Modulation of p53 and MDM2 activity by novel interaction with Ras-GAP binding proteins (G3BP)

Exosomal miRNA-92a derived from cancer-associated fibroblasts promote invasion and metastasis in breast cancer by regulating G3BP2

Cancer-associated Fibroblasts (CAFs) exert a tumor-promoting effect in various cancers, including breast cancer. CAFs secrete exosomes containing miRNA and proteins, influencing the tumor microenvironment. In this study, we identified CAF-derived exosomes that transport functional miR-92a from CAFs to tumor cells, thereby intensifying the aggressiveness of breast cancer. CAFs downregulate the expression of G3BP2 in breast cancer cells, and a significant elevation in miR-92a levels in CAF-derived exosomes was observed. Both in vitro and in vivo experiments demonstrate that miR-92a enhances breast cancer cell migration and invasion by directly targeting G3BP2, functioning as a tumor-promoting miRNA. We validated that the RNA-binding proteins SNRPA facilitate the transfer of CAF-derived exosomal miR-92a to breast cancer cells. The reduction of G3BP2 protein by CAF-derived exosomes releases TWIST1 into the nucleus, promoting epithelial-mesenchymal transition (EMT) and further exacerbating breast cancer progression. Moreover, CAF-derived exosomal miR-92a induces tumor invasion and metastasis in mice. Overall, our study reveals that CAF-derived exosomal miR-92a serves as a promoter in the migration and invasion of breast cancer cells by reducing G3BP2 and may represent a potential novel tumor marker for breast cancer.

Role(s) of G3BPs in Human Pathogenesis

Ras-GTPase-activating protein (SH3 domain)-binding proteins (G3BP) are RNA binding proteins that play a critical role in stress granule (SG) formation. SGs protect critical mRNAs from various environmental stress conditions by regulating mRNA stability and translation to maintain regulated gene expression. Recent evidence suggests that G3BPs can also regulate mRNA expression through interactions with RNA outside of SGs. G3BPs have been associated with a number of disease states, including cancer progression, invasion, metastasis, and viral infections, and may be useful as a cancer therapeutic target. This review summarizes the biology of G3BP including their structure, function, localization, role in cancer progression, virus replication, mRNA stability, and SG formation. We will also discuss the potential of G3BPs as a therapeutic target. SIGNIFICANCE STATEMENT: This review will discuss the molecular mechanism(s) and functional role(s) of Ras-GTPase-activating protein (SH3 domain)-binding proteins in the context of stress granule formation, interaction with viruses, stability of RNA, and tumorigenesis.

Cross-Activation of Regulatory T Cells by Self Antigens Limits Self-Reactive and Activated CD8+ T Cell Responses

The interaction between regulatory T (Treg) cells and self-reactive T cells is a crucial mechanism for maintaining immune tolerance. In this study, we investigated the cross-activation of Treg cells by self-antigens and its impact on self-reactive CD8+ T cell responses, with a focus on the P53 signaling pathway. We discovered that major histocompatibility complex (MHC) I-restricted self-peptides not only activated CD8+ T cells but also induced the delayed proliferation of Treg cells. Following HLA-A*0201-restricted Melan-A-specific (pMelan) CD8+ T cells, we observed the direct expansion of Treg cells and concurrent suppression of pMelan+CD8+ T cell proliferation upon stimulation with Melan-A peptide. Transcriptome analysis revealed no significant alterations in specific signaling pathways in pMelan+CD8+ T cells that were co-cultured with activated Treg cells. However, there was a noticeable upregulation of genes involved in P53 accumulation, a critical regulator of cell survival and apoptosis. Consistent with such observation, the blockade of P53 induced a continuous proliferation of pMelan+CD8+ T cells. The concurrent stimulation of Treg cells through self-reactive TCRs by self-antigens provides insights into the immune system's ability to control activated self-reactive CD8+ T cells as part of peripheral tolerance, highlighting the intricate interplay between Treg cells and CD8+ T cells and implicating therapeutic interventions in autoimmune diseases and cancer immunotherapy.

TRIM25-mediated ubiquitination of G3BP1 regulates the proliferation and migration of human neuroblastoma cells

Neuroblastoma is one of the most severe malignant tumors and accounts for substantial cancer-related mortality in children. Ras-GTPase-activating protein SH3 domain-binding protein 1 (G3BP1) is highly expressed in various cancers and acts as an important biomarker of poor prognosis. The ablation of G3BP1 inhibited the proliferation and migration of human SHSY5Y cells. Because of its important role in neuroblastoma, the regulation of G3BP1 protein homeostasis was probed. TRIM25, which belongs to the tripartite motif (TRIM) family of proteins, was identified as an interacting partner for G3BP1 using the yeast two-hybrid (Y2H) method. TRIM25 mediates the ubiquitination of G3BP1 at multiple sites and stabilizes its protein level. Then, our study found that TRIM25 knockdown also inhibited the proliferation and migration of neuroblastoma cells. The TRIM25 and G3BP1 double knockdown SHSY5Y cell line was generated, and double knockdown cells exhibited lower proliferation and migration ability than cells with only TRIM25 or G3BP1 knockdown. Further study demonstrated that TRIM25 promotes the proliferation and migration of neuroblastoma cells in a G3BP1-dependent manner. Tumor xenograft assays indicated that the ablation of TRIM25 and G3BP1 synergistically suppressed the tumorigenicity of neuroblastoma cells in nude mice, and TRIM25 promoted the tumorigenicity of G3BP1 intact SHSY5Y cells but not G3BP1 knockout cells. Thus, TRIM25 and G3BP1, two oncogenic genes, are suggested as potential therapeutic targets for neuroblastoma.

Effect of P53 nuclear localization mediated by G3BP1 on ferroptosis in acute liver failure

This study investigated whether G3BP1 could regulate ferroptosis in hepatocytes during ALF by affecting the entry of P53 into the nucleus. Promoting G3BP1 expression could inhibit P53 entry by binding to the nuclear localization sequence of P53. The inhibition of SLC7A11 transcription was weakened after blocking of P53 binding to the promoter region of the SLC7A11 gene. The SLC7A11-GSH-GPX4 antiferroptotic pathway was subsequently activated, and the level of ferroptosis in ALF hepatocytes was inhibited.

Stress granules: functions and mechanisms in cancer

Stress granules (SGs) are non-enveloped structures formed primarily via protein and RNA aggregation under various stress conditions, including hypoxia and viral infection, as well as oxidative, osmotic, and heat-shock stress. SGs assembly is a highly conserved cellular strategy to reduce stress-related damage and promote cell survival. At present, the composition and dynamics of SGs are well understood; however, data on the functions and related mechanisms of SGs are limited. In recent years, SGs have continued to attract attention as emerging players in cancer research. Intriguingly, SGs regulate the biological behavior of tumors by participating in various tumor-associated signaling pathways, including cell proliferation, apoptosis, invasion and metastasis, chemotherapy resistance, radiotherapy resistance, and immune escape. This review discusses the roles and mechanisms of SGs in tumors and suggests novel directions for cancer treatment.

Stress granules dynamics and promising functions in pancreatic cancer

Stress granules (SGs), non-membrane subcellular organelles made up of non-translational messenger ribonucleoproteins (mRNPs), assemble in response to various environmental stimuli in cancer cells, including pancreatic cancer, particularly pancreatic ductal adenocarcinoma (PDAC) which has a low 5-year survival rate of 10%. The pertinent research on SGs and pancreatic cancer has not, however, been compiled. In this review, we talk about the dynamics of SGs and their positive effects on pancreatic cancer such as SGs promote PDAC viability and repress apoptosis, meanwhile emphasizing the connection between SGs in pancreatic cancer and signature mutations such KRAS, P53, and SMAD4 as well as the functions of SGs in antitumor drug resistance. This novel stress management technique may open the door to better treatment options in the future.

