Distinct Interactions of EBP1 Isoforms with FBXW7 Elicits Different Functions in Cancer

The structure and function of multifunctional protein ErbB3 binding protein 1 (Ebp1) and its role in diseases

ErbB3-binding protein 1(Ebp1) has two isoforms, p42 Ebp1 and p48 Ebp1, both of which can regulate cell growth and differentiation. But these isoforms often have opposite effects, including contradictory roles in regulation of cell growth in different tissues and cells. P48 Ebp1 belongs to the full-length sequence, while conformational changes in the crystal structure of p42 Ebp1 reveals a lack of an α helix at the amino terminus. Due to the differences in the structures of these two isoforms, they have different binding partners and protein modifications. Ebp1 can function as both an oncogene and a tumor suppressor factor. However, the underlying mechanisms by which these two isoforms exert opposite functions are still not fully understood. In this review, we summarize the genes and the structures of protein of these two isoforms, protein modifications, binding partners and the association of different isoforms with diseases.

EBP1 promotes the malignant biological behaviors of kidney renal clear cell carcinoma through activation of p38/HIF-1α signaling pathway

BACKGROUND

Kidney Renal Clear Cell Carcinoma (KIRC) is a common malignant tumor of the urinary system, and its incidence is increasing. ERBB3 binding protein (EBP1) is upregulated in various cancers. However, the connection between EBP1 and KIRC has not been reported.

METHODS

The expression of EBP1 in normal kidney tissue and KIRC tissue was analyzed through database and tissue microarray. EBP1 was knocked down in KIRC cell lines, and its impact on KIRC proliferation was assessed through CCK-8, soft agar assay, and flow cytometry. Scratch and transwell assays were used to evaluate the influence of EBP1 on KIRC invasion and migration. Nude mice tumor experiment were conducted to examine the effect of EBP1 on tumor tissue. Database analysis explored potential pathways involving EBP1, and validation was performed through Western blot experiments and p38 inhibitor.

RESULTS

EBP1 is upregulated in KIRC and significantly correlates with clinical staging, pathological grading, and lymph node metastasis in patients. The mechanism research showed that knocking down EBP1 inhibited KIRC proliferation, invasion, and migration and inhibited p38 phosphorylation and the expression of hypoxia-inducible factor-1α (HIF-1α) in KIRC. p-38 inhibitor (SB203580) inhibits p38 phosphorylation and HIF-1α expression and suppresses cell viability in a concentration-dependent manner, but has no effect on EBP1 expression. HEK 293T cells overexpressing EBP1 showed increased expression of phosphorylated p38 and HIF-1α and enhanced cell viability, however, SB203580 inhibited this effect of EBP1.

CONCLUSION

EBP1 may promote the occurrence and development of KIRC by regulating the expression of p38/HIF-1α signaling pathway.

Integrated Lactylome Characterization Reveals the Molecular Dynamics of Protein Regulation in Gastrointestinal Cancers

Lysine lactylation (Kla) plays a vital role in several physiological processes. However, the cancer-specific modulation of Kla in gastrointestinal (GI) tumors requires systematic elucidation. Here, global lactylome profiling of cancerous and adjacent tissues is conducted from 40 patients with GI cancer and identified 11698 Kla sites. Lactylome integration revealed that Kla affects proteins involved in hallmark cancer processes, including epigenetic rewiring, metabolic perturbations, and genome instability. Moreover, the study revealed pan-cancer patterns of Kla alterations, among which 37 Kla sites are consistently upregulated in all four GI cancers and are involved in gene regulation. It is further verified that lactylation of CBX3 at K10 mediates its interaction of CBX3 with the epigenetic marker H3K9me3 and facilitates GI cancer progression. Overall, this study provides an invaluable resource for understanding the lactylome landscape in GI cancers, which may provide new paths for drug discovery for these devastating diseases.

Orthogonal proteogenomic analysis identifies the druggable PA2G4-MYC axis in 3q26 AML

The overexpression of the ecotropic viral integration site-1 gene (EVI1/MECOM) marks the most lethal acute myeloid leukemia (AML) subgroup carrying chromosome 3q26 abnormalities. By taking advantage of the intersectionality of high-throughput cell-based and gene expression screens selective and pan-histone deacetylase inhibitors (HDACis) emerge as potent repressors of EVI1. To understand the mechanism driving on-target anti-leukemia activity of this compound class, here we dissect the expression dynamics of the bone marrow leukemia cells of patients treated with HDACi and reconstitute the EVI1 chromatin-associated co-transcriptional complex merging on the role of proliferation-associated 2G4 (PA2G4) protein. PA2G4 overexpression rescues AML cells from the inhibitory effects of HDACis, while genetic and small molecule inhibition of PA2G4 abrogates EVI1 in 3q26 AML cells, including in patient-derived leukemia xenografts. This study positions PA2G4 at the crosstalk of the EVI1 leukemogenic signal for developing new therapeutics and urges the use of HDACis-based combination therapies in patients with 3q26 AML.

