A new ERK2 binding protein, Naf1, attenuates the EGF/ERK2 nuclear signaling

Repressive Control of Keratinocyte Cytoplasmic Inflammatory Signaling

The overactivity of keratinocyte cytoplasmic signaling contributes to several cutaneous inflammatory and immune pathologies. An important emerging complement to proteins responsible for this overactivity is signal repression brought about by several proteins and protein complexes with the native role of limiting inflammation. The signaling repression by these proteins distinguishes them from transmembrane receptors, kinases, and inflammasomes, which drive inflammation. For these proteins, defects or deficiencies, whether naturally arising or in experimentally engineered skin inflammation models, have clearly linked them to maintaining keratinocytes in a non-activated state or returning cells to a post-inflamed state after a signaling event. Thus, together, these proteins help to resolve acute inflammatory responses or limit the development of chronic cutaneous inflammatory disease. We present here an integrated set of demonstrated or potentially inflammation-repressive proteins or protein complexes (linear ubiquitin chain assembly complex [LUBAC], cylindromatosis lysine 63 deubiquitinase [CYLD], tumor necrosis factor alpha-induced protein 3-interacting protein 1 [TNIP1], A20, and OTULIN) for a comprehensive view of cytoplasmic signaling highlighting protein players repressing inflammation as the needed counterpoints to signal activators and amplifiers. Ebb and flow of players on both sides of this inflammation equation would be of physiological advantage to allow acute response to damage or pathogens and yet guard against chronic inflammatory disease. Further investigation of the players responsible for repressing cytoplasmic signaling would be foundational to developing new chemical-entity pharmacologics to stabilize or enhance their function when clinical intervention is needed to restore balance.

A20-Binding Inhibitor of Nuclear Factor-κB Targets β-Arrestin2 to Attenuate Opioid Tolerance

Opioids play an important role in pain relief, but repeated exposure results in tolerance and dependence. To make opioids more effective and useful, research in the field has focused on reducing the tolerance and dependence for chronic pain relief. Here, we showed the effect of A20-binding inhibitor of nuclear factor-κB (ABIN-1) in modulating morphine function. We used hot-plate tests and conditioned place preference (CPP) tests to show that overexpression of ABIN-1 in the mouse brain attenuated morphine dependence. These effects of ABIN-1 are most likely mediated through the formation of ABIN-1-β-arrestin2 complexes, which accelerate β-arrestin2 degradation by ubiquitination. With the degradation of β-arrestin2, ABIN-1 overexpression also decreased μ opioid receptor (MOR) phosphorylation and internalization after opioid treatment, affecting the β-arrestin2-dependent signaling pathway to regulate morphine tolerance. Importantly, the effect of ABIN-1 on morphine tolerance was abolished in β-arrestin2-knockout mice. Taken together, these results suggest that the interaction between ABIN-1 and β-arrestin2 inhibits MOR internalization to attenuate morphine tolerance, revealing a novel mechanism for MOR regulation. Hence, ABIN-1 may be a therapeutic target to regulate MOR internalization, thus providing a foundation for a novel treatment strategy for alleviating morphine tolerance and dependence. SIGNIFICANCE STATEMENT: A20-binding inhibitor of nuclear factor-κB (ABIN-1) overexpression in the mouse brain attenuated morphine tolerance and dependence. The likely mechanism for this finding is that ABIN-1-β-arrestin2 complex formation facilitated β-arrestin2 degradation by ubiquitination. ABIN-1 targeted β-arrestin2 to regulate morphine tolerance. Therefore, the enhancement of ABIN-1 is an important strategy to prevent morphine tolerance and dependence.

RAF-MEK-ERK pathway in cancer evolution and treatment

The RAF-MEK-ERK signaling cascade is a well-characterized MAPK pathway involved in cell proliferation and survival. The three-layered MAPK signaling cascade is initiated upon RTK and RAS activation. Three RAF isoforms ARAF, BRAF and CRAF, and their downstream MEK1/2 and ERK1/2 kinases constitute a coherently orchestrated signaling module that directs a range of physiological functions. Genetic alterations in this pathway are among the most prevalent in human cancers, which consist of numerous hot-spot mutations such as BRAF^V600E. Oncogenic mutations in this pathway often override otherwise tightly regulated checkpoints to open the door for uncontrolled cell growth and neoplasia. The crosstalk between the RAF-MEK-ERK axis and other signaling pathways further extends the proliferative potential of this pathway in human cancers. In this review, we summarize the molecular architecture and physiological functions of the RAF-MEK-ERK pathway with emphasis on its dysregulations in human cancers, as well as the efforts made to target the RAF-MEK-ERK module using small molecule inhibitors.

