The role of ErbB3 binding protein 1 in cancer: Friend or foe?

Ribosomal RNA expansion segments and their role in ribosome biology

Ribosomes are universally conserved cellular machines that catalyze protein biosynthesis. The active sites underly immense evolutionary conservation resulting in virtually identical core structures of ribosomes in all domains of life including organellar ribosomes. However, more peripheral structures of cytosolic ribosomes changed during evolution accommodating new functions and regulatory options. The expansion occurred at the riboprotein level, including more and larger ribosomal proteins and at the RNA level increasing the length of ribosomal RNA. Expansions within the ribosomal RNA occur as clusters at conserved sites that face toward the periphery of the cytosolic ribosome. Recent biochemical and structural work has shed light on how rRNA-specific expansion segments (ESs) recruit factors during translation and how they modulate translation dynamics in the cytosol. Here we focus on recent work on yeast, human and trypanosomal cytosolic ribosomes that explores the role of two specific rRNA ESs within the small and large subunit respectively. While no single regulatory strategy exists, the absence of ESs has consequences for proteomic stability and cellular fitness, rendering them fascinating evolutionary tools for tailored protein biosynthesis.

Identification of Novel Plasma Biomarkers for Abdominal Aortic Aneurysm by Protein Array Analysis

Abdominal aortic aneurysm (AAA) is a potentially life-threatening disease that is common in the aging population. Currently, there are no approved diagnostic biomarkers or therapeutic drugs for AAA. We aimed to identify novel plasma biomarkers or potential therapeutic targets for AAA using a high-throughput protein array-based method. Proteomics expression profiles were investigated in plasma from AAA patients and healthy controls (HC) using 440-cytokine protein array analysis. Several promising biomarkers were further validated in independent cohorts using enzyme-linked immunosorbent assay (ELISA). Thirty-nine differentially expressed plasma proteins were identified between AAA and HC. Legumain (LGMN) was significantly higher in AAA patients and was validated in another large cohort. Additionally, "AAA without diabetes" (AAN) patients and "AAA complicated with type 2 diabetes mellitus" (AAM) patients had different cytokine expression patterns in their plasma, and nine plasma proteins were differentially expressed among the AAN, AAM, and HC subjects. Delta-like protein 1 (DLL1), receptor tyrosine-protein kinase erbB-3 (ERBB3), and dipeptidyl peptidase 4 (DPPIV) were significantly higher in AAM than in AAN. This study identified several promising plasma biomarkers of AAA. Their role as therapeutic targets for AAA warrants further investigation.

ANXA9 as a novel prognostic biomarker associated with immune infiltrates in gastric cancer

Background

Gastric cancer (GC) is the most prevalent malignancy among the digestive system tumors. Increasing evidence has revealed that lower mRNA expression of ANXA9 is associated with a poor prognosis in colorectal cancer. However, the role of ANXA9 in GC remains largely unknown.

Material and Methods

The Gene Expression Profiling Interactive Analysis (GEPIA) and Human Protein Atlas databases were used to investigate the expression of ANXA9 in GC, which was then validated in the four Gene Expression Omnibus (GEO) datasets. The diagnostic value of ANXA9 for GC patients was demonstrated using a receiver operating characteristic (ROC) curve. The correlation between ANXA9 expression and clinicopathological parameters was analyzed in The Cancer Genome Atlas (TCGA) and UALCAN databases. The Kaplan-Meier (K-M) survival curve was used to elucidate the relationship between ANXA9 expression and the survival time of GC patients. We then performed a gene set enrichment analysis (GSEA) to explore the biological functions of ANXA9. The relationship of ANXA9 expression and cancer immune infiltrates was analyzed using the Tumor Immune Estimation Resource (TIMER). In addition, the potential mechanism of ANXA9 in GC was investigated by analyzing its related genes.

Results

ANXA9 was significantly up-regulated in GC tissues and showed obvious diagnostic value. The expression of ANXA9 was related to the age, gender, grade, TP53 mutation, and histological subtype of GC patients. We also found that ANXA9 expression was associated with immune-related biological function. ANXA9 expression was also correlated with the infiltration level of CD8⁺ T cells, neutrophils, and dendritic cells in GC. Additionally, copy number variation (VNV) of ANXA9 occurred in GC patients. Function enrichment analyses revealed that ANXA9 plays a role in the GC progression by interacting with its related genes.

