Differential expression of the eukaryotic release factor 3 (eRF3/GSPT1) according to gastric cancer histological types

Identification of novel GSPT1 degraders by virtual screening and bioassay

GSPT1 plays crucial physiological functions, such as terminating protein translation, overexpressed in various tumors. It is a promising anti-tumor target, but is also considered as an "undruggable" protein. Recent studies have found that a class of small molecules can degrade GSPT1 through the "molecular glue" mechanism with strong antitumor activity, which is expected to become a new therapy for hematological malignancies. Currently available GSPT1 degraders are mostly derived from the scaffold of immunomodulatory imide drug (IMiD), thus more active compounds with novel structure remain to be found. In this work, using computer-assisted multi-round virtual screening and bioassay, we identified a non-IMiD acylhydrazone compound, AN5782, which can reduce the protein level of GPST1 and obviously inhibit the proliferation of tumor cells. Some analogs were obtained by a substructure search of AN5782. The structure-activity relationship analysis revealed possible interactions between these compounds and CRBN-GSPT1. Further biological mechanistic studies showed that AN5777 decreased GSPT1 remarkably through the ubiquitin-proteasome system, and its effective cytotoxicity was CRBN- and GSPT1-dependent. Furthermore, AN5777 displayed good antiproliferative activities against U937 and OCI-AML-2 cells, and dose-dependently induced G1 phase arrest and apoptosis. The structure found in this work could be good start for antitumor drug development.

Molecular glues targeting GSPT1 in cancers: A potent therapy

G1 to S phase transition 1 (GSPT1) is a key translation termination factor that significantly overexpressed in various cancer tissues and cells. Molecular glue is a kind of small molecule, which can bind to an E3 ligase such as cereblon (CRBN) and subsequently recruit neosubstrate proteins for ubiquitination-proteasomal degradation. This emerging therapeutic approach shows great potential in treating cancers and other diseases. This review aims to introduce current understanding of antitumor mechanism of molecular glues targeting GSPT1, summarize pharmacology profiles of existing molecular glues, and outline development strategies of novel molecular glues. The insights provided in this review will be valuable for future studies.

Discovery of new Lenalidomide derivatives as potent and selective GSPT1 degraders

G₁ to S phase transition 1 (GSPT1) is the requisite release factor for the translation termination. GSPT1 is identified as an oncogenic driver of several types of cancer and considered to be a promising cancer therapeutic target. Although two selective GSPT1 degraders were advanced into clinical trials, neither of them has been approved for clinical use. Here we developed a series of new selective GSPT1 degraders, among which the optimal compound 9q potently induced degradation of GSPT1 with a DC₅₀ of 35 nM in U937 cells, and showed good selectivity in the global proteomic profiling study. Mechanism studies revealed that compound 9q induced GSPT1 degradation through the ubiquitin-proteasome system. Consistent with its potent GSPT1 degradation activity, compound 9q displayed good antiproliferative activities against U937 cells, MOLT-4 cells, and MV4-11 cells, with IC₅₀ values of 0.019 μM, 0.006 μM, and 0.027 μM, respectively. Compound 9q also dose-dependently induced G0/G1 phase arrest and apoptosis in U937 cells.

GSPT1 Functions as a Tumor Promoter in Human Liver Cancer

OBJECTIVE

This study analyzed the role of G1 to S phase transition 1 protein (GSPT1) in promoting progression of liver cancer cells.

METHODS

A bioinformatics database was used to analyze the expression levels of GSPT1 in liver cancer tissues and the prognosis of patients. Subsequently, Western blotting and quantitative PCR were used to verify the expression levels of GSPT1 between normal hepatocytes and hepatoma cells. We used a CRISPR/Cas9 system to construct knockouts of GSPT1 in HepG2 and HCCLM9 liver cancer cells. The effect of GSPT1 on liver cancer cell migration and invasion was analyzed using flow cytometry, migration, and tumor formation assays.

RESULTS

The Cancer Genome Atlas Liver Hepatocellular Carcinoma dataset indicated that GSPT1 expression was upregulated in liver cancer cell lines, and patients with liver cancer had poor prognosis. Knockout of GSPT1 in cells significantly inhibited tumor proliferation, cell migration, and growth in vivo.

CONCLUSION

In this study, we found that GSPT1 promotes the migration and invasion of liver cancer cells.

