The signaling pathways of Epstein-Barr virus-encoded latent membrane protein 2A (LMP2A) in latency and cancer.

Epstein-Barr virus (EBV) is a ubiquitous virus with infections commonly resulting in a latency carrier state. Although the exact role of EBV in cancer pathogenesis remains not entirely clear, it is highly probable that it causes several lymphoid and epithelial malignancies, such as Hodgkin's lymphoma, NK-T cell lymphoma, Burkitt's lymphoma, and nasopharyngeal carcinoma. EBV-associated malignancies are associated with a latent form of infection, and several of these EBV-encoded latent proteins are known to mediate cellular transformation. These include six nuclear antigens and three latent membrane proteins. Studies have shown that EBV displays distinct patterns of viral latent gene expression in these lymphoid and epithelial tumors. The constant expression of latent membrane protein 2A (LMP2A) at the RNA level in both primary and metastatic tumors suggests that this protein might be a driving factor in the tumorigenesis of EBV-associated malignancies. LMP2A may cooperate with the aberrant host genome, and thereby contribute to malignant transformation by intervening in signaling pathways at multiple points, especially in the cell cycle and apoptotic pathway. This review summarizes the role of EBV-encoded LMP2A in EBV-associated viral latency and cancers. We will focus our discussions on the molecular interactions of each of the conserved motifs in LMP2A, and their involvement in various signaling pathways, namely the B-cell receptor blockade mechanism, the ubiquitin-mediated (Notch and Wnt) pathways, and the MAPK, PI3-K/Akt, NK-kappaB and STAT pathways, which can provide us with important insights into the roles of LMP2A in the EBV-associated latency state and various malignancies.

Acquisition of Invasiveness by Breast Adenocarcinoma Cells Engages Established Hallmarks and Novel Regulatory Mechanisms.

BACKGROUND/AIM: Proteomics of invasiveness opens a window on the complexity of the metastasis-engaged mechanisms. The extend and types of this complexity require elucidation. MATERIALS AND METHODS: Proteomics, immunohistochemistry, immunoblotting, network analysis and systems cancer biology were used to analyse acquisition of invasiveness by human breast adenocarcinoma cells. RESULTS: We report here that invasiveness network highlighted the involvement of hallmarks such as cell proliferation, migration, cell death, genome stability, immune system regulation and metabolism. Identified involvement of cell-virus interaction and gene silencing are potentially novel cancer mechanisms. Identified 6,113 nodes with 11,055 edges affecting 1,085 biological processes show extensive re-arrangements in cell physiology. These high numbers are in line with a similar broadness of networks built with diagnostic signatures approved for clinical use. CONCLUSION: Our data emphasize a broad systemic regulation of invasiveness, and describe the network of this regulation.

Endings in the middle: current knowledge of interstitial telomeric sequences.

Interstitial telomeric sequences (ITSs) consist of tandem repeats of the canonical telomeric repeat and are common in mammals. They are localized at intrachromosomal sites, including those repeats located close to the centromeres and those found at interstitial sites, i.e., between the centromeres and the telomeres. ITSs might originate from ancestral intrachromosomal rearrangements (inversions and fusions), from differential crossing-over or from the repair of double-strand break during evolution. Three classes of ITSs have been described in the human genome, namely, short ITSs, long subtelomeric ITSs and fusion ITSs. The fourth class of ITSs, pericentromeric ITSs, has been found in other species. The function of ITSs can be inferred from the association of heritable diseases with ITS polymorphic variants, both in copy number and sequence. This is one of the most attractive aspects of ITS studies because it leads to new and useful markers for genetic linkage studies, forensic applications, and detection of genetic instability in tumors. Some ITSs also might be hotspots of chromosome breakage, rearrangement and amplification sites, based on the type of clastogens and the nature of ITSs. This study will contribute new knowledge with respect to ITSs' biology and mechanism, prevalence of diseases, risk evaluation and prevention of related diseases, thus facilitates the design of early detection markers for diseases caused by genomic instability.

21st Century Genetics: Mass Spectrometry of Yeast Telomerase.

Telomerase is a specialized reverse transcriptase that maintains the ends of chromosomes in almost all eukaryotes. The core of telomerase consists of telomerase RNA and the reverse transcriptase that uses a short segment without the RNA to template the addition of telomeric repeats. In addition, one or more accessory proteins are required for telomerase action in vivo. The best-studied accessory protein is Est1, which is conserved from yeasts to humans. In budding yeast, Est1 has two critical in vivo functions: By interaction with Cdc13, a telomere-binding protein, it recruits telomerase to telomeres, and it also increases telomerase activity. Although budding yeast telomerase is highly regulated by the cell cycle, Est1 is the only telomerase subunit whose abundance is cell cycle-regulated. Close to 400 yeast genes are reported to affect telomere length, although the specific function of most of them is unknown. With the goal of identifying novel telomerase regulators by mass spectrometry, we developed methods for purifying yeast telomerase and its associated proteins. We summarize the methods we used and describe the experiments that show that four telomerase-associated proteins identified by mass spectrometry, none of which had been linked previously to telomeres, affect telomere length and cell cycle regulation of telomerase by controlling Est1 abundance.