The FBXW7-binding sites on FAM83D are potential targets for cancer therapy

Increasing evidence shows the oncogenic function of FAM83D in human cancer, but how FAM83D exerts its oncogenic function remains largely unclear. Here, we investigated the importance of FAM83D/FBXW7 interaction in breast cancer (BC). We systematically mapped the FBXW7-binding sites on FAM83D through a comprehensive mutational analysis together with co-immunoprecipitation assay. Mutations at the FBXW7-binding sites on FAM83D led to that FAM83D lost its capability to promote the ubiquitination and proteasomal degradation of FBXW7; cell proliferation, migration, and invasion in vitro; and tumor growth and metastasis in vivo, indicating that the FBXW7-binding sites on FAM83D are essential for its oncogenic functions. A meta-evaluation of FAM83D revealed that the prognostic impact of FAM83D was independent on molecular subtypes. The higher expression of FAM83D has poorer prognosis. Moreover, high expression of FAM83D confers resistance to chemotherapy in BCs, which is experimentally validated in vitro. We conclude that identification of FBXW7-binding sites on FAM83D not only reveals the importance for FAM83D oncogenic function, but also provides valuable insights for drug target.

Functional analysis reveals driver cooperativity and novel mechanisms in endometrial carcinogenesis

High-risk endometrial cancer has poor prognosis and is increasing in incidence. However, understanding of the molecular mechanisms which drive this disease is limited. We used genetically engineered mouse models (GEMM) to determine the functional consequences of missense and loss of function mutations in Fbxw7, Pten and Tp53, which collectively occur in nearly 90% of high-risk endometrial cancers. We show that Trp53 deletion and missense mutation cause different phenotypes, with the latter a substantially stronger driver of endometrial carcinogenesis. We also show that Fbxw7 missense mutation does not cause endometrial neoplasia on its own, but potently accelerates carcinogenesis caused by Pten loss or Trp53 missense mutation. By transcriptomic analysis, we identify LEF1 signalling as upregulated in Fbxw7/FBXW7-mutant mouse and human endometrial cancers, and in human isogenic cell lines carrying FBXW7 mutation, and validate LEF1 and the additional Wnt pathway effector TCF7L2 as novel FBXW7 substrates. Our study provides new insights into the biology of high-risk endometrial cancer and suggests that targeting LEF1 may be worthy of investigation in this treatment-resistant cancer subgroup.

Molecular subtypes of lung adenocarcinoma patients for prognosis and therapeutic response prediction with machine learning on 13 programmed cell death patterns

BACKGROUND

Lung adenocarcinoma (LUAD) seriously threatens people's health worldwide. Programmed cell death (PCD) plays a critical role in regulating LUAD growth and metastasis as well as in therapeutic response. However, currently, there is a lack of integrative analysis of PCD-related signatures of LUAD for accurate prediction of prognosis and therapeutic response.

METHODS

The bulk transcriptome and clinical information of LUAD were obtained from TCGA and GEO databases. A total of 1382 genes involved in regulating 13 various PCD patterns (apoptosis, necroptosis, pyroptosis, ferroptosis, cuproptosis, netotic cell death, entotic cell death, lysosome-dependent cell death, parthanatos, autophagy-dependent cell death, oxeiptosis, alkaliptosis and disulfidptosis) were included in the study. Weighted gene co-expression network analysis (WGCNA) and differential expression analysis were performed to identify PCD-associated differential expression genes (DEGs). An unsupervised consensus clustering algorithm was used to explore the potential subtypes of LUAD based on the expression profiles of PCD-associated DEGs. Univariate Cox regression analysis, Least Absolute Shrinkage and Selection Operator (LASSO) regression, Random Forest (RF) analysis and stepwise multivariate Cox analysis were performed to construct a prognostic gene signature. The "oncoPredict" algorithm was utilized for drug-sensitive analysis. GSVA and GSEA were utilized to perform function enrichment analysis. MCPcounter, quanTIseq, Xcell and ssGSEA algorithms were used for tumor immune microenvironment analysis. A nomogram incorporating PCDI and clinicopathological characteristics was established to predict the prognosis of LUAD patients.

RESULTS

Forty PCD-associated DEGs related to LUAD were obtained by WGCNA analysis and differential expression analysis, followed by unsupervised clustering to identify two LUAD molecular subtypes. A programmed cell death index (PCDI) with a five-gene signature was established by machine learning algorithms. LUAD patients were then divided into a high PCDI group and a low PCDI group using the median PCDI as a cutoff. Survival and therapeutic analysis revealed that the high PCDI group had a poor prognosis and was more sensitive to targeted drugs but less sensitive to immunotherapy compared to the low PCDI group. Further enrichment analysis showed that B cell-related pathways were significantly downregulated in the high PCDI group. Accordingly, the decreased tumor immune cell infiltration and the lower tumor tertiary lymphoid structure (TLS) scores were also found in the high PCDI group. Finally, a nomogram with reliable predictive performance PCDI was constructed by incorporating PCDI and clinicopathological characteristics, and a user-friendly online website was established for clinical reference ( https://nomogramiv.shinyapps.io/NomogramPCDI/ ).

