Ebp1, an ErbB-3 binding protein, interacts with Rb and affects Rb transcriptional regulation

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.

Progression signature underlies clonal evolution and dissemination of multiple myeloma

Clonal evolution drives tumor progression, dissemination, and relapse in multiple myeloma (MM), with most patients dying of relapsed disease. This multistage process requires tumor cells to enter the circulation, extravasate, and colonize distant bone marrow (BM) sites. Here, we developed a fluorescent or DNA-barcode clone-tracking system on MM PrEDiCT (progression through evolution and dissemination of clonal tumor cells) xenograft mouse model to study clonal behavior within the BM microenvironment. We showed that only the few clones that successfully adapt to the BM microenvironment can enter the circulation and colonize distant BM sites. RNA sequencing of primary and distant-site MM tumor cells revealed a progression signature sequentially activated along human MM progression and significantly associated with overall survival when evaluated against patient data sets. A total of 28 genes were then computationally predicted to be master regulators (MRs) of MM progression. HMGA1 and PA2G4 were validated in vivo using CRISPR-Cas9 in the PrEDiCT model and were shown to be significantly depleted in distant BM sites, indicating their role in MM progression and dissemination. Loss of HMGA1 and PA2G4 also compromised the proliferation, migration, and adhesion abilities of MM cells in vitro. Overall, our model successfully recapitulates key characteristics of human MM disease progression and identified potential new therapeutic targets for MM.

Structural insights into the interplay of protein biogenesis factors with the 70S ribosome

Bacterial co-translational N-terminal methionine excision, an early event of nascent polypeptide chain processing, is mediated by two enzymes: peptide deformylase (PDF) and methionine aminopeptidase (MetAP). Trigger factor (TF), the only ribosome-associated bacterial chaperone, offers co-translational chaperoning assistance. Here, we present two high-resolution cryoelectron microscopy structures of tRNA-bound E. coli ribosome complexes showing simultaneous binding of PDF and TF, in the absence (3.4 Å) and presence of MetAP (4.1 Å). These structures establish molecular details of the interactions of the factors with the ribosome, and thereby reveal the structural basis of nascent chain processing. Our results suggest that simultaneous binding of all three factors is not a functionally favorable mechanism of nascent chain processing. Strikingly, an unusual structural distortion of the 70S ribosome, potentially driven by binding of multiple copies of MetAP, is observed when MetAP is incubated with a pre-formed PDF-TF-bound ribosome complex.

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.

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.

Roles of ErbB3-binding protein 1 (EBP1) in embryonic development and gene-silencing control

ErbB3-binding protein 1 (EBP1) is implicated in diverse cellular functions, including apoptosis, cell proliferation, and differentiation. Here, by generating genetic inactivation of Ebp1 mice, we identified the physiological roles of EBP1 in vivo. Loss of Ebp1 in mice caused aberrant organogenesis, including brain malformation, and death between E13.5 and 15.5 owing to severe hemorrhages, with massive apoptosis and cessation of cell proliferation. Specific ablation of Ebp1 in neurons caused structural abnormalities of brain with neuron loss in [Nestin-Cre; Ebp1 ^flox/flox ] mice. Notably, global methylation increased with high levels of the gene-silencing unit Suv39H1/DNMT1 in Ebp1-deficient mice. EBP1 repressed the transcription of Dnmt1 by binding to its promoter region and interrupted DNMT1-mediated methylation at its target gene, Survivin promoter region. Reinstatement of EBP1 into embryo brain relived gene repression and rescued neuron death. Our findings uncover an essential role for EBP1 in embryonic development and implicate its function in transcriptional regulation.

Unraveling proteome changes and potential regulatory proteins of bovine follicular Granulosa cells by mass spectrometry and multi-omics analysis

Background

In previous study, we performed next-gene sequencing to investigate the differentially expressed transcripts of bovine follicular granulosa cells (GCs) at dominant follicle (DF) and subordinate follicle (SF) stages during first follicular wave. Present study is designed to further identify the key regulatory proteins and signaling pathways associated with follicular development using label-free liquid chromatography-tandem mass spectrometry (LC-MS/MS) and multi-omics data analysis approach.

Methods

DF and SF from three cattle were collected by daily ultrasonography. The GCs were isolated from each follicle, total proteins were digested by trypsin, and then proteomic analyzed via LC-MS/MS, respectively. Proteins identified were retrieved from Uniprot-COW fasta database, and differentially expressed proteins were used to functional enrichment and KEGG pathway analysis. Proteome data and transcriptome data obtained from previous studies were integrated.

Results

Total 3409 proteins were identified from 30,321 peptides (FDR ≤0.01) obtained from LC-MS/MS analysis and 259 of them were found to be differentially expressed at different stage of follicular development (fold Change > 2, P < 0.05). KEGG pathway analysis of proteome data revealed important signaling pathways associated with follicular development, multi-omics data analysis results showed 13 proteins were identified as being differentially expressed in DF versus SF.

Conclusions

This study represents the first investigation of transcriptome and proteome of bovine follicles and offers essential information for future investigation of DF and SF in cattle. It also will enrich the theory of animal follicular development.

Electronic supplementary material

The online version of this article (10.1186/s12953-019-0152-1) contains supplementary material, which is available to authorized users.

EBP1 nuclear accumulation negatively feeds back on FERONIA-mediated RALF1 signaling

FERONIA (FER), a plasma membrane receptor-like kinase, is a central regulator of cell growth that integrates environmental and endogenous signals. A peptide ligand rapid alkalinization factor 1 (RALF1) binds to FER and triggers a series of downstream events, including inhibition of Arabidopsis H+-ATPase 2 activity at the cell surface and regulation of gene expression in the nucleus. We report here that, upon RALF1 binding, FER first promotes ErbB3-binding protein 1 (EBP1) mRNA translation and then interacts with and phosphorylates the EBP1 protein, leading to EBP1 accumulation in the nucleus. There, EBP1 associates with the promoters of previously identified RALF1-regulated genes, such as CML38, and regulates gene transcription in response to RALF1 signaling. EBP1 appears to inhibit the RALF1 peptide response, thus forming a transcription-translation feedback loop (TTFL) similar to that found in circadian rhythm control. The plant RALF1-FER-EBP1 axis is reminiscent of animal epidermal growth factor receptor (EGFR) signaling, in which EGF peptide induces EGFR to interact with and phosphorylate EBP1, promoting EBP1 nuclear accumulation to control cell growth. Thus, we suggest that in response to peptide signals, plant FER and animal EGFR use the conserved key regulator EBP1 to control cell growth in the nucleus.

