Glutathione S-Transferase p Elicits Protection against H2O2-induced Cell Death via Coordinated Regulation of Stress Kinases

To elucidate mechanisms underlying glutathione S-transferase p (GSTp)-mediated cellular protection against oxidative stress-induced cell death, the effect of GSTp on stress signaling pathways was investigated before and after H2O2 treatment. Under nonstressed conditions, increased expression of GSTp via a tet-off-inducible GSTp in NIH 3T3 cells increased the phosphorylation of mitogen-activated protein (MAP) kinase kinase 4, p38, extracellular receptor kinase (ERK), and inhibitor of κ-kinase (IKK), and reduced phosphorylation of MAP kinase kinase 7 and Jun NH2-terminal kinase (JNK). Whereas H2O2 treatment of cells induced JNK, p38, and IKK activities, in the presence of H2O2 and elevated GSTp expression there was an additional increase in ERK, p38, and IKK activities and a decrease in JNK activity. GSTp-mediated protection from H2O2-induced death was attenuated upon inhibition of p38, nuclear factor κB, or MAP kinase by dominant negative or pharmacological inhibitors. Conversely, expression of a dominant negative JNK protected cells from H2O2-mediated death. These data suggest that the coordinated regulation of stress kinases by GSTp, as reflected by increased p38, ERK, and nuclear factor κB activities together with suppression of JNK signaling, contributes to protection of cells against reactive oxygen species-mediated death

Inhibition of Ubc13-mediated ubiquitination by GPS2 regulates multiple stages of B cell development

Non-proteolytic ubiquitin signaling mediated by Lys63 ubiquitin chains plays a critical role in multiple pathways that are key to the development and activation of immune cells. Our previous work indicates that GPS2 (G-protein Pathway Suppressor 2) is a multifunctional protein regulating TNF signaling and lipid metabolism in the adipose tissue through modulation of Lys63 ubiquitination events. However, the full extent of GPS2-mediated regulation of ubiquitination and the underlying molecular mechanisms are unknown. Here, we report that GPS2 is required for restricting the activation of TLR and BCR signaling pathways and the AKT/FOXO1 pathway in immune cells based on direct inhibition of Ubc13 enzymatic activity. Relevance of this regulatory strategy is confirmed in vivo by B cell-targeted deletion of GPS2, resulting in developmental defects at multiple stages of B cell differentiation. Together, these findings reveal that GPS2 genomic and non-genomic functions are critical for the development and cellular homeostasis of B cells

Comprehensive Analysis of the Palindromic Motif TCTCGCGAGA: A Regulatory Element of the HNRNPK Promoter

Definitive identification of promoters, their cis-regulatory motifs, and their trans-acting proteins requires experimental analysis. To define the HNRNPK promoter and its cognate DNA–protein interactions, we performed a comprehensive study combining experimental approaches, including luciferase reporter gene assays, chromatin immunoprecipitations (ChIP), electrophoretic mobility shift assays (EMSA), and mass spectrometry (MS). We discovered that out of the four potential HNRNPK promoters tested, the one containing the palindromic motif TCTCGCGAGA exhibited the highest activity in a reporter system assay. Although further EMSA and MS analyses, performed to uncover the identity of the palindrome-binding transcription factor, did identify a complex of DNA-binding proteins, neither method unambiguously identified the pertinent direct trans-acting protein(s). ChIP revealed similar chromatin states at the promoters with the palindromic motif and at housekeeping gene promoters. A ChIP survey showed significantly higher recruitment of PARP1, a protein identified by MS as ubiquitously attached to DNA probes, within heterochromatin sites. Computational analyses indicated that this palindrome displays features that mark nucleosome boundaries, causing the surrounding DNA landscape to be constitutively open. Our strategy of diverse approaches facilitated the direct characterization of various molecular properties of HNRNPK promoter bearing the palindromic motif TCTCGCGAGA, despite the obstacles that accompany in vitro methods