Conclusions

Our results provide strong evidence of ANXA9 expression as a prognostic indicator related to immune responses in GC.

Targeting miR-126 in inv(16) acute myeloid leukemia inhibits leukemia development and leukemia stem cell maintenance

Acute myeloid leukemia (AML) harboring inv(16)(p13q22) expresses high levels of miR-126. Here we show that the CBFB-MYH11 (CM) fusion gene upregulates miR-126 expression through aberrant miR-126 transcription and perturbed miR-126 biogenesis via the HDAC8/RAN-XPO5-RCC1 axis. Aberrant miR-126 upregulation promotes survival of leukemia-initiating progenitors and is critical for initiating and maintaining CM-driven AML. We show that miR-126 enhances MYC activity through the SPRED1/PLK2-ERK-MYC axis. Notably, genetic deletion of miR-126 significantly reduces AML rate and extends survival in CM knock-in mice. Therapeutic depletion of miR-126 with an anti-miR-126 (miRisten) inhibits AML cell survival, reduces leukemia burden and leukemia stem cell (LSC) activity in inv(16) AML murine and xenograft models. The combination of miRisten with chemotherapy further enhances the anti-leukemia and anti-LSC activity. Overall, this study provides molecular insights for the mechanism and impact of miR-126 dysregulation in leukemogenesis and highlights the potential of miR-126 depletion as a therapeutic approach for inv(16) AML.

miR-126 is highly expressed in inv(16) Acute myeloid leukemia (AML) but its role is unclear. Here, the authors show that the aberrant expression of miR-126 in inv(16) AML is directly due to the CBFB-MYH11 fusion gene and that it can promote AML development and leukemia stem cell maintenance, highlighting miR-126 as a therapeutic target for inv(16) AML patients

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.

Y-Box Binding Protein-1 Promotes Epithelial-Mesenchymal Transition in Sorafenib-Resistant Hepatocellular Carcinoma Cells

Hepatocellular carcinoma is one of the most common cancer types worldwide. In cases of advanced-stage disease, sorafenib is considered the treatment of choice. However, resistance to sorafenib remains a major obstacle for effective clinical application. Based on integrated phosphoproteomic and The Cancer Genome Atlas (TCGA) data, we identified a transcription factor, Y-box binding protein-1 (YB-1), with elevated phosphorylation of Ser102 in sorafenib-resistant HuH-7^R cells. Phosphoinositide-3-kinase (PI3K) and protein kinase B (AKT) were activated by sorafenib, which, in turn, increased the phosphorylation level of YB-1. In functional analyses, knockdown of YB-1 led to decreased cell migration and invasion in vitro. At the molecular level, inhibition of YB-1 induced suppression of zinc-finger protein SNAI1 (Snail), twist-related protein 1 (Twist1), zinc-finger E-box-binding homeobox 1 (Zeb1), matrix metalloproteinase-2 (MMP-2) and vimentin levels, implying a role of YB-1 in the epithelial-mesenchymal transition (EMT) process in HuH-7^R cells. Additionally, YB-1 contributes to morphological alterations resulting from F-actin rearrangement through Cdc42 activation. Mutation analyses revealed that phosphorylation at S102 affects the migratory and invasive potential of HuH-7^R cells. Our collective findings suggest that sorafenib promotes YB-1 phosphorylation through effect from the EGFR/PI3K/AKT pathway, leading to significant enhancement of hepatocellular carcinoma (HCC) cell metastasis. Elucidation of the specific mechanisms of action of YB-1 may aid in the development of effective strategies to suppress metastasis and overcome resistance.