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

ErbB3, a member of the epidermal growth factor receptor family, reportedly plays an essential role in the regulation of cancer progression and therapeutic resistance. Numerous studies have indicated that ErbB3 binding protein 1 (Ebp1), a binding partner for ErbB3, plays an important regulatory role in the expression and function of ErbB3, but there is no agreement as to whether Ebp1 also has an ErbB3-independent function in cancer and how it might contribute to tumorigenesis. In this review, we will discuss the different functions of the two Ebp1 isoforms, p48 and p42, that may be responsible for the potentially dual role of Ebp1 in cancer growth.

Neuron-specific expression of p48 Ebp1 during murine brain development and its contribution to CNS axon regeneration

P48 Ebp1 is expressed in rapidly proliferating cells such as cancer cells and accelerates cell growth and survival. However, its expression pattern and role in central nervous system development have not been studied. Here, we demonstrated the spatiotemporal expression pattern of p48 Ebp1 during embryonic development and the postnatal period. During embryonic development, p48 Ebp1 was highly expressed in the brain. Expression gradually decreased after birth but was still more abundant than p42 expression after birth. Strikingly, we found that p48 Ebp1 was expressed in a cell type specific manner in neurons but not astrocytes. Moreover, p48 Ebp1 physically interacted with beta tubulin but not alpha tubulin. This fits with its accumulation in distal microtubule growth cone regions. Furthermore, in injured hippocampal slices, p48 Ebp1 introduction promoted axon regeneration. Thus, we speculate that p48 Ebp1 might contribute to microtubule dynamics acting as an MAP and promotes CNS axon regeneration. [BMB Reports 2017; 50(3): 126-131].

Pa2G4 is a novel Six1 co-factor that is required for neural crest and otic development

Mutations in SIX1 and in its co-factor, EYA1, underlie Branchiootorenal Spectrum disorder (BOS), which is characterized by variable branchial arch, otic and kidney malformations. However, mutations in these two genes are identified in only half of patients. We screened for other potential co-factors, and herein characterize one of them, Pa2G4 (aka Ebp1/Plfap). In human embryonic kidney cells, Pa2G4 binds to Six1 and interferes with the Six1-Eya1 complex. In Xenopus embryos, knock-down of Pa2G4 leads to down-regulation of neural border zone, neural crest and cranial placode genes, and concomitant expansion of neural plate genes. Gain-of-function leads to a broader neural border zone, expanded neural crest and altered cranial placode domains. In loss-of-function assays, the later developing otocyst is reduced in size, which impacts gene expression. In contrast, the size of the otocyst in gain-of-function assays is not changed but the expression domains of several otocyst genes are reduced. Together these findings establish an interaction between Pa2G4 and Six1, and demonstrate that it has an important role in the development of tissues affected in BOS. Thereby, we suggest that pa2g4 is a potential candidate gene for BOS.

Modulation of HCV replication and translation by ErbB3 binding protein1 isoforms

We recently identified a cell-factor, ErbB3 binding protein 1 (Ebp-1), which specifically interacts with the viral RNA genome and modulates HCV replication and translation. Ebp1 has two isoforms, p48, and p42, that result from differential splicing. We found that both isoforms interact with HCV proteins NS5A and NS5B, as well as cell-factor PKR. The p48 isoform, which localizes in the cytoplasm and nuclei, promoted HCV replication, whereas the shorter p42 isoform, which resides exclusively in the cytoplasm, strongly inhibited HCV replication. Transient expression of individual isoforms in Ebp1-knockdown MH14 cells confirmed that the p48 isoform promotes HCV replication, while the p42 isoform inhibits it. We found that Ebp1-p42 significantly enhanced autophosphorylation of PKR, while Ebp1-p48 isoform strongly inhibited it. We propose that modulation of autophosphorylation of PKR by p48 isoform is an important mechanism whereby the HCV virus escapes innate antiviral immune responses by circumventing p42-mediated inhibition of its replication.

C-terminal domain of p42 Ebp1 is essential for down regulation of p85 subunit of PI3K, inhibiting tumor growth

Potential tumor suppressor p42, ErbB3-binding protein 1 (EBP1) inhibits phosphoinositide 3-kinase (PI3K) activity reducing the p85 regulatory subunit. In this study, we demonstrated that overexpression of p42 promoted not only a reduction of wild type of p85 subunit but also oncogenic mutant forms of p85 which were identified in human cancers. Moreover, we identified the small fragment of C-terminal domain of p42 is sufficient to exhibit tumor suppressing activity of p42-WT, revealing that this small fragment (280-394) of p42 is required for the binding of both HSP70 and CHIP for a degradation of p85. Furthermore, we showed the small fragment of p42 markedly inhibited the tumor growth in mouse xenograft models of brain and breast cancer, resembling tumor suppressing activity of p42. Through identification of the smallest fragment of p42 that is responsible for its tumor suppressor activity, our findings represent a novel approach for targeted therapy of cancers that overexpress PI3K.

DNAJC21 Mutations Link a Cancer-Prone Bone Marrow Failure Syndrome to Corruption in 60S Ribosome Subunit Maturation

A substantial number of individuals with bone marrow failure (BMF) present with one or more extra-hematopoietic abnormality. This suggests a constitutional or inherited basis, and yet many of them do not fit the diagnostic criteria of the known BMF syndromes. Through exome sequencing, we have now identified a subgroup of these individuals, defined by germline biallelic mutations in DNAJC21 (DNAJ homolog subfamily C member 21). They present with global BMF, and one individual developed a hematological cancer (acute myeloid leukemia) in childhood. We show that the encoded protein associates with rRNA and plays a highly conserved role in the maturation of the 60S ribosomal subunit. Lymphoblastoid cells obtained from an affected individual exhibit increased sensitivity to the transcriptional inhibitor actinomycin D and reduced amounts of rRNA. Characterization of mutations revealed impairment in interactions with cofactors (PA2G4, HSPA8, and ZNF622) involved in 60S maturation. DNAJC21 deficiency resulted in cytoplasmic accumulation of the 60S nuclear export factor PA2G4, aberrant ribosome profiles, and increased cell death. Collectively, these findings demonstrate that mutations in DNAJC21 cause a cancer-prone BMF syndrome due to corruption of early nuclear rRNA biogenesis and late cytoplasmic maturation of the 60S subunit.