The role of biomarkers in stage III non-small cell lung cancer

INTRODUCTION

Stage III non-small cell lung cancer (NSCLC) is a composite of the regional spread of lung cancer with different levels of potential lymph node involvement and tumor size that often deem the stage at time of diagnosis to be unresectable and suitable for chemoradiation plus consolidation immunotherapy with durvalumab for 12 months. Chemoradiation plus durvalumab consolidation yielded a landmark 49.2% 5-year overall survival in unresectable NSCLC.

AREAS COVERED

Sub-optimal results lead us to focus on the mechanisms of resistance responsible for intractability in a significant proportion of cases that fail with chemoradiation and immunotherapy. In stage III NSCLC it is opportune to explore the accumulated evidence on ferroptosis resistance that can lead to cancer progression and metastasis. Strong data shows that three anti-ferroptosis pathways are principally involved in resistance to chemotherapy, radiation, and immunotherapy.

EXPERT OPINION

Because a large part of stage III NSCLCs is resistant to chemoradiation and durvalumab consolidation, a ferroptosis-based therapeutic approach, combined with standard-of-care therapy, can lead to improved clinical outcomes in patients diagnosed with stage III and possibly stage IV NSCLCs.

RIOK1 mediates p53 degradation and radioresistance in colorectal cancer through phosphorylation of G3BP2

RIO Kinase 1 (RIOK1) is involved in various pathologies, including cancer. However, the role of RIOK1 in radioresistance of colorectal cancer (CRC) remains largely unknown. In this study, we reported that RIOK1 was overexpressed in rectal cancer tissue with weaker tumor regression after neoadjuvant chemoradiotherapy (neoCRT). Moreover, higher RIOK1 expression predicted a poor prognosis in patients with rectal cancer. Blockade of RIOK1 using Toyocamycin, a pharmacological inhibitor of RIOK1, or by knocking down its expression, decreased the resistance of CRC cells to radiotherapy in vitro and in vivo. A mechanistic study revealed that RIOK1 regulates radioresistance by suppressing the p53 signaling pathway. Furthermore, we found that RIOK1 and Ras-GAP SH3 domain binding protein 2 (G3BP2) interact with each other. RIOK1 phosphorylates G3BP2 at Thr226, which increases the activity of G3BP2. RIOK1-mediated phosphorylation of G3BP2 facilitated ubiquitination of p53 by murine double minute 2 protein (MDM2). Altogether, our study revealed the clinical significance of RIOK1 in CRC, and therapies targeting RIOK1 might alleviate the CRC tumor burden in patients.

LncRNAs and their RBPs: How to influence the fate of stem cells?

Stem cells are distinctive cells that have self-renewal potential and unique ability to differentiate into multiple functional cells. Stem cell is a frontier field of life science research and has always been a hot spot in biomedical research. Recent studies have shown that long non-coding RNAs (lncRNAs) have irreplaceable roles in stem cell self-renewal and differentiation. LncRNAs play crucial roles in stem cells through a variety of regulatory mechanisms, including the recruitment of RNA-binding proteins (RBPs) to affect the stability of their mRNAs or the expression of downstream genes. RBPs interact with different RNAs to regulate gene expression at transcriptional and post-transcriptional levels and play important roles in determining the fate of stem cells. In this review, the functions of lncRNAs and their RBPs in self-renewal and differentiation of stem cell are summarized. We focus on the four regulatory mechanisms by which lncRNAs and their RBPs are involved in epigenetic regulation, signaling pathway regulation, splicing, mRNA stability and subcellular localization and further discuss other noncoding RNAs (ncRNAs) and their RBPs in the fate of stem cells. This work provides a more comprehensive understanding of the roles of lncRNAs in determining the fate of stem cells, and a further understanding of their regulatory mechanisms will provide a theoretical basis for the development of clinical regenerative medicine.

Research Progress on the Structure and Function of G3BP

Ras-GTPase-activating protein (SH3 domain)-binding protein (G3BP) is an RNA binding protein. G3BP is a key component of stress granules (SGs) and can interact with many host proteins to regulate the expression of SGs. As an antiviral factor, G3BP can interact with viral proteins to regulate the assembly of SGs and thus exert antiviral effects. However, many viruses can also use G3BP as a proximal factor and recruit translation initiation factors to promote viral proliferation. G3BP regulates mRNA translation and attenuation to regulate gene expression; therefore, it is closely related to diseases, such as cancer, embryonic death, arteriosclerosis, and neurodevelopmental disorders. This review discusses the important discoveries and developments related G3BP in the biological field over the past 20 years, which includes the formation of SGs, interaction with viruses, stability of RNA, and disease progression.

Role of Chikungunya nsP3 in Regulating G3BP1 Activity, Stress Granule Formation and Drug Efficacy

BACKGROUND

Ras-GTPase activating protein SH3-domain-binding proteins (G3BP) are a small family of RNA-binding proteins implicated in regulating gene expression. Changes in expression of G3BPs are correlated to several cancers including thyroid, colon, pancreatic and breast cancer. G3BPs are important regulators of stress granule (SG) formation and function. SG are ribonucleoprotein (RNP) particles that respond to cellular stresses to triage mRNA resulting in transcripts being selectively degraded, stored or translated resulting in a change of gene expression which confers a survival response to the cell. These changes in gene expression contribute to the development of drug resistance. Many RNA viruses, including Chikungunya (and potentially Coronavirus), dismantle SG so that the cell cannot respond to the viral infection. Non-structural protein 3 (nsP3), from the Chikungunya virus, has been shown to translocate G3BP away from SG. Interestingly in cancer cells, the formation of SG is correlated to drug-resistance and blocking SG formation has been shown to reestablish the efficacy of the anticancer drug bortezomib.

METHODS

Chikungunya nsP3 was transfected into breast cancer cell lines T47D and MCF7 to disrupt SG formation. Changes in the cytotoxicity of bortezomib were measured.

RESULTS

Bortezomib cytotoxicity in breast cancer cell lines changed with a 22 fold decrease in its IC₅₀ for T47D and a 7 fold decrease for MCF7 cells.

CONCLUSIONS

Chikungunya nsP3 disrupts SG formation. As a result, it increases the cytotoxicity of the FDA approved drug, bortezomib. In addition, the increased cytotoxicity appears to correlate to improved bortezomib selectivity when compared to control cell lines.

G3BP1 interacts with YWHAZ to regulate chemoresistance and predict adjuvant chemotherapy benefit in gastric cancer

BACKGROUND

A large proportion of gastric cancer patients are susceptible to chemoresistance, while the underlying mechanism remains obscure. Stress granules (SGs) play a self-defence role for tumour cells in inhibiting chemotherapy-induced apoptosis. As an SG assembly effector, G3BP1 (Ras-GTPase-activating protein SH3 domain-binding protein) has been reported to be overexpressed in gastric cancer; thus, here we aim to explore its potent roles in gastric cancer chemoresistance.

METHODS

Kaplan–Meier analysis was used to compare survival rates in gastric cancer patients with different G3BP1 expression. The influence of G3BP1 on gastric cancer cell chemoresistance and apoptosis were evaluated by in vitro and in vivo approaches. The interaction between G3BP1 and YWHAZ was assessed by immunohistochemistry, immunoprecipitation and immunofluorescence.

RESULTS

G3BP1 was associated with the poor outcome of gastric cancer patients who received adjuvant chemotherapy. G3BP1 knockdown significantly increased the sensitivity of gastric cancer cells to chemotherapy drugs. Mechanically, cell apoptosis and pro-apoptotic-associated molecules were significantly elevated upon G3BP1 depletion. Gene co-expression network analyses identified YWHAZ as the critical interlayer of G3BP1; as a result, G3BP1 interacted with YWHAZ to sequester Bax into the cytoplasm. Clinically, G3BP1^highYWHAZ^high gastric cancer patients displayed the worst outcome compared with other patients after chemotherapy.