The Dark Side of EGFP: Defective Polyubiquitination

Enhanced Green Fluorescent Protein (EGFP) is the most commonly used live cell reporter despite a number of conflicting reports that it can affect cell physiology. Thus far, the precise mechanism of GFP-associated defects remained unclear. Here we demonstrate that EGFP and EGFP fusion proteins inhibit polyubiquitination, a posttranslational modification that controls a wide variety of cellular processes, like activation of kinase signalling or protein degradation by the proteasome. As a consequence, the NF-κB and JNK signalling pathways are less responsive to activation, and the stability of the p53 tumour suppressor is enhanced in cell lines and in vivo. In view of the emerging role of polyubiquitination in the regulation of numerous cellular processes, the use of EGFP as a live cell reporter should be carefully considered

Heterogeneous nuclear ribonucleoprotein K is over expressed, aberrantly localised and is associated with poor prognosis in colorectal cancer

Heterogeneous ribonucleoprotein K (hnRNP K) is a member of the hnRNP family which has several different cellular roles including transcription, mRNA shuttling, RNA editing and translation. Several reports implicate hnRNP K having a role in tumorigenesis, for instance hnRNP K increases transcription of the oncogene c-myc and hnRNP K expression is regulated by the p53/MDM 2 pathway. In this study comparing normal colon to colorectal cancer by proteomics, hnRNP K was identified as being overexpressed in this type of cancer. Immunohistochemistry with a monoclonal antibody to hnRNP K (which we developed) on colorectal cancer tissue microarray, confirmed that hnRNP K was overexpressed in colorectal cancer (P<0.001) and also showed that hnRNP K had an aberrant subcellular localisation in cancer cells. In normal colon hnRNP K was exclusively nuclear whereas in colorectal cancer the protein localised both in the cytoplasm and the nucleus. There were significant increases in both nuclear (P=0.007) and cytoplasmic (P=0.001) expression of hnRNP K in Dukes C tumours compared with early stage tumours. In Dukes C patient's good survival was associated with increased hnRNP K nuclear expression (P=0.0093). To elaborate on the recent observation that hnRNP K is regulated by p53, the expression profiles of these two proteins were also analysed. There was no correlation between hnRNP K and p53 expression, however, patients who presented tumours that were positive for hnRNP K and p53 had a poorer survival outcome (P=0.045)

Heterogeneous nuclear ribonucleoprotein K: altered pattern of expression associated with diagnosis and prognosis of prostate cancer

Using proteomic analysis of the nuclear matrix (NM), we found that heterogeneous nuclear ribonucleoprotein K (hnRNP K), a member of the hnRNP family with pleiotropic functions, was differentially expressed in prostate cancer (PCa) tissues. This study aimed to characterise the expression of hnRNP K and its subcellular localisation in PCa, utilising immunohistochemical and quantitative western blot techniques. Furthermore, the hnRNP K expression was studied in human PCa cell lines in order to determine its modulation by bicalutamide, the anti-androgen widely used in PCa therapy. Immunohistochemical staining of paraffin-embedded tissues showed that hnRNP K was overexpressed in PCa, where it was localised both in the cytoplasm and in the nucleus. Staining of non-tumour tissues showed exclusively nuclear localisation and a less intense or absent signal. Immunoblot analysis demonstrated that the hnRNP K level within the NM was higher in PCa compared with non-tumour tissues and closely correlated with Gleason score (P=0.008). Higher expression within the NM was significantly (P=0.032) associated with poor prognosis. In two-dimensional western blot analysis hnRNP K presented several isoforms; the one with pI 5.1 was the most differently expressed between non-tumour and PCa tissues. Preliminary results indicate that hnRNP K can be modulated in vitro by a non-steroidal anti-androgen. Taken together, our findings suggest that hnRNP K has potential implications at the diagnostic, prognostic and therapeutic levels in PCa

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

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