A WD-domain protein that is associated with and phosphorylated by the type II TGF-beta receptor

Genome-wide identification and analysis of WD40 proteins reveal that NtTTG1 enhances drought tolerance in tobacco (Nicotiana tabacum)

BACKGROUND

WD40 proteins, which are highly prevalent in eukaryotes, play important roles in plant development and stress responses. However, systematic identification and exploration of WD40 proteins in tobacco have not yet been conducted.

RESULTS

In this study, a total of 399 WD40 regulatory genes were identified in common tobacco (Nicotiana tabacum). Gene structure and motif analysis revealed structural and functional diversity among different clades of tobacco WD40 regulatory genes. The expansion of tobacco WD40 regulatory genes was mainly driven by segmental duplication and purifying selection. A potential regulatory network of NtWD40s suggested that NtWD40s might be regulated by miRNAs and transcription factors in various biological processes. Expression pattern analysis via transcriptome analysis and qRT-PCR revealed that many NtWD40s exhibited tissue-specific expression patterns and might be involved in various biotic and abiotic stresses. Furthermore, we have validated the critical role of NtTTG1, which was located in the nuclei of trichome cells, in enhancing the drought tolerance of tobacco plants.

CONCLUSIONS

Our study provides comprehensive information to better understand the evolution of WD40 regulatory genes and their roles in different stress responses in tobacco.

Genome-wide identification and bioinformatics analysis of the WD40 transcription factor family and candidate gene screening for anthocyanin biosynthesis in Rhododendron simsii

WD40 transcription factors (TFs) constitute a large gene family in eukaryotes, playing diverse roles in cellular processes. However, their functions in the major ornamental plant, Rhododendron simsii, remain poorly understood. In this study, we identified 258 WD40 proteins in the R. simsii genome, which exhibited an uneven distribution across chromosomes. Based on domain compositions and phylogenetic analysis, we classified these 258 RsWD40 proteins into 42 subfamilies and 47 clusters. Comparative genomic analysis suggested that the expansion of the WD40 gene family predates the divergence of green algae and higher plants, indicating an ancient origin. Furthermore, by analyzing the duplication patterns of RsWD40 genes, we found that transposed duplication played a major role in their expansion. Notably, the majority of RsWD40 gene duplication pairs underwent purifying selection during evolution. Synteny analysis identified significant orthologous gene pairs between R. simsii and Arabidopsis thaliana, Oryza sativa, Vitis vinifera, and Malus domestica. We also investigated potential candidate genes involved in anthocyanin biosynthesis during different flower development stages in R. simsii using RNA-seq data. Specifically, we identified 10 candidate genes during the bud stage and 7 candidate genes during the full bloom stage. GO enrichment analysis of these candidate genes revealed the potential involvement of the ubiquitination process in anthocyanin biosynthesis. Overall, our findings provide a valuable foundation for further investigation and functional analysis of WD40 genes, as well as research on the molecular mechanisms underlying anthocyanin biosynthesis in Rhododendron species.

IGFBP-3 and TGF-β inhibit growth in epithelial cells by stimulating type V TGF-β receptor (TβR-V)-mediated tumor suppressor signaling

The TGF-β type V receptor (TβR-V) mediates growth inhibition by IGFBP-3 and TGF-β in epithelial cells and loss of TβR-V expression in these cells leads to development of carcinoma. The mechanisms by which TβR-V mediates growth inhibition (tumor suppressor) signaling remain elusive. Previous studies revealed that IGFBP-3 and TGF-β inhibit growth in epithelial cells by stimulating TβR-V-mediated IRS-1/2-dependent activation and cytoplasm-to-nucleus translocation of IGFBP-3- or TGF-β-stimulated protein phosphatase (PPase), resulting in dephosphorylation of pRb-related proteins (p107, p130) or pRb, and growth arrest. To define the signaling, we characterized/identified the IGFBP-3- and TGF-β-stimulated PPases in cell lysates and nucleus fractions in Mv1Lu cells treated with IGFBP-3 and TGF-β, using a cell-free assay with 32P-labeled casein as a substrate. Both IGFBP-3- and TGF-β-stimulated PPase activities in cell lysates are abolished when cells are co-treated with TGF-β/IGFBP-3 antagonist or RAP (LRP-1/TβR-V antagonist). However, the IGFBP-3-stimulated PPase activity, but not TGF-β-stimulated PPase activity, is sensitive to inhibition by okadaic acid (OA). In addition, OA or PP2Ac siRNA reverses IGFBP-3 growth inhibition, but not TGF-β growth inhibition, in Mv1Lu and 32D cells. These suggest that IGFBP-3- and TGF-β-stimulated PPases are identical to PP2A and PP1, respectively. By Western blot/phosphorimager/immunofluorescence-microscopy analyses, IGFBP-3 and TGF-β stimulate TβR-V-mediated IRS-2-dependent activation and cytoplasm-to-nucleus translocation of PP2Ac and PP1c, resulting in dephosphorylation of p130/p107 and pRb, respectively, and growth arrest. Small molecule TGF-β enhancers, which potentiate TGF-β growth inhibition by enhancing TβR-I-TβR-II-mediated canonical signaling and thus activating TβR-V-mediated tumor suppressor signaling cascade (TβR-V/IRS-2/PP1/pRb), could be used to prevent and treat carcinoma.

A Profound Basic Characterization of eIFs in Gliomas: Identifying eIF3I and 4H as Potential Novel Target Candidates in Glioma Therapy

Simple Summary

Gliomas are brain tumors with currently limited therapy options. Glioma growth and proliferation is regulated by the mTOR pathway together with eukaryotic initiation factors (eIFs). In this work we show a profound basic characterization of eIFs in human gliomas and demonstrate increased mRNA and protein expressions of several eIFs in gliomas compared to healthy control brain tissue. Moreover, increased eIF3I and eIF4H levels seem to have a negative influence on the survival of patients. Our work suggests eIF3I and eIF4H as potential targets for future glioma therapy.

Abstract

Glioblastoma (GBM) is an utterly devastating cerebral neoplasm and current therapies only marginally improve patients’ overall survival (OS). The PI3K/AKT/mTOR pathway participates in gliomagenesis through regulation of cell growth and proliferation. Since it is an upstream regulator of the rate-limiting translation initiation step of protein synthesis, controlled by eukaryotic initiation factors (eIFs), we aimed for a profound basic characterization of 17 eIFs to identify potential novel therapeutic targets for gliomas. Therefore, we retrospectively analyzed expressions of mTOR-related proteins and eIFs in human astrocytoma samples (WHO grades I–IV) and compared them to non-neoplastic cortical control brain tissue (CCBT) using immunoblot analyses and immunohistochemistry. We examined mRNA expression using qRT-PCR and additionally performed in silico analyses to observe the influence of eIFs on patients’ survival. Protein and mRNA expressions of eIF3B, eIF3I, eIF4A1, eIF4H, eIF5 and eIF6 were significantly increased in high grade gliomas compared to CCBT and partially in low grade gliomas. However, short OS was only associated with high eIF3I gene expression in low grade gliomas, but not in GBM. In GBM, high eIF4H gene expression significantly correlated with shorter patient survival. In conclusion, we identified eIF3I and eIF4H as the most promising targets for future therapy for glioma patients.