The Anti-Inflammatory Protein TNIP1 Is Intrinsically Disordered with Structural Flexibility Contributed by Its AHD1-UBAN Domain

TNFAIP3 interacting protein 1 (TNIP1) interacts with numerous non-related cellular, viral, and bacterial proteins. TNIP1 is also linked with multiple chronic inflammatory disorders on the gene and protein levels, through numerous single-nucleotide polymorphisms and reduced protein amounts. Despite the importance of TNIP1 function, there is limited investigation as to how its conformation may impact its apparent multiple roles. Hub proteins like TNIP1 are often intrinsically disordered proteins. Our initial in silico assessments suggested TNIP1 is natively unstructured, featuring numerous potentials intrinsically disordered regions, including the ABIN homology domain 1-ubiquitin binding domain in ABIN proteins and NEMO (AHD1-UBAN) domain associated with its anti-inflammatory function. Using multiple biophysical approaches, we demonstrate the structural flexibility of full-length TNIP1 and the AHD1-UBAN domain. We present evidence the AHD1-UBAN domain exists primarily as a pre-molten globule with limited secondary structure in solution. Data presented here suggest the previously described coiled-coil conformation of the crystallized UBAN-only region may represent just one of possibly multiple states for the AHD1-UBAN domain in solution. These data also characterize the AHD1-UBAN domain in solution as mostly monomeric with potential to undergo oligomerization under specific environmental conditions (e.g., binding partner availability, pH-dependence). This proposed intrinsic disorder across TNIP1 and within the AHD1-UBAN region is likely to impact TNIP1 function and interaction with its multiple partners.

TNIP1 Polymorphisms with the Risk of Hepatocellular Carcinoma Based on Chronic Hepatitis B Infection in Chinese Han Population

Chronic hepatitis B virus (HBV) infection is an important etiology for the development of hepatocellular carcinoma (HCC). Tumor necrosis factor-α-induced protein 3-interacting protein 1 (TNIP1) is linked to specific inflammatory diseases as a novel type of endogenous inflammatory regulator. However, presently, rare information is found about the association between TNIP1 polymorphisms and HBV-induced HCC risk. In this case control study, we genotyped four single nucleotide polymorphisms (SNPs) in TNIP1 gene in 248 HCC patients and 242 chronic HBV carriers using Sequenom Mass-ARRAY technology. Genetic model and haplotype analysis were performed to evaluate the association between candidate SNPs polymorphisms and HBV-induced HCC susceptibility using Pearson's χ² test and unconditional logistic regression analysis. Overall, we found two risk alleles in TNIP1 for HBV-induced HCC in patients: the allele "G" of rs7708392 by genotype model ("G/C" vs. "C/C": OR 1.88, 95% CI 1.17-3, P = 0.009) and dominant model ("G/C-G/G" vs. "C/C": OR 1.69, 95% CI 1.08-2.65, P = 0.023), and the allele "C" of rs10036748 by genotype model ("C/T" vs. "T/T": OR 1.83, 95% CI 1.14-2.92, P = 0.012) and dominant model ("C/T-C/C" vs. "T/T": OR 1.65, 95% CI 1.05-2.59, P = 0.03). However, rs3792792 and rs4958881 polymorphisms didn't significantly correlate with the risk of HBV-induced HCC. Haplotype analysis showed no significant association between haplotypes and the HCC risk in HBV carriers. This study provides evidence for HBV-induced HCC susceptibility gene TNIP1 in the Chinese Han population.

TNIP1 reduction sensitizes keratinocytes to post-receptor signalling following exposure to TLR agonists