CONCLUSIONS

The expression of G3BP1 and YWHAZ could predict the adjuvant chemotherapy benefit in gastric cancer patients.

Overexpression of G3BP1 facilitates the progression of colon cancer by activating β‑catenin signaling

Ras-GTPase-activating protein SH3 domain-binding protein 1 (G3BP1) has been reported to be of importance in the occurrence and development of colon cancer. However, the underlying mechanisms remain largely unknown. Therefore, the aim of the present study was to investigate the role of Wnt/β-catenin signaling in G3BP1-mediated colon cancer progression. The expression of G3BP1 in colon tissues and cells was detected via reverse transcription-quantitative PCR, western blotting and immunohistochemistry. Gain-of-function assays were performed in colon cancer RKO cells, which have a relatively low expression of G3BP1, while loss-of-function assays were performed in SW620 colon cancer cells, which have a relatively high expression of G3BP1. Cell proliferation, apoptosis and tumorigenesis were assessed using Cell Counting Kit-8, flow cytometry and tumor-bearing mice assays, respectively. The results demonstrated that G3BP1 expression was significantly upregulated in colon cancer tissues and cells compared with healthy colon tissues and cells. It was found that high expression of G3BP1 was closely associated with the poor prognosis and advanced clinical process in patients with colon cancer. Overexpression of G3BP1 in RKO cells enhanced their proliferative ability and decreased their apoptosis tendency, while knockdown of G3BP1 inhibited SW620 cell proliferation and induced apoptosis. In addition, G3BP1 interacted with β-catenin and upregulated its expression and nuclear accumulation. It was identified that β-catenin knockdown abolished the effects of G3BP1 on the enhancement of cell proliferation in vitro and tumor formation in vivo, as well as the inhibition of cell apoptosis. In conclusion, the present study demonstrated that G3BP1 promoted the progression of colon cancer by activating β-catenin signaling, which provided novel evidence for the role of G3BP1 in colon cancer.

O-GlcNAcylation of PFKFB3 is required for tumor cell proliferation under hypoxia

The protein O-GlcNAcylation catalysed by O-GlcNAc transferase (OGT) is tightly regulated by glucose availability. It is upregulated and essential for tumor cell proliferation under hypoxic conditions. However, the mechanism behind is still unclear. Here, we showed that the glycolytic regulator 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFKFB3), which also promotes cell cycle progression in the nucleus, was O-GlcNAcylated in response to hypoxia. The O-GlcNAcylation of PFKFB3 could compete phosphorylation by hypoxia-activated ERK at the same modification site Ser172. Phosphorylated PFKFB3 could interact with the protein G3BP2 and retain in the cytosol; this in turn led to the accumulation of hypoxia-induced-P27 in the nucleus resulting in the cell cycle arrest. Such a pathway was compromised by high level of PFKFB3 O-GlcNAcylation in tumor cells contributing to cell cycle progression. Consistently, the PFKFB3-Ser172 phosphorylation level inversely correlated with the OGT level in pancreatic cancer patients. Our findings uncovered an O-GlcNAcylation mediated mechanism to promote tumor cell proliferation under metabolic stress, linking the aberrant OGT activity to tumorigenesis in pancreatic cancer.

Proteomic Analysis of Quercetin-Treated K562 Cells

Among natural products under investigation for their additive potential in cancer prevention and treatment, the flavonoid quercetin has received attention for its effects on the cell cycle arrest and apoptosis. In the past, we addressed this issue in K562 cells, a cellular model of the human chronic myeloid leukemia. Here, we applied stable isotope labeling by amino acids in cell culture (SILAC) proteomics with the aim to increase knowledge on the regulative and metabolic pathways modulated by quercetin in these cells. After 24 h of quercetin treatment, we observed that apoptosis was not completely established, thus we selected this time range to capture quantitative data. As a result, we were able to achieve a robust identification of 1703 proteins, and to measure fold changes between quercetin-treated and untreated cells for 1206 proteins. Through a bioinformatics functional analysis on a subset of 112 proteins, we propose that the apoptotic phenotype of K562 cells entails a significant modulation of the translational machinery, RNA metabolism, antioxidant defense systems, and enzymes involved in lipid metabolism. Finally, we selected eight differentially expressed proteins, validated their modulated expression in quercetin-treated K562 cells, and discussed their possible role in flavonoid cytotoxicity. This quantitative profiling, performed for the first time on this type of tumor cells upon treatment with a flavonoid, will contribute to revealing the molecular basis of the multiplicity of the effects selectively exerted by quercetin on K562 cells.

The Acetylation of Lysine-376 of G3BP1 Regulates RNA Binding and Stress Granule Dynamics

Stress granules (SGs) are ribonucleoprotein aggregates that form in response to stress conditions. The regulation of SG dynamics is not fully understood. Permanent pathological SG-like structures were reported in neurodegenerative diseases such as amyotrophic lateral sclerosis. The Ras GTPase-activating protein-binding protein G3BP1 is a central regulator of SG dynamics. We found that the lysine 376 residue (K376) of G3BP1, which is in the RRM RNA binding domain, was acetylated. Consequently, G3BP1 RNA binding was impaired by K376 acetylation. In addition, the acetylation-mimicking mutation K376Q impaired the RNA-dependent interaction of G3BP1 with poly(A)-binding protein 1 (PABP1), but its RNA-independent interactions with caprin-1 and USP10 were little affected. The formation of G3BP1 SGs depended on G3BP1 RNA binding; thus, replacement of endogenous G3BP1 with the K376Q mutant or the RNA binding-deficient F380L/F382L mutant interfered with SG formation. Significant G3BP1 K376 acetylation was detected during SG resolution, and K376-acetylated G3BP1 was seen outside SGs. G3BP1 acetylation is regulated by histone deacetylase 6 (HDAC6) and CBP/p300. Our data suggest that the acetylation of G3BP1 facilitates the disassembly of SGs, offering a potential avenue to mitigate hyperactive stress responses under pathological conditions.

The interaction of YBX1 with G3BP1 promotes renal cell carcinoma cell metastasis via YBX1/G3BP1-SPP1- NF-κB signaling axis

Background

Renal cell carcinoma (RCC) is a deadly urological tumor that remains largely incurable. Our limited understanding of key molecular mechanisms underlying RCC invasion and metastasis has hampered efforts to identify molecular drivers with therapeutic potential. With evidence from our previous study revealing that nuclear overexpression of YBX1 is associated with RCC T stage and metastasis, we investigated the effects of YBX1 in RCC migration, invasion, and adhesion, and then characterized its interaction with RCC-associated proteins G3BP1 and SPP1.

Methods

Renal cancer cell lines, human embryonic kidney cells, and clinical samples were analyzed to investigate the functional role of YBX1 in RCC metastasis. YBX1 knockdown cells were established via lentiviral infection and subjected to adhesion, transwell migration, and invasion assay. Microarray, immunoprecipitation, dual-luciferase reporter assay, and classical biochemical assays were applied to characterize the mechanism of YBX1 interaction with RCC-associated proteins G3BP1 and SPP1.

Results

Knockdown of YBX1 in RCC cells dramatically inhibited cell adhesion, migration, and invasion. Mechanistic investigations revealed that YBX1 interaction with G3BP1 upregulated their downstream target SPP1 in vitro and in vivo, which led to an activated NF-κB signaling pathway. Meanwhile, knockdown of SPP1 rescued the YBX1/G3BP1-mediated activation of NF-κB signaling pathway, and RCC cell migration and invasion. We further showed that YBX1 expression was positively correlated with G3BP1 and SPP1 expression levels in clinical RCC samples.

Conclusions

YBX1 interacts with G3BP1 to promote metastasis of RCC by activating the YBX1/G3BP1–SPP1–NF-κB signaling axis.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1347-0) contains supplementary material, which is available to authorized users.