CONCLUSION

We performed the first comprehensive analysis of the clinical relevance of genes regulating 13 PCD patterns in LUAD and identified two LUAD molecular subtypes with distinct PCD-related gene signature which indicated differential prognosis and treatment sensitivity. Our study provided a new index to predict the efficacy of therapeutic interventions and the prognosis of LUAD patients for guiding personalized treatments.

Proliferation-associated 2G4 P48 is stabilized by malignant T-cell amplified sequence 1 and promotes the proliferation of head and neck squamous cell carcinoma

Background/purpose

Proliferation-associated protein 2G4 (PA2G4) has alternative transcriptional and translational initiation. One dominant transcript ENST00000303305 could be translated into two protein isoforms (PA2G4-P42 and PA2G4-P48). In this study, we aimed to explore the effects of PA2G4-P42 and PA2G4-P48 on the proliferation of head and neck squamous cell carcinoma (HNSCC) and the mechanisms regulating PA2G4-P48 stability.

Materials and methods

HNSCC cell lines HSC2 and SCC25 with relatively low PA2G4 expression were used for in-vitro cell studies. PA2G4-P42 and PA2G4-P48 overexpression lentiviruses were generated. In vitro cell proliferation was assessed by CCK-8 and colony formation. In vivo tumor cell proliferation was assessed by HSC2 cell-derived xenograft tumors. Liquid chromatography-mass spectrometry (LC-MS)/MS and co-immunoprecipitation (co-IP) assays were applied to check PA2G4-P48 interacting partners. Cycloheximide (CHX) chase and ubiquitin-based co-IP assays were also performed.

Results

PA2G4-P48 was the dominant isoform, with substantially higher expression than PA2G4-P42 in HNSCC. PA2G4-P48 overexpression enhanced HNSCC cell proliferation, but PA2G4-P42 overexpression slowed the proliferation. MCTS1 interacted with PA2G4-P48, but not PA2G4-P42. PA2G4 protein but not its mRNA expression was decreased in cells with MCTS1 knockdown. MG132 treatment abrogated this alteration. MCTS1 overexpression significantly elevated the half-life of PA2G4-P48, while its knockdown drastically reduced the half-life compared with the control cells. In addition, MCTS1 overexpression significantly decreased the polyubiquitination of exogenous flag-tagged PA2G4-P48. MCTS1 overexpression-induced cell proliferation was hampered by knocking down of PA2G4-P48.

Conclusion

PA2G4-P42 and PA2G4-P48 exert growth-suppressive and growth-promoting effects in HNSCC, respectively. MCTS1 can interact with PA2G4-P48 and prolong its half-life by reducing its poly-ubiquitination.

Cerebellar dysfunction and schizophrenia-like behavior in Ebp1-deficient mice

Cerebellar deficits with Purkinje cell (PCs) loss are observed in several neurologic disorders. However, the underlying mechanisms as to how the cerebellum is affected during development remain unclear. Here we demonstrated that specific inactivation of murine Ebp1 in the central nervous system causes a profound neuropathology characterized by reduced cerebellar volume and PCs loss with abnormal dendritic development, leading to phenotypes including motor defects and schizophrenia (SZ)-like behaviors. Loss of Ebp1 leads to untimely gene expression of Fbxw7, an E3 ubiquitin ligase, resulting in aberrant protein degradation of PTF1A, thereby eliciting cerebellar defects. Reinstatement of Ebp1, but not the Ebp1-E183Ter mutant found in SZ patients, reconstituted cerebellar architecture with increased PCs numbers and improved behavioral phenotypes. Thus, our findings indicate a crucial role for EBP1 in cerebellar development, and define a molecular basis for the cerebellar contribution to neurologic disorders such as SZ.

Clinical significance of FBXW7 loss of function in human cancers

FBXW7 (F-Box and WD Repeat Domain Containing 7) (also referred to as FBW7 or hCDC4) is a component of the Skp1-Cdc53 / Cullin-F-box-protein complex (SCF/β-TrCP). As a member of the F-box protein family, FBXW7 serves a role in phosphorylation-dependent ubiquitination and proteasome degradation of oncoproteins that play critical role(s) in oncogenesis. FBXW7 affects many regulatory functions involved in cell survival, cell proliferation, tumor invasion, DNA damage repair, genomic instability and telomere biology. This thorough review of current literature details how FBXW7 expression and functions are regulated through multiple mechanisms and how that ultimately drives tumorigenesis in a wide array of cell types. The clinical significance of FBXW7 is highlighted by the fact that FBXW7 is frequently inactivated in human lung, colon, and hematopoietic cancers. The loss of FBXW7 can serve as an independent prognostic marker and is significantly correlated with the resistance of tumor cells to chemotherapeutic agents and poorer disease outcomes. Recent evidence shows that genetic mutation of FBXW7 differentially affects the degradation of specific cellular targets resulting in a distinct and specific pattern of activation/inactivation of cell signaling pathways. The clinical significance of FBXW7 mutations in the context of tumor development, progression, and resistance to therapies as well as opportunities for targeted therapies is discussed.

miR-223-3p targets FBXW7 to promote epithelial-mesenchymal transition and metastasis in breast cancer

BACKGROUND

Breast cancer is the most common malignant tumor diagnosed in women. It is the second leading cause of cancer-related death among women in the world. Aberrant expression of microRNAs (miRNAs) have been identified to be involved in the development and progression of breast cancer. The aim of this study was to investigate the function of miR-223-3p in breast cancer progression and metastasis.