Cell level inflammatory signalling is a combination of initiation at cell membrane receptors and modulation by cytoplasmic regulatory proteins. For keratinocytes, the predominant cell type in the epidermis, this would include toll-like receptors (TLR) and cytoplasmic proteins that propagate or dampen post-receptor signalling. We previously reported that increased levels of tumor necrosis factor α induced protein 3-interacting protein 1 (TNIP1) in HaCaT keratinocytes leads to decreased expression of stress response and inflammation-associated genes. This finding suggested decreased TNIP1 levels, as seen in some cutaneous disease states, may produce the opposite effect, sensitizing cells to triggers of inflammatory signalling including those sensed by TLR. In this study of TNIP1-deficient HaCaT keratinocytes we examined intracellular signalling consequences especially those expected to produce gene expression changes downstream of TLR3 or TLR2/6 activation by Poly (I:C) or FSL-1, agonists modeling skin relevant pathogens. We found TNIP1-deficient keratinocytes are hyper-sensitive to TLR activation compared to control cells with a normal complement of TNIP1 and receiving the same agonist stimulation. TNIP1-deficient keratinocytes have increased levels of activated (phosphorylated) cytoplasmic mediators such as JNK and p38 and greater nuclear translocation of NF-κB and phospho-p38 when exposed to TLR ligands. This is consistent with significantly increased expression of several inflammatory cytokines and chemokines, such as IL-6 and IL-8. These results describe how decreased TNIP1 levels promote a hyper-sensitive state in HaCaT keratinocytes evidenced by increased activation of signalling molecules downstream of TLR agonists and increased expression of pro-inflammatory mediators. TNIP1 keratinocyte deficiency as reported for some skin diseases may predispose these cells to excessive inflammatory signalling upon exposure to viral or bacterial ligands for TLR.

ABIN1 inhibits HDAC1 ubiquitination and protects it from both proteasome- and lysozyme-dependent degradation

ABIN1, an important immune regulator, has been shown to be involved in various cellular functions, such as immunity, development, tissue homeostasis, and tumor progression. It inhibits TNF- and TLR-induced NF-κB signaling activation and the consequent gene expression. Despite its functional significance, the mechanism of ABIN1 in the regulation of various cellular functions remains unclear. In this study, we identified HDAC1, a key regulator of eukaryotic gene expression and many important cellular events, including cell proliferation, differentiation, cancer and immunity, as an interacting partner of ABIN1. The results showed that ABIN1 acted as a modulator to down-regulate HDAC1 ubiquitination via three different linkages, thereby stabilizing HDAC1 by inhibiting its lysosomal and proteasomal degradation. Interestingly, the inhibitory function of ABIN1 required direct binding with HDAC1. Moreover, the level of p53, which was a tumor suppressor and a well-studied substrate of HDAC1, was under the regulation of ABIN1 via the modulation of HDAC1 levels, suggesting that ABIN1 was physiologically significant in tumor progression. This study has revealed a new function of ABIN1 in mediating HDAC1 modification and stability.

Immune regulator ABIN1 suppresses HIV-1 transcription by negatively regulating the ubiquitination of Tat

BACKGROUND

A20-binding inhibitor of NF-κB activation (ABIN1), an important immune regulator, was previously shown to be involved in HIV-1 replication. However, the reported studies done with overexpressed ABIN1 provided controversial results.

RESULTS

Here we identified ABIN1 as a suppressor of HIV-1 transcription since transient knockdown of ABIN1 led to increased HIV-1 replication both in transformed Jurkat T cell line and in primary human CD4+ T lymphocytes. Depletion of ABIN1 specifically enhanced the HIV-1 transcription from the integrated genome during viral life cycle, but not the earlier steps such as reverse transcription or integration. Immunoprecipitation assays revealed that ABIN1 specifically inhibits the proto-oncogene HDM2 catalyzed K63-linked polyubiquitination of Tat at Lys71, which is critical for the transactivation activity of Tat. The ubiquitin chain binding activity of ABIN1 carried by UBAN domain turned out to be essential for the inhibitory role of ABIN1. The results of immunofluorescence localization experiments suggested that ABIN1 may obstruct Tat ubiquitination by redistributing some of HDM2 from the nucleus to the cytoplasm.

CONCLUSIONS

Our findings have revealed ABIN1 as intrinsic suppressor of HIV-1 mRNA transcription by regulating the ubiquitination of Tat.

Downregulation of TNIP1 Expression Leads to Increased Proliferation of Human Keratinocytes and Severer Psoriasis-Like Conditions in an Imiquimod-Induced Mouse Model of Dermatitis

Psoriasis is a chronic, inflammatory skin disease involving both environmental and genetic factors. According to genome-wide association studies (GWAS), the TNIP1 gene, which encodes the TNF-α–induced protein 3-interacting protein 1 (TNIP1), is strongly linked to the susceptibility of psoriasis. TNIP1 is a widely expressed ubiquitin sensor that binds to the ubiquitin-editing protein A20 and restricts TNF- and TLR-induced signals. In our study, TNIP1 expression decreased in specimens of epidermis affected by psoriasis. Based on previous studies suggesting a role for TNIP1 in modulating cancer cell growth, we investigated its role in keratinocyte proliferation, which is clearly abnormal in psoriasis. To mimic the downregulation or upregulation of TNIP1 in HaCaT cells and primary human keratinocytes (PHKs), we used a TNIP1 specific small interfering hairpin RNA (TNIP1 shRNA) lentiviral vector or a recombinant TNIP1 (rTNIP1) lentiviral vector, respectively. Blocking TNIP1 expression increased keratinocyte proliferation, while overexpression of TNIP1 decreased keratinocyte proliferation. Furthermore, we showed that TNIP1 signaling might involve extracellular signal-regulated kinase1/2 (Erk1/2) and CCAAT/enhancer-binding protein β (C/EBPβ) activity. Intradermal injection of TNIP1 shRNA in BALB/c mice led to exaggerated psoriatic conditions in imiquimod (IMQ)-induced psoriasis-like dermatitis. These findings indicate that TNIP1 has a protective role in psoriasis and therefore could be a promising therapeutic target.

