A bio-orthogonal linear ubiquitin probe identifies STAT3 as a direct substrate of OTULIN in glioblastoma.

While linear ubiquitin plays critical roles in multiple cell signaling pathways, few substrates have been identified. Global profiling of linear ubiquitin substrates represents a significant challenge because of the low endogenous level of linear ubiquitination and the background interference arising from highly abundant ubiquitin linkages (e.g. K48- and K63-) and from the non-specific attachment of interfering proteins to the linear polyubiquitin chain. We developed a bio-orthogonal linear ubiquitin probe by site-specific encoding of a norbornene amino acid on ubiquitin (NAEK-Ub). This probe facilitates covalent labeling of linear ubiquitin substrates in live cells and enables selective enrichment and identification of linear ubiquitin-modified proteins. Given the fact that the frequent overexpression of the linear linkage-specific deubiquitinase OTULIN correlates with poor prognosis in glioblastoma, we demonstrated the feasibility of the NAEK-Ub strategy by identifying and validating substrates of linear ubiquitination in patient-derived glioblastoma stem-like cells (GSCs). We identified STAT3 as a bona fide substrate of linear ubiquitin, and showed that linear ubiquitination negatively regulates STAT3 activity by recruitment of the phosphatase TC-PTP to STAT3. Furthermore, we demonstrated that preferential expression of OTULIN in GSCs restricts linear ubiquitination on STAT3 and drives persistent STAT3 signaling, and thereby maintains the stemness and self-renewal of GSCs.

Screening and Identification of a Novel Anti-Siglec-15 Human Antibody 3F1 and Relevant Antitumor Activity.

Sialic acid-binding Ig-like lectin-15 is an important immunosuppressive molecule considered to be a key target in next-generation tumor immunotherapy. In this study, we screened 22 high-affinity antibodies that specifically recognize human Siglec-15 by using a large human phage antibody library, and five representative sequences were selected for further study. The results showed the binding activity of five antibodies to Siglec-15 (EC50 ranged from 0.02368 µg/mL to 0.07949 µg/mL), and in two Siglec-15-overexpressed cell lines, three antibodies had the strongest binding activity, so the two clones were discarded for further study. Subsequently, the affinity of three antibodies were measured by bio-layer interferometry technology (5-9 × 10E-09M). As the reported ligands of Siglec-15, the binding activity of Siglec-15 and sialyl-Tn, cluster of differentiation 44, myelin-associated glycoprotein, and leucine-rich repeat-containing protein 4C can be blocked by three of the antibodies. Among these, 3F1 had a competitive advantage. Then, the antibody 3F1 showed an obvious antibody-dependent cell-mediated cytotoxicity effect (EC50 was 0.85 µg/mL). Further, antibody 3F1 can reverse the inhibitory effect of Siglec-15 on lymphocyte proliferation (especially CD4+T and CD8+T) and cytokine release Interferon-γ. Given the above results, 3F1 was selected as a candidate for the in vivo pharmacodynamics study. In the tumor model of Balb/c Nude mice, 3F1 (10 mg/kg) showed certain antitumor effects [tumor growth inhibition (TGI) was 31.5%], while the combination of 3F1 (5 mg/kg) and Erbitux (5 mg/kg) showed significant antitumor effects (TGI was 48.7%) compared with the PBS group. In conclusion, novel human antibody 3F1 has antitumor activity and is expected to be an innovative candidate drug targeting Siglec-15 for tumor immunotherapy. SIGNIFICANCE STATEMENT: Siglec-15 is considered as an important target in the next generation of tumor immunotherapy. 3F1 is expected to be the most promising potential candidate for targeting Siglec-15 for cancer treatment and could provide a reference for the development of antitumor drugs.

COMSUC: A web server for the identification of consensus molecular subtypes of cancer based on multiple methods and multi-omics data.