METHODS

qRT-PCR was used to analyze the expression levels of miR-223-3p in breast cancer tissues and cell lines. Wound healing and Matrigel assays were used to examine cell motility and invasiveness. FBXW7 3'-UTR construct and luciferase reporter assays were performed for the target gene.

RESULTS

miR-223-3p was overexpressed in breast cancer tissue and cell lines. A high level of miR-223-3p was associated with poor prognosis in breast cancer patients. In addition, overexpressed miR-223-3p promoted the migration and invasion of breast cancer cells in vitro and in vivo. Mechanistically, we found that tumor suppressor gene FBXW7 is a target of miR-223-3p. Luciferase activity reporter assay indicated miR-223-3p could directly bind with the 3'-UTR of FBXW7. miR-223-3p exhibited its oncogenic role partly by decreasing FBXW7 expression, and consequently promoted the invasion and metastasis of breast cancer cells.

CONCLUSIONS

Our study revealed a physical and functional relationship among miR-223-3p and FBXW7. By negatively regulating FBXW7 expression, miR-223-3p exerts a tumor promotion role promoting cell invasion and metastasis in breast cancer.

Protein modifications throughout the lung cancer proteome unravel the cancer-specific regulation of glycolysis

Glycolytic reprogramming is a typical feature of cancer. However, the cancer-specific modulation of glycolytic enzymes requires systematic elucidation. Here, we report a range of dysregulated modifications in association with a family of enzymes specifically related to the glycolysis pathway by systematic identification of delta masses at the proteomic scale in human non-small-cell lung cancer. The most significant modification is the delta mass of 79.967 Da at serine 58 (Ser58) of triosephosphate isomerase (TPI), which is confirmed to be phosphorylation. Blocking TPI Ser58 phosphorylation dramatically inhibits glycolysis, cancer growth, and metastasis. The protein kinase PRKACA directly phosphorylates TPI Ser58, thereby enhancing TPI enzymatic activity and glycolysis. The upregulation of TPI Ser58 phosphorylation is detected in various human tumor specimens and correlates with poor survival. Therefore, our study identifies a number of cancer-specific protein modifications spanned on glycolytic enzymes and unravels the significance of TPI Ser58 phosphorylation in glycolysis and lung cancer development.

USP35 mitigates endoplasmic reticulum stress-induced apoptosis by stabilizing RRBP1 in non-small cell lung cancer

Deubiquitinating enzymes (DUBs) serve to maintain cellular homeostasis via protein ubiquitination and exert diverse regulatory functions in cancers and other diseases. Much progress has been made in characterizing biological roles of DUBs over the decades, yet the specific functions of many subclass members remain largely unexplored. It was not until recent years that the role of ubiquitin‐specific‐processing protease 35 (USP35) in cancers began to be understood. Here, we focus on delineating the roles and underlying mechanisms of USP35 in non‐small cell lung cancer (NSCLC). The isobaric tags for relative and absolute quantitation (iTRAQ) comparative proteomic approach were employed to identify differentially expressed proteins (DEPs) in H1299 cells induced by USP35 overexpression or silencing. Among the potential interactome of USP35, ribosome‐binding protein 1 (RRBP1), a membrane‐bound protein in endoplasmic reticulum (ER), captured our attentions. RRBP1 expression was found to positively correlate with USP35 levels in both genetically modified cells and human NSCLC tissues. Concordantly, both RRBP1 expression and USP35 expression were found to positively correlate with poor prognoses in lung adenocarcinoma patients. At the molecular level, USP35 was verified to directly interact with RRBP1 to prevent it from proteasomal‐dependent degradation. Functionally, USP35 alleviated ER stress‐induced cell apoptosis by stabilizing RRBP1 in NSCLC cells. Collectively, these findings indicate that USP35 plays a critical role in resisting ER stress‐induced cell death through deubiquitinating RRBP1, hence providing a rationale to target the USP35‐RRBP1 axis as an alternative therapeutic option for NSCLC.

Clinical significance of FBXW7 tumor suppressor gene mutations and expression in human colorectal cancer: a systemic review and meta-analysis

BACKGROUND

Various studies investigating the clinical significance of FBXW7 mutation and/or expression have yielded inconclusive results in colorectal cancer (CRC) patients. Therefore, the present meta-analysis summarizes previous evidence and evaluates the clinical significance, including the prognostic role, of FBXW7 status in CRCs.

METHODS

The meta-analysis was conducted by searching the databases of PubMed, China National Knowledge Infrastructure (CNKI), WANFANG data, Web of Science, Embase, and Web of Science. Pooled odds ratios (ORs) and hazard ratios (HRs) and corresponding 95% confidence intervals (CIs) were calculated to assess the relationships between FBXW7 status and clinicopathological features and survival in CRC, respectively.