AcEBP1, an ErbB3-Binding Protein (EBP1) from halophyte Atriplex canescens, negatively regulates cell growth and stress responses in Arabidopsis

An ErbB-3-binding protein gene AcEBP1, also known as proliferation-associated 2G4 gene (PA2G4s) belonging to the M24 superfamily, was obtained from the saltbush Atriplex canescens. Subcellular localization imaging showed the fusion protein AcEBP1-eGFP was located in the nucleus of epidermal cells in Nicotiana benthamiana. The AcEBP1 gene expression levels were up-regulated under salt, osmotic stress, and hormones treatment as revealed by qRT-PCR. Overexpression of AcEBP1 in Arabidopsis demonstrated that AcEBP1 was involved in root cell growth and stress responses (NaCl, osmotic stress, ABA, low temperature, and drought). These phenotypic data were correlated with the expression patterns of stress responsive genes and PR genes. The AcEBP1 transgenic Arabidopsis plants also displayed increased sensitivity under low temperature and evaluated resistance to drought stress. Together, these results demonstrate that AcEBP1 negatively affects cell growth and is a regulator under stress conditions.

A polybasic motif in ErbB3-binding protein 1 (EBP1) has key functions in nucleolar localization and polyphosphoinositide interaction

We reveal the identification of a polybasic motif necessary for polyphosphoinositide interaction and nucleolar targeting of ErbB3 binding protein 1 (EBP1). EBP1 interacts directly with phosphatidylinositol(3,4,5)-triphosphate and their association is detected in the nucleolus, implying regulatory roles of nucleolar processes.

Polyphosphoinositides (PPIns) are present in the nucleus where they participate in crucial nuclear processes, such as chromatin remodelling, transcription and mRNA processing. In a previous interactomics study, aimed to gain further insight into nuclear PPIns functions, we identified ErbB3 binding protein 1 (EBP1) as a potential nuclear PPIn-binding protein in a lipid pull-down screen. EBP1 is a ubiquitous and conserved protein, located in both the cytoplasm and nucleolus, and associated with cell proliferation and survival. In the present study, we show that EBP1 binds directly to several PPIns via two distinct PPIn-binding sites consisting of clusters of lysine residues and positioned at the N- and C-termini of the protein. Using interaction mutants, we show that the C-terminal PPIn-binding motif contributes the most to the localization of EBP1 in the nucleolus. Importantly, a K372N point mutation, located within the C-terminal motif and found in endometrial tumours, is sufficient to alter the nucleolar targeting of EBP1. Our study reveals also the presence of the class I phosphoinositide 3-kinase (PI3K) catalytic subunit p110β and its product PtdIns(3,4,5)P₃ together with EBP1 in the nucleolus. Using NMR, we further demonstrate an association between EBP1 and PtdIns(3,4,5)P₃ via both electrostatic and hydrophobic interactions. Taken together, these results show that EBP1 interacts directly with PPIns and associate with PtdIns(3,4,5)P₃ in the nucleolus. The presence of p110β and PtdIns(3,4,5)P₃ in the nucleolus indicates their potential role in regulating nucleolar processes, at least via EBP1.

P42 Ebp1 functions as a tumor suppressor in non-small cell lung cancer

Although the short isoform of ErbB3-binding protein 1 (Ebp1), p42 has been considered to be a potent tumor suppressor in a number of human cancers, whether p42 suppresses tumorigenesis of lung cancer cells has never been clarified. In the current study we investigated the tumor suppressor role of p42 in non-small cell lung cancer cells. Our data suggest that the expression level of p42 is inversely correlated with the cancerous properties of NSCLC cells and that ectopic expression of p42 is sufficient to inhibit cell proliferation, anchorage-independent growth, and invasion as well as tumor growth in vivo. Interestingly, p42 suppresses Akt activation and overexpression of a constitutively active form of Akt restores the tumorigenic activity of A549 cells that is ablated by exogenous p42 expression. Thus, we propose that p42 Ebp1 functions as a potent tumor suppressor of NSCLC through interruption of Akt signaling. [BMB Reports 2015; 48(3): 159-165]

Using Xenopus to discover new genes involved in branchiootorenal spectrum disorders

Congenital hearing loss is an important clinical problem because, without early intervention, affected children do not properly acquire language and consequently have difficulties developing social skills. Although most newborns in the US are screened for hearing deficits, even earlier diagnosis can be made with prenatal genetic screening. Genetic screening that identifies the relevant mutated gene can also warn about potential congenital defects in organs not related to hearing. We will discuss efforts to identify new candidate genes that underlie the Branchiootorenal spectrum disorders in which affected children have hearing deficits and are also at risk for kidney defects. Mutations in two genes, SIX1 and EYA1, have been identified in about half of the patients tested. To uncover new candidate genes, we have used the aquatic animal model, Xenopus laevis, to identify genes that are part of the developmental genetic pathway of Six1 during otic and kidney development. We have already identified a large number of potential Six1 transcriptional targets and candidate co-factor proteins that are expressed at the right time and in the correct tissues to interact with Six1 during development. We discuss the advantages of using this system for gene discovery in a human congenital hearing loss syndrome.

Screening a novel FGF3 antagonist peptide with anti-tumor effects on breast cancer from a phage display library

Accumulating evidence has suggested that fibroblast growth factor 3 (FGF3) is expressed in breast cancer and correlates with the stage and grade of the disease. In the present study, a specific FGF3‑binding peptide (VLWLKNR, termed FP16) was isolated from a phage display heptapeptide library with FGF3. The peptide FP16 contained four identical (WLKN) amino acids and demonstrated high homology to the peptides of the 188‑194 (TMRWLKN) site of the high‑affinity FGF3 receptor fibroblast growth factor receptor 2. Functional analyses indicated that FP16 mediated significant inhibition of FGF3‑induced cell proliferation, arrested the cell cycle at the G0/G1 phase by increasing proliferation‑associated protein 2G4, suppressing cyclin D1 and proliferating cell nuclear antigen, and inhibited the FGF3‑induced activation of extracellular signal‑regulated kinase 1/2 and Akt kinase. Taken together, these results demonstrated that the peptide FP16, acting as an FGF3 antagonist, is a promising therapeutic agent for the treatment of breast cancer.