Extensive amounts of multi-omics data and multiple cancer subtyping methods have been developed rapidly, and generate discrepant clustering results, which poses challenges for cancer molecular subtype research. Thus, the development of methods for the identification of cancer consensus molecular subtypes is essential. The lack of intuitive and easy-to-use analytical tools has posed a barrier. Here, we report on the development of the COnsensus Molecular SUbtype of Cancer (COMSUC) web server. With COMSUC, users can explore consensus molecular subtypes of more than 30 cancers based on eight clustering methods, five types of omics data from public reference datasets or users' private data, and three consensus clustering methods. The web server provides interactive and modifiable visualization, and publishable output of analysis results. Researchers can also exchange consensus subtype results with collaborators via project IDs. COMSUC is now publicly and freely available with no login requirement at http://comsuc.bioinforai.tech/ (IP address: http://59.110.25.27/). For a video summary of this web server, see S1 Video and S1 File.

Novel CRISPR/Cas9-mediated knockout of LIG4 increases efficiency of site-specific integration in Chinese hamster ovary cell line.

AIM: To investigate the impact of deficiency of LIG4 gene on site-specific integration in CHO cells. RESULTS: CHO cells are considered the most valuable mammalian cells in the manufacture of biological medicines, and genetic engineering of CHO cells can improve product yield and stability. The traditional method of inserting foreign genes by random integration (RI) requires multiple rounds of screening and selection, which may lead to location effects and gene silencing, making it difficult to obtain stable, high-yielding cell lines. Although site-specific integration (SSI) techniques may overcome the challenges with RI, its feasibility is limited by the very low efficiency of the technique. Recently, SSI efficiency has been enhanced in other mammalian cell types by inhibiting DNA ligase IV (Lig4) activity, which is indispensable in DNA double-strand break repair by NHEJ. However, this approach has not been evaluated in CHO cells. In this study, the LIG4 gene was knocked out of CHO cells using CRISPR/Cas9-mediated genome editing. Efficiency of gene targeting in LIG4-/--CHO cell lines was estimated by a green fluorescence protein promoterless reporter system. Notably, the RI efficiency, most likely mediated by NHEJ in CHO, was inhibited by LIG4 knockout, whereas SSI efficiency strongly increased 9.2-fold under the precise control of the promoter in the ROSA26 site in LIG4-/--CHO cells. Moreover, deletion of LIG4 had no obvious side effects on CHO cell proliferation. CONCLUSIONS: Deficiency of LIG4 represents a feasible strategy to improve SSI efficiency and suggests it can be applied to develop and engineer CHO cell lines in the future.

Selection and Characterization of FD164, a High-Affinity Signal Regulatory Protein α Variant with Balanced Safety and Effectiveness, from a Targeted Epitope Mammalian Cell-Displayed Antibody Library.

Phagocytic resistance plays a key role in tumor-mediated immune escape, so phagocytosis immune checkpoints are a potential target for cancer immunotherapy. CD47 is one of the important phagocytosis immune checkpoints; thus, blocking the interaction between CD47 and signal regulatory protein α (SIRPα) may provide new options for cancer treatment. Using computer-aided targeted epitope mammalian cell-displayed antibody library, we screened and obtained an engineered SIRPα variant fragment crystallizable fusion protein, FD164, with higher CD47-binding activity than wild-type SIRPα Compared with wild-type SIRPα, FD164 has approximately 3-fold higher affinity for binding to CD47, which further enhanced its phagocytic effect in vitro and tumor suppressor activity in vivo. FD164 maintains the similar antitumor activity of the clinical research drug Hu5F9 in the mouse xenograft model. Furthermore, FD164 combined with rituximab can significantly improve the effect of single-agent therapy. On the other hand, compared with Hu5F9, FD164 does not cause hemagglutination, and its ability to bind to red blood cells or white blood cells is weaker at the same concentration. Finally, it was confirmed by computer structure prediction and alanine scanning experiments that the N45, E47, 52TEVYVK58, K60, 115EVTELTRE122, and E124 residues of CD47 are important for SIRPα or FD164 recognition. Briefly, we obtained a high-affinity SIRPα variant FD164 with balanced safety and effectiveness. SIGNIFICANCE STATEMENT: Up to now, few clinically marketed drugs targeting CD47 have been determined to be effective and safe. FD164, a potential signal regulatory protein α variant fragment crystallizable protein with balanced safety and effectiveness, could provide a reference for the development of antitumor drugs.