The progress of protein synthesis factors eIFs, eEFs and eRFs in inflammatory bowel disease and colorectal cancer pathogenesis

Colorectal diseases are threatening human health, especially inflammatory bowel disease (IBD) and colorectal cancer (CRC). IBD is a group of chronic, recurrent and incurable disease, which may affect the entire gastrointestinal tract, increasing the risk of CRC. Eukaryotic gene expression is a complicated process, which is mainly regulated at the level of gene transcription and mRNA translation. Protein translation in tissue is associated with a sequence of steps, including initiation, elongation, termination and recycling. Abnormal regulation of gene expression is the key to the pathogenesis of CRC. In the early stages of cancer, it is vital to identify new diagnostic and therapeutic targets and biomarkers. This review presented current knowledge on aberrant expression of eIFs, eEFs and eRFs in colorectal diseases. The current findings of protein synthesis on colorectal pathogenesis showed that eIFs, eEFs and eRFs may be potential targets for CRC treatment.

Effects of Essential Amino Acid Deficiency on General Control Nonderepressible 2/Eukaryotic Initiation Factor 2 Signaling and Proteomic Changes in Primary Bovine Mammary Epithelial Cells

We hypothesized that the general control nonderepressible 2 (GCN2)/eukaryotic initiation factor 2 (eIF2) signaling pathway and intracellular protein synthesis (PS) are regulated to maintain milk PS in primary bovine mammary epithelial cells (MECs) under essential amino acid (EAA) starvation conditions. We cultured MECs with 0%, 2% (depletion), and 100% (control) EAA for two exposure times (8 and 24 h), followed by three refeeding (RF) times with 100% EAA (0, 8, and 24 h). Subsequently, we measured cell viability, total protein concentration, and proliferation. Western blotting was used to quantify the levels of casein and the expression of total GCN2 and eIF2, as well as phosphorylated GCN2 (GCN2P) and eIF2 (eIF2P). The ISOQuant method was used to assess MEC proteomes, and the resultant data were analyzed using the Kruskal−Wallis test, nonpaired Wilcoxon rank post-hoc test, and ANOVA−Tukey test, as well as principal component analyses and multiple regressions models. Differences in cell viability were observed between the control versus the depleted and repleted MECs, respectively, where 97.2−99.8% viability indicated low cell death rates. Proliferation (range, 1.02−1.55 arbitrary units (AU)) was affected by starvation for 12 and 24 h and repletion for 24 h, but it was not increased compared with the control. Total protein expression was unaffected by both depletion and repletion treatments (median 3158 µg/mL). eIF2P expression was significantly increased (p < 0.05) after treatment with 2% EAA for 8 and 24 h compared with 2% EAA with 8 h + 24 h RF and 2% EAA with 24 h + 8 h RF. GCN2P also showed significantly increased expression (p < 0.05) after treatment with 2% EAA for 24 h compared with the control and 2% EAA with 24 h + 8 h RF. Intracellular casein/α-tubulin expression was unaffected by 2% EAA compared with control (0.073 ± 0.01 AU versus 0.086 ± 0.02 AU, respectively). We studied 30 of the detected 1180 proteins, 16 of which were differentially expressed in starved and refed MECs. Cells faced with EAA deficiency activated the GCN2P/eIF2P pathway, and the lack of change in the levels of casein and other milk proteins suggested that the EAA deficit was mitigated by metabolic flexibility to maintain homeostasis.

Long non-coding RNA LINC00511 promotes proliferation, invasion, and migration of non-small cell lung cancer cells by targeting miR-625-5p/GSPT1

Background

Lung cancer is a malignant tumor with a high rate of mortality and metastasis. Recently, extensive research has shown that long non-coding RNAs (lncRNAs) play a crucial role in the development and progression of non-small cell lung cancer (NSCLC). In this paper, we aimed to explore the impact of long intergenic non-coding RNA 00511 (LINC00511) on the development and metastasis of NSCLC.