RESULTS

Ten studies involving 4199 patients met the inclusion criteria and included in our meta-analysis. FBXW7 mutation/low expression was obviously correlated with advanced T stage (OR = 0.44, 95% CI: 0.27-0.74, P <  0.01) and lymph node metastasis (OR = 1.88, 95% CI: 1.40-2.53, P <  0.01), but was not associated with other parameters. Further investigation found that FBXW7 mutation/low expression predicted poor OS (HR = 1.25, 95% CI: 1.06-1.47, P <  0.01), but not DFS in CRC (HR = 1.04, 95% CI: 0.60-1.82, P = 0.88). Subgroup analysis found that FBXW7 status was obviously correlated with OS in cohorts recruited after 2009 (HR = 1.32, 95% CI: 1.17-1.50, P <  0.01), from eastern Asia (HR = 1.27, 95% CI: 1.04-1.55, P = 0.02), detected by immunohistochemistry/qRT-PCR (HR = 1.39, 95% CI: 1.22-1.59, P <  0.01), and analysed with multivariate method (HR = 1.47, 95% CI: 1.25-1.74, P <  0.01).

CONCLUSIONS

This study indicates that FBXW7 status, expression level especially, is associated with OS but not DFS in CRC. FBXW7 expression level may function as a prognostic biomarker in CRC.

Ebp1 p48 promotes oncogenic properties in hepatocellular carcinoma through p38 MAPK/HIF1α activation and p53 downregulation

The ErbB3 binding protein 1 (Ebp1) has been reported in several cancers, in which it can act as either a pro-oncogenic regulator or a tumor suppressor. However, the biological function and molecular mechanism of Ebp1 p48 in hepatocellular carcinoma (HCC) remain unclear. Here, we report that the long isoform of Ebp1, p48, is highly expressed in HCC tissues compared with normal tissues. Ebp1 p48 expression was correlated with the tumor size in HCC patients. Silencing Ebp1 p48 by transduction with lentiviral shEbp1 dramatically reduced the proliferation rate, soft agar colony generation, and tumor formation in vivo. We further demonstrated that Ebp1 p48 knockdown resulted in decreased p38 phosphorylation, which subsequently reduced hypoxia-inducible factor 1α (HIF1α) expression. Moreover, Ebp1 p48 knockdown led to an upregulation of p53 expression through MDM2 downregulation. Taken together, these results suggest that the Ebp1/p38/HIF1α signaling pathway and the Ebp1-mediated downregulation of p53 are involved in hepatocarcinogenesis. Therefore, Ebp1 and its downstream signaling pathways may be promising therapeutic targets of HCC.

Kaposi's sarcoma-associated herpesvirus latency-associated nuclear antigen dysregulates expression of MCL-1 by targeting FBW7

Primary effusion lymphoma (PEL) is an aggressive B cell lymphoma that is etiologically linked to Kaposi’s sarcoma-associated herpesvirus (KSHV). Despite standard multi-chemotherapy treatment, PEL continues to cause high mortality. Thus, new strategies to control PEL are needed urgently. Here, we show that a phosphodegron motif within the KSHV protein, latency-associated nuclear antigen (LANA), specifically interacts with E3 ubiquitin ligase FBW7, thereby competitively inhibiting the binding of the anti-apoptotic protein MCL-1 to FBW7. Consequently, LANA-FBW7 interaction enhances the stability of MCL-1 by preventing its proteasome-mediated degradation, which inhibits caspase-3-mediated apoptosis in PEL cells. Importantly, MCL-1 inhibitors markedly suppress colony formation on soft agar and tumor growth of KSHV⁺PEL/BCBL-1 in a xenograft mouse model. These results strongly support the conclusion that high levels of MCL-1 expression enable the oncogenesis of PEL cells and thus, MCL-1 could be a potential drug target for KSHV-associated PEL. This work also unravels a mechanism by which an oncogenic virus perturbs a key component of the ubiquitination pathway to induce tumorigenesis.

Primary effusion lymphoma (PEL), a highly aggressive B cell lymphoma, is associated with Kaposi’s sarcoma-associated herpesvirus (KSHV). However, the underlying mechanisms that govern the aggressiveness of KSHV-associated PEL are poorly understood. Here, we demonstrate that KSHV LANA interacts with cellular ubiquitin E3 ligase FBW7, sequestering MCL-1 from FBW7, which reduces MCL-1 ubiquitination. As such, LANA potently stabilizes and increases MCL-1 protein, leading to inhibition of caspase-3-mediated apoptosis in PEL cells. Furthermore, MCL-1 inhibitors efficiently blocked PEL progression in mouse xenograft model. These results suggest that LANA acts as a proto-oncogene via deregulating tumor suppressor FBW7, which upregulates anti-apoptotic MCL-1 expression. This study suggests drugs that target MCL-1 may serve as an effective therapy against KSHV⁺ PEL.