FKBP12 mediates necroptosis by initiating RIPK1-RIPK3-MLKL signal transduction in response to TNF receptor 1 ligation.

Necroptosis is a regulated form of necrotic cell death that is mediated by receptor-interacting serine/threonine-protein kinase 1 (RIPK1), RIPK3 and mixed-lineage kinase domain-like protein (MLKL), which mediates necroptotic signal transduction induced by tumor necrosis factor (TNF). Although many target proteins for necroptosis have been identified, no report had indicated that FK506-binding protein 12 (FKBP12, also known as FKBP1A), an endogenous protein that regulates protein folding and conformation alteration, is involved in mediating necroptosis. In this study, we found that FKBP12 acts as a novel target protein in mediating necroptosis and the related systemic inflammatory response syndrome triggered by TNF. The mechanistic study discovered that FKBP12 is essential for initiating necrosome formation and RIPK1-RIPK3-MLKL signaling pathway activation in response to TNF receptor 1 ligation. In addition, FKBP12 is indispensable for RIPK1 and RIPK3 expression and subsequent spontaneous phosphorylation, which are essential processes for initial necrosome formation and necroptotic signal transduction; therefore, FKBP12 may target RIPK1 and RIPK3 to mediate necroptosis in vitro and in vivo Collectively, our data demonstrate that FKBP12 could be a potential therapeutic target for the clinical treatment of necroptosis-associated diseases.

Identification of a novel protective human monoclonal antibody, LXY8, that targets the key neutralizing epitopes of staphylococcal enterotoxin B.

Staphylococcal enterotoxin B (SEB), one of the exotoxins produced by Staphylococcus aureus, is the key toxin that causes poisoning reactions and toxic shock syndrome. In the current research work, a novel human antibody named LXY8 was screened from a human phage display antibody library, and LXY8 blocked the interaction between SEB and the T cell receptor (TCR). The binding activity between LXY8 and SEB was 0.525 nM. Furthermore, LXY8 could effectively inhibit the SEB-induced activation of peripheral blood mononuclear cells and release of cytokines. In the BALB/c mouse model, LXY8 effectively neutralized SEB toxicity in vivo. Finally, based on computer-guided molecular modeling, we designed a series of SEB mutation sites; these sites facilitated the determination of the key residues (i.e.176EFNN179) of SEB recognized by LXY8. The research revealed that the 176EFNN179 residues of SEB are important for specific antibody-antigen recognition. The results may be helpful for the development of antibody-based therapy for SEB-induced toxic shock syndrome.

Development of bifunctional anti-PD-L1 antibody MMAE conjugate with cytotoxicity and immunostimulation.

In recent years, tumor immunotherapy, especially the combination of PD1/PD-L1 inhibitors and chemotherapy, has developed rapidly. However, the systemic side effects induced by chemotherapy remain a crucial problem that needs to be addressed. Antibody drug conjugates (ADCs) are exceptional target-specific prodrugs that greatly improve the therapeutic window of chemotherapy drugs. Therefore, designing PD-L1-targeting ADCs is an interesting research project. In this study, we confirmed for the first time that the commercial anti-PD-L1 antibody Atezolizumab has better endocytosis efficiencies than Avelumab, and was more suitable for ADC design. Then, the most popular cytotoxic payload MMAE was conjugated to Atezolizumab via a classical dipeptide (valine-alanine) linker to generate a bifunctional PD-L1 ADC (ADC 3). An in vitro cytotoxicity test indicated the potent tumor cell inhibitory activity of ADC 3, with EC50 values of 9.75 nM to 11.94 nM. In addition, a co-culture of PBMCs in vitro proved that ADC 3 retained the immune activation effect of the Atezolizumab antibody. Moreover, ADC 3 exhibited a higher tumor inhibition rate and tumor regression rate in humanized immune system mice. To the best of our knowledge, this is the most active PD-L1-ADC reported thus far, which may promote the development of immunotherapy and novel ADCs.