EBP1 protein modulates the expression of human MHC class II molecules in non-hematopoietic cancer cells

Many solid tumours including melanoma, glioblastoma, and breast carcinomas express MHC class II molecules (MHC II). The surface expression of these molecules confers to non-hematopoietic tumour cells the role of non-professional antigen presenting cells and the ability to potentially stimulate tumour-specific CD4⁺ T cell response. We studied EBP1, an ErbB3 binding protein, and the effects of p48 and p42 isoforms on the MHC II expression in U87 glioblastoma, M14 melanoma and MCF7 mammary carcinoma cell lines. We found that overexpression of p48 increases MHC II transcription in U87 and M14, through upregulation of CIITA transactivator and STAT1 phosphorylation. In addition, p48 protein influences MHC II expression by increasing mRNA stability. In melanoma and glioblastoma cell lines, p48 isoform functions as oncogene promoting tumour growth, while p42 isoform, that does not affect MHC II expression, acts as a tumour suppressor by blocking cell growth and inducing apoptosis. In contrast, p48 seems to act as tumour suppressor in breast carcinoma inhibiting proliferation, favouring apoptosis, and inducing a slight increase of MHC II expression similar to p42. Our data highlight the tissue specificity function of EBP1 isoforms and demonstrate that only the oncogene p48 activates MHC II expression in human solid tumours, via STAT1 phosphorylation, in order to affect tumour progression by triggering specific immune response.

The ErbB3-binding protein EBP1 modulates lapatinib sensitivity in prostate cancer cells

Although ErbB receptors have been implicated in prostate cancer progression, ErbB-directed drugs have not proven effective for prostate cancer treatment. The ErbB3-binding protein EBP1 affects both ErbB2 and androgen receptor signaling, two components of the response to ErbB-targeted therapies. We therefore examined the effects of EBP1 expression on the response to the ErbB1/2 tyrosine kinase inhibitor lapatinib. We found a negative correlation between endogenous EBP1 levels and lapatinib sensitivity in prostate cancer cell lines. We then overexpressed or inhibited expression of EBP1. Silencing EBP1 expression increased lapatinib sensitivity and overexpression of EBP1 increased resistance in androgen-containing media. Androgen depletion resulted in an increased sensitivity of androgen-dependent EBP1 expressing cells to lapatinib, but did not affect the lapatinib sensitivity of hormone resistant cells. However, EBP1 silenced cells were still more sensitive to lapatinib than EBP1-expressing cells in the absence of androgens. The increase in sensitivity to lapatinib following EBP1 silencing was associated with increased ErbB2 levels. In addition, lapatinib treatment increased ErbB2 levels in sensitive cells that express low levels of EBP1, but decreased ErbB2 levels in resistant EBP1-expressing cells. In contrast, ErbB3 and phospho ErbB3 levels were not affected by either changes in EBP1 levels or lapatinib treatment. The production of the ErbB3/4 ligand heregulin was increased in EBP1-silenced cells. EBP1-induced changes in AR levels were not associated with changes in lapatinib sensitivity. These studies suggest that the ability of EBP1 to activate ErbB2 signaling pathways results in increased lapatinib sensitivity.

CIP2A regulates cancer metabolism and CREB phosphorylation in non-small cell lung cancer

The cancerous inhibitor of protein phosphatase 2A (CIP2A) is a recently characterized endogenous inhibitor of the phosphatase activity of protein phosphatase 2A (PP2A), which extends the half-life of oncogenic protein c-myc and promotes in vivo tumor growth. The function of CIP2A in cancer progression is still poorly understood. To uncover the underlying mechanism of CIP2A-mediated cell proliferation, we implemented a two-dimensional electrophoresis (2DE)-based proteomic approach to examine lung cancer cell H1299 with and without CIP2A. We found 47 proteins differentially expressed where 19 proteins were upregulated and 28 proteins were downregulated. These were categorized into functional groups such as metabolism (25%), transcriptional and translational control (23%), and the signaling pathway and protein degradation (20%). On one hand, we validate our proteomic work by measuring the metabolic change. The knockdown of CIP2A decreased the expression of LDH-A as well as the enzymatic activity, accompanying with a decreased lactate production, an increased NADH/NAD+ ratio and ROS production. On the other hand, we found that CIP2A may regulate CREB activity through bioinformatics analysis. Our following experiments showed that, CIP2A positively regulated the phosphorylation of CREB in response to the serum treatment. Therefore, our proteomic study suggested that CIP2A mediates cancer progression through the metabolic pathway and intracellular signaling cascade.

The downregulation of ErbB3 binding protein 1 (EBP1) is associated with poor prognosis and enhanced cell proliferation in hepatocellular carcinoma

ErbB3 binding protein 1 (EBP1) has been recently reported to function as a tumor suppressor in the progression of multiple cancers, including breast cancer, prostate cancer, salivary adenoid cystic carcinoma (ACC), and oral squamous cell carcinoma (OSCC). However, the expression and physiological significance of EBP1 in hepatocellular carcinoma (HCC) remain unclear. In the study, we showed that EBP1 was significantly downregulated in clinical HCC specimens, and that decreased expression of EBP1 was associated with enhanced proliferation in HCC cells. Western blot and immunohistochemical analyses revealed that EBP1 was remarkably downregulated in HCC tissues compared with the adjacent normal ones. The levels of EBP1 were significantly associated with histological grade (P = 0.034), tumor size (P = 0.001), and Ki67 expression (P < 0.001) in HCC specimens. Univariate and multivariate analyses showed that EBP1 could serve as an independent prognostic indicator of patients' survival. Serum starvation and refeeding assay indicated that EBP1 was accumulated in growth-arrested HCC cells, and was progressively decreased when cells entered into S phase. Moreover, the depletion of EBP1 induced growth acceleration and cell cycle progression in L02 hepatocytes. On the basis of these findings, we conclude that EBP1 may be a valuable prognostic marker and promising therapeutic target of HCC.

Proteomic Identification of Nrf2-Mediated Phase II Enzymes Critical for Protection of Tao Hong Si Wu Decoction against Oxygen Glucose Deprivation Injury in PC12 Cells

Chinese herbal medicine formula Tao Hong Si Wu decoction (THSWD) is traditionally used in China for cerebrovascular diseases. However, the molecular mechanisms of THSWD associated with the cerebral ischemia reperfusion injury are largely unknown. The current study applied the two-dimensional gel electrophoresis-based proteomics to investigate the different protein profiles in PC12 cells with and without the treatment of THSWD. Twenty-six proteins affected by THSWD were identified by MALDI-TOF mass spectrometry. Gene ontology analysis showed that those proteins participated in several important biological processes and exhibited diverse molecular functions. In particular, six of them were found to be phase II antioxidant enzymes, which were regulated by NF-E2-related factor-2 (Nrf2). Quantitative PCR further confirmed a dose-dependent induction of the six phase II enzymes by THSWD at the transcription level. Moreover, the individual ingredients of THSWD were discovered to synergistically contribute to the induction of phase II enzymes. Importantly, THSWD's protection against oxygen-glucose deprivation-reperfusion (OGD-Rep) induced cell death was significantly attenuated by antioxidant response element (ARE) decoy oligonucleotides, suggesting the protection of THSWD may be likely regulated at least in part by Nrf2-mediated phase II enzymes. Thus, our data will help to elucidate the molecular mechanisms underlying the neuroprotective effect of THSWD.

