Interaction of N-WASP with hnRNPK and its role in filopodia formation and cell spreading

The methyltransferase SETD3 regulates mRNA alternative splicing through interacting with hnRNPK

The methyltransferase SETD3 is an enzyme essential for catalyzing histidine-73 methylation on β-Actin, thereby promoting its polymerization and regulating muscle contraction. Although increasing evidence suggests that SETD3 is involved in multiple physiological or pathological events, its biological functions remain incompletely understood. In this study, we utilize in situ proximity labeling combined with mass spectrometry analysis to detect potential interacting partners of SETD3. Unexpectedly, we find that many splicing factors are associated with SETD3. Genome-wide RNA sequencing reveals that SETD3 regulates pre-mRNA splicing events, predominantly influencing exon skipping. Biochemical and bioinformatic analyses suggest that SETD3 interacts with hnRNPK, and they collaboratively regulate exon skipping in a common subset of genes. Functionally, we demonstrate that SETD3 and hnRNPK are required for retention of exon 7 skipping in the FNIP1 gene. This promotes FNIP1-mediated nuclear translocation of the transcription factor TFEB and the subsequent induction of lysosomal and mitochondrial biogenesis. Overall, this study uncovers a novel function of SETD3 in modulating mRNA exon splicing.

The "Biological Weapons" of Ehrlichia chaffeensis: Novel Molecules and Mechanisms to Subjugate Host Cells

Ehrlichia chaffeensis is an obligatory intracellular bacterium that causes human monocytic ehrlichiosis, an emerging, potentially fatal tick-borne infectious disease. The bacterium enters human cells via the binding of its unique outer-membrane invasin EtpE to the cognate receptor DNase X on the host-cell plasma membrane; this triggers actin polymerization and filopodia formation at the site of E. chaffeensis binding, and blocks activation of phagocyte NADPH oxidase that catalyzes the generation of microbicidal reactive oxygen species. Subsequently, the bacterium replicates by hijacking/dysregulating host-cell functions using Type IV secretion effectors. For example, the Ehrlichia translocated factor (Etf)-1 enters mitochondria and inhibits mitochondria-mediated apoptosis of host cells. Etf-1 also induces autophagy mediated by the small GTPase RAB5, the result being the liberation of catabolites for proliferation inside host cells. Moreover, Etf-2 competes with the RAB5 GTPase-activating protein, for binding to RAB5-GTP on the surface of E. chaffeensis inclusions, which blocks GTP hydrolysis and consequently prevents the fusion of inclusions with host-cell lysosomes. Etf-3 binds ferritin light chain to induce ferritinophagy to obtain intracellular iron. To enable E. chaffeensis to rapidly adapt to the host environment and proliferate, the bacterium must acquire host membrane cholesterol and glycerophospholipids for the purpose of producing large amounts of its own membrane. Future studies on the arsenal of unique Ehrlichia molecules and their interplay with host-cell components will undoubtedly advance our understanding of the molecular mechanisms of obligatory intracellular infection and may identify hitherto unrecognized signaling pathways of human hosts. Such data could be exploited for development of treatment and control measures for ehrlichiosis as well as other ailments that potentially could involve the same host-cell signaling pathways that are appropriated by E. chaffeensis.

Weighted Gene Co-Expression Network Analysis and Treatment Strategies of Tumor Recurrence-Associated Hub Genes in Lung Adenocarcinoma

Despite the recent progress of lung adenocarcinoma (LUAD) therapy, tumor recurrence remained to be a challenging factor that impedes the effectiveness of treatment. The objective of the present study was to predict the hub genes affecting LUAD recurrence via weighted gene co-expression network analysis (WGCNA). Microarray samples from LUAD dataset of GSE32863 were analyzed, and the modules with the highest correlation to tumor recurrence were selected. Functional enrichment analysis was conducted, followed by establishment of a protein-protein interaction (PPI) network. Subsequently, hub genes were identified by overall survival analyses and further validated by evaluation of expression in both myeloid populations and tissue samples of LUAD. Gene set enrichment analysis (GSEA) was then carried out, and construction of transcription factors (TF)-hub gene and drug-hub gene interaction network was also achieved. A total of eight hub genes (ACTR3, ARPC5, RAB13, HNRNPK, PA2G4, WDR12, SRSF1, and NOP58) were finally identified to be closely correlated with LUAD recurrence. In addition, TFs that regulate hub genes have been predicted, including MYC, PML, and YY1. Finally, drugs including arsenic trioxide, cisplatin, Jinfukang, and sunitinib were mined for the treatment of the eight hub genes. In conclusion, our study may facilitate the invention of targeted therapeutic drugs and shed light on the understanding of the mechanism for LUAD recurrence.