Protein Synthesis in the Developing Neocortex at Near-Atomic Resolution Reveals Ebp1-Mediated Neuronal Proteostasis at the 60S Tunnel Exit

Protein synthesis must be finely tuned in the developing nervous system as the final essential step of gene expression. This study investigates the architecture of ribosomes from the neocortex during neurogenesis, revealing Ebp1 as a high-occupancy 60S peptide tunnel exit (TE) factor during protein synthesis at near-atomic resolution by cryoelectron microscopy (cryo-EM). Ribosome profiling demonstrated Ebp1-60S binding is highest during start codon initiation and N-terminal peptide elongation, regulating ribosome occupancy of these codons. Membrane-targeting domains emerging from the 60S tunnel, which recruit SRP/Sec61 to the shared binding site, displace Ebp1. Ebp1 is particularly abundant in the early-born neural stem cell (NSC) lineage and regulates neuronal morphology. Ebp1 especially impacts the synthesis of membrane-targeted cell adhesion molecules (CAMs), measured by pulsed stable isotope labeling by amino acids in cell culture (pSILAC)/bioorthogonal noncanonical amino acid tagging (BONCAT) mass spectrometry (MS). Therefore, Ebp1 is a central component of protein synthesis, and the ribosome TE is a focal point of gene expression control in the molecular specification of neuronal morphology during development.

Pseudogene PA2G4P4 promotes oncogene PA2G4 expression and nuclear translocation to affect glioblastoma cell viability and apoptosis

Dysregulation of pseudogenes is involved in the progression of various types of cancer, including glioblastoma (GBM). Proliferation associated-2G4 (PA2G4) pseudogene 4 (PA2G4P4) has been shown to play an oncogenic role in bladder cancer development. Our study aimed to explore the role and mechanism of PA2G4P4 in GBM progression. PA2G4P4 and PA2G4 expression in GBM tissues was analyzed using the GEPIA database. Cell viability, apoptosis, and activities of caspase-3 and caspase-9 in GBM cells were explored by CCK-8, flow cytometry analysis, and colorimetric activity assay kits, respectively. GEPIA database showed that PA2G4P4 and PA2G4 were both upregulated in GBM tissues. PA2G4P4 expression was also boosted in GBM cells. Knockdown of PA2G4P4 or PA2G4 inhibited cell viability, induced apoptosis, and increased caspase-3 and caspase-9 activities in GBM cells. Data from UALCAN database showed that among top 15 genes correlated with PA2G4P4, PA2G4 had the highest correlation coefficient. Additionally, knockdown of PA2G4P4 inhibited PA2G4 expression and nuclear translocation in GBM cells. Overexpression of PA2G4 abolished the functions of PA2G4P4 knockdown on viability and apoptosis in GBM cells. Summarily, pseudogene PA2G4P4 promotes oncogene PA2G4 expression and nuclear translocation to affect cell viability and apoptosis in GBM cells.

Structural snapshots of human pre-60S ribosomal particles before and after nuclear export

Ribosome biogenesis is an elaborate and energetically expensive program that involve two hundred protein factors in eukaryotes. Nuclear export of pre-ribosomal particles is one central step which also serves as an internal structural checkpoint to ensure the proper completion of nuclear assembly events. Here we present four structures of human pre-60S particles isolated through a nuclear export factor NMD3, representing assembly stages immediately before and after nuclear export. These structures reveal locations of a dozen of human factors, including an uncharacterized factor TMA16 localized between the 5S RNA and the P0 stalk. Comparison of these structures shows a progressive maturation for the functional regions, such as peptidyl transferase centre and peptide exit tunnel, and illustrate a sequence of factor-assisted rRNA maturation events. These data facilitate our understanding of the global conservation of ribosome assembly in eukaryotes and species-specific features of human assembly factors.

Structure and function of yeast Lso2 and human CCDC124 bound to hibernating ribosomes

Cells adjust to nutrient deprivation by reversible translational shutdown. This is accompanied by maintaining inactive ribosomes in a hibernation state, in which they are bound by proteins with inhibitory and protective functions. In eukaryotes, such a function was attributed to suppressor of target of Myb protein 1 (Stm1; SERPINE1 mRNA-binding protein 1 [SERBP1] in mammals), and recently, late-annotated short open reading frame 2 (Lso2; coiled-coil domain containing short open reading frame 124 [CCDC124] in mammals) was found to be involved in translational recovery after starvation from stationary phase. Here, we present cryo-electron microscopy (cryo-EM) structures of translationally inactive yeast and human ribosomes. We found Lso2/CCDC124 accumulating on idle ribosomes in the nonrotated state, in contrast to Stm1/SERBP1-bound ribosomes, which display a rotated state. Lso2/CCDC124 bridges the decoding sites of the small with the GTPase activating center (GAC) of the large subunit. This position allows accommodation of the duplication of multilocus region 34 protein (Dom34)-dependent ribosome recycling system, which splits Lso2-containing, but not Stm1-containing, ribosomes. We propose a model in which Lso2 facilitates rapid translation reactivation by stabilizing the recycling-competent state of inactive ribosomes.

