates development of acute myeloid leukemia induced by Trib1, which pathologically resembles that of p42C/EBPα-deficient mice. Interestingly, coexpression of ligase activity-deficient COP1 mutant abrogated Trib1-induced leukemogenesis. These results indicate that COP1 and Trib1 act as an oncoprotein complex functioning upstream of C/EBPα, and its ligase activity is crucial for leukemogenesis.

COP9 signalosome subunit Csn8 is involved in maintaining proper duration of the G1 phase

The COP9 signalosome (CSN) is a conserved protein complex known to be involved in developmental processes of eukaryotic organisms. Genetic disruption of a CSN gene causes arrest during early embryonic development in mice. The Csn8 subunit is the smallest and the least conserved subunit, being absent from the CSN complex of several fungal species. Nevertheless, Csn8 is an integral component of the CSN complex in higher eukaryotes, where it is essential for life. By characterizing the mouse embryonic fibroblasts (MEFs) that express Csn8 at a low level, we found that Csn8 plays an important role in maintaining the proper duration of the G1 phase of the cell cycle. A decreased level of Csn8, either in Csn8 hypomorphic MEFs or following siRNA-mediated knockdown in HeLa cells, accelerated cell growth rate. Csn8 hypomorphic MEFs exhibited a shortened G1 duration and affected expression of G1 regulators. In contrast to Csn8, down-regulation of Csn5 impaired cell proliferation. Csn5 proteins were found both as a component of the CSN complex and outside of CSN (Csn5-f), and the amount of Csn5-f relative to CSN was increased in the Csn8 hypomorphic cells. We conclude that CSN harbors both positive and negative regulators of the cell cycle and therefore is poised to influence the fate of a cell at the crossroad of cell division, differentiation, and senescence.

Myeloma overexpressed 2 (Myeov2) regulates L11 subnuclear localization through Nedd8 modification

Nucleolus is a dynamic structure that controls biogenesis of ribosomal RNA and senses cellular stresses. Nucleolus contains a number of proteins including ribosomal proteins that conduct cellular stresses to downstream signaling such as p53 pathway. Recently, it has been reported that modification by a ubiquitin-like molecule, Nedd8, regulates subnuclear localization of ribosomal protein L11. Most of L11 is normally localized and neddylated in nucleolus. However, cellular stress triggers deneddylation and redistribution of L11, and subsequent activation of p53. Although Nedd8 modification is thought to be important for L11 localization, the mechanism of how neddylation of L11 is regulated remains largely unknown. Here, we show that Myeloma overexpressed 2 (Myeov2) controls L11 localization through down-regulation of Nedd8 modification. Expression of Myeov2 reduced neddylation of proteins including L11. We also found that Myeov2 associates with L11 and withholds L11 in nucleoplasm. Although Myeov2 interacted with a Nedd8 deconjugation enzyme COP9 signalosome, L11 deneddylation was mediated by another deneddylase Nedp1, independently of Myeov2. Finally, p53 transcriptional activity is upregulated by Myeov2 expression. These data demonstrate that Myeov2 hampers L11 neddylation through their interactions and confines L11 to nucleoplasm to modulate nucleolar integrity. Our findings provide a novel link between oncogenic stress and p53 pathway and may shed light on the protective mechanism against cancer.

CSN5 specifically interacts with CDK2 and controls senescence in a cytoplasmic cyclin E-mediated manner

The fifth component (CSN5) of the mammalian COP9 signalosome complex plays an essential role in cell proliferation and senescence, but its molecular mediator remains to be determined. Here, we searched for interactors among various cell cycle regulators, and found that CSN5, but not the CSN holo-complex, bound to CDK2 in vivo and in vitro. Depletion of CSN5 enhanced phosphorylation of CDK2 by Akt, resulting in cytoplasmic accumulation of CDK2 together with cyclin E in a leptomycin B-resistant manner, and impaired phosphorylation of the retinoblastoma protein. Additional knockdown of CDK2, which reduced the expression of cyclin E to the normal level, did not restore cell proliferation, but significantly suppressed senescence in CSN5-depleted cells. Enforced expression of cytoplasmic cyclin E induced premature senescence in immortalized cell lines. These results show that CSN5 functions through CDK2 to control premature senescence in a novel way, depending on cyclin E in the cytoplasm.

The COP1 E3-ligase interacts with FIP200, a key regulator of mammalian autophagy

Background

The ubiquitin ligase COP1, COnstitutively Photomorphogenic 1, functions in many biological responses in mammalian cells, but its downstream pathway remains unclear.

Results

Here, we identified FIP200, a key regulator of mammalian autophagy, as a novel COP1-interacting protein by yeast two-hybrid screening. The interaction was confirmed by a GST-pulldown assay. Split-GFP analysis revealed that interaction between COP1 and FIP200 predominantly occurred in the cytoplasm and was enhanced in cells treated with UV irradiation. Different forms of FIP200 protein were expressed in cultured mammalian cells, and ectopic expression of COP1 reduced one of such forms.

Conclusions

These data suggest that COP1 modulates FIP200-associated activities, which may contribute to a variety of cellular functions that COP1 is involved in.