eIF3i regulation of protein synthesis, cell proliferation, cell cycle progression, and tumorigenesis

eIF3i, a 36-kDa protein, is a putative subunit of the eIF3 complex important for translation initiation of mRNAs. It is a WD40 domain-containing protein with seven WD40 repeats that forms a β-propeller structure with an important function in pre-initiation complex formation and mRNA translation initiation. In addition to participating in the eIF3 complex formation for global translational control, eIF3i may bind to specific mRNAs and regulate their translation individually. Furthermore, eIF3i has been shown to bind to TGF-β type II receptor and participate in TGF-β signaling. It may also participate in and regulate other signaling pathways including Wnt/β-catenin pathway via translational regulation of COX-2 synthesis. These multiple canonical and noncanonical functions of eIF3i in translational control and in regulating signal transduction pathways may be responsible for its role in cell differentiation, cell cycle regulation, proliferation, and tumorigenesis. In this review, we will critically evaluate recent progresses and assess future prospects in studying eIF3i.

SIRT7 Deacetylates STRAP to Regulate p53 Activity and Stability

Serine-threonine kinase receptor-associated protein (STRAP) functions as a regulator of both TGF-β and p53 signaling that participates in the regulation of cell proliferation and cell death in response to various stresses. Here, we demonstrate that STRAP acetylation plays an important role in p53-mediated cell cycle arrest and apoptosis. STRAP is acetylated at lysines 147, 148, and 156 by the acetyltransferases CREB-binding protein (CBP) and that the acetylation is reversed by the deacetylase sirtuin7 (SIRT7). Hypo- or hyperacetylation mutations of STRAP at lysines 147, 148, and 156 (3KR or 3KQ) influence its activation and stabilization of p53. Moreover, following 5-fluorouracil (5-FU) treatment, STRAP is mobilized from the cytoplasm to the nucleus and promotes STRAP acetylation. Our finding on the regulation of STRAP links p53 with SIRT7 influencing p53 activity and stability.

TGF-β induces ST2 and programs ILC2 development

The molecular pathways underlying the development of innate lymphoid cells (ILCs) are mostly unknown. Here we show that TGF-β signaling programs the development of ILC2s from their progenitors. Specifically, the deficiency of TGF-β receptor II in bone marrow progenitors results in inefficient development of ILC2s, but not ILC1s or ILC3s. Mechanistically, TGF-β signaling is required for the generation and maintenance of ILC2 progenitors (ILC2p). In addition, TGF-β upregulates the expression of the IL-33 receptor gene Il1rl1 (encoding IL-1 receptor-like 1, also known as ST2) in ILC2p and common helper-like innate lymphoid progenitors (CHILP), at least partially through the MEK-dependent pathway. These findings identify a function of TGF-β in the development of ILC2s from their progenitors.

TGF-β is thought to be important for group 2 innate lymphoid cell (ILC2) function. Here the authors show that TGF-β drives expression of ST2 specifically in ILC2 progenitors and thereby is also important for the development of ILC2s in the bone marrow.

Genome-wide identification and analysis of WD40 proteins in wheat (Triticum aestivum L.)

BACKGROUND

WD40 domains are abundant in eukaryotes, and they are essential subunits of large multiprotein complexes, which serve as scaffolds. WD40 proteins participate in various cellular processes, such as histone modification, transcription regulation, and signal transduction. WD40 proteins are regarded as crucial regulators of plant development processes. However, the systematic identification and analysis of WD40 proteins have yet to be reported in wheat.

RESULTS

In this study, a total of 743 WD40 proteins were identified in wheat, and they were grouped into 5 clusters and 11 subfamilies. Their gene structures, chromosomal locations, and evolutionary relationships were analyzed. Among them, 39 and 46 pairs of TaWD40s were distinguished as tandem duplication and segmental duplication genes. The 123 OsWD40s were identified to exhibit synteny with TaWD40s. TaWD40s showed the specific characteristics at the reproductive developmental stage, and numerous TaWD40s were involved in responses to stresses, including cold, heat, drought, and powdery mildew infection pathogen, based on the result of RNA-seq data analysis. The expression profiles of some TaWD40s in wheat seed development were confirmed through qRT-PCR technique.

CONCLUSION

In this study, 743 TaWD40s were identified from the wheat genome. As the main driving force of evolution, duplication events were observed, and homologous recombination was another driving force of evolution. The expression profiles of TaWD40s revealed their importance for the growth and development of wheat and their response to biotic and abiotic stresses. Our study also provided important information for further functional characterization of some WD40 proteins in wheat.

Lung epithelial-specific TRIP-1 overexpression maintains epithelial integrity during hyperoxia exposure

The onset and degree of injury occurring in animals that develop hyperoxic acute lung injury (HALI) is dependent on age at exposure, suggesting that developmentally regulated pathways/factors must underlie initiation of the epithelial injury and subsequent repair. Type II TGFβ receptor interacting protein-1 (TRIP-1) is a negative regulator of TGFβ signaling, which we have previously shown is a developmentally regulated protein with modulatory effects on epithelial-fibroblastic signaling. The aim of this study was to assess if type II alveolar epithelial cells overexpressing TRIP-1 are protected against hyperoxia-induced epithelial injury, and in turn HALI. Rat lung epithelial cells (RLE) overexpressing TRIP-1 or LacZ were exposed to 85% oxygen for 4 days. A surfactant protein C (SPC)-driven TRIP-1 overexpression mouse (TRIP-1AECTg+ ) was generated and exposed to hyperoxia (>95% for 4 days) at 4 weeks of age to assess the effects TRIP-1 overexpression has on HALI. RLE overexpressing TRIP-1 resisted hyperoxia-induced apoptosis. Mice overexpressing TRIP-1 in their lung type II alveolar epithelial cells (TRIP-1AECTg+ ) showed normal lung development, increased phospho-AKT level and E-cadherin, along with resistance to HALI, as evidence by less TGFβ activation, apoptosis, alveolar macrophage influx, KC expression. Taken together, these findings point to existence of a TRIP-1 mediated molecular pathway affording protection against epithelial/acute lung injury.

Genome-Wide Identification and Characterization of WD40 Protein Genes in the Silkworm, Bombyx mori

WD40 proteins are scaffolding molecules in protein-protein interactions and play crucial roles in fundamental biological processes. Genome-wide characterization of WD40 proteins in animals has been conducted solely in humans. We retrieved 172 WD40 protein genes in silkworm (BmWD40s) and identified these genes in 7 other insects, 9 vertebrates and 5 nematodes. Comparative analysis revealed that the WD40 protein gene family underwent lineage-specific expansions during animal evolution, but did not undergo significant expansion during insect evolution. The BmWD40s were categorized into five clusters and 12 classes according to the phylogenetic classification and their domain architectures, respectively. Sequence analyses indicated that tandem and segmental duplication played minor roles in producing the current number of BmWD40s, and domain recombination events of multi-domain BmWD40s might have occurred mainly after gene duplication events. Gene Ontology (GO) analysis revealed that a higher proportion of BmWD40s was involved in processes, such as binding, transcription-regulation and cellular component biogenesis, compared to all silkworm genes annotated in GO. Microarray-based analysis demonstrated that many BmWD40s had tissue-specific expression and exhibited high and/or sex-related expression during metamorphosis. These findings contribute to a better understanding of the evolution of the animal WD40 protein family and assist the study of the functions of BmWD40s.