Methods

A dataset containing 501 lung squamous cell carcinoma (LUSC) samples and 49 normal samples was downloaded from The Cancer Genome Atlas (TCGA). The differential gene expression and prognostic potential of LINC00511 in LUSC were analyzed by “limma” in R software. Samples of tumor tissues and normal tissues from 67 patients with NSCLC were obtained, along with clinical features. NSCLC cell proliferation, cell cycle, migration, and invasion were detected by LINC00511 knockdown with Cell Counting Kit-8 (CCK-8), flow cytometry, wound-healing assay, and Transwell experiment. The regulatory relationship between LINC00511 and microRNA (miR)-625-5p, or between miR-625-5p and G1 to S phase transition 1 (GSPT1), was detected by luciferase reporter gene assay. LINC00511, miR-625-5p, and GSPT1 expression in tumor and normal tissues and cells was determined by real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) and western blot. A xenograft experiment in nude mice was performed. Ki67 and GSPT1 expression in the tumor tissues of the nude mice was assessed by immunohistochemistry.

Results

LINC00511 expression was clearly higher in the tumor tissues of the NSCLC patients than in normal tissues (P<0.001). High LINC00511 expression was related to larger tumor size, positive lymph node metastasis, advanced TNM stage, and a lower 5-year survival rate. Compared with those of the shNC group, the NSCLC cells of the shLINC00511 group had a prominently lower optical density (OD) 450 value at 72 h, a lower percentage of cells in S phase, a higher relative wound width, and a lower invasive cell number (P<0.01 or P<0.001). LINC00511 promoted GSPT1 expression via suppressing miR-625-5p. Compared with those of the shNC group, the nude mice of the shLINC00511 group had a much lower subcutaneous tumor volume and weight (P<0.05 or P<0.001).

Conclusions

lncRNA LINC00511 promotes proliferation, invasion, and migration of NSCLC cells by targeting miR-625-5p/GSPT. LINC00511 may be a potential diagnostic marker and therapeutic target for NSCLC.

Overexpression of eRF3a Promotes Cell Proliferation and Migration in Liver Cancer

OBJECTIVE

The eukaryotic release factor 3a (eRF3a), a member of the eukaryotic peptide chain release factor family, is overexpressed in several types of cancer. This study aims to investigate the biological role and mechanism of eRF3a in the progression of liver cancer.

METHODS

Western blotting and RT-qPCR were used to detect the expression level of eRF3a in normal liver cells and liver cancer cells. The cell transfection experiments were performed to overexpress eRF3a levels in liver cancer cells HCCLM9 and Huh7, and then cell cycle and apoptosis experiments, Cell Counting Kit-8 (CCK8), plate cloning, and Transwell experiments were done to evaluate the function of eRF3a in the progression of liver cancer. The Western blotting was done to explore the mechanism of eRF3a promoting the development of liver cancer. Western blotting and RT-qPCR were used to detect the expression level of eRF3a in normal liver cells and liver cancer cells. The cell transfection experiments were performed to overexpress eRF3a levels in liver cancer cells HCCLM9 and Huh7, and then cell cycle and apoptosis experiments, Cell Counting Kit-8 (CCK8), plate cloning, and Transwell experiments were done to evaluate the function of eRF3a in the progression of liver cancer. The Western blotting was done to explore the mechanism of eRF3a promoting the development of liver cancer.

RESULTS

eRF3a was significantly highly expressed in liver cancer cells, and its expression level was negatively correlated with the clinical prognosis of patients. In addition, in vitro experiments showed that eRF3a could promote the proliferation and migration of liver cancer cells through the ERK and JNK signaling pathways.

CONCLUSION

This study suggests that eRF3a may be a potential prognostic marker for liver cancer and act as an oncogene by activating JNK and ERK signaling; therefore, eRF3a may be a new target for the treatment of liver cancer.