Loss of G3BP1 suppresses proliferation, migration, and invasion of esophageal cancer cells via Wnt/β-catenin and PI3K/AKT signaling pathways

Accumulating evidence suggests that Ras GTPase-activating protein SH3 domain-binding protein 1 (G3BP1) is very crucial to regulate tumorigenesis and metastasis. Recently, many research works have suggested that G3BP1 is overexpressed in many human cancers including esophageal cancer. Nevertheless, the functional roles of G3BP1 in esophageal cancer are still unknown. Here, the results suggested that silencing of G3BP1 inhibited proliferation, migration, and invasion of esophageal cancer cells, whereas overexpression of G3BP1 led to opposite effects on the growth and metastasis. Surprisingly, G3BP1-depletion had no effect on cell death but caused the arrest of cell cycle in the G₀ /G₁ phase and increased the levels of p53 and p21. In addition, loss of G3BP1 led to a significant elevation of E-cadherin and decrease of N-cadherin, Vimentin, Snail, MMP-9, and MMP-2. Mechanistically, loss of G3BP1 dramatically suppressed Wnt-stimulated T-cell factor/lymphoid enhancer factor (TCF/LEF) transcription factor activity and downregulated its target genes including c-Myc, Axin2, and cyclin D1. Moreover, knockdown of G3BP1 downregulated the expression levels of p-PI3K, p-AKT, and p-GSK-3β, but the total PI3K, AKT, and GSK-3β were not changed. Furthermore, our data proved that the promoting effects of G3BP1-overexpression on cell proliferation, migration, and invasion could be rescued by PI3K inhibitor LY294002 treatment. Collectively, our results here elucidate that G3BP1-depletion suppresses proliferation, migration, and invasion capabilities of esophageal cancer cells via the inactivation of Wnt/β-catenin and PI3K/AKT signaling pathways. Furthermore, our findings imply that G3BP1 can participate in the regulation of esophageal cancer progression, and will be taken as a promising target to treat esophageal cancer.

α-Parvin promotes breast cancer progression and metastasis through interaction with G3BP2 and regulation of TWIST1 signaling

Identification of molecular alterations driving breast cancer progression is critical for the development of effective therapy. In this study, we show that the level of α-parvin is elevated in triple-negative breast cancer cells. The depletion of α-parvin from triple-negative breast cancer cells effectively inhibits breast cancer cell growth, migration, and invasion in vitro, and tumor progression and metastasis in vivo. At the molecular level, we identify Ras-GTPase-activing protein SH3-domain-binding protein 2 (G3BP2) as an α-parvin-binding protein. Knockdown of α-parvin promotes G3BP2 interaction with TWIST1, increases ubiquitination and proteasome-dependent degradation of TWIST1, and consequently reduces the cellular level of TWIST1 and its downstream signaling. Importantly, the depletion of G3BP2 reverses the reduction in the level and signaling of TWIST1 and the suppression of breast cancer progression induced by the loss of α-parvin. Furthermore, the re-expression of an α-parvin mutant in which the G3BP2-binding site is ablated, unlike that of wild-type α-parvin, in α-parvin-deficient breast cancer cells, is unable to restore the level and signaling of TWIST1 and promote breast cancer progression. Finally, we show that protein level of α-parvin is highly positively correlated with that of TWIST1 in human triple-negative breast cancer patients. Our studies reveal a novel signaling pathway consisting of α-parvin, G3BP2, and TWIST1 that regulates breast cancer progression and metastasis, and suggest that the activation of this signaling pathway is a key factor for driving the progression and poor clinical outcome of human ER-negative breast cancer.

Carcinogenic Helicobacter pylori Strains Selectively Dysregulate the In Vivo Gastric Proteome, Which May Be Associated with Stomach Cancer Progression

Helicobacter pylori is the strongest risk factor for gastric cancer. Initial interactions between H. pylori and its host originate at the microbial-gastric epithelial cell interface, and contact between H. pylori and gastric epithelium activates signaling pathways that drive oncogenesis. One microbial constituent that increases gastric cancer risk is the cag pathogenicity island, which encodes a type IV secretion system that translocates the effector protein, CagA, into host cells. We previously demonstrated that infection of Mongolian gerbils with a carcinogenic cag+H. pylori strain, 7.13, recapitulates many features of H. pylori-induced gastric cancer in humans. Therefore, we sought to define gastric proteomic changes induced by H. pylori that are critical for initiation of the gastric carcinogenic cascade. Gastric cell scrapings were harvested from H. pylori-infected and uninfected gerbils for quantitative proteomic analyses using isobaric tags for relative and absolute quantitation (iTRAQ). Quantitative proteomic analysis of samples from two biological replicate experiments quantified a total of 2764 proteins, 166 of which were significantly altered in abundance by H. pylori infection. Pathway mapping identified significantly altered inflammatory and cancer-signaling pathways that included Rab/Ras signaling proteins. Consistent with the iTRAQ results, RABEP2 and G3BP2 were significantly up-regulated in vitro, ex vivo in primary human gastric monolayers, and in vivo in gerbil gastric epithelium following infection with H. pylori strain 7.13 in a cag-dependent manner. Within human stomachs, RABEP2 and G3BP2 expression in gastric epithelium increased in parallel with the severity of premalignant and malignant lesions and was significantly elevated in intestinal metaplasia and dysplasia, as well as gastric adenocarcinoma, compared with gastritis alone. These results indicate that carcinogenic strains of H. pylori induce dramatic and specific changes within the gastric proteome in vivo and that a subset of altered proteins within pathways with oncogenic potential may facilitate the progression of gastric carcinogenesis in humans.

The roles and mechanisms of G3BP1 in tumour promotion

Ras-GTPase-activating protein SH3 domain-binding protein 1 (G3BP1) is a SH3 domain-binding protein that is overexpressed in a variety of tumour tissues and cancers, such as head and neck cancer, lung cancer, prostate cancer, colon cancer and breast cancer. G3BP1 promotes tumour cell proliferation and metastasis and inhibits apoptosis by regulating the Ras, TGF-β/Smad, Src/FAK and p53 signalling pathways. At present, polypeptides targeting G3BP1 have shown anti-tumour activity and G3BP1 also involved in anti-cancer effects of some polyphenolic compounds (resveratrol and EGCG). Therefore G3BP1 may be a potential target for tumour treatment.

Negative regulation of Candida glabrata Pdr1 by the deubiquitinase subunit Bre5 occurs in a ubiquitin independent manner

The primary route for development of azole resistance in the fungal pathogen Candida glabrata is acquisition of a point mutation in the PDR1 gene. This locus encodes a transcription factor that upon mutation drives high level expression of a range of genes including the ATP-binding cassette transporter-encoding gene CDR1. Pdr1 activity is also elevated in cells that lack the mitochondrial genome (ρ^° cells), with associated high expression of CDR1 driving azole resistance. To gain insight into the mechanisms controlling activity of Pdr1, we expressed a tandem affinity purification (TAP)-tagged form of Pdr1 in both wild-type (ρ⁺ ) and ρ^° cells. Purified proteins were analyzed by multidimensional protein identification technology mass spectrometry identifying a protein called Bre5 as a factor that co-purified with TAP-Pdr1. In Saccharomyces cerevisiae, Bre5 is part of a deubiquitinase complex formed by association with the ubiquitin-specific protease Ubp3. Genetic analyses in C. glabrata revealed that loss of BRE5, but not UBP3, led to an increase in expression of PDR1 and CDR1 at the transcriptional level. These studies support the view that Bre5 acts as a negative regulator of Pdr1 transcriptional activity and behaves as a C. glabrata-specific modulator of azole resistance.