EIF3i affects vesicular stomatitis virus growth by interacting with matrix protein

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VSV M protein interacts with the i subunit of eIF3.

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The region of M that interacts with eIF3i is located within the 122- to -181 amino acids.

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M–eIF3i interaction affects VSV growth.

The matrix protein of vesicular stomatitis virus (VSV) performs multiple functions during viral genome replication and virion production and is involved in modulating multiple host signaling pathways that favor virus replication. To perform numerous functions within infected cells, the M protein needs to recruit cellular partners. To better understand the role of M during VSV replication, we looked for interacting partners by using the two-hybrid system. The eukaryotic translation initiation factor 3, subunit i (eIF3i) was identified to be an M-binding partner, and this interaction was validated by GST pull-down and laser confocal assays. Through a mutagenesis analysis, we found that some mutants of M between amino acids 122 and 181 impaired but did not completely abolish the M–eIF3i interaction. Furthermore, the knockdown of eIF3i by RNA interference decreased viral replication and transcription in the early stages but led to increase in later stages. VSV transcription was increased at 4 h post-infection but was not changed at 8 and 12 h post-infection after the over-expression of eIF3i. Finally, we also demonstrated that VSV could inhibit the activity of Akt1 and that the knockdown of eIF3i inhibited the expression of the ISGs regulated by phospho-Akt1. These results indicated that eIF3i may affect VSV growth by regulating the host antiviral response in HeLa cells.

Binding of coronin 1B to TβRI negatively regulates the TGFβ1 signaling pathway

Coronin 1B is an actin-binding protein that regulates several actin-dependent cellular processes including migration and endocytosis. However, the role of coronin 1B in the tumor growth factor (TGF)β signaling pathway is largely unknown. Here, we investigated whether coronin 1B affects the TGFβ signaling cascade and found that coronin 1B negatively regulates the TGFβ signaling pathway. Immunoprecipitation and glutathione-S-transferase-pulldown assays revealed that coronin 1B directly associated with TGFβ receptor I (TβRI). Overexpression of coronin 1B inhibited the TGFβ1-induced interaction between TβRI and Smad2/3 in plasmid-transfected HEK293T cells. Coronin 1B was basally bound to TβRI in vascular smooth muscle cells (VSMCs), but TGFβ1 stimulation did not affect their association, suggesting constitutive binding between coronin 1B and TβRI. Overexpression of coronin 1B suppressed TGFβ1-induced activation of a Smad-binding element-luciferase reporter construct and a plasminogen activator inhibitor (PAI)-1 promoter-luciferase reporter construct in HEK293T cells. By contrast, depletion of coronin 1B by siRNA transfection increased TGFβ1-induced Smad2/3 phosphorylation and PAI-1 expression in VSMCs. These results suggest that coronin 1B regulates the TGFβ1 signaling cascade by constitutively interacting with TβRI and inhibiting the binding of Smad2/3 to TβRI in response to TGFβ1 stimulation.

Systematic comparison of lncRNAs with protein coding mRNAs in population expression and their response to environmental change

BACKGROUND

Long non-coding RNA (lncRNA) is a class of non-coding RNA with important regulatory roles in biological process of organisms. The systematic comparison of lncRNAs with protein coding mRNAs in population expression and their response to environmental change are still poorly understood. Here we identified 17,610 lncRNAs and calculated their expression levels based on RNA-seq of 80 individuals of Miscanthus lutarioriparius from two environments, the nearly native habitats and transplanted field, respectively.

RESULTS

LncRNAs had significantly higher expression diversity and lower expression frequency in population than protein coding mRNAs in both environments, which suggested that lncRNAs may experience more relaxed selection or divergent evolution in population compared with protein coding RNAs. In addition, the increase of expression diversity for lncRNAs was always significantly higher and the magnitude of fold change of expression in new stress environment was significantly larger than protein-coding mRNAs. These results suggested that lncRNAs may be more sensitive to environmental change than protein-coding mRNAs. Analysis of environment-robust and environment-specific lncRNA-mRNA co-expression network between two environments revealed the characterization of lncRNAs in response to environmental change. Furthermore, candidate lncRNAs contributing to water use efficiency (WUE) identified based on the WUE-lncRNA-mRNA co-expression network suggested the roles of lncRNAs in response to environmental change.

CONCLUSION

Our study provided a comprehensive understanding of expression characterization of lncRNAs in population for M. lutarioriparius under field condition, which would be useful to explore the roles of lncRNAs and could accelerate the process of adaptation in new environment for many plants.

Identification of novel and differentially expressed MicroRNAs in goat enzootic nasal adenocarcinoma

Background

MicroRNAs (miRNAs) post-transcriptionally regulate a variety of genes involved in eukaryotic cell growth, development, metabolism and other biological processes, and numerous miRNAs are implicated in the initiation and progression of cancer. Enzootic nasal adenocarcinoma (ENA), an epithelial tumor induced in goats and sheep by enzootic nasal tumor virus (ENTV), is a chronic, progressive, contact transmitted disease.

Methods

In this work, small RNA Illumina high-throughput sequencing was used to construct a goat nasal miRNA library. This study aimed to identify novel and differentially expressed miRNAs in the tumor and para-carcinoma nasal tissues of Nanjiang yellow goats with ENA.

Results

Four hundred six known miRNAs and 29 novel miRNAs were identified. A total of 116 miRNAs were significantly differentially expressed in para-carcinoma nasal tissues and ENA (54 downregulated; 60 upregulated; two only expressed in control group); Target gene prediction and functional analysis revealed that 6176 non-redundancy target genes, 1792 significant GO and 97 significant KEGG pathway for 121 miRNAs (116 significant expression miRNAs and five star sequence) were predicted. GO and KEGG pathway analysis revealed the majority of target genes in ENA are involved in cell proliferation, signal transduction and other processes associated with cancer.

Conclusions

This is the first large-scale identification of miRNAs in Capra hircus ENA and provides a theoretical basis for investigating the complicated miRNA-mediated regulatory networks involved in the pathogenesis and progression of ENA.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3238-5) contains supplementary material, which is available to authorized users.

