Kinase Site Research Articles

1,2,3-Triazole tethered 2-mercaptobenzimidazole derivatives: design, synthesis and molecular assessment toward C6 glioma cell line.

Aim: Glioblastoma multiforme (GBM) is an aggressive cancer with very limited clinical therapies. Herein, we have designed novel mercaptobenzimidazole derivatives (1-7) as multitarget antineoplastic drugs and assessed their antiproliferative profiles on an experimental model for GBM, the C6 glioma line. Results: The target compounds were synthesized in few steps with reasonable yields (33-90%). Compounds 1 (∼18μM) and 4 (∼20μM) showed dose-dependent antiproliferative effects on C6 glioma and significantly increased early apoptosis, but only 4 disrupted the cell cycle progression and did not induce autophagy. Docking simulations suggested these compounds as dual kinase and colchicine binding site inhibitors. Conclusion:In spite of the limited selective toxicity, 4 hold the potential to be further optimized for the treatment of GBM.

The effect of abiraterone acetate treatment on CREB and the development of abiraterone acetate resistance in prostate cancer cells.

177 Background: The androgen receptor (AR) remains an essential target in castration resistant prostate cancer (CRPC). Abiraterone acetate (AA), an inhibitor of CYP17A1, is an FDA approved drug for metastatic CRPC. AA can also be converted to the more active metabolite 4-abiraterone in vivo, which blocks multiple steroidogenic enzymes and antagonizes AR. However, not all patients respond to AA and AA resistance ultimately develops in those patients who initially respond. Methods: We established several AA resistant prostate cancer cell lines and performed a comprehensive study of mechanisms involved in the development of AA resistance. The AA-resistant cell lines are phenotypically stable with aggressive invasive features. By RNA-seq and phospho-kinase array screening, we found that the cAMP response element-CRE binding protein 1 (CREB1) is activated in AA resistant cell lines. Results: Over-expression of the wild type CREB1 or treatment with Forskolin desensitizes the cellular response to AA, while over-expressing the mutated CREB1 (S133A, an essential kinase site) did not significantly affect cell sensitivity to AA. Blocking pCREB1 with the CREB inhibitor increased the sensitivity of AA resistant cell lines to AA. The activation of pCREB1 in AA resistant cell lines may potentially activate the CBP/p300 complex. Our data demonstrated that treatment with a low dose of AA strongly synergistic the efficacy of CBP/p300 inhibitors in prostate cancer cell lines. Taken together, we found that AA treatment activates CREB1 and pCREB1 may interact with the CBP/p300 complex, leading to global gene expression alterations, which subsequently result in the development of drug resistance. Conclusions: Our study indicates that AR-targeted treatment potentially fosters de novo genetic and epigenetic alterations associated with progression. A more effective AR-targeted treatment for CRPC may be developed by considering low doses of multiple targets involved in the development of resistance pathways.

Pharmacophore-guided fragment-based design of novel mammalian target of rapamycin inhibitors: extra precision docking, fingerprint-based 2D and atom-based 3D-QSAR modelling

Rapamycin and their derivatives known as rapalogs were the first-generation mTOR inhibitors which interacted with mTORC1 but not with the mTORC2 protein. Second-generation inhibitors could bind with both and showed excellent anti-proliferative activity. Our aim was to design novel mTOR inhibitors which could bind at both the allosteric and the kinase site. The FRB domain is present in both the mTORC1 and mTORC2 protein complexes. We have employed e-pharmacophore-guided fragment-based design to develop novel mTOR inhibitors. The affinity of designed molecules at both the sites was analysed using molecular docking in extra precision mode. The atom-based 3D-QSAR model was developed to predict the activity while the fingerprint-based 2D-QSAR model was employed to refine an identified hit as potent dual mTOR inhibitor. Ligand ASK23 showed a docking score of −15.452 kcal/mol at the allosteric site (PDB ID 5GPG) while ASK38 showed a docking score of −11.535 kcal/mol at the kinase site (PDB ID 4JT6). Ligand ASK12 showed binding energy of −106.23 kcal/mol at the allosteric site. Refined molecule ASK12a from ASK12 showed the highest predicted activity (pIC50: 6.512). The stability of the best hits and receptor complex was analysed using molecular dynamics simulation studies. Herein we report five potential mTOR dual inhibitors based on the predicted activity, drug-likeness analysis and off-target effects. To the best of our knowledge, this is the first report on pharmacophore-guided fragment-based drug design for mTOR inhibitors. This design strategy can be used for the rational drug design against other proteins for which only apo-structures are available. Communicated by Ramaswamy H. Sarma