Energy Platform for Directed Charge Transfer in the Cascade Z-Scheme Heterojunction: CO2 Photoreduction without a Cocatalyst.

A universal strategy is developed to construct a cascade Z-Scheme system, in which an effective energy platform is the core to direct charge transfer and separation, blocking the unexpected type-II charge transfer pathway. The dimension-matched (001)TiO2 -g-C3 N4 /BiVO4 nanosheet heterojunction (T-CN/BVNS) is the first such model. The optimized cascade Z-Scheme exhibits ≈19-fold photoactivity improvement for CO2 reduction to CO in the absence of cocatalysts and costly sacrificial agents under visible-light irradiation, compared with BVNS, which is also superior to other reported Z-Scheme systems even with noble metals as mediators. The experimental results and DFT calculations based on van der Waals structural models on the ultrafast timescale reveal that the introduced T as the platform prolongs the lifetimes of spatially separated electrons and holes and does not compromise their reduction and oxidation potentials.

A novel human anti-AXL monoclonal antibody attenuates tumour cell migration.

TAM family members (TYRO3, AXL and MERTK) play essential roles in the resolution of inflammation and in infectious diseases and cancer. AXL, a tyrosine kinase receptor, is commonly overexpressed in several solid tumours and numerous hematopoietic malignancies including acute myeloid leukaemia, acute lymphocytic leukaemia, chronic myeloid leukaemia, chronic lymphocytic leukaemia and multiple myeloma. AXL significantly promotes tumour cell migration, invasion and metastasis, as well as angiogenesis. AXL also plays an important role in inflammation and macrophage ontogeny. Recent studies have revealed that AXL contributes to leukaemic phenotypes through activation of oncogenic signalling pathways that lead to increased cell migration and proliferation. To evaluate the mechanisms underlying the role of AXL signalling in tumour metastasis, we screened a phage display library to generate a novel human monoclonal antibody, named DAXL-88, that recognizes both human and murine AXL. The concentrations of DAXL-88 required for 50% maximal binding to human and murine AXL were 0.118 and 0.164 µg/mL, respectively. Furthermore, DAXL-88 bound to human AXL with high affinity (KD  ~ 370 pM). DAXL-88 blocked the interaction between AXL and its ligand, growth arrest-specific gene 6 (GAS6), with a half maximal inhibitory concentration of 2.16 µg/mL. Moreover, DAXL-88 inhibited AXL/GAS6-dependent cell signalling, which is implicated in cell migration and invasion. In conclusion, the novel anti-AXL DAXL-88 high-affinity antibody blocks the interaction between AXL and GAS6 and inhibits tumour cell migration and invasion induced by GAS6. Thus, DAXL-88 offers promise for the development of targeted therapeutic strategies in solid tumours, leukaemias and other lymphoid neoplasms.

Monoclonal antibody against human Tim-3 enhances antiviral immune response.

T cell immunoglobulin and mucin domain protein 3 (Tim-3) is an immune checkpoint inhibitor in T cells and innate immune cells. The deregulated upregulation of Tim-3 is related to immune exhaustion in tumour and viral infection. To overcome Tim-3-mediated immune tolerance, we developed a novel monoclonal antibody against human Tim-3 (L3G) and investigated its roles in inhibiting Tim-3 signalling and overcoming immune tolerance in T cells and monocytes/macrophages. The administration of L3G to cultured peripheral blood mononuclear cells (PBMCs) significantly increased the production of IFN-γ and IL-2 and the expression of type I interferon. The administration of L3G also increased the production of IFN-γ, IL-8 and type I interferon in U937 cells and primary monocytes. We investigated the mechanisms by which L3G enhances pro-inflammatory cytokine expression, and our data show that L3G enhances STAT1 phosphorylation in both monocytes/macrophages and T cells. Finally, in an H1N1 infection model of PBMCs and U937 cells, L3G decreased the viral load and enhanced the expression of interferon. Thus, we developed a functional antibody with therapeutic potential against Tim-3-mediated infection tolerance.

Dimension-Matched Zinc Phthalocyanine/BiVO4 Ultrathin Nanocomposites for CO2 Reduction as Efficient Wide-Visible-Light-Driven Photocatalysts via a Cascade Charge Transfer.