TGF-β Signaling from Receptors to Smads

Transforming growth factor β (TGF-β) and related growth factors are secreted pleiotropic factors that play critical roles in embryogenesis and adult tissue homeostasis by regulating cell proliferation, differentiation, death, and migration. The TGF-β family members signal via heteromeric complexes of type I and type II receptors, which activate members of the Smad family of signal transducers. The main attribute of the TGF-β signaling pathway is context-dependence. Depending on the concentration and type of ligand, target tissue, and developmental stage, TGF-β family members transmit distinct signals. Deregulation of TGF-β signaling contributes to developmental defects and human diseases. More than a decade of studies have revealed the framework by which TGF-βs encode a context-dependent signal, which includes various positive and negative modifiers of the principal elements of the signaling pathway, the receptors, and the Smad proteins. In this review, we first introduce some basic components of the TGF-β signaling pathways and their actions, and then discuss posttranslational modifications and modulatory partners that modify the outcome of the signaling and contribute to its context-dependence, including small noncoding RNAs.

The Discovery and Early Days of TGF-β: A Historical Perspective

Transforming growth factors (TGFs) were discovered as activities that were secreted by cancer cells, and later by normal cells, and had the ability to phenotypically and reversibly transform immortalized fibroblasts. TGF-β distinguished itself from TGF-α because it did not bind to the same epidermal growth factor (EGF) receptor as TGF-α and, therefore, acted through different cell-surface receptors and signaling mediators. This review summarizes the discovery of TGF-β, the early developments in its molecular and biological characterization with its many biological activities in different cell and tissue contexts and its roles in disease, the realization that there is a family of secreted TGF-β-related proteins with many differentiation functions in development and activities in normal cell and tissue physiology, and the subsequent identification and characterization of the receptors and effectors that mediate TGF-β family signaling responses.

Identification of WD40 repeats by secondary structure-aided profile-profile alignment

A WD40 protein typically contains four or more repeats of ~40 residues ended with the Trp-Asp dipeptide, which folds into β-propellers with four β strands in each repeat. They often function as scaffolds for protein-protein interactions and are involved in numerous fundamental biological processes. Despite their important functional role, the "velcro" closure of WD40 propellers and the diversity of WD40 repeats make their identification a difficult task. Here we develop a new WD40 Repeat Recognition method (WDRR), which uses predicted secondary structure information to generate candidate repeat segments, and further employs a profile-profile alignment to identify the correct WD40 repeats from candidate segments. In particular, we design a novel alignment scoring function that combines dot product and BLOSUM62, thereby achieving a great balance of sensitivity and accuracy. Taking advantage of these strategies, WDRR could effectively reduce the false positive rate and accurately identify more remote homologous WD40 repeats with precise repeat boundaries. We further use WDRR to re-annotate the Pfam families in the β-propeller clan (CL0186) and identify a number of WD40 repeat proteins with high confidence across nine model organisms. The WDRR web server and the datasets are available at http://protein.cau.edu.cn/wdrr/.

The role of eIF3 and its individual subunits in cancer

Specific individual subunits of eIF3 are elevated or reduced in numerous human tumors, and their ectopic overexpression in immortal cells can result in malignant transformation. The structure and assembly of eIF3 and its role in promoting mRNA and methionyl-tRNAi binding to the ribosome during the initiation phase of protein synthesis are described. Methods employed to detect altered levels of eIF3 subunits in cancers are critically evaluated in order to conclude rigorously that such subunits may cause malignant transformation. Strong evidence is presented that the individual overexpression of eIF3 subunits 3a, 3b, 3c, 3h, 3i and 3m may cause malignant transformation, whereas underexpression of subunits 3e and 3f may cause a similar outcome. Possible mechanisms to explain the malignant phenotypes are examined. The involvement of eIF3 in cancer reinforces the view that translational control plays an important role in the regulation of cell proliferation, and provides new targets for the development of therapeutic agents. This article is part of a Special Issue entitled: Translation and Cancer.

The growth factor-like adipokine tartrate-resistant acid phosphatase 5a interacts with the rod G3 domain of adipocyte-produced nidogen-2

The adipokine tartrate resistant acid phosphatase (TRAP) 5a isoform exerts a growth factor-effect on pre-adipocytes. This study aimed to identify potential TRAP 5a interacting proteins in pre-adipocytes using pull down assays in combination with mass spectrometry. Nidogen-2, a protein shown to be expressed intracellularly and for secretion by pre-adipocytes, was shown to interact, through its globular G3 domain, with TRAP 5a in vitro. In vivo, TRAP 5a interacted with nidogen-2 in cultured 3T3-L1 mouse pre-adipocytes, as well as with transforming growth factor-β (TGF-β) interacting protein (TRIP-1), which is a protein that has previously been suggested to interact with TRAP in bone. In addition, TRAP 5a and nidogen-2 co-localized in adipose tissue cells in situ. These results indicate that TRAP 5a interacts with nidogen-2 and TRIP-1 in pre-adipocytic cells.

The translation initiation factor eIF3i up-regulates vascular endothelial growth factor A, accelerates cell proliferation, and promotes angiogenesis in embryonic development and tumorigenesis

Vascular endothelial growth factor A (VEGFA) is a critical proangiogenic factor that is activated by hypoxia at both the transcriptional and post-transcriptional levels. In hypoxia conditions, stabilized hypoxia-inducible factor 1α (HIF1A) is the key regulator for transcriptional activation of VEGFA. However, the post-transcriptional control of VEGFA expression remains poorly understood. Here, we report that the eukaryotic translation initiation factor 3i (eIF3i) is required for VEGFA protein expression in both normal embryonic and tumorigenic angiogenesis. eIF3i is dynamically expressed in the early stages of zebrafish embryogenesis and in human hepatocellular carcinoma tissues. eIF3i homozygous mutant zebrafish embryos show severe angiogenesis defects and human hepatocellular cancer cells with depletion of eIF3i to induce less angiogenesis in tumor models. Under hypoxia, the HIF1A protein can interact with its binding sequence in the eIF3i promoter and activate eIF3i transcription. The expression of VEGFA, which should rise in hypoxia, is significantly inhibited by eIF3i siRNA treatment. Moreover, eIF3i knockdown did not cause a general translation repression but specifically reduced the translation efficiency of the VEGFA mRNAs. Taken together, our results suggest that eIF3i is induced by HIF1A under hypoxia and controls normal and tumorigenic angiogenesis through regulating VEGFA protein translation.

Growth inhibition and differences in protein profiles in azadirachtin-treated Drosophila melanogaster larvae

Azadirachtin A is a very effective biopesticide widely used in insect pest control. It has strong antifeeding and growth inhibitory activity against most insects, however, its mode of action is still unclear. Proteomic experiments using 2DE indicate significant effects of Azadirachtin A on the amount of proteins related to growth inhibition in Drosophila melanogaster larvae. Twenty-one spots with different intensity in azadirachtin-treated larvae were identified. These proteins are involved in cytoskeletal organization, transcription and translation, hormonal regulation, and energy metabolism. Protein network analysis reveals heat shock protein 23 to be a potential target of azadirachtin. These results provide new insights into understanding the mechanism of growth inhibition in insects in response to azadirachtin.