Rasputin a decade on and more promiscuous than ever? A review of G3BPs

Ras-GTPase-activating protein (SH3 domain)-binding proteins (G3BPs, also known as Rasputin) are a family of RNA binding proteins that regulate gene expression in response to environmental stresses by controlling mRNA stability and translation. G3BPs appear to facilitate this activity through their role in stress granules for which they are considered a core component, however, it should be noted that not all stress granules contain G3BPs and this appears to be contextual depending on the environmental stress and the cell type. Although the role of G3BPs in stress granules appears to be one of its major roles, data also strongly suggests that they interact with mRNAs outside of stress granules to regulate gene expression. G3BPs have been implicated in several diseases including cancer progression, invasion, and metastasis as well as virus survival. There is now a body of evidence that suggests targeting of G3BPs could be explored as a form of cancer therapeutic. This review discusses the important discoveries and advancements made in the field of G3BPs biology over the last two decades including their roles in RNA stability, translational control of cellular transcripts, stress granule formation, cancer progression and its interactions with viruses during infection. An emerging theme for G3BPs is their ability to regulate gene expression in response to environmental stimuli, disease progression and virus infection making it an intriguing target for disease therapies.

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Triage of many cellular mRNA occurs via stress granules in a G3BP-dependant manner.

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G3BPs control intra cellular responses to viral infection.

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Transcript stability, degradation and translation are controlled by G3BPs.

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G3BPs can control cancer progression.

A G3BP1-Interacting lncRNA Promotes Ferroptosis and Apoptosis in Cancer via Nuclear Sequestration of p53

Long noncoding RNAs (lncRNA) have been associated with various types of cancer; however, the precise role of many lncRNAs in tumorigenesis remains elusive. Here we demonstrate that the cytosolic lncRNA P53RRA is downregulated in cancers and functions as a tumor suppressor by inhibiting cancer progression. Chromatin remodeling proteins LSH and Cfp1 silenced or increased P53RRA expression, respectively. P53RRA bound Ras GTPase-activating protein-binding protein 1 (G3BP1) using nucleotides 1 and 871 of P53RRA and the RRM interaction domain of G3BP1 (aa 177-466). The cytosolic P53RRA-G3BP1 interaction displaced p53 from a G3BP1 complex, resulting in greater p53 retention in the nucleus, which led to cell-cycle arrest, apoptosis, and ferroptosis. P53RRA promoted ferroptosis and apoptosis by affecting transcription of several metabolic genes. Low P53RRA expression significantly correlated with poor survival in patients with breast and lung cancers harboring wild-type p53. These data show that lncRNAs can directly interact with the functional domain of signaling proteins in the cytoplasm, thus regulating p53 modulators to suppress cancer progression.Significance: A cytosolic lncRNA functions as a tumor suppressor by activating the p53 pathway. Cancer Res; 78(13); 3484-96. ©2018 AACR.

G3BP1 promotes tumor progression and metastasis through IL-6/G3BP1/STAT3 signaling axis in renal cell carcinomas

The chronic inflammatory microenvironment within or surrounding the primary renal cell carcinoma (RCC) site promotes oncogenic transformation as well as contributes to the development of metastasis. G3BP stress granule assembly factor 1 (G3BP1) was found to be involved in the regulation of multiple cellular functions. However, its functions in RCC have not been previously explored. Here, we first showed that the expression of G3BP1 is elevated in human RCC and correlates with RCC progression. In cultured RCC cells, knockdown of G3BP1 results in inhibition of tumor cell proliferation, migration, and invasion, consistently with the alteration of epithelial–mesenchymal transition (EMT) and cell proliferative markers, including Cadherins, Vimentin, Snail, Slug, c-Myc, and cyclin D1. Remarkably, knockdown of G3BP1 dramatically impaired the signaling connection of pro-inflammatory cytokine IL-6 stimulation and downstream STAT3 activation in RCC, thus eventually contributing to the disruption of IL-6-elicited RCC migration and metastasis. In addition, in vivo orthotopic tumor xenografts results confirmed that knockdown of G3BP1 suppressed RCC tumor growth and metastasis in mice. Collectively, our findings support the notion that G3BP1 promotes tumor progression and metastasis through IL-6/G3BP1/STAT3 signaling axis in RCC.

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

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

Selective targeting p53WT lung cancer cells harboring homozygous p53 Arg72 by an inhibitor of CypA

TP53 plays essential roles in tumor initiation and progression, and is frequently mutated in cancer. However, pharmacological stabilization and reactivation of p53 have not been actively explored for targeted cancer therapies. Herein, we identify a novel Cyclophilin A (CypA) small molecule inhibitor (HL001) that induces non-small cell lung cancer (NSCLC) cell cycle arrest and apoptosis via restoring p53 expression. We find that HL001 stabilizes p53 through inhibiting the MDM2-mediated p53 ubiquitination. Further mechanistic studies reveal that the downregulation of G3BP1 and the induction of reactive oxygen species and DNA damage by HL001 contribute to p53 stabilization. Surprisingly, HL001 selectively suppresses tumor growth in p53 wild-type NSCLC harboring Arg72 homozygous alleles (p53-72R) through disrupting interaction between MDM2 and p53-72R in a CypA-dependent manner. Moreover, combining HL001 with cisplatin synergistically enhance tumor regression in orthotopic NSCLC mouse model. Collectively, this study demonstrates that pharmacologic inhibition of CypA offers a potential therapeutic strategy via specific activation of p53-72R in NSCLC.

Clonal cooperativity in heterogenous cancers

Tumor heterogeneity is a major obstacle to the development of effective therapies and is thus an important focus of cancer research. Genetic and epigenetic alterations, as well as altered tumor microenvironments, result in tumors made up of diverse subclones with different genetic and phenotypic characteristics. Intratumor heterogeneity enables competition, but also supports clonal cooperation via cell-cell contact or secretion of factors, resulting in enhanced tumor progression. Here, we summarize recent findings related to interclonal interactions within a tumor and the therapeutic implications of such interactions, with an emphasis on how different subclones collaborate with each other to promote proliferation, metastasis and therapy-resistance. Furthermore, we propose that disruption of clonal cooperation by targeting key factors (such as Wnt and Hedgehog, amongst others) can be an alternative approach to improving clinical outcomes.

Analysis of G3BP1 and VEZT Expression in Gastric Cancer and Their Possible Correlation with Tumor Clinicopathological Factors

Purpose

This study aimed to analyze G3BP1 and VEZT expression profiles in patients with gastric cancer, and examine the possible relationship between the expressions of each gene and clinicopathological factors.

Materials and Methods

Expression of these genes in formalin-fixed paraffin embedded (FFPE) tissues, collected from 40 patients with gastric cancer and 40 healthy controls, was analyzed. Differences in gene expression among patient and normal samples were identified using the GraphPad Prism 5 software. For the analysis of real-time polymerase chain reaction products, GelQuantNET software was used.

Results

Our findings demonstrated that both VEZT and G3BP1 mRNA expression levels were downregulated in gastric cancer samples compared with those in the normal controls. No significant relationship was found between the expression of these genes and gender (P-value, 0.4835 vs. 0.6350), but there were significant changes associated with age (P-value, 0.0004 vs. 0.0001) and stage of disease (P-value, 0.0019 vs. 0.0001). In addition, there was a direct relationship between VEZT gene expression and metastasis (P-value, 0.0462), in contrast to G3BP1 that did not demonstrate any significant correlation (P-value, 0.1833).

Conclusions

The results suggest that expression profiling of VEZT and G3BP1 can be used for diagnosis of gastric cancer, and specifically, VEZT gene could be considered as a biomarker for the detection of gastric cancer progression.