A structural view of PA2G4 isoforms with opposing functions in cancer

The role of proliferation-associated protein 2G4 (PA2G4), alternatively known as ErbB3-binding protein 1 (EBP1), in cancer has become apparent over the past 20 years. PA2G4 expression levels are correlated with prognosis in a range of human cancers, including neuroblastoma, cervical, brain, breast, prostate, pancreatic, hepatocellular, and other tumors. There are two PA2G4 isoforms, PA2G4-p42 and PA2G4-p48, and although both isoforms of PA2G4 regulate cellular growth and differentiation, these isoforms often have opposing roles depending on the context. Therefore, PA2G4 can function either as a contextual tumor suppressor or as an oncogene, depending on the tissue being studied. However, it is unclear how distinct structural features of the two PA2G4 isoforms translate into different functional outcomes. In this review, we examine published structures to identify important structural and functional components of PA2G4 and consider how they may explain its crucial role in the malignant phenotype. We will highlight the lysine-rich regions, protein-protein interaction sites, and post-translational modifications of the two PA2G4 isoforms and relate these to the functional cellular role of PA2G4. These data will enable a better understanding of the function and structure relationship of the two PA2G4 isoforms and highlight the care that will need to be undertaken for those who wish to conduct isoform-specific structure-based drug design campaigns.

The roles of multifunctional protein ErbB3 binding protein 1 (EBP1) isoforms from development to disease

The roles of the two isoforms of ErbB3-binding protein 1 (Ebp1) in cellular function and its regulation in disease and development is a stimulating area in current fields of biology, such as neuroscience, cancer biology, and structural biology. Over the last two decades, a growing body of studies suggests have suggested different functions for the EBP1 isoforms in various cancers, along with their specific binding partners in the ubiquitin-proteasome system. Owing to the specific cellular context or spatial/temporal expression of the EBP1 isoforms, either transcriptional repression or the activation function of EBP1 has been proposed, and epigenetic regulation by p48 EBP1 has also been observed during in the embryo development, including in brain development and neurologic disorders, such as schizophrenia, in using an Ebp1 knockout mouse model. Here, we review recent findings that have shaped our current understanding of the emerging function of EBP1 isoforms in cellular events and gene expression, from development to disease.

A pair of proteins that originate from a common gene exert strikingly different effects on embryonic development as well as tumor growth and progression. RNA transcripts generated from the PA2G4 gene can undergo enzymatic processing to yield two different protein products, p42 EB1 and p48 EB1. These proteins differ by the presence or absence of 54 amino acids at one end, and Jee-Yin Ahn at the Sungkyunkwan University School of Medicine, Suwon, South Korea, and colleagues have reviewed current insights into the functional consequences of this difference. The two proteins bind to distinct sets of molecular partners. The p48 form appears to regulate a host of genes involved in brain development, but also appears to drive cancerous growth in various tumors. In contrast, p42 is scarcer during development, and appears to inhibit tumor formation.

Ehrlichia chaffeensis TRP120-mediated ubiquitination and proteasomal degradation of tumor suppressor FBW7 increases oncoprotein stability and promotes infection

Ehrlichia chaffeensis (E. chaffeensis) exploits evolutionarily conserved Notch and Wnt host cell signaling pathways to downregulate innate immune host defenses and promote infection. The multifunctional E. chaffeensis TRP120 effector which has HECT E3 ubiquitin ligase activity, interacts with the host nuclear tumor suppressor F-BOX and WD domain repeating-containing 7 (FBW7). FBW7 is the substrate recognition subunit of the Skp1-cullin-1-FBOX E3 ubiquitin (Ub) ligase complex (SCF) known to negatively regulate a network of oncoproteins (Notch, cyclin E, c-Jun, MCL1 and cMYC). In this study, we demonstrate that TRP120 and FBW7 colocalize strongly in the nucleus by confocal immunofluorescent microscopy and interactions between TRP120 and FBW7 FBOX and WD40 domains were demonstrated by ectopic expression and co-immunoprecipitation. Although FBW7 gene expression increased during E. chaffeensis infection, FBW7 levels significantly decreased (>70%) by 72 h post infection. Moreover, an iRNA knockdown of FBW7 coincided with increased E. chaffeensis infection and levels of Notch intracellular domain (NICD), phosphorylated c-Jun, MCL-1 and cMYC, which are negatively regulated by FBW7. An increase in FBW7 K48 ubiquitination was detected during infection by co-IP, and FBW7 degradation was inhibited in infected cells treated with the proteasomal inhibitor bortezomib. Direct TRP120 ubiquitination of native and recombinant FBW7 was demonstrated in vitro and confirmed by ectopic expression of TRP120 HECT Ub ligase catalytic site mutant. This study identifies the tumor suppressor, FBW7, as a TRP120 HECT E3 Ub ligase substrate, and demonstrates that TRP120 ligase activity promotes ehrlichial infection by degrading FBW7 to maintain stability of Notch and other oncoproteins involved in cell survival and apoptosis.