A genotypic difference in primary root length is associated with the inhibitory role of transforming growth factor-beta receptor-interacting protein-1 on root meristem size in wheat

Previously we identified a major quantitative trait locus (QTL) qTaLRO-B1 for primary root length (PRL) in wheat. Here we compare proteomics in the roots of the qTaLRO-B1 QTL isolines 178A, with short PRL and small meristem size, and 178B, with long PRL and large meristem size. A total of 16 differentially expressed proteins were identified: one, transforming growth factor (TGF)-beta receptor-interacting protein-1 (TaTRIP1), was enriched in 178A, while various peroxidases (PODs) were more abundantly expressed in 178B. The 178A roots showed higher TaTRIP1 expression and lower levels of the unphosphorylated form of the brassinosteroid (BR) signaling component BZR1, lower expression of POD genes and reduced POD activity and accumulation of the superoxide anion O2(-) in the root elongation zone compared with the 178B roots. Low levels of 24-epibrassinolide increased POD gene expression and root meristem size, and rescued the short PRL phenotype of 178A. TaTRIP1 directly interacted with the BR receptor TaBRI1 of wheat. Moreover, overexpressing TaTRIP1 in Arabidopsis reduced the abundance of unphosphorylated BZR1 protein, altered the expression of BR-responsive genes, inhibited POD activity and accumulation of the O2(-) in the root tip and inhibited root meristem size. Our data suggested that TaTRIP1 is involved in BR signaling and inhibited root meristem size, possibly by reducing POD activity and accumulation of O2(-) in the root tip. We further demonstrated a negative correlation between the level of TaTRIP1 mRNA and PRL of landraces and modern wheat varieties, providing a valuable insight for better understanding of the molecular mechanism underlying the genotypic differences in root morphology of wheat in the future.

TRIP-1 via AKT modulation drives lung fibroblast/myofibroblast trans-differentiation

BACKGROUND

Myofibroblasts are the critical effector cells in the pathogenesis of pulmonary fibrosis which carries a high degree of morbidity and mortality. We have previously identified Type II TGFβ receptor interacting protein 1 (TRIP-1), through proteomic analysis, as a key regulator of collagen contraction in primary human lung fibroblasts--a functional characteristic of myofibroblasts, and the last, but critical step in the process of fibrosis. However, whether or not TRIP-1 modulates fibroblast trans-differentiation to myofibroblasts is not known.

METHODS

TRIP-1 expression was altered in primary human lung fibroblasts by siRNA and plasmid transfection. Transfected fibroblasts were then analyzed for myofibroblast features and function such as α-SMA expression, collagen contraction ability, and resistance to apoptosis.

RESULTS

The down-regulation of TRIP-1 expression in primary human lung fibroblasts induces α-SMA expression and enhances resistance to apoptosis and collagen contraction ability. In contrast, TRIP-1 over-expression inhibits α-SMA expression. Remarkably, the effects of the loss of TRIP-1 are not abrogated by blockage of TGFβ ligand activation of the Smad3 pathway or by Smad3 knockdown. Rather, a TRIP-1 mediated enhancement of AKT phosphorylation is the implicated pathway. In TRIP-1 knockdown fibroblasts, AKT inhibition prevents α-SMA induction, and transfection with a constitutively active AKT construct drives collagen contraction and decreases apoptosis.

CONCLUSIONS

TRIP-1 regulates fibroblast acquisition of phenotype and function associated with myofibroblasts. The importance of this finding is it suggests TRIP-1 expression could be a potential target in therapeutic strategy aimed against pathological fibrosis.

WITHDRAWN: TRIP-1 interacts with ezrin to regulate ezrin phosphorylation, cell protrusion formation and cell migration

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Mitochondrial proteomic analysis of human host cells infected with H3N2 swine influenza virus

Swine influenza viruses (SIV) are zoonotic pathogens that pose a potential threat to human health. In this study, we analyzed the differential mitochondrial proteomes of H3N2 SIV-infected human lung A549 cells using two-dimensional gel electrophoresis (2-DE) followed by matrix-assisted laser desorption ionization time-of-flight/time-of-flight (MALDI-TOF/TOF) analysis. In the comparative analysis, 24 altered proteins (13 upregulated and 11 downregulated) were identified in the mitochondria of H3N2 SIV-infected cells; these proteins were involved in cell-to-cell signaling and interaction, cellular movement, and post-translational modification. Moreover, the transcriptional profiles of 16 genes corresponding to the identified proteins were estimated by real time RT-PCR. IPA analysis suggested that the differentially expressed proteins were clustered primarily into the mammalian target of rapamycin (mTOR) and d-glucose signaling pathways. In addition, oxidative phosphorylation and integrin signaling appeared to be major pathways modulated in the mitochondria of infected cells. We further demonstrated that apolipoprotein L2 was upregulated in the cytoplasm and translocated to mitochondria during virus infection. These results were verified by Western blot analysis coupled with confocal microscopy. Collectively, the mitochondrial proteome data provide insights to further understand the underlying mechanisms of H3N2 SIV cross-species infection.

BIOLOGICAL SIGNIFICANCE

In recent years, proteomics has emerged as an indispensable tool to unveil the complex molecular events in virology. we firstly perform mitochondrial proteomic profiles of human cells infected with H3N2 subtype SIV to understand virus-host interactions, and 24 differentially expressed proteins in mitochondrial proteomes were identified in SIV-infected cells. The proteins that were identified to have differential expression were involved in cell-to-cell signaling and interaction, post-translational modification, cell morphology, cellular assembly, cell death, and energy production. Furthermore, Western blot analysis and a confocal assay further demonstrated that the cellular protein APOL2 partially co-localized with mitochondria after virus infection. This is a very important discovery in the underlying replication and pathogenesis of SIV which provides a potential target clue for the design of anti-SIV drugs. Our results will inspire basic study on SIV infection and drive the understanding for replication and pathogenesis of SIV to control this disease.

Eukaryotic translation initiation factors in cancer development and progression

Eukaryotic gene expression is a complicated process primarily regulated at the levels of gene transcription and mRNA translation. The latter involves four main steps: initiation, elongation, termination and recycling. Translation regulation is primarily achieved during initiation which is orchestrated by 12 currently known eukaryotic initiation factors (eIFs). Here, we review the current state of eIF research and present a concise summary of the various eIF subunits. As eIFs turned out to be critically implicated in different oncogenic processes the various eIF members and their contribution to onset and progression of cancer are featured.

Overexpressed-eIF3I interacted and activated oncogenic Akt1 is a theranostic target in human hepatocellular carcinoma

Eukaryotic translation initiation factor 3 subunit I (eIF3I) with transforming capability is often overexpressed in human hepatocellular carcinoma (HCC) but its oncogenic mechanisms remain unknown. We demonstrate that eIF3I is overexpressed in various cancers along with activated Akt1 phosphorylation and kinase activity in an eIF3I dose-dependent manner. A novel eIF3I and Akt1 protein interaction was identified in HCC cell lines and tissues and was required for eIF3I-mediated activation of Akt1 signaling. Expression of either antisense eIF3I or dominant negative Akt1 mutant suppressed eIF3I-mediated Akt1 oncogenic signaling and various other tumorigenic effects. Oncogenic domain mapping of the eIF3I and Akt1 interaction suggested that the C-terminal eIF3I interacted with the Akt1 kinase domain and conferred the majority of oncogenic functions. In addition, eIF3I interaction with Akt1 prevented PP2A dephosphorylation of Akt1 and resulted in constitutively active Akt1 oncogenic signaling. Importantly, concordant expression of endogenous eIF3I and phospho-Akt1 was detected in HCC cell lines and tissues. Treatment of eIF3I overexpressing HCC cells with the Akt1 specific inhibitor API-2 suppressed eIF3I-mediated tumorigenesis in vitro and in vivo.