[Regulator proteins of actin dynamics as possible targets of antineoplastic therapies]

BACKGROUND

The ability of tumor cells to leave the primary tumor is prerequisite for metastatic spread. In previous studies, we identified regulator proteins of actin reorganization with essential functions in both synaptogenesis and tumor cell migration.

OBJECTIVE

The aim of the studies summarized in this article is to identify signaling pathways associated with actin-related proteins that might represent potential molecular targets for antiinvasive and/or antineoplastic therapies.

MATERIALS AND METHODS

We used immunohistochemical analyses of protein expression as well as in vitro techniques (cell culture, fluorescence microscopy, RNAi-based knockdown of protein expression, protein biochemistry and in vivo animal experiment substitutes).

RESULTS

We show that phosphorylation of Abelson interactor 1 (Abi1) is essential for the adhesion and invasion of colorectal carcinoma cells and might be targeted by the tyrosine kinase inhibitor STI571/Glivec®. HnRNP K, a protein interaction partner of Abi1, is upregulated in malignant melanoma in response to ionizing radiation; this upregulation is impaired upon application of the MEK inhibitor PD98059, enhancing radiosensivity of melanoma. Edelfosin, an alkyl-lipid blocker of the Abi1 interaction partner SK3, inhibits invasion of urothelial carcinoma cells.

CONCLUSION

The studies summarized in this overview confirm a central role for the investigated proteins in tumor cell invasion and resistance to antineoplastic therapies and identify possible molecular targets for novel therapeutic compounds.

The RNA-Binding Protein hnRNP K Mediates the Effect of BDNF on Dendritic mRNA Metabolism and Regulates Synaptic NMDA Receptors in Hippocampal Neurons

Brain-derived neurotrophic factor (BDNF) is an important mediator of long-term synaptic potentiation (LTP) in the hippocampus. The local effects of BDNF depend on the activation of translation activity, which requires the delivery of transcripts to the synapse. In this work, we found that neuronal activity regulates the dendritic localization of the RNA-binding protein heterogeneous nuclear ribonucleoprotein K (hnRNP K) in cultured rat hippocampal neurons by stimulating BDNF-Trk signaling. Microarray experiments identified a large number of transcripts that are coimmunoprecipitated with hnRNP K, and about 60% of these transcripts are dissociated from the protein upon stimulation of rat hippocampal neurons with BDNF. In vivo studies also showed a role for TrkB signaling in the dissociation of transcripts from hnRNP K upon high-frequency stimulation (HFS) of medial perforant path-granule cell synapses of male rat dentate gyrus (DG). Furthermore, treatment of rat hippocampal synaptoneurosomes with BDNF decreased the coimmunoprecipitation of hnRNP K with mRNAs coding for glutamate receptor subunits, Ca²⁺- and calmodulin-dependent protein kinase IIβ (CaMKIIβ) and BDNF. Downregulation of hnRNP K impaired the BDNF-induced enhancement of NMDA receptor (NMDAR)-mediated mEPSC, and similar results were obtained upon inhibition of protein synthesis with cycloheximide. The results demonstrate that BDNF regulates specific populations of hnRNP-associated mRNAs in neuronal dendrites and suggests an important role of hnRNP K in BDNF-dependent forms of synaptic plasticity.