Drugging MYCN Oncogenic Signaling through the MYCN-PA2G4 Binding Interface

MYCN is a major driver for the childhood cancer, neuroblastoma, however, there are no inhibitors of this target. Enhanced MYCN protein stability is a key component of MYCN oncogenesis and is maintained by multiple feedforward expression loops involving MYCN transactivation target genes. Here, we reveal the oncogenic role of a novel MYCN target and binding protein, proliferation-associated 2AG4 (PA2G4). Chromatin immunoprecipitation studies demonstrated that MYCN occupies the PA2G4 gene promoter, stimulating transcription. Direct binding of PA2G4 to MYCN protein blocked proteolysis of MYCN and enhanced colony formation in a MYCN-dependent manner. Using molecular modeling, surface plasmon resonance, and mutagenesis studies, we mapped the MYCN-PA2G4 interaction site to a 14 amino acid MYCN sequence and a surface crevice of PA2G4. Competitive chemical inhibition of the MYCN-PA2G4 protein-protein interface had potent inhibitory effects on neuroblastoma tumorigenesis in vivo. Treated tumors showed reduced levels of both MYCN and PA2G4. Our findings demonstrate a critical role for PA2G4 as a cofactor in MYCN-driven neuroblastoma and highlight competitive inhibition of the PA2G4-MYCN protein binding as a novel therapeutic strategy in the disease. SIGNIFICANCE: Competitive chemical inhibition of the PA2G4-MYCN protein interface provides a basis for drug design of small molecules targeting MYC and MYCN-binding partners in malignancies driven by MYC family oncoproteins.

ErbB3-binding protein 1 (EBP1) represses HNF4α-mediated transcription and insulin secretion in pancreatic β-cells

HNF4α (hepatocyte nuclear factor 4α) is one of the master regulators of pancreatic β-cell development and function, and mutations in the HNF4α gene are well-known monogenic causes of diabetes. As a member of the nuclear receptor family, HNF4α exerts its gene regulatory function through various molecular interactions; however, there is a paucity of knowledge of the different functional complexes in which HNF4α participates. Here, to find HNF4α-binding proteins in pancreatic β-cells, we used yeast two-hybrid screening, a mammalian two-hybrid assay, and glutathione S-transferase pulldown approaches, which identified EBP1 (ErbB3-binding protein 1) as a factor that binds HNF4α in a LXXLL motif-mediated manner. In the β-cells, EBP1 suppressed the expression of HNF4α target genes that are implicated in insulin secretion, which is impaired in HNF4α mutation-driven diabetes. The crystal structure of the HNF4α ligand-binding domain in complex with a peptide harboring the EBP1 LXXLL motif at 3.15Å resolution hinted at the molecular basis of the repression. The details of the structure suggested that EBP1's LXXLL motif competes with HNF4α coactivators for the same binding pocket and thereby prevents recruitment of additional transcriptional coactivators. These findings provide further evidence that EBP1 plays multiple cellular roles and is involved in nuclear receptor-mediated gene regulation. Selective disruption of the HNF4α-EBP1 interaction or tissue-specific EBP1 inactivation can enhance HNF4α activities and thereby improve insulin secretion in β-cells, potentially representing a new strategy for managing diabetes and related metabolic disorders.

Regulation of Fn14 stability by SCFFbxw7α during septic acute kidney injury

Acute kidney injury (AKI) initiated by sepsis remains a thorny problem despite recent advancements in its clinical management. Having been found to be activated during AKI, fibroblast growth factor-inducible molecule 14 (Fn14) may be a potential therapeutic target because of its involvement in the molecular basis of injury. Here, we report that LPS induces apoptosis of mouse cortical tubule cells mediated by Fn14, for which simultaneous Toll-like receptor (TLR)4 activation is required. Mechanistically, TLR4 activation by lipopolysaccharide, through disassociating E3 ligase SCFFbxw7α from Fn14, dismantles Lys48-linked polyubiquitination of Fn14 and stabilizes it. Pharmacological deactivation of Fn14 with monoclonal antibody ITEM-2 provides effective protection against lethal sepsis and AKI in mice. Our study underscores an adaptive mechanism whereby TLR4 regulates SCFFbxw7α-dependent Fn14 stabilization during inflammatory tubular damage and further supports investigation of targeting Fn14 in clinical trials of patients with septic AKI.

YC-1 Antagonizes Wnt/β-Catenin Signaling Through the EBP1 p42 Isoform in Hepatocellular Carcinoma

Novel drugs targeting Wnt signaling are gradually being developed for hepatocellular carcinoma (HCC) treatment. In this study, we used a Wnt-responsive Super-TOPflash (STF) luciferase reporter assay to screen a new compound targeting Wnt signaling. 3-(5'-Hydroxymethyl-2'-furyl)-1-benzylindazole (YC-1) was identified as a small molecule inhibitor of the Wnt/β-catenin pathway. Our coimmunoprecipitation (co-IP) data showed that YC-1 did not affect the β-catenin/TCF interaction. Then, by mass spectrometry, we identified the ErbB3 receptor-binding protein 1 (EBP1) interaction with the β-catenin/TCF complex upon YC-1 treatment. EBP1 encodes two splice isoforms, p42 and p48. We further demonstrated that YC-1 enhances p42 isoform binding to the β-catenin/TCF complex and reduces the transcriptional activity of the complex. The suppression of colony formation by YC-1 was significantly reversed after knockdown of both isoforms (p48 and p42); however, the inhibition of colony formation was maintained when only EBP1 p48 was silenced. Taken together, these results suggest that YC-1 treatment results in a reduction in Wnt-regulated transcription through EBP1 p42 and leads to the inhibition of tumor cell proliferation. These data imply that YC-1 is a drug that antagonizes Wnt/β-catenin signaling in HCC.