Role of PA2G4P4 pseudogene in bladder cancer tumorigenesis

BACKGROUND

Many pseudogenes possess biological activities and play important roles in the pathogenesis of various types of cancer including bladder cancer (BlCa), which still lacks suitable molecular biomarkers. Recently, pseudogenes were found to be significantly enriched in a pan-cancer classification based on the Cancer Genome Atlas gene expression data. Among them, the top-ranking pseudogene was the proliferation-associated 2G4 pseudogene 4 (PA2G4P4).

METHODS

Genomic and transcript features of PA2G4P4 were determined by GeneBank database analysis followed by 5' RACE experiments. Therefore, we conducted a retrospective molecular study on a cohort of 45 patients of BlCa. PA2G4P4 expression was measured by RT-qPCR, whereas PA2G4P4 transcript distribution was analyzed by in situ hybridization on both normal and cancerous histological sections and compared to the immunolocalization of its parental PA2G4/EBP1 protein. Finally, we tested the effects of PA2G4P4 depletion on proliferation, migration, and death of BlCa cells.

RESULTS

We showed for the first time PA2G4P4 overexpression in BlCa tissues and in cell lines. PA2G4P4 distribution strictly overlaps PA2G4/EBP1 protein localization. Moreover, we showed that PA2G4P4 knockdown affects both proliferation and migration of BlCa cells, highlighting its potential oncogenic role.

CONCLUSIONS

PA2G4P4 may play a functional role as an oncogene in BlCa development, suggesting it as a good candidate for future investigation and new clinical applications.

Requirement of GTP binding for TIF-90-regulated ribosomal RNA synthesis and oncogenic activities in human colon cancer cells

Transcription initiation factor 90 (TIF-90), an alternatively spliced variant of TIF-IA, differs by a 90 base pair deletion of exon 6. TIF-90 has been shown to regulate ribosomal RNA (rRNA) synthesis by interacting with polymerase I (Pol I) during the initiation of ribosomal DNA (rDNA) transcription in the nucleolus. Recently, we showed that TIF-90-mediated rRNA synthesis can play an important role in driving tumorigenesis in human colon cancer cells. Here we show that TIF-90 binds GTP at threonine 310, and that GTP binding is required for TIF-90-enhanced rRNA synthesis. Overexpression of activated AKT induces TIF-90 T310, but not a GTP-binding site (TIF-90 T310N) mutant, to translocate into the nucleolus and increase rRNA synthesis. Complementing this result, treatment with mycophenolic acid (MPA), an inhibitor of GTP production, dissociates TIF-90 from Pol I and hence abolishes AKT-increased rRNA synthesis by way of TIF-90 activation. Thus, TIF-90 requires bound GTP to fulfill its function as an enhancer of rRNA synthesis. Both TIF variants are highly expressed in colon cancer cells, and depletion of TIF-IA expression in these cells results in significant sensitivity to MPA-inhibited rRNA synthesis and reduced cell proliferation. Finally, a combination of MPA and AZD8055 (an inhibitor of both AKT and mTOR) synergistically inhibits rRNA synthesis, in vivo tumor growth, and other oncogenic activities of primary human colon cancer cells, suggesting a potential avenue for the development of therapeutic treatments by targeting the regulation of rRNA synthesis by TIF proteins.