TNIP1 reduction of HSPA6 gene expression occurs in promoter regions lacking binding sites for known TNIP1-repressed transcription factors

TNFα-induced protein 3-interacting protein 1 (TNIP1) represses signaling pathways initiated by specific nuclear and transmembrane receptors. This effect results in reduced activity of distinct transcription factors such as retinoic acid receptors (RAR), peroxisome-proliferator-activated receptors (PPAR), and NFκB. TNIP1-null and TNIP1-knockin defective for ubiquitin-binding mice show increased liver apoptosis, and enlarged spleen and lymph nodes, respectively. To complement current knowledge of TNIP1's broad physiologic functions as interpreted from in vivo studies and specific expression consequences from transcription factor repression, we determined effects of excess TNIP1 on global gene regulation. Following experimentally increased expression of TNIP1 in cultured keratinocytes, our gene expression microarray analysis not only confirmed TNIP1's association in previously known pathways and functions but also found a novel TNIP1-regulated pathway - the cell stress response. Under standard culture conditions, expression of several heat shock proteins, including HSPA1A, HSPA6, DNAJA1 and DNAJB1, was reduced. In heat-stressed conditions, differential regulation of HSPA1A and HSPA6 was observed, where only HSPA6 expression was reduced after heat-shock. Using HSPA6 as a model to elucidate the mechanism of the TNIP1-mediated HSP repression, we determined that TNIP1 likely represses HSPs through factors other than RAR, PPAR or NFκB despite the presence of these factors' binding sites in the HSPA6 promoter. These results indicate that regulation of HSPs may be through a yet unknown TNIP1-associated pathway. Additionally, these results suggest that TNIP1's reduction of HSP expression levels could negatively impact HSP chaperone capacity or their participation in the cell stress response.

The biology of A20-binding inhibitors of NF-kappaB activation (ABINs)

The family of A20-Binding Inhibitors of NF-kappaB (ABINs) consists of three proteins, ABIN-1, ABIN-2 and ABIN-3, which were originally identified as A20-binding proteins and inhibitors of cytokines and Lipopolysaccharide (LPS) induced NF-kappaB activation. ABIN family members have limited sequence homology in a number of short regions that mediate A20-binding, ubiquitin-binding, and NF-kappaB inhibition. The functional role of A20 binding to ABINs remains unclear, although an adaptor function has been suggested. ABIN-1 and ABIN-3 expression is upregulated when cells are triggered by NF-kappaB-activating stimuli, suggesting a role for these ABINs in a negative feedback regulation of NF-kappaB signaling. Additional ABIN functions have been reported such as inhibition of TNF-induced hepatocyte apoptosis, regulation of HIV-1 replication for ABIN-1, and Tumor Progression Locus 2 (TPL-2)-mediated Extracellular signal-Regulated Kinase (ERK) activation for ABIN-2. In mice, ABIN-1 overexpression reduces allergic airway inflammation and TNF-mediated liver injury, ABIN-2 overexpression delays liver regeneration, and ABIN-3 overexpression partially protects against LPS-induced acute liver failure. Analysis of mice deficient in ABIN-1 or ABIN-2 demonstrates the important immune regulatory function of ABINs. Future studies should clarify the functional implication of the A20-ABIN interaction in supporting ABINs' mechanisms of action.