A highly selective inhibitor of interleukin-1 receptor–associated kinases 1/4 (IRAK-1/4) delineates the distinct signaling roles of IRAK-1/4 and the TAK1 kinase

Interleukin-1 receptor-associated kinase-1 (IRAK-1) and IRAK-4, as well as transforming growth factor β-activated kinase 1 (TAK1), are protein kinases essential for transducing inflammatory signals from interleukin receptors. IRAK family proteins and TAK1 have high sequence identity within the ATP-binding pocket, limiting the development of highly selective IRAK-1/4 or TAK1 inhibitors. Beyond kinase activity, IRAKs and TAK1 act as molecular scaffolds along with other signaling proteins, complicating the interpretation of experiments involving knockin or knockout approaches. In contrast, pharmacological manipulation offers the promise of targeting catalysis-mediated signaling without grossly disrupting the cellular architecture. Recently, we reported the discovery of takinib, a potent and highly selective TAK1 inhibitor that has only marginal activity against IRAK-4. On the basis of the TAK1-takinib complex structure and the structure of IRAK-1/4, here we defined critical contact sites of the takinib scaffold within the nucleotide-binding sites of each respective kinase. Kinase activity testing of takinib analogs against IRAK-4 identified a highly potent IRAK-4 inhibitor (HS-243). In a kinome-wide screen of 468 protein kinases, HS-243 had exquisite selectivity toward both IRAK-1 (IC50 = 24 nm) and IRAK-4 (IC50 = 20 nm), with only minimal TAK1-inhibiting activity (IC50 = 0.5 μm). Using HS-243 and takinib, we evaluated the consequences of cytokine/chemokine responses after selective inhibition of IRAK-1/4 or TAK1 in response to lipopolysaccharide challenge in human rheumatoid arthritis fibroblast-like synoviocytes. Our results indicate that HS-243 specifically inhibits intracellular IRAKs without TAK1 inhibition and that these kinases have distinct, nonredundant signaling roles.

Enhancing Activity of Pleurotus sajor-caju (Fr.) Sing β-1,3-Glucanoligosaccharide (Ps-GOS) on Proliferation, Differentiation, and Mineralization of MC3T3-E1 Cells through the Involvement of BMP-2/Runx2/MAPK/Wnt/β-Catenin Signaling Pathway.

Osteoporosis is a leading world health problem that results from an imbalance between bone formation and bone resorption. β-glucans has been extensively reported to exhibit a wide range of biological activities, including antiosteoporosis both in vitro and in vivo. However, the molecular mechanisms responsible for β-glucan-mediated bone formation in osteoblasts have not yet been investigated. The oyster mushroom Pleurotus sajor-caju produces abundant amounts of an insoluble β-glucan, which is rendered soluble by enzymatic degradation using Hevea glucanase to generate low-molecular-weight glucanoligosaccharide (Ps-GOS). This study aimed to investigate the osteogenic enhancing activity and underlining molecular mechanism of Ps-GOS on osteoblastogenesis of pre-osteoblastic MC3T3-E1 cells. In this study, it was demonstrated for the first time that low concentrations of Ps-GOS could promote cell proliferation and division after 48 h of treatment. In addition, Ps-GOS upregulated the mRNA and protein expression level of bone morphogenetic protein-2 (BMP-2) and runt-related transcription factor-2 (Runx2), which are both involved in BMP signaling pathway, accompanied by increased alkaline phosphatase (ALP) activity and mineralization. Ps-GOS also upregulated the expression of osteogenesis related genes including ALP, collagen type 1 (COL1), and osteocalcin (OCN). Moreover, our novel findings suggest that Ps-GOS may exert its effects through the mitogen-activated protein kinase (MAPK) and wingless-type MMTV integration site (Wnt)/β-catenin signaling pathways.