RTVP-1 regulates glioma cell migration and invasion via interaction with N-WASP and hnRNPK

Glioblastoma (GBM) are characterized by increased invasion into the surrounding normal brain tissue. RTVP-1 is highly expressed in GBM and regulates the migration and invasion of glioma cells. To further study RTVP-1 effects we performed a pull-down assay using His-tagged RTVP-1 followed by mass spectrometry and found that RTVP-1 was associated with the actin polymerization regulator, N-WASP. This association was further validated by co-immunoprecipitation and FRET analysis. We found that RTVP-1 increased cell spreading, migration and invasion and these effects were at least partly mediated by N-WASP. Another protein which was found by the pull-down assay to interact with RTVP-1 is hnRNPK. This protein has been recently reported to associate with and to inhibit the effect of N-WASP on cell spreading. hnRNPK decreased cell migration, spreading and invasion in glioma cells. Using co-immunoprecipitation we validated the interactions of hnRNPK with N-WASP and RTVP-1 in glioma cells. In addition, we found that overexpression of RTVP-1 decreased the association of N-WASP and hnRNPK. In summary, we report that RTVP-1 regulates glioma cell spreading, migration and invasion and that these effects are mediated via interaction with N-WASP and by interfering with the inhibitory effect of hnRNPK on the function of this protein.

RasGRP3 regulates the migration of glioma cells via interaction with Arp3

Glioblastoma (GBM), the most aggressive primary brain tumors, are highly infiltrative. Although GBM express high Ras activity and Ras proteins have been implicated in gliomagenesis, Ras-activating mutations are not frequent in these tumors. RasGRP3, an important signaling protein responsive to diacylglycerol (DAG), increases Ras activation. Here, we examined the expression and functions of RasGRP3 in GBM and glioma cells. RasGRP3 expression was upregulated in GBM specimens and glioma stem cells compared with normal brains and neural stem cells, respectively. RasGRP3 activated Ras and Rap1 in glioma cells and increased cell migration and invasion partially via Ras activation. Using pull-down assay and mass spectroscopy we identified the actin-related protein, Arp3, as a novel interacting protein of RasGRP3. The interaction of RasGRP3 and Arp3 was validated by immunofluorescence staining and co-immunoprecipitation, and PMA, which activates RasGRP3 and induces its translocation to the peri-nuclear region, increased the association of Arp3 and RasGRP3. Arp3 was upregulated in GBM, regulated cell spreading and migration and its silencing partially decreased these effects of RasGRP3 in glioma cells. In summary, RasGRP3 acts as an important integrating signaling protein of the DAG and Ras signaling pathways and actin polymerization and represents an important therapeutic target in GBM.

EtpE Binding to DNase X Induces Ehrlichial Entry via CD147 and hnRNP-K Recruitment, Followed by Mobilization of N-WASP and Actin

Obligate intracellular bacteria, such as Ehrlichia chaffeensis, perish unless they can enter eukaryotic cells. E. chaffeensis is the etiological agent of human monocytic ehrlichiosis, an emerging infectious disease. To infect cells, Ehrlichia uses the C terminus of the outer membrane invasin entry-triggering protein (EtpE) of Ehrlichia (EtpE-C), which directly binds the mammalian cell surface glycosylphosphatidyl inositol-anchored protein, DNase X. How this binding drives Ehrlichia entry is unknown. Here, using affinity pulldown of host cell lysates with recombinant EtpE-C (rEtpE-C), we identified two new human proteins that interact with EtpE-C: CD147 and heterogeneous nuclear ribonucleoprotein K (hnRNP-K). The interaction of CD147 with rEtpE-C was validated by far-Western blotting and coimmunoprecipitation of native EtpE with endogenous CD147. CD147 was ubiquitous on the cell surface and also present around foci of rEtpE-C-coated-bead entry. Functional neutralization of surface-exposed CD147 with a specific antibody inhibited Ehrlichia internalization and infection but not binding. Downregulation of CD147 by short hairpin RNA (shRNA) impaired E. chaffeensis infection. Functional ablation of cytoplasmic hnRNP-K by a nanoscale intracellular antibody markedly attenuated bacterial entry and infection but not binding. EtpE-C also interacted with neuronal Wiskott-Aldrich syndrome protein (N-WASP), which is activated by hnRNP-K. Wiskostatin, which inhibits N-WASP activation, and cytochalasin D, which inhibits actin polymerization, inhibited Ehrlichia entry. Upon incubation with host cell lysate, EtpE-C but not an EtpE N-terminal fragment stimulated in vitro actin polymerization in an N-WASP- and DNase X-dependent manner. Time-lapse video images revealed N-WASP recruitment at EtpE-C-coated bead entry foci. Thus, EtpE-C binding to DNase X drives Ehrlichia entry by engaging CD147 and hnRNP-K and activating N-WASP-dependent actin polymerization.