Sp sites contribute to basal and inducible expression of the human TNIP1 (TNFα-inducible protein 3-interacting protein 1) promoter

TNIP1 [TNFα (tumour necrosis factor α)-induced protein 3-interacting protein 1] is a co-repressor of RAR (retinoic acid receptor) and PPAR (peroxisome-proliferator-activated receptor). Additionally, it can reduce signalling stemming from cell membrane receptors such as those for TNFα and EGF (epidermal growth factor). Consequently, it influences a variety of receptor-mediated events as diverse as transcription, programmed cell death and cell cycling. Thus changes in TNIP1 expression levels are likely to affect multiple important biological end points. TNIP1 expression level changes have been linked to psoriasis and systemic sclerosis. As such, it is crucial to determine what controls its expression levels, starting with constitutive control of its promoter. Our analysis of the TNIP1 promoter revealed multiple transcription start sites in its GC-rich proximal regions along with two transcriptionally active Sp (specificity protein) sites, responsive to both Sp1 and Sp3. EMSA (electrophoretic mobility-shift assay) and ChIP (chromatin immunoprecipitation) demonstrated physical binding between Sp1 and Sp3 at these sites. A decrease in Sp1 protein levels via siRNA (short interfering RNA) or diminished Sp1 DNA binding by mithramycin decreased TNIP1 mRNA levels. This Sp-binding GC-rich region of the TNIP1 promoter also participates in transcriptional activation by ligand-bound RAR. Together, these results demonstrate newly identified regulators of TNIP1 expression and suggest possible transcription factor targets which in turn control TNIP1-related biological end points ranging from apoptosis to inflammatory diseases.

Genetic susceptibility to lupus: the biological basis of genetic risk found in B cell signaling pathways

Over 50 genetic variants have been statistically associated with the development of SLE (or lupus). Each genetic association is a key component of a pathway to lupus pathogenesis, the majority of which requires further mechanistic studies to understand the functional changes to cellular physiology. Whereas their use in clinical practice has yet to be established, these genes guide efforts to develop more specific therapeutic approaches. The BCR signaling pathways are rich in lupus susceptibility genes and may well provide novel opportunities for the understanding and clinical treatment of this complex disease.

Emerging roles for TNIP1 in regulating post-receptor signaling

A vast number of cellular processes and signaling pathways are regulated by various receptors, ranging from transmembrane to nuclear receptors. These receptor-mediated processes are modulated by a diverse set of regulatory proteins. TNFα-induced protein 3-interacting protein 1 is such a protein that inhibits both transduction by transmembrane receptors, such as TNFα-receptor, EGF-R, and TLR, and nuclear receptors' PPAR and RAR activity. These receptors play key roles in regulating inflammation and inflammatory diseases. A growing number of references have implicated TNIP1 through GWAS and expression studies in chronic inflammatory diseases such as psoriasis and rheumatoid arthritis, although TNIP1s exact role has yet been determined. In this review, we aim to integrate the current knowledge of TNIP1s functions with the diseases in which it has been associated to potentially elucidate the role this regulator has in promoting or alleviating these inflammatory diseases.

TNIP1, a retinoic acid receptor corepressor and A20-binding inhibitor of NF-κB, distributes to both nuclear and cytoplasmic locations

An increasingly wide range of functions, from repression of NF-κB signaling to protection from apoptosis, is being recognized for tumor necrosis factor α-induced protein 3-interacting protein 1 (TNIP1). The authors recently demonstrated TNIP1 interaction with and repression of liganded retinoic acid receptors, distinguishing it from the more typical NCoR and SMRT corepressors, which function only in the absence of ligand. To improve their understanding of TNIP1's roles in physiologic and pathologic events, the authors examined its distribution in normal and malignant human tissues and cultured cells. They found cytoplasmic and nuclear TNIP1 in normal skin keratinocytes as it colocalized with retinoic acid receptor α, one of the nuclear receptors it corepresses. Nuclear and cytoplasmic TNIP1 was also found in the malignant keratinocytes of squamous cell carcinomas. Compared to adjacent normal tissues of other organs, TNIP1 staining and distribution varied with increased levels in esophageal cancer and marked decreases in prostate cancer. The varying levels and distribution of TNIP1 in normal and disease state tissues could be expected to affect processes in which TNIP1 is involved, such as NF-κB and nuclear receptor signaling, possibly contributing to the disease course or response to therapies targeting these key players of cell growth and differentiation.