Human Ebp1 rescues the synthetic lethal growth of fission yeast cells lacking Cdb4 and Nup184

Cdb4 is a protein with unknown functions that binds to curved DNA in vitro in the fission yeast Schizosaccharomyces pombe. Homologues of Cdb4 were identified in a wide range of eukaryotes, including human Ebp1. Both S. pombe Cdb4 and human Ebp1 are nonpeptidase members of the methionine aminopeptidase family. It has been reported that Ebp1 homologues are involved in cell growth regulation and differentiation. However, opposing functions have also been considered and debated upon, and the precise biological functions of this conserved protein are largely unknown. S. pombe cdb4 is a nonessential gene, and no obvious phenotypes have been detected in cells with cdb4 gene deletion. In this study, we identified nup184, encoding a component of the nuclear pore complex, as a gene responsible for the synthetic lethal phenotype associated with cdb4. Furthermore, the synthetic lethal phenotype of Cdb4 was suppressed by over-expression of human Ebp1, suggesting that it has conserved crucial functions in S. pombe Cdb4 and human Ebp1. This synthetic lethal phenotype associated with Cdb4 and Nup184 provides a molecular genetics tool to study the functions of S. pombe Cdb4 and its conserved members of proteins, including human Ebp1.

MetAP-like Ebp1 occupies the human ribosomal tunnel exit and recruits flexible rRNA expansion segments

Human Ebp1 is a member of the proliferation-associated 2G4 (PA2G4) family and plays an important role in cancer regulation. Ebp1 shares the methionine aminopeptidase (MetAP) fold and binds to mature 80S ribosomes for translational control. Here, we present a cryo-EM single particle analysis reconstruction of Ebp1 bound to non-translating human 80S ribosomes at a resolution range from 3.3 to ~8 Å. Ebp1 blocks the tunnel exit with major interactions to the general uL23/uL29 docking site for nascent chain-associated factors complemented by eukaryote-specific eL19 and rRNA helix H59. H59 is defined as dynamic adaptor undergoing significant remodeling upon Ebp1 binding. Ebp1 recruits rRNA expansion segment ES27L to the tunnel exit via specific interactions with rRNA consensus sequences. The Ebp1-ribosome complex serves as a template for MetAP binding and provides insights into the structural principles for spatial coordination of co-translational events and molecular triage at the ribosomal tunnel exit.

The ErbB3 receptor binding protein Ebp1 binds to ribosomes and is linked to translational control. Here, the authors present the cryo-EM structure of human Ebp1 bound to a non-translating 80S ribosome and find that Ebp1 blocks the tunnel exit and recruits the rRNA expansion segment ES27L to the tunnel exit.

Somatic Mutations and Intratumoral Heterogeneity of Cancer-Related Genes NLK, YY1 and PA2G4 in Gastric and Colorectal Cancers

Many genes act as both tumor suppressor gene (TSG) and proto-oncogene depending on cellular context and cancer type. Nemo-like kinase (NLK) encoding a serine/threonine kinase, Yin Yang 1 (YY1) encoding a zinc-finger transcription factor and PA2G4 encoding an ErbB3 binding protein have both of these two opposing functions. In the present study, we analyzed NLK, YY1 and PA2G4 frameshift mutations in sporadic GC and CRC with high microsatellite instability (MSI-H). Also, regional intratumoral heterogeneity (ITH) of frameshift mutations of these genes was analyzed in CRCs. We found frameshift mutations of NLK, YY1 and PA2G4 in CRC and GC with MSI-H (17/132: 12.9%), but not in those with MSS (0/90). Two (12.5%), one (6.3%) and one (6.3%) CRC (s) of the 16 CRCs exhibited ITH of NLK, YY1 and PA2G4 mutations among the 4-7 regions, suggesting that ITH of the frameshift mutations might be frequent in the CRCs. These results suggest that frameshift mutations of NLK, YY1 and PA2G4 along with the ITH might contribute to MSI-H cancer pathogenesis.

Circular RNA circERBB2 promotes gallbladder cancer progression by regulating PA2G4-dependent rDNA transcription

BACKGROUND

CircRNAs are found to affect initiation and progression of several cancer types. However, whether circRNAs are implicated in gallbladder cancer (GBC) progression remains obscure.

METHODS

We perform RNA sequencing in 10 pairs of GBC and para-cancer tissues. CCK8 and clone formation assays are used to evaluate proliferation ability of GBC cells. qPCR and Western blot are used to determine expression of RNAs and proteins, respectively. CircRNA-protein interaction is confirmed by RNA pulldown, RNA immunoprecipitation, and fluorescence in situ hybridization.