Ehrlichia chaffeensis, an obligate intracellular bacterium, causes a blood-borne disease called human monocytic ehrlichiosis, one of the most prevalent life-threatening emerging tick-transmitted infectious diseases in the United States. The survival of Ehrlichia bacteria, and hence, their ability to cause disease, depends on their specific mode of entry into eukaryotic host cells. Understanding the mechanism by which E. chaffeensis enters cells will create new opportunities for developing effective therapies to prevent bacterial entry and disease in humans. Our findings reveal a novel cellular signaling pathway triggered by an ehrlichial surface protein called EtpE to induce its infectious entry. The results are also important from the viewpoint of human cell physiology because three EtpE-interacting human proteins, DNase X, CD147, and hnRNP-K, are hitherto unknown partners that drive the uptake of small particles, including bacteria, into human cells.

Loss of hnRNP K impairs synaptic plasticity in hippocampal neurons

Heterogeneous nuclear ribonucleoprotein K (hnRNP K) is an RNA-binding protein implicated in RNA metabolism. Here, we investigated the role of hnRNP K in synapse function. We demonstrated that hnRNP K regulates dendritic spine density and long-term potentiation (LTP) in cultured hippocampal neurons from embryonic rats. LTP requires the extracellular signal-regulated kinase (ERK)1/2-mediated phosphorylation and cytoplasmic accumulation of hnRNP K. Moreover, hnRNP K knockdown prevents ERK cascade activation and GluA1-S845 phosphorylation and surface delivery, which are essential steps for LTP. These findings establish hnRNP K as a new critical regulator of synaptic transmission and plasticity in hippocampal neurons.

40LoVe and Samba are involved in Xenopus neural development and functionally distinct from hnRNP AB

Heterogeneous nuclear ribonucleoproteins (hnRNPs) comprise a large group of modular RNA-binding proteins classified according to their conserved domains. This modular nature, coupled with a large choice of alternative splice variants generates functional diversity. Here, we investigate the biological differences between 40LoVe, its splice variant Samba and its pseudoallele hnRNP AB in neural development. Loss of function experiments lead to defects in neural development with reduction of eye size, which stem primarily from increased apoptosis and reduced proliferation in neural tissues. Despite very high homology between 40LoVe/Samba and hnRNP AB, these proteins display major differences in localization, which appear to be in part responsible for functional differences. Specifically, we show that the 40Love/Samba carboxy-terminal domain (GRD) enables nucleocytoplasmic shuttling behavior. This domain is slightly different in hnRNP AB, leading to nuclear-restricted localization. Finally, we show that shuttling is required for 40LoVe/Samba function in neural development.

Heterogeneous nuclear ribonucleoprotein K (hnRNP-K) promotes tumor metastasis by induction of genes involved in extracellular matrix, cell movement, and angiogenesis

Cancer is a leading cause of death and still awaits effective therapies. Rapid industrialization has contributed to increase in incidence of cancer. One of the reasons why most of the cancers fail therapy is due to their metastatic property. Hence identification of factors leading to metastasis is highly important to design effective and novel anti-cancer therapeutics. In our earlier study (Inoue, A., Sawata, S. Y., Taira, K., and Wadhwa, R. (2007) Loss-of-function screening by randomized intracellular antibodies: identification of hnRNP-K as a potential target for metastasis. Proc. Natl. Acad. Sci. U.S.A. 104, 8983-8988), we had reported that the involvement of heterogeneous nuclear ribonucleoprotein K (hnRNP-K) in metastasis. Here, we established hnRNP-K-overexpressing and -underexpressing derivative cell lines and examined their proliferation and metastatic properties in vitro and in vivo. Whereas hnRNP-K compromised cells showed delayed tumor growth, its overexpression resulted in enhanced malignancy and metastasis. Molecular basis of the hnRNP-K induced malignant and metastatic phenotypes was dissected by cDNA microarray and pathway analyses. We found that the hnRNP-K regulates extracellular matrix, cell motility, and angiogenesis pathways. Involvement of the selected genes (Cck, Mmp-3, Ptgs2, and Ctgf) and pathways was validated by gene-specific expression analysis. Our results demonstrated that the hnRNP-K is a potential target for metastasis therapy.