4210 Da and 1866 Da polypeptides as potential biomarkers of liver disease progression in hepatitis B virus patients

HBV infection is recognized as a serious global health problem, and hepatitis B virus infection is a complicated chronic disease leading to liver cirrhosis (LC) and hepatocellular carcinoma (HCC). New biochemical serum markers could be used to advance the diagnosis and prognosis of HBV-associated liver diseases during the progression of chronic hepatitis B into cirrhosis and HCC. We determined whether the 4210 Da and 1866 Da polypeptides are serum metabolite biomarkers of hepatopathy with hepatitis B virus. A total of 570 subjects were divided into five groups: healthy controls, those with natural clearance, and patients with CHB, LC, and HCC. The 1866 Da and 4210 Da polypeptides were measured by Clin-ToF II MALDI-TOF-MS. There were significant differences in 4210 Da and 1866 Da levels among the five groups (P < 0.001). For the differential diagnosis of CHB from normal liver, the areas under the receiver operating characteristic (ROC) curve of 4210 Da and 1866 Da and their combination via logistic regression were 0.961, 0.849 and 0.967. For the differential diagnosis of LC from CHB, the areas under the ROC curve were 0.695, 0.841 and 0.826. For the differential diagnosis of HCC from CHB, the areas under the ROC curve were 0.744, 0.710 and 0.761, respectively. For the differential diagnosis of HCC from LC, the areas under the ROC curve of 4210 Da and 1866 Da were 0.580 and 0.654. The positive rate of 1866 Da was 45.5% and 69.0% in AFP-negative HCC patients and that of 4210 Da was 60.6% 58.6% in AFP-negative HCC patients of the study HCC vs. CHB and HCC vs. LC. The 4210 Da and 1866 Da polypeptide levels were positively correlated with HBV DNA levels (P < 0.001, r = 0.269; P < 0.001, r = 0.285). The 4210 Da and 1866 Da polypeptides had good diagnostic value for the occurrence and progression of HBV-related chronic hepatitis, liver cirrhosis and hepatocellular carcinoma and could serve to accurately guide treatment management and predict clinical outcomes.

Identification of Potent, Selective, and Orally Bioavailable Small-Molecule GSPT1/2 Degraders from a Focused Library of Cereblon Modulators

Whereas the PROTAC approach to target protein degradation greatly benefits from rational design, the discovery of small-molecule degraders relies mostly on phenotypic screening and retrospective target identification efforts. Here, we describe the design, synthesis, and screening of a large diverse library of thalidomide analogues against a panel of patient-derived leukemia and medulloblastoma cell lines. These efforts led to the discovery of potent and novel GSPT1/2 degraders displaying selectivity over classical IMiD neosubstrates, such as IKZF1/3, and high oral bioavailability in mice. Taken together, this study offers compound 6 (SJ6986) as a valuable chemical probe for studying the role of GSPT1/2 in vitro and in vivo, and it supports the utility of a diverse library of CRBN binders in the pursuit of targeting undruggable oncoproteins.

Glucocorticoid counteracts cellular mechanoresponses by LINC01569-dependent glucocorticoid receptor-mediated mRNA decay

Mechanical stimuli on cells and mechanotransduction are essential in many biological and pathological processes. Glucocorticoid is an important hormone, roles, and mechanisms of which in cellular mechanotransduction remain unknown. Here, we report that glucocorticoid counteracted cellular mechanoresponses dependently on a novel long noncoding RNA (lncRNA), LINC01569 Further, LINC01569 mediated glucocorticoid effects on mechanotransduction by destabilizing messenger RNA (mRNA) of mechanosensors including early growth response protein 1 (EGR1), Cbp/P300-interacting transactivator 2 (CITED2), and bone morphogenic protein 7 (BMP7) in glucocorticoid receptor-mediated mRNA decay (GMD) manner. Mechanistically, LINC01569 directly bound to the GMD factor Y-box-binding protein 1 (YBX1). Then, the LINC01569-YBX1 complex was guided to the mRNAs of EGR1, CITED2, and BMP7 through specific LINC01569-mRNA interaction, thereby contributing to the successful assembly of GMD complex and triggering GMD. Our results uncovered roles of glucocorticoid in cellular mechanotransduction and novel lncRNA-dependent GMD machinery and provided potential strategy for early intervention in mechanical disorder-associated diseases.

Role of GSPT1 and GSPT2 polymorphisms in different outcomes upon Hepatitis B virus infection and prognosis to lamivudine therapy

Purpose. ERF3, having been found expressing differently in liver tissues in our previous work, including eRF3a and eRF3b, which are structural homologs named GSPT1 and GSPT2 Recent studies have indicated that eRF3b involved in the development and proliferation of HepG2 cell, and eRF3a may be associated with tumor susceptibility. Based on this, we tested the effects of GSPT1 and GSPT2 single-nucleotide polymorphisms for all major Hepatitis B virus (HBV) outcomes and lamivudine (LAM) treatment in Han Chinese. Method. A total of 1649 samples were enrolled, and peripheral blood samples were collected in the present study. The single-nucleotide polymorphisms in the GSPT1 and GSPT2 region were genotyped using MALDI-TOF MS. Results. Our study demonstrated there was no obvious relevance of either GSPT1-rs33635 or GSPT2-rs974285 polymorphisms with HBV susceptibility, spontaneous recovery, and development of HBV-related diseases. However, we showed for the first time to our knowledge that GSPT1-rs33635C was a predictor for LAM therapy (viral response: odds ratio (OR) = 2.436, P=0.022; biochemical response: OR = 3.328, P=1.73 × 10^-4). Conclusions. These findings might provide potential implications for therapeutic guidance.