Cascade charge transfer was realized by a H-bond linked zinc phthalocyanine/BiVO4 nanosheet (ZnPc/BVNS) composite, which subsequently works as an efficient wide-visible-light-driven photocatalyst for converting CO2 into CO and CH4 , as shown by product analysis and 13 C isotopic measurement. The optimized ZnPc/BVNS nanocomposite exhibits a ca. 16-fold enhancement in the quantum efficiency compared with the reported BiVO4 nanoparticles at the excitation of 520 nm with an assistance of 660 nm photons. Experimental and theoretical results show the exceptional activities are attributed to the rapid charge separation by a cascade Z-scheme charge transfer mechanism formed by the dimension-matched ultrathin (ca. 8 nm) heterojunction nanostructure. The central Zn2+ in ZnPc could accept the excited electrons from the ligand and then provide a catalytic function for CO2 reduction. This Z-scheme is also feasible for other MPc, such as FePc and CoPc, together with BVNS.

Negative regulation of Nod-like receptor protein 3 inflammasome activation by T cell Ig mucin-3 protects against peritonitis.

The Nod-like receptor protein 3 (NLRP3) inflammasome plays roles in host defence against invading pathogens and in the development of autoimmune damage. Strict regulation of these responses is important to avoid detrimental effects. Here, we demonstrate that T cell Ig mucin-3 (Tim-3), an immune checkpoint inhibitor, inhibits NLRP3 inflammasome activation by damping basal and lipopolysaccharide-induced nuclear factor-κB-mediated up-regulation of NLRP3 and interleukin-1ß during the priming step and basal and ATP/lipopolysaccharide-induced ATP production, K+ efflux, and reactive oxygen species production during the activation step. Residues Y256/Y263 in the C-terminal region of Tim-3 are required for these inhibitory effects on the NLRP3 inflammasome. In mice with alum-induced peritonitis, blockade of Tim-3 exacerbates peritonitis by overcoming the inhibitory effect of Tim-3 on NLRP3 inflammasome activation, while transgenic expression of Tim-3 attenuates inflammation by inhibiting NLRP3 inflammasome activation. Our results show that Tim-3 is a critical negative regulator of NLRP3 inflammasome and provides a potential target for intervention of diseases with uncontrolled inflammasome activation.

Multi-parametric analysis reveals enhanced G2-phase arrest of an optimized anti-HER2 antibody to inhibit breast cancer.

OBJECTIVES: To find a "me-better" antibody by epitope-specific antibody optimization and multi-parametric analysis. RESULTS: Using epitope-specific library based on the commercial drug, Pertuzumab/2C4, we screened a novel human anti-HER2 antibody, MIL5, which has slightly higher affinity than the drug. MIL5 and 2C4 share the same epitope to bind HER2; however, MIL5 bound to HER2 His235-His245 more tightly than 2C4, which could be the main reason of its enhanced affinity. In vivo experiments also showed MIL5 had stronger anti-cancer activity than 2C4; however, the classical flow cytometry assays to detect cell apoptosis or cycling did not show convincing evidence of the advantages of MIL5. Thus we introduced the multi-parameter in-cell analysis method to evaluate the superiority of MIL5 to 2C4 in arresting cancer cells in G2-phase to inhibit cell growth and/or proliferation. CONCLUSION: Multi-parametric method confirmed stronger arrest of G2 by MIL5 to show better anti-cancer function both in vitro and in vivo than 2C4.

Anticancer efficacy of a nitric oxide-modified derivative of bifendate against multidrug-resistant cancer cells.