Neuronal Wiskott-Aldrich syndrome protein (N-WASP) is critical for formation of α-smooth muscle actin filaments during myofibroblast differentiation

Myofibroblasts are implicated in pathological stromal responses associated with lung fibrosis. One prominent phenotypic marker of fully differentiated myofibroblasts is the polymerized, thick cytoplasmic filaments containing newly synthesized α-smooth muscle actin (α-SMA). These α-SMA-containing cytoplasmic filaments are important for myofibroblast contractility during tissue remodeling. However, the molecular mechanisms regulating the formation and maturation of α-SMA-containing filaments have not been defined. This study demonstrates a critical role for neuronal Wiskott-Aldrich syndrome protein (N-WASP) in regulating the formation of α-SMA-containing cytoplasmic filaments during myofibroblast differentiation and in myofibroblast contractility. Focal adhesion kinase (FAK) is activated by transforming growth factor-β1 (TGF-β1) and is required for phosphorylation of tyrosine residue 256 (Y256) of N-WASP. Phosphorylation of Y256 of N-WASP is essential for TGF-β1-induced formation of α-SMA-containing cytoplasmic filaments in primary human lung fibroblasts. In addition, we demonstrate that actin-related protein (Arp) 2/3 complex is downstream of N-WASP and mediates the maturation of α-SMA-containing cytoplasmic filaments. Together, this study supports a critical role of N-WASP in integrating FAK and Arp2/3 signaling to mediate formation of α-SMA-containing cytoplasmic filaments during myofibroblast differentiation and maturation.

Heterogeneous nuclear ribonucleoprotein k interacts with Abi-1 at postsynaptic sites and modulates dendritic spine morphology

Background

Abelson-interacting protein 1 (Abi-1) plays an important role for dendritic branching and synapse formation in the central nervous system. It is localized at the postsynaptic density (PSD) and rapidly translocates to the nucleus upon synaptic stimulation. At PSDs Abi-1 is in a complex with several other proteins including WASP/WAVE or cortactin thereby regulating the actin cytoskeleton via the Arp 2/3 complex.

Principal Findings

We identified heterogeneous nuclear ribonucleoprotein K (hnRNPK), a 65 kDa ssDNA/RNA-binding-protein that is involved in multiple intracellular signaling cascades, as a binding partner of Abi-1 at postsynaptic sites. The interaction with the Abi-1 SH3 domain is mediated by the hnRNPK-interaction (KI) domain. We further show that during brain development, hnRNPK expression becomes more and more restricted to granule cells of the cerebellum and hippocampal neurons where it localizes in the cell nucleus as well as in the spine/dendritic compartment. The downregulation of hnRNPK in cultured hippocampal neurons by RNAi results in an enlarged dendritic tree and a significant increase in filopodia formation. This is accompanied by a decrease in the number of mature synapses. Both effects therefore mimic the neuronal morphology after downregulation of Abi-1 mRNA in neurons.

Conclusions

Our findings demonstrate a novel interplay between hnRNPK and Abi-1 in the nucleus and at synaptic sites and show obvious similarities regarding both protein knockdown phenotypes. This indicates that hnRNPK and Abi-1 act synergistic in a multiprotein complex that regulates the crucial balance between filopodia formation and synaptic maturation in neurons.

Computational prediction and experimental verification of new MAP kinase docking sites and substrates including Gli transcription factors

In order to fully understand protein kinase networks, new methods are needed to identify regulators and substrates of kinases, especially for weakly expressed proteins. Here we have developed a hybrid computational search algorithm that combines machine learning and expert knowledge to identify kinase docking sites, and used this algorithm to search the human genome for novel MAP kinase substrates and regulators focused on the JNK family of MAP kinases. Predictions were tested by peptide array followed by rigorous biochemical verification with in vitro binding and kinase assays on wild-type and mutant proteins. Using this procedure, we found new ‘D-site’ class docking sites in previously known JNK substrates (hnRNP-K, PPM1J/PP2Czeta), as well as new JNK-interacting proteins (MLL4, NEIL1). Finally, we identified new D-site-dependent MAPK substrates, including the hedgehog-regulated transcription factors Gli1 and Gli3, suggesting that a direct connection between MAP kinase and hedgehog signaling may occur at the level of these key regulators. These results demonstrate that a genome-wide search for MAP kinase docking sites can be used to find new docking sites and substrates.