Clinical Categorization of Chronic Myelomonocytic Leukemia into Proliferative and Dysplastic Subtypes Correlates with Distinct Genomic, Transcriptomic and Epigenomic Signatures

Introduction: Chronic myelomonocytic leukemia (CMML), an aggressive myeloid malignancy, can be categorized into two subtypes, proliferative CMML (pCMML) and dysplastic (dCMML), based on a white blood cell (WBC) count of ≥ 13 x 109/L for the former (Arber et al. Blood 2016). While this WBC cut off is somewhat arbitrary, patients with pCMML have unique phenotypic features and a shorter survival. We carried out this study to assess the genomic, transcriptomic and epigenetic landscapes of these two CMML subtypes. Methods: Peripheral blood (PB) and bone marrow (BM) mononuclear cells (MNC) were obtained from WHO-defined CMML patients. Next generation sequencing (NGS) using a 36-gene panel was performed on 350 patients with Illumina HiSeq4000 platform with median read depth of 400X. RNA sequencing (RNA-seq) was performed on 25 patients by bulk whole transcriptome sequencing using Illumina TruSeq. DNA immunoprecipitation sequencing (DIP-seq) was performed on 18 patients using 5-methylcystocine (5mC), 5-hydroxymethylcytosine (5hmC) and bridging monoclonal antibodies with subsequent paired-end sequencing using HiSeq4000. Chromatin immunoprecipitation sequencing (ChIP-seq) was performed on 30 patients with Illumina HiSeq2500 to a depth of 25 million for histone 3 lysine 4 monomethylation (H3K4me1) and histone 3 lysine 4 trimethylation (H3K4me3) and 50 million reads for histone 3 lysine 27 trimethylation (H3K27me3) and Input per sample. Results: Five hundred and seventy-three patients with WHO defined CMML were included; median age 71 years (range 18-95 years), 67% males. 282 patients had pCMML (49%), while 291 (51%) had dCMML. As pre-defined, patients with pCMML were more likely to have higher absolute monocyte counts (p<0.0001), circulating immature myeloid cells (p<0.0001), PB blasts (p<0.0001), and higher lactate dehydrogenase levels (p=0.03). At last follow up 234 (41%) deaths and 70 (20%) leukemic transformations were documented. The median OS for pCMML vs dCMML in this cohort was 19 months vs 30 months (p<0.0001, Figure 1A) and validated in an independent Austrian cohort (p=0.02). Genomic profiling: NGS performed on 350 patients (BM MNC) revealed a higher frequency of NRAS (35 vs 17%, p=0.004), cumulative RAS pathway (NRAS, KRAS, CBL and PTPN11) (73 vs 47%, p=0.001), ASXL1 (p=0.003) and JAK2V617F (p=0.04) mutations in pCMML relative to dCMML (Figure 1B); while dCMML had a higher frequency of SF3B1 mutations (p=0.02). There were no differences in distribution of TET2 and SRSF2Transcriptomic analysis: RNA-seq was performed on PB MNC from RAS pathway mutant pCMML patients (n=12) and RAS pathway wildtype dCMML patients (n=13). Unsupervised clustering analysis resulted in appropriate segregation revealing distinct expression profiles between disease subtypes (Figure 1C). Compared to dCMML, 3729 genes were significantly differentially upregulated and 2658 genes were differentially downregulated in pCMML. Among genes most highly upregulated were mitotic checkpoint kinases including AURBK, PLK1, PLK2, PLK4 andEpigenetic profiling: ChIP-seq of PB and BM MNC from pCMML (n=18) and dCMML (n=12) patients and healthy, age-matched controls (n=10) revealed a global increase in H3K4me1, without significant differences in H3K4me3 or H3K27me3 occupancies (regardless of stratification by ASXL1 mutational status; 40% ASXL1mt in pCMML, 30% dCMML) in pCMML vs dCMML (Figure 1D). H3K4me1 occupancy was also increased in a sequence-specific manner at the transcription start sites of the aforementioned mitotic kinases (PLK1 and WEE1). DIP-seq was performed on PB MNC to assess global differences in 5-mC and 5-hmC levels, between pCMML (n=9) and dCMML (n=9), with no differences seen between the two subtypes (regardless of TET2 mutational status, 40% TET2mt in each subtype) (Figure 1E). Conclusions: Despite the somewhat arbitrary WBC distinction between pCMML and dCMML, clear phenotypic, genetic, transcriptomic, epigenetic and survival differences exist between the two subtypes, providing strong biological rationale for this distinction. pCMML patients have a higher frequency of oncogenic RAS pathway mutations, a unique transcriptomic profile enriched in mitotic check point kinases and a unique chromatin configuration with global and sequence specific enrichment in H3K4me1, with no significant global differences in 5mC, 5hmC, or H3K4me3 and H3K27me3 occupancy. Figure 1 Disclosures Geissler: AOP: Honoraria; Pfizer: Honoraria; AstraZeneca: Honoraria; Novartis: Honoraria; Celgene: Honoraria; Roche: Honoraria; Abbvie: Honoraria; Ratiopharm: Honoraria; Amgen: Honoraria. Al-Kali:Astex Pharmaceuticals, Inc.: Research Funding. Patnaik:Stem Line Pharmaceuticals.: Membership on an entity's Board of Directors or advisory committees.