The development of multidrug resistance (MDR) not only actively transports a wide range of cytotoxic drugs across drug transporters but is also a complex interaction between a number of important cellular signalling pathways. Nitric oxide donors appear to be a new class of anticancer therapeutics for satisfying all the above conditions. Previously, we reported furoxan-based nitric oxide-releasing compounds that exhibited selective antitumour activity in vitro and in vivo. Herein, we demonstrate that bifendate (DDB)-nitric oxide, a synthetic furoxan-based nitric oxide-releasing derivative of bifendate, effectively inhibits the both sensitive and MDR tumour cell viability at a comparatively low concentration. Interestingly, the potency of DDB-nitric oxide is the independent of inhibition of the functions and expressions of three major ABC transporters. The mechanism of DDB-nitric oxide appears to be in two modes of actions by inducing mitochondrial tyrosine nitration and apoptosis, as well as by down-regulating HIF-1α expression and protein kinase B (AKT), extracellular signal-regulated kinases (ERK), nuclear factor κB (NF-κB) activation in MDR cells. Moreover, the addition of a typical nitric oxide scavenger significantly attenuated all the effects of DDB-nitric oxide, indicating that the cytotoxicity of DDB-nitric oxide is as a result of higher levels of nitric oxide release in MDR cancer cells. Given that acquired MDR to nitric oxide donors is reportedly difficult to achieve and genetically unstable, compound like DDB-nitric oxide may be a new type of therapeutic agent for the treatment of MDR tumours.

Tim-3 promotes intestinal homeostasis in DSS colitis by inhibiting M1 polarization of macrophages.

Tim-3 is involved in the physiopathology of inflammatory bowel disease (IBD), but the underlying mechanism is unknown. Here, we demonstrated that, in mouse with DSS colitis, Tim-3 inhibited the polarization of pathogenic pro-inflammatory M1 macrophages, while Tim-3 downregulation or blockade resulted in an increased M1 response. Adoptive transfer of Tim-3-silenced macrophages worsened DSS colitis and enhanced inflammation, while Tim-3 overexpression attenuated DSS colitis by decreasing the M1 macrophage response. Co-culture of Tim-3-overexpressing macrophages with intestinal lymphocytes decreased the pro-inflammatory response. Tim-3 shaped intestinal macrophage polarization may be TLR-4 dependent since Tim-3 blockade failed to exacerbate colitis or increase M1 macrophage response in the TLR-4 KO model. Finally, Tim-3 signaling inhibited phosphorylation of IRF3, a TLR-4 downstream transcriptional factor regulating macrophage polarization. A better understanding of this pathway may shed new light on colitis pathogenesis and result in a new therapeutic strategy.

T cell Ig mucin-3 promotes homeostasis of sepsis by negatively regulating the TLR response.

Sepsis is an excessive inflammatory condition with a high mortality rate and limited prediction and therapeutic options. In this study, for the first time, to our knowledge, we found that downregulation and/or blockade of T cell Ig and mucin domain protein 3 (Tim-3), a negative immune regulator, correlated with severity of sepsis, suggesting that Tim-3 plays important roles in maintaining the homeostasis of sepsis in both humans and a mouse model. Blockade and/or downregulation of Tim-3 led to increased macrophage activation, which contributed to the systemic inflammatory response in sepsis, whereas Tim-3 overexpression in macrophages significantly suppressed TLR-mediated proinflammatory cytokine production, indicating that Tim-3 is a negative regulator of TLR-mediated immune responses. Cross-talk between the Tim-3 and TLR4 pathways makes TLR4 an important contributor to Tim-3-mediated negative regulation of the innate immune response. Tim-3 signaling inhibited LPS-TLR4-mediated NF-κB activation by increasing PI3K-AKT phosphorylation and A20 activity. This negative regulatory role of Tim-3 reflects a new adaptive compensatory and protective mechanism in sepsis victims, a finding of potential importance for modulating innate responses in these patients.

Pharmacological characteristics and efficacy of a novel anti-angiogenic antibody FD006 in corneal neovascularization.