Protein kinases are enzymes that regulate key cellular processes by covalently attaching a phosphate group to substrate proteins; they are crucial components of signaling pathways involved in cancer, diabetes, and many other diseases. Identifying the substrates of particular protein kinases is challenging, and many existing biochemical methods are biased against weakly expressed proteins like transcription factors. Here we exploited the observation that mitogen-activated protein kinases (MAPKs) briefly attach to many of their substrates before phosphorylating them, docking onto a sequence known as the ‘D-site’. We developed D-finder, a computational tool that uses a combination of expert knowledge and machine learning to search genome databases for D-sites. We then verified several of D-finder's predictions using rigorous and well-established biochemical assays. The most intriguing predicted and verified substrates were the Gli1 and Gli3 transcription factors of the ‘hedgehog’ signaling pathway. Gli transcription factors are involved in embryonic development and stem cell differentiation, and have also been found to be hyperactive in several types of cancer. There is emerging evidence that crosstalk with MAPK pathways is important in Gli-mediated regulation. Our study, however, is the first to show that MAPKs directly phosphorylate Gli transcription factors.

Regulation of Integrin β 1 recycling to lipid rafts by Rab1a to promote cell migration

Rab1a is a member of the Rab family of small GTPases with a well characterized function in the regulation of vesicle trafficking from the endoplasmic reticulum to the Golgi apparatus and within Golgi compartments. The integrin family heterodimeric transmembrane proteins serve as major receptors for extracellular matrix proteins, which play essential roles in cell adhesion and migration. Although effects on intracellular trafficking of integrins or other key cargos by Rab1a could influence cell migration, the regulatory mechanisms linking Rab1a to cell migration are not well understood. Here, we report identification of Rab1a as a novel regulator of cell migration using an unbiased RNAi screen targeting GTPases. Inhibition of Rab1a reduced integrin-mediated cell adhesion and spreading on fibronectins, reduced integrin β1 localization to lipid rafts, and decreased recycling of integrin β1 to the plasma membrane. Analysis of Rab1a effector molecules showed that p115 mediated Rab1a regulation of integrin recycling and lipid raft localization in cell migration. Taken together, these results suggest a novel function for Rab1a in the regulation of cell migration through controlling integrin β1 recycling and localization to lipid rafts via a specific downstream effector pathway.

Tyrosine phosphorylation of cofilin at Y68 by v-Src leads to its degradation through ubiquitin-proteasome pathway

Cofilin is a major regulator of actin dynamics involved in the regulation of cell spreading and migration through its actin depolymerizing and severing activities. V-Src is an activated Src tyrosine kinase and a potent oncogene known to phosphorylate a variety of cellular proteins in cell transformation process including altered cell adhesion, spreading and migration. Recently, it has been suggested that cofilin is a potential substrate of v-Src (Rush et al., 2005). Here, we show direct tyrosine phosphorylation of cofilin by v-Src and identify Y68 as the major phosphorylation site. Cofilin phosphorylation at Y68 did not change its activity per se, but induced increased ubiquitination of cofilin and its degradation through the proteosome pathway. Furthermore, the negative effect of cofilin on cellular F-actin contents was inhibited by co-expression of v-Src, whereas that of cofilin mutant Y68F (Y68 mutated to F) was not affected, suggesting that v-Src-mediated cofilin phosphorylation at Y68 is required for degradation of cofilin in vivo. Lastly, inhibition of cell spreading by v-Src was rescued partially by co-expression of cofilin, and to a greater extent by the Y68F mutant which is not subjected to v-Src induced degradation through phosphorylation, suggesting that v-Src mediated changes in cell spreading is, at least in part, through inhibiting the function of cofilin via phosphorylating it at Y68. Together, these results suggest a novel mechanism by which cofilin is regulated by v-Src through tyrosine phosphorylation at Y68 that triggers degradation of cofilin via ubiquitination-proteosome pathway and consequently inhibits cofilin activity in reducing cellular F-actin contents and cell spreading.