Changes in liver proteins of rats fed standard and high-fat and sucrose diets induced by fish omega-3 PUFAs and their combination with grape polyphenols according to quantitative proteomics

This study considered the physiological modulation of liver proteins due to the supplementation with fish oils under two dietary backgrounds: standard or high in fat and sucrose (HFHS), and their combination with grape polyphenols. By using a quantitative proteomics approach, we showed that the capacity of the supplements for regulating proteins depended on the diet; namely, 10 different proteins changed into standard diets, while 45 changed into the HFHS diets and only scarcely proteins were found altered in common. However, in both contexts, fish oils were the main regulatory force, although the addition of polyphenols was able to modulate some fish oils' effects. Moreover, we demonstrated the ability of fish oils and their combination with grape polyphenols in improving biochemical parameters and reducing lipogenesis and glycolysis enzymes, enhancing fatty acid beta-oxidation and insulin signaling and ameliorating endoplasmic reticulum stress and protein oxidation when they are included in an unhealthy diet.

ALS mutant SOD1 interacts with G3BP1 and affects stress granule dynamics

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease. Mutations in Cu/Zn superoxide dismutase (SOD1) are responsible for approximately 20 % of the familial ALS cases. ALS-causing SOD1 mutants display a gain-of-toxicity phenotype, but the nature of this toxicity is still not fully understood. The Ras GTPase-activating protein-binding protein G3BP1 plays a critical role in stress granule dynamics. Alterations in the dynamics of stress granules have been reported in several other forms of ALS unrelated to SOD1. To our surprise, the mutant G93A SOD1 transgenic mice exhibited pathological cytoplasmic inclusions that co-localized with G3BP1-positive granules in spinal cord motor neurons. The co-localization was also observed in fibroblast cells derived from familial ALS patient carrying SOD1 mutation L144F. Mutant SOD1, unlike wild-type SOD1, interacted with G3BP1 in an RNA-independent manner. Moreover, the interaction is specific for G3BP1 since mutant SOD1 showed little interaction with four other RNA-binding proteins implicated in ALS. The RNA-binding RRM domain of G3BP1 and two particular phenylalanine residues (F380 and F382) are critical for this interaction. Mutant SOD1 delayed the formation of G3BP1- and TIA1-positive stress granules in response to hyperosmolar shock and arsenite treatment in N2A cells. In summary, the aberrant mutant SOD1-G3BP1 interaction affects stress granule dynamics, suggesting a potential link between pathogenic SOD1 mutations and RNA metabolism alterations in ALS.

An ANCCA/PRO2000-miR-520a-E2F2 regulatory loop as a driving force for the development of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common malignancies in Asia especially in China. We previously identified that ANCCA/PRO2000 as an important proliferation-associated protein predicted poor prognosis of patients with HCC. However, the molecular mechanisms of ANCCA/PRO2000 leading to hepatocarcinogenesis and progression are still obscure. In the present study, we found that ANCCA/PRO2000 overexpression in HCC specimens correlated with aggressive tumor behavior and poor survival. Furthermore, ANCCA/PRO2000 exerts strong oncogenic function in HCC and promotes cell proliferation by regulating E2F2 expression, a critical cell cycle regulator. Notably, miR-520a is an intermediate regulator between ANCCA/PRO2000 and E2F2. Mechanistically, ANCCA/PRO2000 not only interacts with E2F2 but also negatively regulates miR-520a that inhibits E2F2 to cooperatively promote in vitro and in vivo growth of HCC cells. Moreover, we demonstrated that ANCCA/PRO2000 enhances the migratory capacity of HCC cells partially by suppressing ERO1L and G3BP2 expression. Additional research identified that miR-372, as a prognostic factor for HCC, could directly target ANCCA/PRO2000. Our results suggest the ANCCA/PRO2000-miR-520a-E2F2 regulatory loop as a driving force for HCC development and ANCCA/PRO2000 as a potential therapeutic target for HCC.

MicroRNA-23b Targets Ras GTPase-Activating Protein SH3 Domain-Binding Protein 2 to Alleviate Fibrosis and Albuminuria in Diabetic Nephropathy

Diabetic nephropathy (DN) is a frequent and severe complication of diabetes that is structurally characterized by glomerular basement membrane thickening, extracellular matrix accumulation, and destabilization of podocyte foot processes. MicroRNAs (miRNAs) are dysregulated in DN, but identification of the specific miRs involved remains incomplete. Here, we confirm that the peripheral blood from patients with diabetes and the kidneys of animals with type 1 or 2 diabetes have low levels of miR-23b compared with those of their nondiabetic counterparts. Furthermore, exposure to high glucose downregulated miR-23b in cultured kidney cells. In contrast, renal expression of Ras GTPase-activating protein SH3 domain-binding protein 2 (G3BP2), a putative miR-23b target, increased in DN. In vitro, overexpression of miR-23b decreased, and inhibition of miR-23b increased, G3BP2 expression levels. Bioinformatics analysis also revealed p53 binding sites in the miR-23b promoter; in vitro inhibition of p53 or the upstream p38 mitogen-activated protein kinase (p38MAPK) upregulated miR-23b expression in high-glucose conditions. In turn, inhibition of G3BP2 or overexpression of miR-23b downregulated p53 and p38MAPK expression in high-glucose conditions. In vivo, overexpression of miR-23b or inhibition of p53 in db/db mice reversed hyperalbuminuria and kidney fibrosis, whereas miR-23b antagomir treatment promoted renal fibrosis and increased albuminuria in wild-type mice. These data suggest that hyperglycemia regulates pathogenic processes in DN through an miR-23b/G3BP2 feedback circuit involving p38MAPK and p53. In conclusion, these results reveal a role for miR-23b in DN and indicate a novel potential therapeutic target.

Genetic analysis of the clonal stability of Chinese hamster ovary cells for recombinant protein production

Chinese hamster ovary (CHO) cells are frequently used for the production of recombinant proteins for therapeutical applications. However, the recombinant protein expression level of CHO cells may reduce during long-term culture. The physiological changes related to the stability of expression were not well understood. In this study, we performed a series of genetic analysis on stable and unstable clonal derived populations. Transcriptome analysis revealed that a large number of differentially expressed genes (>100) were identified in the unstable population between early and late generations, while only a few differentially expressed genes were found in the stable population, suggesting that the gene expression change is related to the instability of recombinant protein production. On the other hand, no significant differences were found in promoter methylation or gene copy numbers in the unstable population. Taken together, our data help better understand the molecular mechanism underlying the stability of recombinant protein production in CHO cells.

Overexpression of Ras-GTPase-activating protein SH3 domain-binding protein 1 correlates with poor prognosis in gastric cancer patients

AIMS

Ras-GTPase-activating protein SH3 domain-binding protein 1 (G3BP1) is a downstream effector of Ras signalling, and is overexpressed in several types of human malignancy. However, its role in gastric cancer remains unclear. The aim of this study was to investigate the prognostic significance of G3BP1 in gastric cancer.

METHODS AND RESULTS

G3BP1 mRNA and protein levels in paired frozen tumour samples were detected by real-time polymerase chain reaction and western blotting, respectively. Paraffin-embedded tumour samples were used for immunohistochemistry. Gastric cancer cells were used to detect the tumorigenic role of G3BP1 in vitro. We found that G3BP1 protein expression was markedly increased in gastric cancer tissues as compared with corresponding non-malignant mucosa, whereas corresponding changes in mRNA levels were not observed. G3BP1 staining was positively correlated with tumour size, vascular invasion, T classification, lymph node metastasis, TNM stage, and reduced overall survival. Further analysis identified G3BP1 as an independent prognostic factor for poor prognosis, and combining G3BP1 with TNM stage generated a better predictive model for patient outcomes. G3BP1 also promoted proliferation, migration/invasion and extracellular signal-related kinase and AKT activation in gastric cancer cells.

CONCLUSIONS

Our data define G3BP1 as a novel independent prognostic factor that is correlated with gastric cancer progression.