Identification of a novel aFGF-binding peptide with anti-tumor effect on breast cancer from phage display library

It has been reported that acidic fibroblast growth factor (aFGF) is expressed in breast cancer and via interactions with fibroblast growth factor receptors (FGFRs) to promote the stage and grade of the disease. Thus, aFGF/FGFRs have been considered essential targets in breast cancer therapy. We identified a specific aFGF-binding peptide (AGNWTPI, named AP8) from a phage display heptapeptide library with aFGF after four rounds of biopanning. The peptide AP8 contained two (TP) amino acids identical and showed high homology to the peptides of the 182-188 (GTPNPTL) site of high-affinity aFGF receptor FGFR1. Functional analyses indicated that AP8 specifically competed with the corresponding phage clone A8 for binding to aFGF. In addition, AP8 could inhibit aFGF-stimulated cell proliferation, arrested the cell cycle at the G0/G1 phase by increasing PA2G4 and suppressing Cyclin D1 and PCNA, and blocked the aFGF-induced activation of Erk1/2 and Akt kinase in both breast cancer cells and vascular endothelial cells. Therefore, these results indicate that peptide AP8, acting as an aFGF antagonist, is a promising therapeutic agent for the treatment of breast cancer.

ErbB3 binding protein-1 (Ebp1) controls proliferation and myogenic differentiation of muscle stem cells

Satellite cells are resident stem cells of skeletal muscle, supplying myoblasts for post-natal muscle growth, hypertrophy and repair. Many regulatory networks control satellite cell function, which includes EGF signalling via the ErbB family of receptors. Here we investigated the role of ErbB3 binding protein-1 (Ebp1) in regulation of myogenic stem cell proliferation and differentiation. Ebp1 is a well-conserved DNA/RNA binding protein that is implicated in cell growth, apoptosis and differentiation in many cell types. Of the two main Ebp1 isoforms, only p48 was expressed in satellite cells and C2C12 myoblasts. Although not present in quiescent satellite cells, p48 was strongly induced during activation, remaining at high levels during proliferation and differentiation. While retroviral-mediated over-expression of Ebp1 had only minor effects, siRNA-mediated Ebp1 knockdown inhibited both proliferation and differentiation of satellite cells and C2C12 myoblasts, with a clear failure of myotube formation. Ebp1-knockdown significantly reduced ErbB3 receptor levels, yet over-expression of ErbB3 in Ebp1 knockdown cells did not rescue differentiation. Ebp1 was also expressed by muscle cells during developmental myogenesis in mouse. Since Ebp1 is well-conserved between mouse and chick, we switched to chick to examine its role in muscle formation. In chick embryo, Ebp1 was expressed in the dermomyotome, and myogenic differentiation of muscle progenitors was inhibited by specific Ebp1 down-regulation using shRNA electroporation. These observations demonstrate a conserved function of Ebp1 in the regulation of embryonic muscle progenitors and adult muscle stem cells, which likely operates independently of ErbB3 signaling.

EBP1, a novel host factor involved in primer binding site-dependent restriction of moloney murine leukemia virus in embryonic cells

Mouse embryonic cells are unable to support the replication of Moloney murine leukemia virus (MLV). The integrated viral DNA is transcriptionally silenced, largely due to binding of host transcriptional repressors to the primer binding site (PBS) of the provirus. We have previously shown that a PBS DNA-binding repressor complex contains ZFP809 and TRIM28. Here, we identified ErbB3-binding protein 1 (EBP1) to be a novel component of the ZFP809-TRIM28 silencing complex and show that EBP1 depletion reduces PBS-mediated retroviral silencing.

A novel single virus infection system reveals that influenza virus preferentially infects cells in g1 phase

BACKGROUND

Influenza virus attaches to sialic acid residues on the surface of host cells via the hemagglutinin (HA), a glycoprotein expressed on the viral envelope, and enters into the cytoplasm by receptor-mediated endocytosis. The viral genome is released and transported in to the nucleus, where transcription and replication take place. However, cellular factors affecting the influenza virus infection such as the cell cycle remain uncharacterized.

METHODS/RESULTS

To resolve the influence of cell cycle on influenza virus infection, we performed a single-virus infection analysis using optical tweezers. Using this newly developed single-virus infection system, the fluorescence-labeled influenza virus was trapped on a microchip using a laser (1064 nm) at 0.6 W, transported, and released onto individual H292 human lung epithelial cells. Interestingly, the influenza virus attached selectively to cells in the G1-phase. To clarify the molecular differences between cells in G1- and S/G2/M-phase, we performed several physical and chemical assays. Results indicated that: 1) the membranes of cells in G1-phase contained greater amounts of sialic acids (glycoproteins) than the membranes of cells in S/G2/M-phase; 2) the membrane stiffness of cells in S/G2/M-phase is more rigid than those in G1-phase by measurement using optical tweezers; and 3) S/G2/M-phase cells contained higher content of Gb3, Gb4 and GlcCer than G1-phase cells by an assay for lipid composition.

CONCLUSIONS

A novel single-virus infection system was developed to characterize the difference in influenza virus susceptibility between G1- and S/G2/M-phase cells. Differences in virus binding specificity were associated with alterations in the lipid composition, sialic acid content, and membrane stiffness. This single-virus infection system will be useful for studying the infection mechanisms of other viruses.

Quantitative proteomics analysis of BMS-214662 effects on CD34 positive cells from chronic myeloid leukaemia patients

Chronic myeloid leukaemia (CML) arises in a haemopoietic stem cell and is driven by the Bcr-Abl oncoprotein. Abl kinase inhibitors (protein tyrosine kinase inhibitors) represent standard treatment for CML and induce remission in the majority of patients with early disease, however these drugs do not target leukaemic stem cells (LSCs) effectively, thus preventing cure. Previously, we identified the farnesyl transferase inhibitor BMS-214662 as a selective inducer of apoptosis in LSCs of CML patients relative to normal controls; however, the mechanism underlying LSC-specific apoptosis remains unclear. To identify pathways involved in the favourable effects of BMS-214662 in CML, we employed a proteomic approach (based on iTRAQ) to analyse changes in protein expression in response to drug treatment in the nuclear and cytoplasmic fractions of CD34(+) CML cells. The study identified 88 proteins as altered after drug treatment, which included proteins known to be involved in nucleic acid metabolism, oncogenesis, developmental processes and intracellular protein trafficking. We found that expression of Ebp1, a negative regulator of proliferation, was upregulated in the nucleus of BMS-214662-treated cells. Furthermore, proteins showing altered levels in the cytosol, such as histones, were predominantly derived from the nucleus and BMS-214662 affected expression levels of nuclear pore complex proteins. Validation of key facets of these observations suggests that drug-induced alterations in protein localisation, potentially via loss of nuclear membrane integrity, contributes to the LSC specificity of BMS-214662, possibly via Ran proteins as targets.