Proteomics of yeast telomerase identified Cdc48-Npl4-Ufd1 and Ufd4 as regulators of Est1 and telomere length.

Almost 400 genes affect yeast telomere length, including Est1, which is critical for recruitment and activation of telomerase. Here we use mass spectrometry to identify novel telomerase regulators by their co-purification with the telomerase holoenzyme. In addition to all known subunits, over 100 proteins are telomerase associated, including all three subunits of the essential Cdc48-Npl4-Ufd1 complex as well as three E3 ubiquitin ligases. The Cdc48 complex is evolutionarily conserved and targets ubiquitinated proteins for degradation. Est1 levels are ∼40-fold higher in cells with reduced Cdc48, yet, paradoxically, telomeres are shorter. Furthermore, Est1 is ubiquitinated and its cell cycle-regulated abundance is lost in Cdc48-deficient cells. Deletion of the telomerase-associated E3 ligase, Ufd4, in cdc48-3 cells further increases Est1 abundance but suppresses the telomere length phenotype of the single mutant. These data argue that, in concert with Ufd4, the Cdc48 complex regulates telomerase by controlling the level and activity of Est1.

Translational connection of TGFß signaling: Phosphorylation of eEF1A1 by TßR-I inhibits protein synthesis.

Transforming growth factor-ß (TGFß) signaling pathways regulate a wide array of cellular activities that are crucial for cell proliferation, apoptosis, migration and differentiation. TGFß signaling pathways are initiated by ligand-activated TGFß receptors, with type I TGFß receptors (TßR-I) kinase being essential for phosphorylation of downstream targets. Until now, a prevalent view was that the TGFß intracellular signaling targets would regulate transcription. Recently, we uncovered a novel TGFß signaling pathway that exerts a direct regulatory effect on mRNA translation and protein synthesis. Eukaryotic elongation factor eEF1A1 is a GTP-binding protein that plays a central role in protein synthesis. By using a screening method for kinase substrate that was developed in our laboratory, we identified eEF1A1 as a novel substrate of TßR-I. This shed a new light on the convergence of TGFß signaling and protein synthesis. We also showed phosphorylation of eEF1A1 at Ser300 by TßR-I prevents aa-tRNA binding to eEF1A1. As a consequence, TGFß-dependent phosphorylation of eEF1A1 has an inhibitory effect on protein synthesis and cell proliferation. Therefore, we unveiled a novel regulatory mechanism of cellular proliferation by TGFß at the translational level. Here we discuss this finding in the context of its potential role in the multiplicity of TGFß signaling, and in the regulation of fundamental cellular functions, such as proliferation.

Phosphorylation of eEF1A1 at Ser300 by TßR-I results in inhibition of mRNA translation.

BACKGROUND: Transforming growth factor ß (TGF-ß) is a potent inhibitor of cell proliferation that regulates cell functions by activating specific serine/threonine kinase receptors on the cell surface. Type I TGF-ß receptor (TßR-I) is essential for TGF-ß signaling, and substrates of TßR-I provide insights into molecular mechanisms of TGF-ß signaling. RESULTS: Here we identify eukaryotic elongation factor 1A1 (eEF1A1) as a novel substrate of TßR-I. We show that TßR-I phosphorylates eEF1A1 at Ser300 in vitro and in vivo. Ser300 was found to be important for aminoacyl-tRNA (aa-tRNA) binding to eEF1A1. Ser300 phosphorylation or mutations of Ser300 correlate with inhibition of protein synthesis in vitro and in vivo. We show that mimicking eEF1A1 phosphorylation at Ser300 results in inhibition of cell proliferation, and that mutations of Ser300 affect TGF-ß dependency in inhibition of protein synthesis and cell proliferation. Increased expression of eEF1A has been reported to enhance carcinogenesis. An analysis of human breast cancer cases revealed a decrease of eEF1A1 phosphorylation at Ser300 in malignant tumor cells as compared to epithelial cells in noncancerous tissues. CONCLUSIONS: Phosphorylation of eEF1A1 by TßR-I is a novel regulatory mechanism that provides a direct link to regulation of protein synthesis by TGF-ß, as an important component in the TGF-ß-dependent regulation of protein synthesis and cell proliferation.

Comparative proteome profiling of MCF10A and 184A1 human breast epithelial cells emphasized involvement of CDK4 and cyclin D3 in cell proliferation.