Resveratrol induces apoptosis by directly targeting Ras-GTPase-activating protein SH3 domain-binding protein 1

Resveratrol (trans-3,5,4'-truhydroxystilbene) possesses a strong anticancer activity exhibited as the induction of apoptosis through p53 activation. However, the molecular mechanism and direct target(s) of resveratrol-induced p53 activation remain elusive. Here, the Ras-GTPase-activating protein SH3 domain-binding protein 1 (G3BP1) was identified as a potential target of resveratrol, and in vitro binding assay results using resveratrol-conjugated Sepharose 4B beads confirmed their direct binding. Depletion of G3BP1 significantly diminishes resveratrol-induced p53 expression and apoptosis. We also found that G3BP1 negatively regulates p53 expression by interacting with ubiquitin-specific protease 10 (USP10), a deubiquitinating enzyme of p53. Disruption of the interaction of p53 with USP10 by G3BP1 interference leads to the suppression of p53 deubiquitination. Resveratrol, on the other hand, directly binds to G3BP1 and prevents the G3BP1/USP10 interaction, resulting in enhanced USP10-mediated deubiquitination of p53, and consequently increased p53 expression. These findings disclose a novel mechanism of resveratrol-induced p53 activation and resveratrol-induced apoptosis by direct targeting of G3BP1.

Matrix stiffness drives epithelial-mesenchymal transition and tumour metastasis through a TWIST1-G3BP2 mechanotransduction pathway

Matrix stiffness potently regulates cellular behaviour in various biological contexts. In breast tumours, the presence of dense clusters of collagen fibrils indicates increased matrix stiffness and correlates with poor survival. It is unclear how mechanical inputs are transduced into transcriptional outputs to drive tumour progression. Here we report that TWIST1 is an essential mechanomediator that promotes epithelial-mesenchymal transition (EMT) in response to increasing matrix stiffness. High matrix stiffness promotes nuclear translocation of TWIST1 by releasing TWIST1 from its cytoplasmic binding partner G3BP2. Loss of G3BP2 leads to constitutive TWIST1 nuclear localization and synergizes with increasing matrix stiffness to induce EMT and promote tumour invasion and metastasis. In human breast tumours, collagen fibre alignment, a marker of increasing matrix stiffness, and reduced expression of G3BP2 together predict poor survival. Our findings reveal a TWIST1-G3BP2 mechanotransduction pathway that responds to biomechanical signals from the tumour microenvironment to drive EMT, invasion and metastasis.

G3BP1, G3BP2 and CAPRIN1 are required for translation of interferon stimulated mRNAs and are targeted by a dengue virus non-coding RNA

Viral RNA-host protein interactions are critical for replication of flaviviruses, a genus of positive-strand RNA viruses comprising major vector-borne human pathogens including dengue viruses (DENV). We examined three conserved host RNA-binding proteins (RBPs) G3BP1, G3BP2 and CAPRIN1 in dengue virus (DENV-2) infection and found them to be novel regulators of the interferon (IFN) response against DENV-2. The three RBPs were required for the accumulation of the protein products of several interferon stimulated genes (ISGs), and for efficient translation of PKR and IFITM2 mRNAs. This identifies G3BP1, G3BP2 and CAPRIN1 as novel regulators of the antiviral state. Their antiviral activity was antagonized by the abundant DENV-2 non-coding subgenomic flaviviral RNA (sfRNA), which bound to G3BP1, G3BP2 and CAPRIN1, inhibited their activity and lead to profound inhibition of ISG mRNA translation. This work describes a new and unexpected level of regulation for interferon stimulated gene expression and presents the first mechanism of action for an sfRNA as a molecular sponge of anti-viral effectors in human cells.

Crystal structures of the human G3BP1 NTF2-like domain visualize FxFG Nup repeat specificity

Ras GTPase Activating Protein SH3 Domain Binding Protein (G3BP) is a potential anti-cancer drug target implicated in several cellular functions. We have used protein crystallography to solve crystal structures of the human G3BP1 NTF2-like domain both alone and in complex with an FxFG Nup repeat peptide. Despite high structural similarity, the FxFG binding site is located between two alpha helices in the G3BP1 NTF2-like domain and not at the dimer interface as observed for nuclear transport factor 2. ITC studies showed specificity towards the FxFG motif but not FG and GLFG motifs. The unliganded form of the G3BP1 NTF2-like domain was solved in two crystal forms to resolutions of 1.6 and 3.3 Å in space groups P2₁2₁2₁ and P6₃22 based on two different constructs, residues 1–139 and 11–139, respectively. Crystal packing of the N-terminal residues against a symmetry related molecule in the P2₁2₁2₁ crystal form might indicate a novel ligand binding site that, however, remains to be validated. The crystal structures give insight into the nuclear transportation mechanisms of G3BP and provide a basis for future structure based drug design.

A proteomic perspective of Sirtuin 6 (SIRT6) phosphorylation and interactions and their dependence on its catalytic activity

Sirtuin 6 (SIRT6), a member of the mammalian sirtuin family, is a nuclear deacetylase with substrate-specific NAD(+)-dependent activity. SIRT6 has emerged as a critical regulator of diverse processes, including DNA repair, gene expression, telomere maintenance, and metabolism. However, our knowledge regarding its interactions and regulation remains limited. Here, we present a comprehensive proteomics-based analysis of SIRT6 protein interactions and their dependence on SIRT6 catalytic activity. We also identify evolutionarily conserved SIRT6 phosphorylations, including four within a proline-rich disordered region, and show that the conserved S338 phosphorylation can modulate selected SIRT6 interactions. By integrating molecular biology tools, microscopy, immunoaffinity purifications, label-free quantitative mass spectrometry, and bioinformatic analyses, we have established the first large-scale SIRT6 interaction network. Relative protein abundances and gene ontology functional assessment highlighted proteins involved in transcription regulation, chromatin organization, nuclear transport, telomerase function, and RNA processing. Independent immunoisolations under increased stringency distinguished the most stable SIRT6 interactions. One prominent interaction with Ras-GTPase-activating protein-binding protein 1 (G3BP1) was further validated by microscopy, reciprocal purifications, and isolations in different cell types and of endogenous SIRT6. Interestingly, a subset of specific interactions, including G3BP1, were significantly reduced or abolished in isolations of catalytically deficient SIRT6 mutant, revealing previously unknown interplay between SIRT6 activity and its associations. Overall, our study reveals putative means of regulation of SIRT6 functions via interactions and modifications, providing an important resource for future studies on the molecular mechanisms underlying sirtuin functions.

Downregulation of G3BPs inhibits the growth, migration and invasion of human lung carcinoma H1299 cells by suppressing the Src/FAK-associated signaling pathway

G3BP is a RasGAP binding protein that is overexpressed in many human cancers. We previously reported that downregulation of G3BP suppressed cell growth and induced apoptosis in HCT116 cells. Here we report that both transient and stable knockdown of G3BP suppressed the growth, migration and invasion capability of human lung carcinoma H1299 cells. Moreover, downregulation of G3BP significantly inhibited the phosphorylation of Src, FAK and ERK, and the levels of NF-κB were also markedly decreased in H1299 cells. Knockdown of G3BP also decreased the expression of matrix metalloproteinase-2 (MMP-2), MMP-9 and plasminogen activator (uPA), and in vivo data demonstrated that downregulation of G3BP markedly inhibited the growth of H1299 tumor xenografts. Together, these data revealed that knockdown of G3BP inhibited the migration and invasion of human lung carcinoma cells through the inhibition of Src, FAK, ERK and NF-κB and decreased levels of MMP-2, MMP-9 and uPA.