Proteins recruited by SH3 domains of Ruk/CIN85 adaptor identified by LC-MS/MS

Background

Ruk/CIN85 is a mammalian adaptor molecule with three SH3 domains. Using its SH3 domains Ruk/CIN85 can cluster multiple proteins and protein complexes, and, consequently, facilitates organisation of elaborate protein interaction networks with diverse regulatory roles. Previous research linked Ruk/CIN85 with the regulation of vesicle-mediated transport and cancer cell invasiveness. Despite the recent findings, precise molecular functions of Ruk/CIN85 in these processes remain largely elusive and further research is hampered by a lack of complete lists of its partner proteins.

Results

In the present study we employed a LC-MS/MS-based experimental pipeline to identify a considerable number (over 100) of proteins recruited by the SH3 domains of Ruk/CIN85 in vitro. Most of these identifications are novel Ruk/CIN85 interaction candidates. The identified proteins have diverse molecular architectures and can interact with other proteins, as well as with lipids and nucleic acids. Some of the identified proteins possess enzymatic activities. Functional profiling analyses and literature mining demonstrate that many of the proteins recruited by the SH3 domains of Ruk/CIN85 identified in this work were involved in the regulation of membranes and cytoskeletal structures necessary for vesicle-mediated transport and cancer cell invasiveness. Several groups of the proteins were also associated with few other cellular processes not previously related to Ruk/CIN85, most prominently with cell division.

Conclusion

Obtained data support the notion that Ruk/CIN85 regulates vesicle-mediated transport and cancer cell invasiveness through the assembly of multimeric protein complexes governing coordinated remodelling of membranes and underlying cytoskeletal structures, and imply its important roles in formation of coated vesicles and biogenesis of invadopodia. In addition, this study points to potential involvement of Ruk/CIN85 in other cellular processes, chiefly in cell division.

Immunomodulatory effects of holothurian triterpene glycosides on mammalian splenocytes determined by mass spectrometric proteome analysis

Spleen is a prime organ in which immuno-stimulation takes place in mammalians. Proteome analysis was used to investigate the elicited effects on mouse splenocytes upon exposure to holothurian triterpene glycosides. Cucumarioside A(2)-2, and Frondoside A, respectively, have been used to in-vitro stimulate primary splenocyte cultures. Differential protein expression was monitored by 2D gel analysis and proteins in spots of interest were identified by MALDI ToF MS and nano LC-ESI Q-ToF MS/MS, respectively. Differential image analysis of gels from control vs. gels from stimulated primary splenocyte cultures showed that approximately thirty protein spots were differentially expressed. Prime examples of differentially expressed proteins are NSFL1 cofactor p47 and hnRNP K (down-regulated), as well as Septin-2, NADH dehydrogenase [ubiquinone] iron-sulfur protein 3, and GRB2-related adaptor protein 2 (up-regulated). Immuno-analytical assays confirmed differential protein expression. Together with results from proliferation and cell adhesion assays, our results show that cellular proliferation is stimulated by holothurian triterpene glycosides. In conclusion, holothurian triterpene glycosides are thought to express their immuno-stimulatory effects by enhancing the natural cellular defense barrier that is necessary to fight pathogens and for which lymphocytes and splenocytes have to be recruited constantly due to limited lifetimes of B-cells and T-cells in the body.

An adaptor role for cytoplasmic Sam68 in modulating Src activity during cell polarization

The Src-associated substrate during mitosis with a molecular mass of 68 kDa (Sam68) is predominantly nuclear and is known to associate with proteins containing the Src homology 3 (SH3) and SH2 domains. Although Sam68 is a Src substrate, little is known about the signaling pathway that link them. Src is known to be activated transiently after cell spreading, where it modulates the activity of small Rho GTPases. Herein we report that Sam68-deficient cells exhibit loss of cell polarity and cell migration. Interestingly, Sam68-deficient cells exhibited sustained Src activity after cell attachment, resulting in the constitutive tyrosine phosphorylation and activation of p190RhoGAP and its association with p120rasGAP. Consistently, we observed that Sam68-deficient cells exhibited deregulated RhoA and Rac1 activity. By using total internal reflection fluorescence microscopy, we observed Sam68 near the plasma membrane after cell attachment coinciding with phosphorylation of its C-terminal tyrosines and association with Csk. These findings show that Sam68 localizes near the plasma membrane during cell attachment and serves as an adaptor protein to modulate Src activity for proper signaling to small Rho GTPases.