Eukaryotic translational termination efficiency is influenced by the 3' nucleotides within the ribosomal mRNA channel

When a stop codon is at the 80S ribosomal A site, there are six nucleotides (+4 to +9) downstream that are inferred to be occupying the mRNA channel. We examined the influence of these downstream nucleotides on translation termination success or failure in mammalian cells at the three stop codons. The expected hierarchy in the intrinsic fidelity of the stop codons (UAA>UAG>>UGA) was observed, with highly influential effects on termination readthrough mediated by nucleotides at position +4 and position +8. A more complex influence was observed from the nucleotides at positions +5 and +6. The weakest termination contexts were most affected by increases or decreases in the concentration of the decoding release factor (eRF1), indicating that eRF1 binding to these signals was rate-limiting. When termination efficiency was significantly reduced by cognate suppressor tRNAs, the observed influence of downstream nucleotides was maintained. There was a positive correlation between experimentally measured signal strength and frequency of the signal in eukaryotic genomes, particularly in Saccharomyces cerevisiae and Drosophila melanogaster. We propose that termination efficiency is not only influenced by interrogation of the stop signal directly by the release factor, but also by downstream ribosomal interactions with the mRNA nucleotides in the entry channel.

miRNA-144 suppresses proliferation and migration of colorectal cancer cells through GSPT1

MicroRNAs play a key role in carcinogenesis or tumor progression, which negatively and posttranscriptionally regulate gene expression and function as oncogenes or tumor suppressors, as well as regulators of cell cycle, proliferation, apoptosis, migration and other processes. A number of miRNAs are reported be related to the occurrence and development of colorectal cancer (CRC). However, these studies were not involved in the effect of miRNA 144 of CRC, whose function remains unclear. In this study, we demonstrated that the expression level of miRNA 144 was markedly down-regulated in colorectal cancer HCT116 cells compared with normal control FHC cells. Meanwhile, we found that GSPT1 was over-expressed in human colorectal cancer HCT116 cells. Subsequently, GSPT1 was identified as a target of miRNA 144 through bioinformatics and luciferase reporter assays. Besides, we also confirmed that miRNA 144 can inhibit the proliferation and migration of colorectal cancer HCT116 cells . Next, we observed RNA-mediated knockdown of GSPT1 can also inhibit the proliferation and migration of colorectal cancer cells. Thus, we concluded that miRNA 144 inhibits cell proliferation and migration through GSPT1 in CRC. In addition, further mechanic investigations revealed that miRNA-144 suppressed the expression of GSPT1 to regulate the expression of c-myc, survivin and Bcl2L15 which are involved in cell proliferation, and that metastasis related factor MMP28 was also down-regulated by miRNA144. Our findings suggested that microRNA 144 might be an important element to control the status of colorectal cancer, which has provided a new insight into the mechanism of proliferation and migration and a new target in therapy against colorectal cancer.

Nicotine-mediated invasion and migration of non-small cell lung carcinoma cells by modulating STMN3 and GSPT1 genes in an ID1-dependent manner

Background

Inhibitor of DNA binding/Differentiation 1 (ID1) is a helix loop helix transcription factor that lacks the basic DNA binding domain. Over-expression of ID1 has been correlated with a variety of human cancers; our earlier studies had shown that reported ID1 is induced by nicotine or EGF stimulation of non-small cell lung cancer (NSCLC) cells and its down regulation abrogates cell proliferation, invasion and migration. Here we made attempts to identify downstream targets of ID1 that mediate these effects.

Methods

A microarray analysis was done on two different NSCLC cell lines (A549 and H1650) that were transfected with a siRNA to ID1 or a control, non-targeting siRNA. Cells were stimulated with nicotine and genes that were differentially expressed upon nicotine stimulation and ID1 depletion were analyzed to identify potential downstream targets of ID1. The prospective role of the identified genes was validated by RT-PCR. Additional functional assays were conducted to assess the role of these genes in nicotine induced proliferation, invasion and migration. Experiments were also conducted to elucidate the role of ID1, which does not bind to DNA directly, affects the expression of these genes at transcriptional level.