ABINs: A20 binding inhibitors of NF-kappa B and apoptosis signaling

ABINs have been described as three different proteins (ABIN-1, ABIN-2, ABIN-3) that bind the ubiquitin-editing nuclear factor-kappaB (NF-kappaB) inhibitor protein A20 and which show limited sequence homology. Overexpression of ABINs inhibits NF-kappaB activation by tumor necrosis factor (TNF) and several other stimuli. Similar to A20, ABIN-1 and ABIN-3 expression is NF-kappaB dependent, implicating a potential role for the A20/ABIN complex in the negative feedback regulation of NF-kappaB activation. Adenoviral gene transfer of ABIN-1 has been shown to reduce NF-kappaB activation in mouse liver and lungs. However, ABIN-1 as well as ABIN-2 deficient mice exhibit only slightly increased or normal NF-kappaB activation, respectively, possibly reflecting redundant NF-kappaB inhibitory activities of multiple ABINs. Other functions of ABINs might be non-redundant. For example, ABIN-1 shares with A20 the ability to inhibit TNF-induced apoptosis and as a result ABIN-1 deficient mice die during embryogenesis due to TNF-dependent fetal liver apoptosis. On the other hand, ABIN-2 is required for optimal TPL-2 dependent extracellularly regulated kinase activation in macrophages treated with TNF or Toll-like receptor ligands. ABINs have recently been shown to contain an ubiquitin-binding domain that is essential for their NF-kappaB inhibitory and anti-apoptotic activities. In this context, ABINs were proposed to function as adaptors between ubiquitinated proteins and other regulatory proteins. Alternatively, ABINs might disrupt signaling complexes by competing with other ubiquitin-binding proteins for the binding to specific ubiquitinated targets. Altogether, these findings implicate an important role for ABINs in the regulation of immunity and tissue homeostasis.

Cyclin-dependent kinase-3-mediated c-Jun phosphorylation at Ser63 and Ser73 enhances cell transformation

c-Jun is a component of the activator protein-1 (AP-1) complex, which plays a crucial role in the regulation of gene expression, cell proliferation, and cell transformation, as well as cancer development. Herein, we found that cyclin-dependent kinase (Cdk)-3, but not Cdk2 or c-Jun NH(2)-terminal kinase, is a novel kinase of c-Jun induced by stimulation with growth factors such as epidermal growth factor (EGF). Cdk3 was shown to phosphorylate c-Jun at Ser63 and Ser73 in vitro and ex vivo. EGF-induced Cdk3 activation caused c-Jun phosphorylation at Ser63 and Ser73, resulting in increased AP-1 transactivation. Ectopic expression of Cdk3 resulted in anchorage-independent cell transformation of JB6 Cl41 cells induced by EGF and foci formation stimulated by constitutively active Ras (Ras(G12V)), which was mediated by AP-1 in NIH3T3 cells. These results showed that the Cdk3/c-Jun signaling axis plays an important role in EGF-stimulated cell proliferation and cell transformation.

ABINs inhibit EGF receptor-mediated NF-kappaB activation and growth of EGF receptor-overexpressing tumour cells

The epidermal growth factor receptor (EGFR) is frequently overexpressed in various tumours of epidermal origin and is held responsible for tumourigenicity and tumour persistence. Increased nuclear factor (NF)-kappaB activity has been suggested to be involved in the malignant behaviour of EGFR-overexpressing cells. However, the mechanisms that regulate EGF-induced NF-kappaB activation are still largely unknown. Here we show that EGF can induce NF-kappaB-dependent gene expression independently from IkappaBalpha degradation or p100 processing in EGFR-overexpressing HEK293T cells. Moreover, EGF-induced NF-kappaB activation could be inhibited by overexpression of ABINs, which were previously identified as intracellular inhibitors of tumour necrosis factor, interleukin-1 and lipopolysaccharide-induced NF-kappaB activation. Knockdown of ABIN-1 by RNA interference boosted the NF-kappaB response upon EGF stimulation. The C-terminal ubiquitin-binding domain containing region of ABINs was crucial and sufficient for NF-kappaB inhibition. Adenoviral gene transfer of ABINs reduced constitutive NF-kappaB activity as well as the proliferation of EGFR-overexpressing A431 and DU145 human carcinoma cells. Altogether, these results demonstrate an important role for an ABIN-sensitive non-classical NF-kappaB signalling pathway in the proliferation of EGFR-overexpressing tumour cells, and indicate a potential use for ABIN gene therapy in the treatment of cancer.

Identification of ERK2-binding domain of EBITEIN1, a novel ERK2-binding protein

We recently cloned a cDNA encoding a novel extracellular signal-regulated kinase 2 (ERK2) binding protein, EBITEIN1, by yeast two-hybrid screening. In this study, we further characterized EBITEIN1. Binding experiments using various deletion mutants identified a 40-amino acid minimal sequence for binding ERK2. Binding experiments using substitution mutants indicated the crucial role of arginine residues in this sequence. Based on empirical and bioinformatic analyses, we propose two domains in EBITEIN1. One is the minimal sequence for binding ERK2 (EB domain) and the other is the EBITEIN1 C-terminal domain (ECT domain). These results might pave the way for further empirical and bioinformatic analyses of EBITEIN1- and ERK2-mediated events.