Regulation of tamoxifen sensitivity by a PAK1-EBP1 signalling pathway in breast cancer

Background:

EBP1, an ErbB3-binding protein, sensitises breast cancer cells to tamoxifen in part by decreasing ErbB2 protein levels. The p21-regulated serine/threonine kinase PAK1, implicated in tamoxifen resistance, phosphorylates EBP1 in vitro and in vivo at T261. Phosphorylation of EBP1 at this site induces tamoxifen resistance. We thus postulated that inhibition of PAK1 activity, by restoring EBP1 function, could ameliorate the hormone refractory phenotype of ErbB2-overexpressing breast cancer cells.

Methods:

Effects of EBP1 on ErbB2 levels were measured by western blotting. Effects of EBP1 and IPA-3 on tamoxifen sensitivity were measured using a tetrazolium based cell viability assay.

Results:

Transient transfection studies indicated that an EBP1 T261E mutant, which mimics EPB1 phosphorylated by PAK1, increased ErbB2 protein levels. An EBP1 T261A mutant, unable to be phosphorylated by PAK1, ameliorated PAK1-induced tamoxifen resistance, suggesting that phosphorylation of EBP1 by PAK1 contributes to tamoxifen resistance. We then tested if pharmacological inhibition of PAK1 activity might render hormone resistant cells, which endogenously overexpress PAK1, tamoxifen sensitive. IPA-3, a specific small MW PAK1 inhibitor, sensitised cells to tamoxifen only when EBP1 was ectopically expressed. IPA had no effect on tamoxifen resistance in T47D cells in which EBP1 protein had been ablated by shRNA. The IPA-induced increase in tamoxifen sensitivity was accompanied by a decrease in ErbB2 levels only in EBP1-overexpressing cells.

Conclusion:

These studies suggest that phosphorylation of EBP1 may be one mechanism of PAK1-induced hormone resistance and that PAK1 inhibitors may be useful in cells in which EBP1 is overexpressed.

Down-regulation of the ErbB3 binding protein 1 in human bladder cancer promotes tumor progression and cell proliferation

The ErbB3 binding protein 1 (Ebp1) represents a downstream effector of the ErbB signaling network and has been demonstrated to be a potent tumor suppressor in various human malignancies, however, its involvement in human bladder cancer is still unclear.To investigate the clinical significance and potential role of ErbB3 binding protein 1 (Ebp1) in bladder cancer. Ebp1 expression at protein and gene levels in 52 surgically removed bladder cancer specimens as well as 21 adjacent normal bladder specimens were respectively detected by immunohistochemistry and qRT-PCR. The association of Ebp1 protein expression with the clinicopathological features of bladder cancer was also statistically analyzed. Its roles in bladder cancer cell line were further evaluated. The expression level of Ebp1 protein and gene in bladder cancer tissues was significantly lower than that in adjacent normal bladder tissues (P < 0.01). When categorized into low vs. high expression, the down-regulation of Ebp1 protein was associated with the advanced pathologic stage (P = 0.036) and the high histologic grade (P = 0.001) of patients with bladder cancer. Moreover, following the transfection of Ebp1 in bladder cancer cells, not only cell proliferation and cell invasion decreased significantly, but also the cell cycle was blocked at G0/G1 stage. Our data suggest for the first time that the down-regulation of Ebp1 closely correlates with advanced clinicopathological characteristics of human bladder cancer. Furthermore, Ebp1 plays an important role in the bladder cancer cells' proliferation by regulating the cancer cell cycle from G0/G1 to S.

Quantitative proteomics with siRNA screening identifies novel mechanisms of trastuzumab resistance in HER2 amplified breast cancers

HER2 is a receptor tyrosine kinase that is overexpressed in 20% to 30% of human breast cancers and which affects patient prognosis and survival. Treatment of HER2-positive breast cancer with the monoclonal antibody trastuzumab (Herceptin) has improved patient survival, but the development of trastuzumab resistance is a major medical problem. Many of the known mechanisms of trastuzumab resistance cause changes in protein phosphorylation patterns, and therefore quantitative proteomics was used to examine phosphotyrosine signaling networks in trastuzumab-resistant cells. The model system used in this study was two pairs of trastuzumab-sensitive and -resistant breast cancer cell lines. Using stable isotope labeling, phosphotyrosine immunoprecipitations, and online TiO(2) chromatography utilizing a dual trap configuration, ~1700 proteins were quantified. Comparing quantified proteins between the two cell line pairs showed only a small number of common protein ratio changes, demonstrating heterogeneity in phosphotyrosine signaling networks across different trastuzumab-resistant cancers. Proteins showing significant increases in resistant versus sensitive cells were subjected to a focused siRNA screen to evaluate their functional relevance to trastuzumab resistance. The screen revealed proteins related to the Src kinase pathway, such as CDCP1/Trask, embryonal Fyn substrate, and Paxillin. We also identify several novel proteins that increased trastuzumab sensitivity in resistant cells when targeted by siRNAs, including FAM83A and MAPK1. These proteins may present targets for the development of clinical diagnostics or therapeutic strategies to guide the treatment of HER2+ breast cancer patients who develop trastuzumab resistance.

EBP1 and DRBP76/NF90 binding proteins are included in the major histocompatibility complex class II RNA operon

Major histocompatibility complex class II mRNAs encode heterodimeric proteins involved in the presentation of exogenous antigens during an immune response. Their 3'UTRs bind a protein complex in which we identified two factors: EBP1, an ErbB3 receptor-binding protein and DRBP76, a double-stranded RNA binding nuclear protein, also known as nuclear factor 90 (NF90). Both are well-characterized regulatory factors of several mRNA molecules processing. Using either EBP1 or DRBP76/NF90-specific knockdown experiments, we established that the two proteins play a role in regulating the expression of HLA-DRA, HLA-DRB1 and HLA-DQA1 mRNAs levels. Our study represents the first indication of the existence of a functional unit that includes different transcripts involved in the adaptive immune response. We propose that the concept of 'RNA operon' may be suitable for our system in which MHCII mRNAs are modulated via interaction of their 3'UTR with same proteins.