CONCLUSION

We describe a constitutive Akt1 oncogenic mechanism resulting from interaction of overexpressed eIF3I with Akt1 that prevents PP2A-mediated dephosphorylation. Overexpression of eIF3I in HCC is oncogenic and is a surrogate marker and therapeutic target for treatment with Akt1 inhibitors.

Shotgun proteomic analysis of the Mexican lime tree infected with "CandidatusPhytoplasma aurantifolia"

Infection of Mexican lime trees (Citrus aurantifolia L.) with the specialized bacterium "CandidatusPhytoplasma aurantifolia" causes witches' broom disease. Witches' broom disease has the potential to cause significant economic losses throughout western Asia and North Africa. We used label-free quantitative shotgun proteomics to study changes in the proteome of Mexican lime trees in response to infection by "Ca. Phytoplasma aurantifolia". Of 990 proteins present in five replicates of healthy and infected plants, the abundances of 448 proteins changed significantly in response to phytoplasma infection. Of these, 274 proteins were less abundant in infected plants than in healthy plants, and 174 proteins were more abundant in infected plants than in healthy plants. These 448 proteins were involved in stress response, metabolism, growth and development, signal transduction, photosynthesis, cell cycle, and cell wall organization. Our results suggest that proteomic changes in response to infection by phytoplasmas might support phytoplasma nutrition by promoting alterations in the host's sugar metabolism, cell wall biosynthesis, and expression of defense-related proteins. Regulation of defense-related pathways suggests that defense compounds are induced in interactions with susceptible as well as resistant hosts, with the main differences between the two interactions being the speed and intensity of the response.

TRIP-1: a regulator of osteoblast function

Transforming growth factor β (TGFβ) receptor interacting protein-1 (TRIP-1) is an intracellular protein expressed in osteoblasts with high affinity for type 5b tartrate resistant acid phosphatase (TRAP). It is suggested that through this interaction, TRIP-1 serves as a positive regulator of TGFβ signaling and osteoblast differentiation during bone remodeling. We show here that TRIP-1 is abundant in osteoblasts in vivo and in vitro. TRIP-1 mRNA and protein expression were increased at early stages and decreased at later stages during osteoblast differentiation, suggesting a predominant role during early maturation. To investigate a role during bone remodeling, primary osteoblasts were treated with different hormones and factors that are known to affect remodeling. TRIP-1 levels were decreased with dexamethasone and increased with vitamin D(3) , dihydrotestosterone (DHT), TGFβ1, and bone morphogenic protein 2 (BMP-2). Treatment with parathyroid hormone (PTH) and β-estradiol did not affect TRIP-1 levels. Transfected small interfering RNA (siRNA) against TRIP-1 inhibited osteoblast differentiation as characterized by a decrease in alkaline phosphatase staining and enzyme activity, and decrease in the expression of collagen I, alkaline phosphatase, Runx2, osteopontin, and osteocalcin. The proliferation of osteoblasts was also affected by TRIP-1 siRNA. This particular effect was defined by decreased cell number, marked reduction of cyclin D1, a 38% decrease of cells in S phase (p < 0.001) and a 97% increase of cells in the G2/M phase (p < 0.01) of the cell cycle. However, TRIP-1 siRNA did not induce an effect in apoptosis. Using a TGFβ luciferase reporter we found that knocking down TRIP-1 decreased the activation of TGFβ signaling by 40% percent (p < 0.001). In conclusion, our characterization of TRIP-1 in osteoblasts provides the first evidence of its key role as a positive regulator of osteoblast function.

The protein partners of GTP cyclohydrolase I in rat organs

OBJECTIVE

GTP cyclohydrolase I (GCH1) is the rate-limiting enzyme for tetrahydrobiopterin biosynthesis and has been shown to be a promising therapeutic target in ischemic heart disease, hypertension, atherosclerosis and diabetes. The endogenous GCH1-interacting partners have not been identified. Here, we determined endogenous GCH1-interacting proteins in rat.

METHODS AND RESULTS

A pulldown and proteomics approach were used to identify GCH1 interacting proteins in rat liver, brain, heart and kidney. We demonstrated that GCH1 interacts with at least 17 proteins including GTP cyclohydrolase I feedback regulatory protein (GFRP) in rat liver by affinity purification followed by proteomics and validated six protein partners in liver, brain, heart and kidney by immunoblotting. GCH1 interacts with GFRP and very long-chain specific acyl-CoA dehydrogenase in the liver, tubulin beta-2A chain in the liver and brain, DnaJ homolog subfamily A member 1 and fatty aldehyde dehydrogenase in the liver, heart and kidney and eukaryotic translation initiation factor 3 subunit I (EIF3I) in all organs tested. Furthermore, GCH1 associates with mitochondrial proteins and GCH1 itself locates in mitochondria.

CONCLUSION

GCH1 interacts with proteins in an organ dependant manner and EIF3I might be a general regulator of GCH1. Our finding indicates GCH1 might have broader functions beyond tetrahydrobiopterin biosynthesis.

Localization of transforming growth factor beta receptor II interacting protein-1 in bone and teeth: implications in matrix mineralization

Transforming growth factor beta receptor II (TGFβR-II) interacting protein 1 (TRIP-1) is a WD-40 protein that binds to the cytoplasmic domain of the TGF-β type II receptor in a kinase-dependent manner. To investigate the role of TRIP-1 in mineralized tissues, we examined its pattern of expression in cartilage, bone, and teeth and analyzed the relationship between TRIP-1 overexpression and mineralized matrix formation. Results demonstrate that TRIP-1 was predominantly expressed by osteoblasts, odontoblasts, and chondrocytes in these tissues. Interestingly, TRIP-1 was also localized in the extracellular matrix of bone and at the mineralization front in dentin, suggesting that TRIP-1 is secreted by nonclassical secretory mechanisms, as it is devoid of a signal peptide. In vitro nucleation studies demonstrate a role for TRIP-1 in nucleating calcium phosphate polymorphs. Overexpression of TRIP-1 favored osteoblast differentiation of undifferentiated mesenchymal cells with an increase in mineralized matrix formation. These data indicate an unexpected role for TRIP-1 during development of bone, teeth, and cartilage.

Brassinosteroids

Brassinosteroids (BRs) are endogenous plant hormones essential for the proper regulation of multiple physiological processes required for normal plant growth and development. Since their discovery more than 30 years ago, extensive research on the mechanisms of BR action using biochemistry, mutant studies, proteomics and genome-wide transcriptome analyses, has helped refine the BR biosynthetic pathway, identify the basic molecular components required to relay the BR signal from perception to gene regulation, and expand the known physiological responses influenced by BRs. These mechanistic advances have helped answer the intriguing question of how BRs can have such dramatic pleiotropic effects on a broad range of diverse developmental pathways and have further pointed to BR interactions with other plant hormones and environmental cues. This chapter briefly reviews historical aspects of BR research and then summarizes the current state of knowledge on BR biosynthesis, metabolism and signal transduction. Recent studies uncovering novel phosphorelays and gene regulatory networks through which BR influences both vegetative and reproductive development are examined and placed in the context of known BR physiological responses including cell elongation and division, vascular differentiation, flowering, pollen development and photomorphogenesis.