Myelodysplastic syndromes: molecular pathogenesis and genomic changes

Myelodysplastic syndromes (MDS) are characterized by ineffective hematopoiesis presenting with peripheral cytopenias in combination with a hyperplastic bone marrow and an increased risk of evolution to acute myeloid leukemia. The classification systems such as the WHO classification mainly rely on morphological criteria and are supplemented by the International Prognostic Scoring System which takes cytogenetical changes into consideration when determining the prognosis of MDS but wide intra-subtype variations do exist. The pathomechanisms causing primary MDS require further work. Development and progression of MDS is suggested to be a multistep alteration to hematopoietic stem cells. Different molecular alterations have been described, affecting genes involved in cell-cycle control, mitotic checkpoints, and growth factor receptors. Secondary signal proteins and transcription factors, which gives the cell a growth advantage over its normal counterpart, may be affected as well. The accumulation of such defects may finally cause the leukemic transformation of MDS.

Protein-protein interactions in the regulation of the extracellular signal-regulated kinase

The extracellular signal-regulated kinase (ERK) cascade is a central intracellular signaling pathway that is activated by a variety of extracellular stimuli, and thereby regulates cellular processes such as proliferation, differentiation, and oncogenic transformation. To execute these functions, the signals of those stimuli are transmitted to the cytosolic and nuclear targets in a rapid and specific manner. In the last few years it has become clear that the specificity and the rapid function of the ERK cascade is largely determined by protein-protein interactions with various signaling components and substrates. This review describes interactions of ERK with its immediate regulators, scaffold proteins, substrates, and localizing proteins, and shows their involvement in the functioning of the ERK cascade. Understanding the full scope of ERK-interactions is important for the development of new drugs for the treatment of cancer and other diseases.

The extracellular signal-regulated kinase: multiple substrates regulate diverse cellular functions

The extracellular signal-regulated kinase (ERK) cascade is a central pathway that transmits signals from many extracellular agents to regulate cellular processes such as proliferation, differentiation and cell cycle progression. The signaling via the ERK cascade is mediated by sequential phosphorylation and activation of protein kinases in the different tiers of the cascade. Although the main core phosphorylation chain of the cascade includes Raf kinases, MEK1/2, ERK1/2 (ERKs) and RSKs, other alternatively spliced forms and distinct components exist in the different tiers, and participate in ERK signaling under specific conditions. These components enhance the complexity of the ERK cascade and thereby, enable the wide variety of functions that are regulated by it. Another factor that is important for the dissemination of ERKs' signals is the multiplicity of the cascade's substrates, which include transcription factors, protein kinases and phosphatases, cytoskeletal elements, regulators of apoptosis, and a variety of other signaling-related molecules. About 160 substrates have already been discovered for ERKs, and the list of these substrates, as well as the function and mechanism of activation of representative substrates, are described in the current review. Many of these substrates are localized in the nucleus, and seem to participate in the regulation of transcription upon stimulation. However, other substrates are found in the cytosol as well as in other cellular organelles, and those are responsible for processes such as translation, mitosis and apoptosis. Understanding of these processes may provide a full picture of the distinct, and even opposing cellular processes that are regulated by the ERK cascade.

Production and characterization of a monoclonal antibody specific to Nef-associated factor 1 (Naf1)/A20-binding inhibitor of NF-kappaB activation (ABIN-1)

Cellular protein Naf1 (Nef-associated factor 1) or ABIN-1 (A20-binding inhibitor of NF-kappaB activation) is an important cellular protein, expressed in various human tissues and T-cell lines. Naf1 protein has two isoforms (Naf1alpha and Naf1beta) with different C-termini, produced by alternative splicing. Naf1alpha and Naf1beta have approximately 2800 and 2600 nucleotides, with an open reading frame of 1941 and 1781 nucleotides, encoding the 72-kDa Naf1alpha and 68-kDa Naf1beta proteins, respectively. In the present study, we generated a monoclonal antibody (MAb) against human Naf1, which recognizes full-length, endogenous Naf1 of both isotypes. For this purpose, recombinant 6xHis and myc-tagged N-terminal Naf1(38135), Naf1(N) protein was produced by using the baculovirus expression system. Recombinant Naf1(N) protein was used to immunize Balb/c mice, and a hybridoma cell line producing stable and highly specific MAb with strong affinity to Naf1 was established. We further characterized this antibody by immunofluorescent assay and Western blot analysis to confirm effectiveness in detecting recombinant and endogenous Naf1. By Western blot analysis of recombinant Naf1-N fusion proteins with overlapping N-terminal sequences, the epitope targeted by anti-Naf1 MAb was determined as the 81-88-amino acid region of human Naf1.