RB1, development, and cancer

The RB1 gene is the first tumor suppressor gene identified whose mutational inactivation is the cause of a human cancer, the pediatric cancer retinoblastoma. The 25 years of research since its discovery has not only illuminated a general role for RB1 in human cancer, but also its critical importance in normal development. Understanding the molecular function of the RB1 encoded protein, pRb, is a long-standing goal that promises to inform our understanding of cancer, its relationship to normal development, and possible therapeutic strategies to combat this disease. Achieving this goal has been difficult, complicated by the complexity of pRb and related proteins. The goal of this review is to explore the hypothesis that, at its core, the molecular function of pRb is to dynamically regulate the location-specific assembly or disassembly of protein complexes on the DNA in response to the output of various signaling pathways. These protein complexes participate in a variety of molecular processes relevant to DNA including gene transcription, DNA replication, DNA repair, and mitosis. Through regulation of these processes, RB1 plays a uniquely prominent role in normal development and cancer.

p48 Ebp1 acts as a downstream mediator of Trk signaling in neurons, contributing neuronal differentiation

Two Ebp1 isoproteins, p48 and p42, regulate cell survival and differentiation distinctively. Here we show that p48 is the major isoform in hippocampal neurons and is localized throughout the entire neuron. Notably, reduction of p48 Ebp1 expression inhibited BDNF-mediated neurite outgrowth in hippocampal neurons. The p48 protein acts as a downstream effector of the Trk receptor, which mediates the functions of nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) in hippocampal cells. Trk receptor activation by both NGF and BDNF induced phosphorylation of Ebp1 at the S360 upon the activation of protein kinase Cδ (PKCδ) and triggered dissociation of p48 from retinoblastoma (Rb). Although both NGF and BDNF activate mitogen-activated protein kinase (MAPK; extracellular signal-related kinase (ERK)) as well as phosphatidylinositide 3-kinase (PI3K)/Akt, their activation is regulated in different time-frame upon growth factor specificity, especially, eliciting PKCδ mediated p48 S360 phosphorylation. Thus, p48 Ebp1 contributes to neuronal cell differentiation and growth factor specificity through the activation of PKCδ, acting as a crucial downstream effector of neurotrophin signaling.

Novel snail1 target proteins in human colon cancer identified by proteomic analysis

Background

The transcription factor Snail1 induces epithelial-to-mesenchymal transition (EMT), a process responsible for the acquisition of invasiveness during tumorigenesis. Several transcriptomic studies have reported Snail1-regulated genes in different cell types, many of them involved in cell adhesion. However, only a few studies have used proteomics as a tool for the characterization of proteins mediating EMT.

Methodology/Principal Findings

We identified by proteomic analysis using 2D-DIGE electrophoresis combined with MALDI-TOF-TOF and ESI-linear ion trap mass spectrometry a number of proteins with variable functions whose expression is modulated by Snail1 in SW480-ADH human colon cancer cells. Validation was performed by Western blot and immunofluorescence analyses. Snail1 repressed several members of the 14-3-3 family of phosphoserine/phosphothreonine binding proteins and also the expression of the Proliferation-associated protein 2G4 (PA2G4) that was mainly localized at the nuclear Cajal bodies. In contrast, the expression of two proteins involved in RNA processing, the Cleavage and polyadenylation specificity factor subunit 6 (CPSF6) and the Splicing factor proline/glutamine-rich (SFPQ), was higher in Snail1-expressing cells than in controls. The regulation of 14-3-3ε, 14-3-3τ, 14-3-3ζ and PA2G4 by Snail1 was reproduced in HT29 colon cancer cells. In addition, we found an inverse correlation between 14-3-3σ and Snail1 expression in human colorectal tumors.

Conclusions/Significance

We have identified a set of novel Snail1 target proteins in colon cancer that expand the cellular processes affected by Snail1 and thus its relevance for cell function and phenotype.

The ErbB3 binding protein EBP1 regulates ErbB2 protein levels and tamoxifen sensitivity in breast cancer cells

The ErbB2/3 heterodimer plays a critical role in breast cancer progression and in the development of endocrine resistance. EBP1, an ErbB3 binding protein, inhibits HRG-stimulated breast cancer growth, decreases ErbB2 protein levels and contributes to tamoxifen sensitivity. We report here that ectopic expression of EBP1 in Estrogen Receptor (ER) positive breast cancers that express ErbB2 at both high and low levels decreased ErbB2 protein levels. ErbB2 protein expression was also increased in mammary glands of Ebp1 knock out mice. To define the mechanism of ErbB2 down regulation, we examined the effects of EBP1 on ErbB2 mRNA levels, transcription of the ErbB2 gene and ErbB2 protein stability. We found that ectopic expression of EBP1 decreased steady state levels of endogenous ErbB2 mRNA in all cell lines tested. EBP1 overexpression decreased the activity of an ErbB2 promoter reporter in cells which overxpress ErbB2. However, reporter activity was unchanged or increased in cells which express low endogenous levels of ErbB2. We also found that ectopic expression of EBP1 accelerated ErbB2 protein degradation and enhanced ErbB2 ubiquitination in cells which express both low and high levels of ErbB2. Treatment with proteasome inhibitors prevented this decrease in ErbB2 protein levels. Ablation of EBP1 expression led to tamoxifen resistance that was abrogated by inhibition of ErbB2 activity. These results suggest that EBP1 inhibits expression of ErbB2 protein levels by multiple mechanisms and that EBP1's effects on tamoxifen sensitivity are mediated in part by its ability to modulate ErbB2 levels.

Ebp1 sumoylation, regulated by TLS/FUS E3 ligase, is required for its anti-proliferative activity

Ebp1, an ErbB3 receptor-binding protein, inhibits cell proliferation and acts as a putative tumor suppressor. Ebp1 translocates into the nucleus and functions as a transcription corepressor for E2F-1. Here, we show that Ebp1 p42 isoform can be sumoylated on both K93 and K298 residues, which mediate its nuclear translocation and is required for its anti-proliferative activity. We find that TLS/FUS, an RNA-binding nuclear protein that is involved in pre- mRNA processing and nucleocytoplasmic shuttling, has Sumo1 E3 ligase activity for Ebp1 p42. Ebp1 directly binds TLS/FUS, which is regulated by genotoxic stress-triggered phosphorylation on Ebp1. Ebp1 sumoylation facilitates its nucleolar distribution and protein stability. Overexpression of TLS enhances Ebp1 sumoylation, while depletion of TLS abolishes Ebp1 sumoylation. Moreover, Unsumoylated Ebp1 mutants fail to suppress E2F-1- regulated transcription, resulting in loss of its anti-proliferation activity. Hence, TLS-mediated sumoylation is required for Ebp1 transcription repressive activity.