Translational control gone awry: a new mechanism of tumorigenesis and novel targets of cancer treatments

Translational control is one of primary regulation mechanisms of gene expression. Eukaryotic translational control mainly occurs at the initiation step, the speed-limiting step, which involves more than ten translation initiation factors [eIFs (eukaryotic initiation factors)]. Changing the level or function of these eIFs results in abnormal translation of specific mRNAs and consequently abnormal growth of cells that leads to human diseases, including cancer. Accumulating evidence from recent studies showed that the expression of many eIFs was associated with malignant transformation, cancer prognosis, as well as gene expression regulation. In the present paper, we perform a critical review of recent advances in understanding the role and mechanism of eIF action in translational control and cancer as well as the possibility of targeting eIFs for therapeutic development.

TGF-beta-dependent and -independent roles of STRAP in cancer

The serine-threonine kinase receptor-associated protein (STRAP) was initially identified as a putative inhibitor of the canonical TGF-beta signaling pathway. Because the Smad-dependent TGF-beta pathway negatively regulates cellular growth, early functional studies suggested that STRAP behaves as an oncogene. Indeed, a correlation between STRAP overexpression and various cancers has been identified. With the emergence of new studies on the biological function of STRAP, it is becoming clear that STRAP regulates several distinct cellular processes and modulates multiple signaling pathways. While STRAP itself does not possess enzymatic activity, it appears that STRAP influences biological processes through associations with cellular proteins. In this review, we will describe the TGF-beta-dependent and -independent functions of STRAP and provide a context for the significance of STRAP activity in the development of cancer.

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

BACKGROUND

Transforming growth factor β (TGF-β) 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-β receptor (TβR-I) is essential for TGF-β signaling, and substrates of TβR-I provide insights into molecular mechanisms of TGF-β signaling.

RESULTS

Here we identify eukaryotic elongation factor 1A1 (eEF1A1) as a novel substrate of TβR-I. We show that TβR-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-β 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 TβR-I is a novel regulatory mechanism that provides a direct link to regulation of protein synthesis by TGF-β, as an important component in the TGF-β-dependent regulation of protein synthesis and cell proliferation.

Cell signaling in protein synthesis ribosome biogenesis and translation initiation and elongation

Protein synthesis is a highly energy-consuming process that must be tightly regulated. Signal transduction cascades respond to extracellular and intracellular cues to phosphorylate proteins involved in ribosomal biogenesis and translation initiation and elongation. These phosphorylation events regulate the timing and rate of translation of both specific and total mRNAs. Alterations in this regulation can result in dysfunction and disease. While many signaling pathways intersect to control protein synthesis, the mTOR and MAPK pathways appear to be key players. This chapter briefly reviews the mTOR and MAPK pathways and then focuses on individual phosphorylation events that directly control ribosome biogenesis and translation.

New regulatory mechanisms of TGF-beta receptor function

Transforming growth factor-beta (TGF-beta) regulates cell proliferation, differentiation and apoptosis, and TGF-beta-related proteins have key roles in development, tissue homeostasis and disease. Upon binding to their cell surface receptors, TGF-beta family proteins signal through Smads to induce changes in gene expression. TGF-beta-induced Smad signaling and additional non-Smad pathways have been studied extensively in an effort to understand the complex and versatile responses to TGF-beta family proteins. Recently, it has become increasingly apparent that the signaling responses are also extensively defined by regulatory mechanisms at the level of the receptors themselves. Here, we discuss recent insights into the effects of post-translational modifications, protein associations and mode of internalization on the functions of the TGF-beta receptors and their signaling responses.

Molecular cloning and expression analysis of riceOsTVLP1, encoding a protein with similarity to TGF-β receptor interacting proteins and vacuolar assembly Vam6p/Vps39p proteins

We describe the cloning and identification of a rice cDNA, OsTVLP1, encoding a protein with similarity to TGF-beta receptor interacting proteins and vacuolar assembly Vam6p/Vps39p proteins. OsTVLP1 has an open reading frame of 2955 bp, which encodes a 984 amino acid protein, containing a citron homology (CNH) domain at its N-terminal and a clathrin heavy-chain repeat homology (CLH) domain at its C-terminal. The expression of OsTVLP1 was induced by treatments with benzothiadiazole (BTH), a chemical activator of plant disease resistance responses, and by infection of the blast fungus, Magnaporthe grisea. Importantly, the expression of OsTVLP1 was activated specifically in disease resistance response induced by BTH and in an incompatible interaction between rice and the blast fungus. Our observations suggest that OsTVLP1 may play a role in rice disease resistance response against pathogen infection.

Phospho-control of TGF-beta superfamily signaling

Members of the transforming growth factor-beta (TGF-beta) family control a broad range of cellular responses in metazoan organisms via autocrine, paracrine, and endocrine modes. Thus, aberrant TGF-beta signaling can play a key role in the pathogenesis of several diseases, including cancer. TGF-beta signaling pathways are activated by a short phospho-cascade, from receptor phosphorylation to the subsequent phosphorylation and activation of downstream signal transducers called R-Smads. R-Smad phosphorylation state determines Smad complex assembly/disassembly, nuclear import/export, transcriptional activity and stability, and is thus the most critical event in TGF-beta signaling. Dephosphorylation of R-Smads by specific phosphatases prevents or terminates TGF-beta signaling, highlighting the need to consider Smad (de)phosphorylation as a tightly controlled and dynamic event. This article illustrates the essential roles of reversible phosphorylation in controlling the strength and duration of TGF-beta signaling and the ensuing physiological responses.

Differential proteome expression associated with urokinase plasminogen activator receptor (uPAR) suppression in malignant epithelial cancer

Dysregulation of the plasminogen activation cascade is a prototypic feature in many malignant epithelial cancers. Principally, this is thought to occur through activation of overexpressed urokinase plasminogen activator (uPA) concomitant with binding to its high specificity cell surface receptor urokinase plasminogen activator receptor (uPAR). Up-regulation of uPA and uPAR in cancer appears to potentiate the malignant phenotype, either (i) directly by triggering plasmin-mediated degradation or activation of uPA's or plasmin's proteolytic targets (e.g., extracellular matrix zymogen proteases or nascent growth factors) or indirectly by simultaneously altering a range of downstream functions including signal transduction pathways ( Romer, J. ; Nielsen, B. S. ; Ploug, M. The urokinase receptor as a potential target in cancer therapy Curr. Pharm. Des. 2004, 10 ( 19), 235976 ). Because many malignant epithelial cancers express high levels of uPAR, uPA or other components of the plasminogen activation cascade and because these are often associated with poor prognosis, characterizing how uPAR changes the downstream cellular "proteome" is fundamental to understanding any role in cancer. This study describes a carefully designed proteomic study of the effects of antisense uPAR suppression in a previously studied colon cancer cell line (HCT116). The study utilized replicate 2DE gels and two independent gel image analysis software packages to confidently identify 64 proteins whose expression levels changed (by > or =2 fold) coincident with a moderate ( approximately 40%) suppression of cell-surface uPAR. Not surprisingly, many of the altered proteins have previously been implicated in the regulation of tumor progression (e.g., p53 tumor suppressor protein and c-myc oncogene protein among many others). In addition, through a combination of proteomics and immunological methods, this study demonstrates that stathmin 1alpha, a cytoskeletal protein implicated in tumor progression, undergoes a basic isoelectric point shift (p I) following uPAR suppression, suggesting that post-translational modification of stathmin occur secondary to uPAR suppression. Overall, these results shed new light on the molecular mechanisms involved in uPAR signaling and how it may promulgate the malignant phenotype.