RESULTS

We find that circRNA expression pattern is tremendously changed during GBC development. Among dozens of significantly changed circRNAs, a circRNA generated from the oncogene ERBB2, named as circERBB2, is one of the most significant changes. CircERBB2 promotes GBC proliferation, in vitro and in vivo. Other than being a miRNA sponge, circERBB2 accumulates in the nucleoli and regulates ribosomal DNA transcription, which is one of the rate-limiting steps of ribosome synthesis and cellular proliferation. CircERBB2 regulates nucleolar localization of PA2G4, thereby forming a circERBB2-PA2G4-TIFIA regulatory axis to modulate ribosomal DNA transcription and GBC proliferation. Increased expression of circERBB2 is associated with worse prognosis of GBC patients.

CONCLUSIONS

Our findings demonstrate that circERBB2 serves as an important regulator of cancer cell proliferation and shows the potential to be a new therapeutic target of GBC.

8-chloro-adenosine activity in FLT3-ITD acute myeloid leukemia

Nucleoside analogs represent the backbone of several distinct chemotherapy regimens for acute myeloid leukemia (AML) and combination with tyrosine kinase inhibitors has improved survival of AML patients, including those harboring the poor-risk FLT3-ITD mutation. Although these compounds are effective in killing proliferating blasts, they lack activity against quiescent leukemia stem cells (LSCs), which contributes to initial treatment refractoriness or subsequent disease relapse. The reagent 8-chloro-adenosine (8-Cl-Ado) is a ribose-containing, RNA-directed nucleoside analog that is incorporated into newly transcribed RNA rather than in DNA, causing inhibition of RNA transcription. In this report, we demonstrate antileukemic activities of 8-Cl-Ado in vitro and in vivo and provide mechanistic insight into the mode of action of 8-Cl-Ado in AML. 8-Cl-Ado markedly induced apoptosis in LSC, with negligible effects on normal stem cells. 8-Cl-Ado was particularly effective against AML cell lines and primary AML blast cells harboring the FLT3-ITD mutation. FLT3-ITD is associated with high expression of miR-155. Furthermore, we demonstrate that 8-Cl-Ado inhibits miR-155 expression levels accompanied by induction of DNA-damage and suppression of cell proliferation, through regulation of miR-155/ErbB3 binding protein 1(Ebp1)/p53/PCNA signaling. Finally, we determined that combined treatment of NSG mice engrafted with FLT3-ITD + MV4-11 AML cells with 8-Cl-Ado and the FLT3 inhibitor AC220 (quizartinib) synergistically enhanced survival, compared with that of mice treated with the individual drugs, suggesting a potentially effective approach for FLT3-ITD AML patients.

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.

Ebp1 p48 promotes oncogenic activities in human colon cancer cells through regulation of TIF-90-mediated ribosomal RNA synthesis

The ErbB3-binding protein 1 (Ebp1) has been reported as either an oncogenic regulator or a tumor suppressor in a variety of cancers. Here, we show that Ebp1 p48, a predominant expression isoform, is highly expressed in the majority of human colon tumor cells compared with normal adjacent tissues and its expression is required for the oncogenic activities of these cells. Depletion of Ebp1 expression in primary colon cancer cells inhibits cell proliferation, colony forming, and invasion in vitro as well as tumor formation in vivo and enhances cell sensitivity to irradiation. We further demonstrated that Ebp1 interacts with TIF-90, a splice variant of transcription initiation factor IA (TIF-IA) of the RNA polymerase I complex, allowing for regulation of ribosomal RNA (rRNA) synthesis and oncogenesis in human colon cancer cells. Moreover, Ebp1 expression is essential for Akt protected TIF-90 stability by preventing TIF-90's ubiquitination by Mdm2 and hence, its proteasomal degradation. The results of the present study support a mechanism of underlying oncogenic activities by means of Ebp1 through regulation of TIF-90-mediated rRNA synthesis and suggest the potential therapeutic treatment of colon cancer by targeting Ebp1 and its signaling.