Acquiring high proliferation rate is crucial for carcinogenic transformation of cells. We report here proteome profiling of human breast epithelial cells with low (184A1) and high (MCF10A) proliferation rates. We identified 183 proteins in 184A1 and 318 proteins in MCF10A cells. These datasets provide the most comprehensive proteome annotations of 184A1 and MCF10A cells. Proteins were taken for identification from 2-D gels in a systematic and unbiased way. Functional clustering of the identified proteins showed similarities in distribution of proteins to the same functional domains, indicating similarities in proteomes of 184A1 and MCF10A cells. Among observed differences in protein expression, we validated correlation of expression of endogenous cyclin-dependent kinase 4 (CDK4), cyclin D3, cdc25B, and p38γ with cell proliferation. Furthermore, down-regulation of CDK4 and cyclin D3 with specific siRNA inhibited cell proliferation, which emphasized the role of CDK4 and cyclin D3 in enhancement of cell proliferation rate of human breast epithelial cells.

Differential effect of sanguinarine, chelerythrine and chelidonine on DNA damage and cell viability in primary mouse spleen cells and mouse leukemic cells.

Sanguinarine, chelerythrine and chelidonine are isoquinoline alkaloids derived from the greater celandine. They possess a broad spectrum of pharmacological activities. It has been shown that their anti-tumor activity is mediated via different mechanisms, which can be promising targets for anti-cancer therapy. We focused our study on the differential effects of these alkaloids upon cell viability, DNA damage effect and nucleus integrity in mouse primary spleen cells and mouse lymphocytic leukemic cells, L1210. Sanguinarine and chelerythrine produce a dose-dependent increase in DNA damage and cytotoxicity in both primary mouse spleen cells and L1210 cells. Chelidonine did not show a significant cytotoxicity or damage DNA in both cell types, but completely arrested growth of L1210 cells. Examination of nuclear morphology revealed more cells with apoptotic features upon treatment with chelerythrine and sanguinarine, but not chelidonine. In contrast to primary mouse spleen cells, L1210 cells showed slightly higher sensitivity to sanguinarine and chelerythrine treatment. This suggests that cytotoxic and DNA damaging effects of chelerythrine and sanguinarine are more selective against mouse leukemic cells and primary mouse spleen cells, whereas chelidonine blocks proliferation of L1210 cells. The action of chelidonine on normal and tumor cells requires further investigation.

Dendritic cells heterogeneity and its role in cancer immunity.

Dendritic cells are the most potent 'professional' antigen-presenting cells, with high ability of primary immune response initiation. Dendritic cells originate from bone marrow progenitors, which circulate in peripheral blood and subsequently give rise to immature dendritic cells, which reside in peripheral tissues. When dendritic cells encounter danger signals, they undergo differentiation and maturation; thereafter they migrate to lymphatic tissues, where they synapse with T-cells and initiate primary immune response. The immune response efficiency is determined by Th1/Th2 balance. Although dendritic cells represent a rare group of leukocytes, their functional and phenotypical heterogeneity confer a great challenge to immunologists. In this review, the myeloid and lymphoid development pathways of dendritic cells, are discussed. The heterogeneity of dendritic cells will be reviewed, based on their anatomical locations, phenotypes and functions. This section focuses on blood and lymphoid tissue dendritic cells. Subsequently, the roles of dendritic cells in the immunity of cancer and how cancer bypasses the dendritic cell-mediated immune responses, are discussed.

The telomere length dynamic and methods of its assessment.

Human telomeres are composed of long repeating sequences of TTAGGG, associated with a variety of telomere-binding proteins. Its function as an end-protector of chromosomes prevents the chromosome from end-to-end fusion, recombination and degradation. Telomerase acts as reverse transcriptase in the elongation of telomeres, which prevent the loss of telomeres due to the end replication problems. However, telomerase activity is detected at low level in somatic cells and high level in embryonic stem cells and tumor cells. It confers immortality to embryonic stem cells and tumor cells. In most tumor cells, telomeres are extremely short and stable. Telomere length is an important indicator of the telomerase activity in tumor cells and it may be used in the prognosis of malignancy. Thus, the assessment of telomeres length is of great experimental and clinical significance. This review describes the role of telomere and telomerase in cancer pathogenesis and the dynamics of the telomeres length in different cell types. The various methods of measurement of telomeres length, i.e. southern blot, hybridization protection assay, fluorescence in situ hybridization, primed in situ, quantitative PCR and single telomere length analysis are discussed. The principle and comparative evaluation of these methods are reviewed. The detection of G-strand overhang by telomeric-oligonucleotide ligation assay, primer extension/nick translation assay and electron microscopy are briefly discussed.