Results

A microarray analysis showed multiple genes are affected by the depletion of ID1; we focused on two of them: Stathmin-like3 (STMN3), a microtubule destabilizing protein, and GSPT1, a protein involved in translation termination; these proteins were induced by both nicotine and EGF in an ID1 dependent fashion. Overexpression of ID1 in two different cell lines induced STMN3 and GSPT1 at the transcriptional level, while depletion of ID1 reduced their expression. STMN3 and GSPT1 were found to facilitate the proliferation, invasion and migration of NSCLC cells in response to nAChR activation. Attempts made to assess how ID1, which is a transcriptional repressor, induces these genes showed that ID1 down regulates the expression of two transcriptional co-repressors, NRSF and ZBP89, involved in the repression of these genes.

Conclusions

Collectively, our data suggests that nicotine and EGF induce genes such as STMN3 and GSPT1 to promote the proliferation, invasion and migration of NSCLC, thus enhancing their tumorigenic properties. These studies thus reveal a central role for ID1 and its downstream targets in facilitating lung cancer progression.

eRF3b, a biomarker for hepatocellular carcinoma, influences cell cycle and phosphoralation status of 4E-BP1

Background

Hepatitis B virus (HBV) infection and its sequelae are now recognized as serious problems globally. Our aime is to screen hepatocellular carcinoma (HCC) from chronic hepatitis B (CHB) and identify the characteristics of proteins involved.

Methodology/Principal Findings

We affinity-purified sample serum with weak cation-exchange (WCX) magnetic beads and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) analysis to search for potential markers. The 4210 Da protein, which differed substantially between HCC and CHB isolates, was later identified to be eukaryotic peptide chain release factor GTP-binding subunit eRF3b. Further research showed that eRF3b/GSPT2 was positively expressed in liver tissues. GSPT2 mRNA was, however differentially expressed in blood. Compared with normal controls, the relative expression of GSPT2/18s rRNA was higher in CHB patients than in patients with either LC or HCC (P = 0.035 for CHB vs. LC; P = 0.020 for CHB vs. HCC). The data of further research showed that eRF3b/GSPT2 promoted the entrance of the HepG2 cells into the S-phase and that one of the substrates of the mTOR kinase, 4E-BP1, was hyperphosphorylated in eRF3b-overexpressing HepG2 cells.

Conclusions

Overall, the differentially expressed protein eRF3b, which was discovered as a biomarker for HCC, could change the cell cycle and influence the phosphorylation status of 4E-BP1 on Ser65 in HepG2.

Monoclonal antibodies against human translation termination factor eRF3 and their utilization for sub-cellular localization of eRF3

Eukaryotic translation termination is triggered by peptide release factors eRF1 and eRF3. eRF1 recognizes the stop codon and promotes nascent peptide chain release, while eRF3 facilitates this peptide release in a GTP-dependent manner. In addition to its role in termination, eRF3 is involved in normal and nonsense-mediated mRNA decay. Despite extensive investigation, the complete understanding of eRF3 function have been hampered by the lack of specific anti-eRF3 monoclonal antibodies (Mabs). The purpose of the study was production of recombinant eRF3a/GSPT1, development of anti-eRF3a/GSPT1 Mabs and their utilization for eRF3a/GSPT1 sub-cellular localization. Plasmid encoding C-terminal part of human GSPT1/eRF3a was constructed. Purified protein, which was predominantly present in the inclusion bodies, was used for the development of Mabs. Characterization of the regions recognized by Mabs using GSPT1/eRF3a mutants and its visualization in the 3D space suggested that Mabs recognize different epitopes. Consistent with its function in translational termination, immunostaining of the cells with developed Mabs revealed that the endogenous GSPT1/eRF3a localized in endoplasmic reticulum. Taking into account the important role of eRF3 for the fundamental research one can suggests that developed Mabs have great prospective to be used as a research reagent in a wide range of applications.