Toll-like receptor 2-mediated gene expression in epithelial cells during Helicobacter pylori infection

BACKGROUND

Helicobacter pylori is the major pathogen causing chronic gastritis and peptic ulcer disease and is closely linked to gastric malignancy. We have previously shown that H. pylori-induced NF-(kappa)B activation and interleukin (IL)-8 secretion are mediated by Toll-like receptor (TLR) 2 in epithelial cells. However, the TLR2-mediated global gene expression profile of the epithelial cell during H. pylori infection is still unknown. The goal of this study was to identify TLR2-regulated genes in epithelial cells induced by H. pylori.

MATERIALS AND METHODS

The HEK293 and HEK-TLR2 cells were cocultured with H. pylori 26695 for 6 hours. Total RNA was extracted and hybridized to the Affymetrix human U133A microarray chipset, which contains 22,283 total probe sets including 14,285 genes. Data analyses were performed using affymetrix suite 5 software. The expression of selected genes in gastric epithelial cells AGS and MKN45 was monitored by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

Forty-six genes, contained in 57 probe sets, were induced > 2-fold and three genes (five probe sets) decreased > 2-fold by H. pylori infection of HEK293 cells. Fifty-four genes, contained in 69 probe sets, were induced > 2-fold, whereas only 1 gene was repressed > 2-fold in H. pylori-infected HEK-TLR2 cells. Comparisons of genes induced in HEK293 or HEK-TLR2 cells identified 28 genes whose expression was dependent on the presence of TLR2. Seventeen genes were selected and their expression was assessed using the quantitative RT-PCR in gastric epithelial cells during H. pylori infection. Eight of the 17 genes showed distinct expression patterns in AGS and MKN45 cells after H. pylori stimulation.

CONCLUSIONS

The current study investigated the TLR2-mediated global gene changes after H. pylori stimulation in the epithelial cell system. This approach will be helpful in identifying genes whose expression is mediated by specific TLRs and in determining the cellular responses that are responsible for diverse signal pathways during H. pylori infection.

SNT-2 interacts with ERK2 and negatively regulates ERK2 signaling in response to EGF stimulation

The control of cellular responses with fibroblast growth factors and neurotrophins is mediated through membrane-linked docking proteins, SNT (suc1-binding neurotrophic target)-1/FRS2alpha and SNT-2/FRS2beta. ERK1/2 are members of the mitogen-activated protein kinase family that regulate diverse cellular activities in response to various stimuli. Here, we demonstrate that SNT-2 does not become tyrosine phosphorylated significantly in response to EGF but forms a complex with ERK2 via the region of 186-252 amino acid residues, and the complex formation is enhanced upon EGF stimulation. SNT-2 downregulates ERK2 phosphorylation, suppresses and delays ERK2 nuclear accumulation which occurs following EGF stimulation. In contrast, the mutant SNT-2 which carries deletion of 186-252 amino acids and lacks ERK2 binding does not have these effects. These observations suggest that SNT-2 negatively regulates ERK2 signaling activated via EGF stimulation through direct binding to ERK2.

Identification of Naf1/ABIN-1 among TNF-alpha-induced expressed genes in human synoviocytes using oligonucleotide microarrays

The cytokine tumor necrosis factor alpha (TNF-alpha) is a critical effector of the pathogenesis of rheumatoid arthritis (RA). We used oligonucleotide microarray (OM) analysis to assess TNF-alpha-modulated gene expression in cultured primary human synoviocytes in vitro. Genes identified include cytokines and inflammatory mediators, extracellular matrix and adhesion molecules, cell cycle and proliferation related proteins, transcription related proteins, and apoptotic mediators. OM identified 1185 differentially expressed genes in TNF-alpha-treated synoviocytes. The regulation of Nef-associated factor-1 (Naf1), an A20-binding, nuclear factor kappa B (NFkappaB) inhibitory protein was probed further given its putative role as an endogenous brake for the expression of some TNF-alpha-driven genes. Naf1 mRNA levels were higher in synovial biopsies from patients with active RA and seronegative arthropathy than in those from patients with osteoarthritis. These findings underscore the value of transcriptome analysis in cytokine-activated synoviocyte cultures in vitro as a means of identifying disease-associated genes in human arthritis, and implicate Naf1 as a potential modulator of TNF-alpha bioactivity in RA.