Effect of Kinase Inhibiting RNase Attenuator (KIRA) Compounds on the Formation of Face-to-Face Dimers of Inositol-Requiring Enzyme 1: Insights from Computational Modeling.

Inositol-requiring enzyme 1α (IRE1α) is a transmembrane dual kinase/ribonuclease protein involved in propagation of the unfolded protein response (UPR). Inositol-requiring enzyme 1α is currently being explored as a potential drug target due to the growing evidence of its role in variety of disease conditions. Upon activation, IRE1 cleaves X-box binding protein 1 (XBP1) mRNA through its RNase domain. Small molecules targeting the kinase site are known to either increase or decrease RNase activity, but the allosteric relationship between the kinase and RNase domains of IRE1α is poorly understood. Subsets of IRE1 kinase inhibitors (known as “KIRA” compounds) bind to the ATP-binding site and allosterically impede the RNase activity. The KIRA compounds are able to regulate the RNase activity by stabilizing the monomeric form of IRE1α. In the present work, computational analysis, protein–protein and protein–ligand docking studies, and molecular dynamics simulations were applied to different IRE1 dimer systems to provide structural insights into the perturbation of IRE1 dimers by small molecules kinase inhibitors that regulate the RNase activity. By analyzing structural deviations, energetic components, and the number of hydrogen bonds in the interface region, we propose that the KIRA inhibitors act at an early stage of IRE1 activation by interfering with IRE1 face-to-face dimer formation thus disabling the activation of the RNase domain. This work sheds light on the mechanism of action of KIRA compounds and may assist in development of further compounds in, for example, cancer therapeutics. The work also provides information on the sequence of events and protein–protein interactions initiating the unfolded protein response.

Human cardiac myosin–binding protein C restricts actin structural dynamics in a cooperative and phosphorylation-sensitive manner

Cardiac myosin–binding protein C (cMyBP-C) is a thick filament-associated protein that influences actin-myosin interactions. cMyBP-C alters myofilament structure and contractile properties in a protein kinase A (PKA) phosphorylation-dependent manner. To determine the effects of cMyBP-C and its phosphorylation on the microsecond rotational dynamics of actin filaments, we attached a phosphorescent probe to F-actin at Cys-374 and performed transient phosphorescence anisotropy (TPA) experiments. Binding of cMyBP-C N-terminal domains (C0–C2) to labeled F-actin reduced rotational flexibility by 20–25°, indicated by increased final anisotropy of the TPA decay. The effects of C0–C2 on actin TPA were highly cooperative (n = ∼8), suggesting that the cMyBP-C N terminus impacts the rotational dynamics of actin spanning seven monomers (i.e. the length of tropomyosin). PKA-mediated phosphorylation of C0–C2 eliminated the cooperative effects on actin flexibility and modestly increased actin rotational rates. Effects of Ser to Asp phosphomimetic substitutions in the M-domain of C0–C2 on actin dynamics only partially recapitulated the phosphorylation effects. C0–C1 (lacking M-domain/C2) similarly exhibited reduced cooperativity, but not as reduced as by phosphorylated C0–C2. These results suggest an important regulatory role of the M-domain in cMyBP-C effects on actin structural dynamics. In contrast, phosphomimetic substitution of the glycogen synthase kinase (GSK3β) site in the Pro/Ala-rich linker of C0–C2 did not significantly affect the TPA results. We conclude that cMyBP-C binding and PKA-mediated phosphorylation can modulate actin dynamics. We propose that these N-terminal cMyBP-C–induced changes in actin dynamics help explain the functional effects of cMyBP-C phosphorylation on actin-myosin interactions.