In utero exposure to low doses of environmental pollutants disrupts fetal ovarian development in sheep

Epidemiological studies of the impact of environmental chemicals on reproductive health demonstrate consequences of exposure but establishing causative links requires animal models using 'real life' in utero exposures. We aimed to determine whether prolonged, low-dose, exposure of pregnant sheep to a mixture of environmental chemicals affects fetal ovarian development. Exposure of treated ewes (n = 7) to pollutants was maximized by surface application of processed sewage sludge to pasture. Control ewes (n = 10) were reared on pasture treated with inorganic fertilizer. Ovaries and blood were collected from fetuses (n = 15 control and n = 8 treated) on Day 110 of gestation for investigation of fetal endocrinology, ovarian follicle/oocyte numbers and ovarian proteome. Treated fetuses were 14% lighter than controls but fetal ovary weights were unchanged. Prolactin (48% lower) was the only measured hormone significantly affected by treatment. Treatment reduced numbers of growth differentiation factor (GDF9) and induced myeloid leukaemia cell differentiation protein (MCL1) positive oocytes by 25-26% and increased pro-apoptotic BAX by 65% and 42% of protein spots in the treated ovarian proteome were differently expressed compared with controls. Nineteen spots were identified and included proteins involved in gene expression/transcription, protein synthesis, phosphorylation and receptor activity. Fetal exposure to environmental chemicals, via the mother, significantly perturbs fetal ovarian development. If such effects are replicated in humans, premature menopause could be an outcome.

Sequence and transcriptional study of HNRPK pseudogenes, and expression and molecular modeling analysis of hnRNP K isoforms

The heterogeneous nuclear ribonucleoproteins (hnRNPs) comprise a large family of proteins that play important roles in telomere biogenesis, DNA repair, cellular signaling, and the regulation of expression at both the transcriptional and translational levels. One of the most extensively studied hnRNP family members, hnRNP K, has been implicated in a variety of processes, including chromatin remodeling, transcription, splicing, and translation events. In this study, we analyzed processed HNRPK pseudogenes (HNRPK psi1-psi4) and coding sequences. HNRPK pseudogenes are apparently nonfunctional, and psi1 might correspond to transcripts from an ancestral gene. Phylogenetic and sequence analyses suggest that HNRP genes arose by duplication, and that new structural and sequence features expanded the functions of hnRNPs. The expression analysis of hnRNP K isoforms showed that isoform a is expressed in normal testis and in non-small cell lung cancer (NCI-H1155 NSCLC cell line), although the shorter isoform (isoform b) is expressed in different tumor cell lines (IM9 B-lymphoblastoid, Hs578T human breast cancer epithelial, T98G human glioma cell lines). Using molecular modeling, we obtained KH1 and KH3 models, which pointed to important residues for DNA-protein binding and no structural differences between isoforms a and b. To our knowledge, this is the first phylogenetic study including vertebrate HNRP genes and HNRPK pseudogenes, and the first report comparing the KH1 and KH3 domains of isoforms a and b of the hnRNP K protein. New investigations in tumor samples must be done to validate the differential expression observed here. The results shown are important because the hnRNP K protein might represent a new target for pharmacologic intervention in virus replication and cancer.

Formation of cellular projections in neural progenitor cells depends on SK3 channel activity

Ion channels are potent modulators for developmental processes in progenitor cells. In a screening approach for different ion channels in neural progenitor cells (NPCs) we observed a 1-ethyl-2-benzimidazolinone (1-EBIO) activated inward current, which could be blocked by scyllatoxin (ScTX, IC50=2+/- 0.3 nmol/L). This initial evidence for the expression of the small conductance Ca2+ activated K+-channel SK3 was confirmed by the detection of SK3 transcripts and protein in NPCs. Interestingly, SK3 proteins were highly expressed in non-differentiated NPCs with a focused localization in lamellipodia as well as filopodial structures. The activation of SK3 channels using 1-EBIO lead to an immediate filopodial sprouting and the translocation of the protein into these novel filopodial protrusions. Both effects could be prevented by the pre-incubation of NPCs with ScTX. Our study gives first evidence that the formation and prolongation of filopodia in NPCs is, at least in part, effectively induced and regulated by SK3 channels.