Differential expression of GSPT1 GGCn alleles in cancer

The human eukaryotic release factor 3a (eRF3a), encoded by the G1 to S phase transition 1 gene (GSPT1; alias eRF3a), is upregulated in various human cancers. GSPT1 contains a GGC(n) polymorphism in exon 1, encoding a polyglycine expansion in the N-terminal of the protein. The longer allele, GGC(12), was previously shown to be associated to cancer. The GGC(12) allele was present in 2.2% of colorectal cancer patients but was absent in Crohn disease patients and in the control group. Real-time quantitative RT-PCR analysis showed that the GGC(12) allele was present at up to 10-fold higher transcription levels than the GGC(10) allele (P < 0.001). No GSPT1 amplifications were detected, and there was no correlation between the length of the alleles and methylation levels of the CpG sites inside the GGC expansion. Using flow cytometry, we compared the levels of apoptosis and proliferation rates between cell lines with different genotypes, but detected no significant differences. Finally, we used a cytokinesis-block micronucleus assay to evaluate the frequency of micronuclei in the same cell lines. Cell lines with the longer alleles had higher frequencies of micronuclei in binucleated cells, which is probably a result of defects in mitotic spindle formation. Altogether, these findings indicate that GSPT1 should be considered a potential proto-oncogene.

BCL6 degradation caused by the interaction with the C-terminus of pro-HB-EGF induces cyclin D2 expression in gastric cancers

BCL6 is a transcriptional repressor that has important functions in lymphocyte differentiation and lymphomagenesis, but there have been no reports of BCL6 expression in gastric cancers. In the present study, we investigated the BCL6 function in gastric cancers. Treatment with TPA resulted in BCL6 degradation and cyclin D2 upregulation. This phenomenon was inhibited by the suppression of the nuclear translocation of HB-EGF-CTF (C-terminal fragment of pro-HB-EGF). The HB-EGF-CTF nuclear translocation leads to the interaction of BCL6 with HB-EGF-CTF and the nuclear export of BCL6, and after that BCL6 degradation was mediated by ubiquitin/proteasome pathway. Real-time RT-PCR and siRNA targeting BCL6 revealed that BCL6 suppresses cyclin D2 expression. Our data indicate that BCL6 interacts with nuclear-translocated HB-EGF-CTF and that the nuclear export and degradation of BCL6 induces cyclin D2 upregulation. We performed immunohistochemical analyses of BCL6, HB-EGF and cyclin D2 in human gastric cancers. The inverse correlation between BCL6 and cyclin D2 was also found in HB-EGF-positive human gastric cancers. BCL6 degradation caused by the HB-EGF-CTF also might induce cyclin D2 expression in human gastric cancers. Inhibition of HB-EGF-CTF nuclear translocation and maintenance of BCL6 function are important for the regulation of gastric cancer progression.

G1 to S phase transition protein 1 induces apoptosis signal-regulating kinase 1 activation by dissociating 14-3-3 from ASK1

Apoptosis signal-regulating kinase 1 (ASK1), a member of the mitogen-activated protein kinase kinase kinase family, plays a critical role in mediating apoptosis signals initiated by a variety of death stimuli such as hydrogen peroxide and tumor necrosis factor-alpha. Owing to its critical role in inducing apoptosis, the activity of ASK1 is tightly regulated by various mechanisms such as post-translational modifications and protein-protein interactions. Here we describe the identification of G(1) to S phase transition protein 1 (GSPT1), which is associated with protein translation, as a regulator of ASK1. GSPT1 interacts with ASK1 and enhances ASK1-induced apoptotic activity through the activation of caspase-3. In vitro kinase assay data show that GSPT1 enhances ASK1 autophosphorylation and its kinase activity. Cell cycle-dependent GSPT1 induction and small interfering RNA analyses show that ASK1 autophosphorylation is dependent on the expression level of endogenous GSPT1 in cells. GSPT1 inhibits the binding of ASK1 to the 14-3-3 protein, an ASK1 inhibitor, while GSPT1 has no effect on the interaction between ASK1 and TRAF2, a C-terminal-binding activator of ASK1. Thus, our results reveal a novel role of GSPT1 in the regulation of ASK1-mediated apoptosis.

Translation matters: protein synthesis defects in inherited disease

The list of genetic diseases caused by mutations that affect mRNA translation is rapidly growing. Although protein synthesis is a fundamental process in all cells, the disease phenotypes show a surprising degree of heterogeneity. Studies of some of these diseases have provided intriguing new insights into the functions of proteins involved in the process of translation; for example, evidence suggests that several have other functions in addition to their roles in translation. Given the numerous proteins involved in mRNA translation, it is likely that further inherited diseases will turn out to be caused by mutations in genes that are involved in this complex process.