MDM2's social network

MDM2 is considered a hub protein due to its capacity to interact with a large number of different partners of which p53 is most well described. MDM2 is an E3 ubiquitin ligase, and many, but not all, of its interactions relate directly to this activity, such as substrates, adaptors or bridges, promoters, inhibitors or complementary factors. Some interactions serve regulatory functions that in response to cellular stresses control the localisation and functions of MDM2 including protein kinases, ribosomal proteins and proteases. Moreover, interactions with nucleotides serve other functions such as mRNA to regulate protein synthesis and DNA to control transcription. To perform such a pleiotropic panorama of different functions, MDM2 is subjected to a multitude of post-translational modifications and is expressed in different isoforms. The large and diverse interactome is made possible due to the plasticity of MDM2 and in this review we have listed the MDM2 interactions until now and we will discuss how this multifaceted protein can interact with such a variety of substrates to provide a key intermediary role in different signalling pathways.

Integrative genomics in combination with RNA interference identifies prognostic and functionally relevant gene targets for oral squamous cell carcinoma

In oral squamous cell carcinoma (OSCC), metastasis to lymph nodes is associated with a 50% reduction in 5-year survival. To identify a metastatic gene set based on DNA copy number abnormalities (CNAs) of differentially expressed genes, we compared DNA and RNA of OSCC cells laser-microdissected from non-metastatic primary tumors (n = 17) with those from lymph node metastases (n = 20), using Affymetrix 250K Nsp single-nucleotide polymorphism (SNP) arrays and U133 Plus 2.0 arrays, respectively. With a false discovery rate (FDR)<5%, 1988 transcripts were found to be differentially expressed between primary and metastatic OSCC. Of these, 114 were found to have a significant correlation between DNA copy number and gene expression (FDR<0.01). Among these 114 correlated transcripts, the corresponding genomic regions of each of 95 transcripts had CNAs differences between primary and metastatic OSCC (FDR<0.01). Using an independent dataset of 133 patients, multivariable analysis showed that the OSCC–specific and overall mortality hazards ratio (HR) for patients carrying the 95-transcript signature were 4.75 (95% CI: 2.03–11.11) and 3.45 (95% CI: 1.84–6.50), respectively. To determine the degree by which these genes impact cell survival, we compared the growth of five OSCC cell lines before and after knockdown of over-amplified transcripts via a high-throughput siRNA–mediated screen. The expression-knockdown of 18 of the 26 genes tested showed a growth suppression ≥30% in at least one cell line (P<0.01). In particular, cell lines derived from late-stage OSCC were more sensitive to the knockdown of G3BP1 than cell lines derived from early-stage OSCC, and the growth suppression was likely caused by increase in apoptosis. Further investigation is warranted to examine the biological role of these genes in OSCC progression and their therapeutic potentials.

Neck lymph node metastasis is the most important prognostic factor in oral squamous cell carcinoma (OSCC). To identify genes associated with this critical step of OSCC progression, we compared DNA copy number aberrations and gene expression differences between tumor cells found in metastatic lymph nodes versus those in non-metastatic primary tumors. We identified 95 transcripts (87 genes) with metastasis-specific genome abnormalities and gene expression. Tested in an independent cohort of 133 OSCC patients, the 95 gene signature was an independent risk factor of disease-specific and overall death, suggesting a disease progression phenotype. We knocked down the expression of over-amplified genes in five OSCC cell lines. Knockdown of 18 of the 26 tested genes suppressed the cell growth in at least one cell line. Interestingly, cell lines derived from late-stage OSCC were more sensitive to the knockdown of G3BP1 than cell lines derived from early-stage OSCC. The knockdown of G3BP1 increased programmed cell death in the p53-mutant but not wild-type OSCC cell lines. Taken together, we demonstrate that CNA–associated transcripts differentially expressed in carcinoma cells with an aggressive phenotype (i.e., metastatic to lymph nodes) can be biomarkers with both prognostic information and functional relevance. Moreover, results suggest that G3BP1 is a potential therapeutic target against late-stage p53-negative OSCC.

The essential polysome-associated RNA-binding protein RBP42 targets mRNAs involved in Trypanosoma brucei energy metabolism

RNA-binding proteins that target mRNA coding regions are emerging as regulators of post-transcriptional processes in eukaryotes. Here we describe a newly identified RNA-binding protein, RBP42, which targets the coding region of mRNAs in the insect form of the African trypanosome, Trypanosoma brucei. RBP42 is an essential protein and associates with polysome-bound mRNAs in the cytoplasm. A global survey of RBP42-bound mRNAs was performed by applying HITS-CLIP technology, which captures protein-RNA interactions in vivo using UV light. Specific RBP42-mRNA interactions, as well as mRNA interactions with a known RNA-binding protein, were purified using specific antibodies. Target RNA sequences were identified and quantified using high-throughput RNA sequencing. Analysis revealed that RBP42 bound mainly within the coding region of mRNAs that encode proteins involved in cellular energy metabolism. Although the mechanism of RBP42's function is unclear at present, we speculate that RBP42 plays a critical role in modulating T. brucei energy metabolism.

GAP161 targets and downregulates G3BP to suppress cell growth and potentiate cisplaitin-mediated cytotoxicity to colon carcinoma HCT116 cells

Ras-GTPase-activating protein SH3 domain-binding proteins (G3BP) are overexpressed in various human tumors and participate in several signaling pathways involved in growth, differentiation and apoptosis. G3BP interact with RasGAP (Ras-GTPase activating protein) only in growing cells and depend on Ras activation, and participate in the Ras signal pathway. Therefore, the blockage and downregulation of G3BP may be a new strategy for cancer therapy. In this report, we demonstrate that a novel peptide GAP161 blocked the functions of G3BP and markedly suppressed HCT116 cell growth through the induction of apoptosis. The peptide bound with G3BP, which interfered with the interaction of G3BP1 with RasGAP and further suppressed Ras signaling pathways. GAP161 downregulated G3BP1 and G3BP2 proteins. Similarly, the knockdown of G3BP substantially decreased the proliferation of HCT116 cells and inhibited Ras signal pathways. Furthermore, the downregulation of G3BP could enhance cisplatin-induced apoptosis and growth inhibition of HCT116 cells. We also found that GAP161 suppressed the growth of BALB/c mice bearing colon CT26 tumors and nude mice bearing HCT116 xenografts. These results suggest that downregulation of G3BP might be useful in cancer therapy and that GAP161 is a promising new therapeutic agent for cancers.

Proteomic profiling of the human cytomegalovirus UL35 gene products reveals a role for UL35 in the DNA repair response

Human cytomegalovirus infections involve the extensive modification of host cell pathways, including cell cycle control, the regulation of the DNA damage response, and averting promyelocytic leukemia (PML)-mediated antiviral responses. The UL35 gene from human cytomegalovirus is important for viral gene expression and efficient replication and encodes two proteins, UL35 and UL35a, whose mechanism of action is not well understood. Here, affinity purification coupled with mass spectrometry was used to identify previously unknown human cellular targets of UL35 and UL35a. We demonstrate that both viral proteins interact with the ubiquitin-specific protease USP7, and that UL35 expression can alter USP7 subcellular localization. In addition, UL35 (but not UL35a) was found to associate with three components of the Cul4(DCAF1) E3 ubiquitin ligase complex (DCAF1, DDB1, and DDA1) previously shown to be targeted by the HIV-1 Vpr protein. The coimmunoprecipitation and immunofluorescence microscopy of DCAF1 mutants revealed that the C-terminal region of DCAF1 is required for association with UL35 and mediates the dramatic relocalization of DCAF1 to UL35 nuclear bodies, which also contain conjugated ubiquitin. As previously reported for the Vpr-DCAF1 interaction, UL35 (but not UL35a) expression resulted in the accumulation of cells in the G(2) phase of the cell cycle, which is typical of a DNA damage response, and activated the G(2) checkpoint in a DCAF1-dependent manner. In addition, UL35 (but not UL35a) induced γ-H2AX and 53BP1 foci, indicating the activation of DNA damage and repair responses. Therefore, the identified interactions suggest that UL35 can contribute to viral replication through the manipulation of host responses.