BACKGROUND: Vascular endothelial growth factor (VEGF) is a key angiogenic factors. It plays an important role in both physiologic and pathologic angiogenesis and increases permeability across the vessels. Using antibody phage display technology, we obtained a novel anti-VEGFA IgG, named as FD006. In this study, the pharmacological characteristics and efficacy of FD006 in corneal neovascularization (CoNV) were evaluated. RESULTS: FD006 was predicted to have similar binding mode to bevacizumab. Experimental analysis showed that the binding ability of FD006 seemed a little stronger than bevacizumab, for the EC50 of FD006 to bind VEGF analyzed by ELISA was about 0.037 µg/mL while that of bevacizumab was 0.18 µg/mL. Binding kinetics assays showed similar results that FD006 possessed 2-fold higher affinity to bind VEGF than bevacizumab due to slower dissociation rate of FD006; meanwhile, FD006 inhibited the VEGF-induced proliferation of HUVEC with an IC50 value of 0.031 ± 0.0064 µg/ml, which seemed similar or a litter better than bevacizumab (0.047 ± 0.0081 µg/ml). The subconjunctival administration of FD006, bevacizumab or dexamethasone could significantly inhibit the growth of CoNV contrasting to N.S (p < 0.01). At the early stage, FD006 showed better inhibitory effect on the growth of CoNV compared with bevacizumab (p < 0.05). Western blot analysis showed that FD006 could inhibit the expression of VEGF, VEGFR-1, VEGFR-2, MMP-9 and ICAM-1, which could explain its favorable anti-angiogenic activity. CONCLUSIONS: The pharmacological characteristics of FD006 were similar or even a little better than bevacizumab in inhibiting corneal neovascularization.

Receptor for activated C kinase 1 promotes hepatocellular carcinoma growth by enhancing mitogen-activated protein kinase kinase 7 activity.

UNLABELLED: c-Jun N-terminal protein kinase (JNK) is a member of the mitogen-activated protein kinase (MAPK) superfamily. The activation of JNK is mediated by sequential protein phosphorylation through a MAPK module, namely, MAPK kinase kinase (MAP3K or MEKK) → MAPK kinase (MAP2K or MKK) → MAPK. Elevated levels of JNK activity have been frequently observed in hepatocellular carcinoma (HCC) and have been demonstrated to contribute to HCC growth by promoting HCC cell proliferation and resistance to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)- or Fas-mediated apoptosis. Chronic inflammation contributes to the up-regulation of JNK activity in HCC. However, it remains unknown whether aberrant JNK activity also results from some cell intrinsic defect(s). Here, we show that receptor for activated C kinase 1 (RACK1), an adaptor protein implicated in the regulation of multiple signaling pathways, could engage in a direct interaction with MKK7, the JNK-specific MAP2K, in human HCC cells. Levels of RACK1 protein show correlation with the activity of the JNK pathway in human HCC tissues and cell lines. RACK1 loss-of-function or gain-of-function analyses indicate that RACK1 enhances MKK7/JNK activity in human HCC cells. Further exploration reveals that the interaction of RACK1 with MKK7 is required for the enhancement of MKK7/JNK activity by RACK1. RACK1/MKK7 interaction facilitates the association of MKK7 with MAP3Ks, thereby enhancing MKK7 activity and promoting in vitro HCC cell proliferation and resistance to TRAIL- or Fas-mediated apoptosis as well as in vivo tumor growth. CONCLUSION: Overexpressed RACK1 augments JNK activity and thereby promotes HCC growth through directly binding to MKK7 and enhancing MKK7 activity.

Disruption of TAB1/p38α interaction using a cell-permeable peptide limits myocardial ischemia/reperfusion injury.

Targeting the adaptor protein (transforming growth factor-ß (TGF-ß)-activated protein kinase 1 (TAK1)-binding protein 1) (TAB1)-mediated non-canonical activation of p38α to limit ischemia/reperfusion (I/R) injury after an acute myocardial infarction seems to be attractive since TAB1/p38α interaction occurs specifically in very limited circumstances and possesses unique structural basis. However, so far no TAB1/p38α interaction inhibitor has been reported due to the limited knowledge about the interfaces. In this study, we sought to identify key amino acids essential for the unique mode of interaction with computer-guided molecular simulations and molecular docking. After validation of the predicted three-dimensional (3-D) structure of TAB1/p38α complex, we designed several peptides and evaluated whether they could block TAB1/p38α interaction with selectivity. We found that a cell-permeable peptide worked as a selective TAB1/p38α interaction inhibitor and decreased myocardial I/R injury. To our knowledge, this is the first TAB1/p38α interaction inhibitor.