Phosphorylation of mouse sperm axoneme central apparatus protein SPAG16L by a testis-specific kinase, TSSK2

The mammalian protein SPAG16L, the ortholog of Chlamydomonas Pf20, is an axoneme central apparatus protein necessary for flagellar motility. The SPAG16L protein sequence contains multiple potential phosphorylation sites, and the protein was confirmed to be phosphorylated in vivo. A yeast two-hybrid screen identified the testis-specific kinase, TSSK2, to be a potential SPAG16L binding partner. SPAG16L and TSSK2 interactions were confirmed by coimmunoprecipitation of both proteins from testis extracts and cell lysates expressing these proteins, and their colocalization was also noted by confocal microscopy in Chinese hamster ovary cells, where they were coexpressed. TSSK2 associates with SPAG16L via its C-terminal domain bearing WD repeats. The N-terminal domain containing a coiled coil motif does not associate with TSSK2. SPAG16L can be phosphorylated by TSSK2 in vitro. Finally, TSSK2 is absent or markedly reduced from the testes in most of the SPAG16L-null mice. These data support the conclusion that SPAG16L is a TSSK2 substrate.

Transforming growth factor-beta signaling and ubiquitinators in cancer

Transforming growth factor-beta (TGF-beta) represents a large family of growth and differentiation factors that mobilize complex signaling networks to regulate cellular differentiation, proliferation, motility, adhesion, and apoptosis. TGF-beta signaling is tightly regulated by multiple complex mechanisms, and its deregulation plays a key role in the progression of many forms of cancer. Upon ligand binding, TGF-beta signals are transduced by Smad proteins, which in turn are tightly dependent on modulation by adaptor proteins such as embryonic liver fodrin, Smad anchor for receptor activation, filamin, and crkl. A further layer of regulation is imposed by ubiquitin-mediated targeting and proteasomal degradation of specific components of the TGF-beta signaling pathway. This review focuses on the ubiquitinators that regulate TGF-beta signaling and the association of these ubiquitin ligases with various forms of cancer. Delineating the role of ubiquitinators in the TGF-beta signaling pathway could yield powerful novel therapeutic targets for designing new cancer treatments.

Carcinoma-associated eIF3i overexpression facilitates mTOR-dependent growth transformation

Molecular processes controlling mRNA translation are complex, multilayered, and their deregulation can lead to cancer pathogenesis. Eukaryotic initiation factor 3 (eIF3) is involved in the initiation process of protein translation and overexpression of its subunit eukaryotic translation initiation factor i (eIF3i) has been observed in carcinomas. Nevertheless, the potential role of eIF3i in carcinogenesis is poorly understood. Here, we show that in vitro overexpression of human eIF3i resulted in cell size increase, proliferation enhancement, cell-cycle progression, and anchorage-independent growth. Without external stimuli, eIF3i overexpressing cells arrested in G1/G0 phase, demonstrating the requirement of additional growth signals. Inhibition of the kinase mTOR, a key player in the integration of nutrition and growth signals into protein synthesis, with rapamycin reduced serine phosphorylation of eIF3i and resulted in a loss of anchorage-independent growth. Thus, eIF3i overexpression fosters the integration of growth signals by mTOR into the mRNA translation process, promoting protein synthesis and tumor growth.

Oncogenic function of a novel WD-domain protein, STRAP, in human carcinogenesis

The development and progression of malignancies is a complex multistage process that involves the contribution of a number of genes giving growth advantage to cells when transformed. The role of transforming growth factor-beta (TGF-beta) in carcinogenesis is complex with tumor-suppressor or prooncogenic activities depending on the cell type and the stage of the disease. We have previously reported the identification of a novel WD-domain protein, STRAP, that associates with both TGF-beta receptors and that synergizes with the inhibitory Smad, Smad7, in the negative regulation of TGF-beta-induced transcription. Here, we show that STRAP is ubiquitously expressed and is localized in both cytoplasm and nucleus. STRAP is up-regulated in 60% colon and in 78% lung carcinomas. Stable expression of STRAP results in activation of mitogen-activated protein kinase/extracellular signal-regulated kinase pathway and in down-regulation of the cyclin-dependent kinase inhibitor p21(Cip1), which results in retinoblastoma protein hyperphosphorylation. In addition, we have observed that Smad2/3 phosphorylation, TGF-beta-mediated transcription, and growth inhibition are induced in STRAP-knockout mouse embryonic fibroblasts compared with wild-type cells. Ectopic expression of STRAP in A549 lung adenocarcinoma cell line inhibits TGF-beta-induced growth inhibition and enhances anchorage-independent growth of these cells. Moreover, overexpression of STRAP increases tumorigenicity in athymic nude mice. Knockdown of endogenous STRAP by small interfering RNA increases TGF-beta signaling, reduces ERK activity, increases p21(Cip1) expression, and decreases tumorigenicity. Taken together, these results suggest that up-regulation of STRAP in human cancers may provide growth advantage to tumor cells via TGF-beta-dependent and TGF-beta-independent mechanisms, thus demonstrating the oncogenic function of STRAP.

mTOR-dependent stimulation of the association of eIF4G and eIF3 by insulin

Insulin stimulates protein synthesis by increasing translation initiation. This response is mediated by mTOR and is believed to result from 4EBP1 phosphorylation, which allows eIF4E to bind eIF4G. Here, we present evidence that mTOR interacts directly with eIF3 and that mTOR controls the association of eIF3 and eIF4G. Activating mTOR signaling with insulin increased by as much as five-fold the amount of eIF4G bound to eIF3. This novel effect was blocked by rapamycin and other inhibitors of mTOR, and it required neither eIF4E binding to eIF4G nor eIF3 binding to the 40S ribosomal subunit. The increase in eIF4G associated with eIF3 occurred rapidly and at physiological concentrations of insulin. Moreover, the magnitude of the response was similar to the increase in eIF4E binding to eIF4G produced by insulin. Thus, increasing eIF4G association with eIF3 represents a potentially important mechanism by which insulin, as well as amino acids and growth factors that activate mTOR, stimulate translation.