Alterations in cell growth and signaling in ErbB3 binding protein-1 (Ebp1) deficient mice

Background

The ErbB3 binding protein-1 (Ebp1) belongs to a family of DNA/RNA binding proteins implicated in cell growth, apoptosis and differentiation. However, the physiological role of Ebp1 in the whole organism is not known. Therefore, we generated Ebp1-deficient mice carrying a gene trap insertion in intron 2 of the Ebp1 (pa2g4) gene.

Results

Ebp1^-/- mice were on average 30% smaller than wild type and heterozygous sex matched littermates. Growth retardation was apparent from Day 10 until Day 30. IGF-1 production and IGBP-3 and 4 protein levels were reduced in both embryo fibroblasts and adult knock-out mice. The proliferation of fibroblasts derived from Day 12.5 knock out embryos was also decreased as compared to that of wild type cells. Microarray expression analysis revealed changes in genes important in cell growth including members of the MAPK signal transduction pathway. In addition, the expression or activation of proliferation related genes such as AKT and the androgen receptor, previously demonstrated to be affected by Ebp1 expression in vitro, was altered in adult tissues.

Conclusion

These results indicate that Ebp1 can affect growth in an animal model, but that the expression of proliferation related genes is cell and context specific. The Ebp1^-/- mouse line represents a new in vivo model to investigate Ebp1 function in the whole organism.

Human BRE1 is an E3 ubiquitin ligase for Ebp1 tumor suppressor

Human Bre1, an E3 ligase for H2B monoubiquitination, binds p53 and enhances activator-dependent transcription. Ebp1, an ErbB3 receptor-binding protein, inhibits cell proliferation and acts as a tumor suppressor. Here, we show that hBre1 acts as an E3 ubiquitin ligase for Ebp1 tumor suppressor and promotes its polyubiquitination and degradation. Ebp1 is polyubiquitinated in cancer cells, which is regulated by its phosphorylation. We identified hBre1 acting as an E3 ligase for Ebp1 and increasing its polyubiquitination. Depletion of hBre1 blocks Ebp1's polyubiquitination and elevates its protein level, preventing cancer proliferation. hBre1 binds Ebp1 and suppresses its repressive effect on E2F-1. Moreover, Ebp1 protein level is substantially diminished in human cancers. It is robustly phosphorylated and localized in the nucleus of primary gliomas, correlating with hBre1 subcellular residency. Thus, hBre1 inhibits Ebp1's tumor suppressive activity through mediating its polyubiquitination and degradation.

The Pseudomonas aeruginosa autoinducer dodecanoyl-homoserine lactone inhibits the putrescine synthesis in human cells

Pseudomonas aeruginosa uses acyl-homoserine lactones to coordinate gene transcription in a process called quorum sensing (QS). The QS molecules C4-HSL and C12-oxo-HSL are synthesized from the universal precursor S-adenosyl methionine, which is also a precursor of polyamines in human cells. Polyamines are required for mitotic cell division and peak during this phase. The polyamine putrescine is synthesized by ornithine decarboxylase (ODC) as a rate-limiting step. The ODC enzyme concentration also peaks during the mitotic phase. This peak is mediated by translation of ODC mRNA by the ITAF45 protein, which translocates from the nuclear compartment to the cytoplasm in a phosphorylation-dependent manner. We observed that C12-HSL-treated human epidermal cells had a higher cytoplasm-to-nuclear ITAF45 protein concentration and this translocation was dependent on the dephosphorylation of ITAF45. Finally, C12-HSL-treated cells also had a time-course-dependent higher concentration of ODC mRNA. Based on these mitotic markers, more human cells were apparently trapped in the mitotic phase when treated with C12-HSL. This should normally imply higher levels of putrescine. However, C12-HSL-treated human cells had a significantly lower concentration of putrescine and displayed a lower cell proliferation rate. In conclusion, the P. aeruginosa autoinducer C12-oxo-HSL apparently arrests human cells in the mitotic phase by lowering the concentration of putrescine.

The role of ErbB3 and its binding partners in breast cancer progression and resistance to hormone and tyrosine kinase directed therapies

An increasingly important role for the ErbB3 receptor in the genesis and progression of breast cancer is emerging. ErbB3 is frequently overexpressed in breast cancer and coexpression of ErbB2/3 is a poor prognostic indicator. ErbB3 has also been implicated in the development of resistance to antiestrogens such as tamoxifen and ErbB tyrosine kinase inhibitors such as gefitinib. Persistent activation of the AKT pathway has been postulated to contribute to ErbB3-mediated resistance to these therapies. This activation may be due in part to the inappropriate production of the ErbB3 ligand heregulin. ErbB3 binding proteins, which negatively regulate ErbB3 protein levels and the ability of ErbB3 to transmit proliferative signals, also contribute to breast cancer progression and treatment resistance. These proteins include the intracellular RING finger E3 ubiquitin ligase Nrdp1 and the leucine-rich protein LRIG-1 that mediate receptor degradation. Ebp1, another ErbB3 binding protein, suppresses HRG driven breast cancer cell growth and contributes to tamoxifen sensitivity. These studies point to the importance of the evaluation of protein levels and functional activity of ErbB3 and its binding proteins in breast cancer prognosis and prediction of clinical response to treatment.

The ERBB3 receptor in cancer and cancer gene therapy

ERBB3, a member of the epidermal growth factor receptor (EGFR) family, is unique in that its tyrosine kinase domain is functionally defective. It is activated by neuregulins, by other ERBB and nonERBB receptors as well as by other kinases, and by novel mechanisms. Downstream it interacts prominently with the phosphoinositol 3-kinase/AKT survival/mitogenic pathway, but also with GRB, SHC, SRC, ABL, rasGAP, SYK and the transcription regulator EBP1. There are likely important but poorly understood roles for nuclear localization and for secreted isoforms. Studies of ERBB3 expression in primary cancers and of its mechanistic contributions in cultured cells have implicated it, with varying degrees of certainty, with causation or sustenance of cancers of the breast, ovary, prostate, certain brain cells, retina, melanocytes, colon, pancreas, stomach, oral cavity and lung. Recent results link high ERBB3 activity with escape from therapy targeting other ERBBs in lung and breast cancers. Thus a wide and centrally important role for ERBB3 in cancer is becoming increasingly apparent. Several approaches for targeting ERBB3 in cancers have been tested or proposed. Small inhibitory RNA (siRNA) to ERBB3 or AKT is showing promise as a therapeutic approach to treatment of lung adenocarcinoma.