FBXW7: a critical tumor suppressor of human cancers

The ubiquitin-proteasome system (UPS) is involved in multiple aspects of cellular processes, such as cell cycle progression, cellular differentiation, and survival (Davis RJ et al., Cancer Cell 26:455-64, 2014; Skaar JR et al., Nat Rev Drug Discov 13:889-903, 2014; Nakayama KI and Nakayama K, Nat Rev Cancer 6:369-81, 2006). F-box and WD repeat domain containing 7 (FBXW7), also known as Sel10, hCDC4 or hAgo, is a member of the F-box protein family, which functions as the substrate recognition component of the SCF E3 ubiquitin ligase. FBXW7 is a critical tumor suppressor and one of the most commonly deregulated ubiquitin-proteasome system proteins in human cancer. FBXW7 controls proteasome-mediated degradation of oncoproteins such as cyclin E, c-Myc, Mcl-1, mTOR, Jun, Notch and AURKA. Consistent with the tumor suppressor role of FBXW7, it is located at chromosome 4q32, a genomic region deleted in more than 30% of all human cancers (Spruck CH et al., Cancer Res 62:4535-9, 2002). Genetic profiles of human cancers based on high-throughput sequencing have revealed that FBXW7 is frequently mutated in human cancers. In addition to genetic mutations, other mechanisms involving microRNA, long non-coding RNA, and specific oncogenic signaling pathways can inactivate FBXW7 functions in cancer cells. In the following sections, we will discuss the regulation of FBXW7, its role in oncogenesis, and the clinical implications and prognostic value of loss of function of FBXW7 in human cancers.

Alterations of Notch pathway in patients with adenoid cystic carcinoma of the trachea and its impact on survival

INTRODUCTION

Adenoid cystic carcinoma (ACC) of the trachea lacks of well-characterized molecular markers. There is currently no specific treatment for metastatic ACC of the trachea. This study aimed to identify genomic mutations of Notch pathway and investigate the efficacy of NOTCH inhibitor in ACC of the trachea.

METHODS

73 Patients with ACC of the trachea at four institutions from 2008 to 2016 were identified. Analysis of hotspot mutations in cancer-related genes of Notch pathway was performed using next generation sequencing. Gene-expression and functional analyses were performed to study the mechanism of activation through mutation. Univariable and multivariable Cox regression models were used to predict overall survival (OS). Patient-derived xenograft (PDX) models were established and treated with NOTCH inhibitor Brontictuzumab.

RESULTS

Gain-of-function mutations of the NOTCH1 gene occurred in 12 (16.4%) tumors, leading to stabilization of the intracellular cleaved form of NOTCH1 (ICN1). NOTCH1 mutation was associated with increased NOTCH1 activation and its target gene HES1. Mutations in NOTCH2 (3/73), NOTCH4 (2/73), JAG1 (1/73) and FBXW7 (2/73) were also identified in 8 (11.0%) patients. A strong inverse correlation of expression was observed between FBXW7 and HES1. NOTCH1 mutation was associated with solid subtype (P = 0.02), younger age at diagnosis (P = 0.041) and shorter overall survival (OS) (P = 0.017). NOTCH1 mutation was not an independent prognostic factor in the presence of histologic subtype and resection margin. Brontictuzumab significantly reduced tumor growth in NOTCH1-mutated PDX.

CONCLUSION

NOTCH1 mutation is associated with activation of Notch pathway in ACC of the trachea. NOTCH1 is a potential target for therapeutic intervention in patients with ACC of the trachea.

Sirtuin 7 plays an oncogenic role in human osteosarcoma via downregulating CDC4 expression

It is still a controversy whether the role of Sirtuin 7 (SIRT7) is an oncogene or a tumor suppressor gene in cancer as SIRT7 may have different functions in different types of cancer. Particularly, the specific roles of SIRT7 in the progression of osteosarcoma remain undiscovered. The main aim of this study is to identify the expression of SIRT7 in osteosarcoma and explore the biological functions of SIRT7 in regulating cellular processes of osteosarcoma cells. Here, we show that SIRT7 expression was significantly higher in osteosarcoma tissues and osteosarcoma cell lines than in non-tumor tissues and an immortalized normal cell line, respectively. Moreover, elevated SIRT7 levels in clinical samples indicate a poor prognosis of osteosarcoma patients. SIRT7 knockdown reduces proliferation, migration, invasion, tumor formation, and metastasis of osteosarcoma cells, while SIRT7 overexpression has the opposite effects. Mechanistically, SIRT7 down regulates H3K18ac expression and decreases H3K18ac binding to the promoter region of CDC4, leading to the inhibition of CDC4 transcription. Furthermore, the silencing of CDC4 partially rescued SIRT7 knockdown-mediated inhibitory effects on proliferation, migration, and invasion of osteosarcoma cells. In summary, our results show that SIRT7 promotes proliferation, migration, and invasion of osteosarcoma cells through targeting CDC4, suggesting a potential therapeutic target for SIRT7 based therapy for osteosarcoma.