Human eukaryotic release factor 3a depletion causes cell cycle arrest at G1 phase through inhibition of the mTOR pathway

Eukaryotic release factor 3 (eRF3) is a GTPase associated with eRF1 in a complex that mediates translation termination in eukaryotes. Studies have related eRF3 with cell cycle regulation, cytoskeleton organization, and tumorigenesis. In mammals, two genes encode two distinct forms of eRF3, eRF3a and eRF3b, which differ in their N-terminal domains. eRF3a is the major factor acting in translation termination, and its expression level controls termination complex formation. Here, we investigate the role of eRF3a in cell cycle progression using short interfering RNAs and flow cytometry. We show that eRF3a depletion induces a G1 arrest and that eRF3a GTP-binding activity, but not the eRF3a N-terminal domain, is required to restore G1-to-S-phase progression. We also show that eRF3a depletion decreases the global translation rate and reduces the polysome charge of mRNA. Finally, we show that two substrates of the mammalian TOR (mTOR) kinase, 4E-BP1 and protein kinase S6K1, are hypophosphorylated in eRF3a-depleted cells. These results strongly suggest that the G1 arrest and the decrease in translation induced by eRF3a depletion are due to the inhibition of mTOR activity and hence that eRF3a belongs to the regulatory pathway of mTOR activity.

EPO modulation of cell-cycle regulatory genes, and cell division, in primary bone marrow erythroblasts

Erythropoietin (EPO's) actions on erythroblasts are ascribed largely to survival effects. Certain studies, however, point to EPO-regulated proliferation. To investigate this problem in a primary system, Kit(pos)CD71(high) erythroblasts were prepared from murine bone marrow, and were first used in the array-based discovery of EPO-modulated cell-cycle regulators. Five cell-cycle progression factors were rapidly up-modulated: nuclear protein 1 (Nupr1), G1 to S phase transition 1 (Gspt1), early growth response 1 (Egr1), Ngfi-A binding protein 2 (Nab2), and cyclin D2. In contrast, inhibitory cyclin G2, p27/Cdkn1b, and B-cell leukemia/lymphoma 6 (Bcl6) were sharply down-modulated. For CYCLIN G2, ectopic expression also proved to selectively attenuate EPO-dependent UT7epo cell-cycle progression at S-phase. As analyzed in primary erythroblasts expressing minimal EPO receptor alleles, EPO repression of cyclin G2 and Bcl6, and induction of cyclin D2, were determined to depend on PY343 (and Stat5) signals. Furthermore, erythroblasts expressing a on PY-null EPOR-HM allele were abnormally distributed in G0/G1. During differentiation divisions, EPOR-HM Ter119(pos) erythroblasts conversely accumulated in S-phase and faltered in an apparent EPO-directed transition to G0/G1. EPO/EPOR signals therefore control the expression of select cell-cycle regulatory genes that are proposed to modulate stage-specific decisions for erythroblast cell-cycle progression.

Polyglycine expansions in eRF3/GSPT1 are associated with gastric cancer susceptibility

Gastric cancer remains a major cause of death in the developed countries, and a large percentage is still genetically unexplained. Because of their major role in cell survival, mutations in translation factors and altered expression of these genes have been associated with cancer development. Apart from its role in translation termination, the eukaryotic translation release factor 3 (eRF3) is involved in several critical cellular processes, such as cell cycle regulation, cytoskeleton organization and apoptosis. The aim of this study was to evaluate eRF3/GSPT1 gene as a potential genetic susceptibility associated locus for gastric cancer, analysing a stable GGC expansion in exon 1 encoding a polyglycine tract in the N-terminal domain of the protein. DNA was obtained from 139 patients with gastric cancer and from 100 individuals of a healthy control population. The GGC expansion was amplified by PCR and the number of repeats determined by genotyping in an automatic sequencer. There are five known alleles encoding from 8 to 12 glycines. The most common allele encodes 10 glycines. The 12-Gly allele was detected exclusively in the cancer patients (allelic frequency = 5%). Regardless of the genotype, patients with the 12-Gly allele had a 20-fold increased risk for gastric cancer. We also detected a single-base alteration in the gene (G274T) although no correlation with cancer development has been found. Thus, our results show that the GGC expansion may have a potential role in regulating eRF3/GSPT1 expression and/or changing the protein function that can lead to gastric cancer development.