Cryo-EM structure of a dimeric B-Raf:14-3-3 complex reveals asymmetry in the active sites of B-Raf kinases.

Raf kinases are important cancer drug targets. Paradoxically, many B-Raf inhibitors induce the activation of Raf kinases. Cryo-electron microscopy structural analysis of a phosphorylated B-Raf kinase domain dimer in complex with dimeric 14-3-3, at a resolution of ~3.9 angstroms, shows an asymmetric arrangement in which one kinase is in a canonical "active" conformation. The distal segment of the C-terminal tail of this kinase interacts with, and blocks, the active site of the cognate kinase in this asymmetric arrangement. Deletion of the C-terminal segment reduces Raf activity. The unexpected asymmetric quaternary architecture illustrates how the paradoxical activation of Raf by kinase inhibitors reflects an innate mechanism, with 14-3-3 facilitating inhibition of one kinase while maintaining activity of the other. Conformational modulation of these contacts may provide new opportunities for Raf inhibitor development.

Identification of a New Inhibitor That Stabilizes Interleukin-2-Inducible T-Cell Kinase in Its Inactive Conformation

Interleukin-2-inducible T-cell kinase (ITK) plays an important role in T-cell signaling and is considered a promising drug target. As the ATP binding sites of protein kinases are highly conserved, the design of selective kinase inhibitors remains a challenge. Targeting inactive kinase conformations can address the issue of kinase inhibitor selectivity. It is important for selectivity considerations to identify compounds that stabilize inactive conformations from the primary screen hits. Here we screened a library of 390,000 compounds with an ADP-Glo assay using dephosphorylated ITK. After a surface plasmon resonance (SPR) assay was used to filter out promiscuous inhibitors, 105 hits were confirmed. Next, we used a fluorescent biosensor to enable the detection of conformational changes to identify inactive conformation inhibitors. A single-cysteine-substituted ITK mutant was labeled with acrylodan, and fluorescence emission was monitored. Using a fluorescent biosensor assay, we identified 34 inactive conformation inhibitors from SPR hits. Among them, one compound was bound to a site other than the ATP pocket and exhibited excellent selectivity against a kinase panel. Overall, (1) biochemical screening using dephosphorylated kinase, (2) hit confirmation by SPR assay, and (3) fluorescent biosensor assay that can distinguish inactive compounds provide a useful platform and offer opportunities to identify selective kinase inhibitors.

Cryo-EM reveals active site coordination within a multienzyme pre-rRNA processing complex.

Ribosome assembly is a complex process reliant on the coordination of trans-acting enzymes to produce functional ribosomal subunits and secure the translational capacity of cells. The endoribonuclease (RNase) Las1 and the poly-nucleotide kinase (PNK) Grc3 assemble into a multienzyme complex, herein designated RNase PNK, to orchestrate processing of precursor ribosomal RNA. RNase PNK belongs to the functionally-diverse HEPN nuclease superfamily, whose members rely on distinct cues for nuclease activation. To establish how RNase PNK coordinates its dual enzymatic activities, we solved a series of cryo-electron microscopy structures of Chaetomium thermophilum RNase PNK in multiple conformational states. The structures reveal that RNase PNK adopts a butterfly-like architecture harboring a composite HEPN nuclease active site flanked by discrete RNA kinase sites. We identify two molecular switches that coordinate nuclease and kinase function. Together our structures and corresponding functional studies establish a new mechanism of HEPN nuclease activation essential for ribosome production.

Antibiotic resistance and inhibition mechanism of novel aminoglycoside phosphotransferase APH(5) from B. subtilis subsp. subtilis strain RK.

Bacterial resistance towards aminoglycoside antibiotics mainly occurs because of aminoglycoside phosphotransferases (APHs). It is thus necessary to provide a rationale for focusing inhibitor development against APHs. The nucleotide triphosphate (NTP) binding site of eukaryotic protein kinases (ePKs) is structurally conserved with APHs. However, ePK inhibitors cannot be used against APHs due to cross reactivity. Thus, understanding bacterial resistance at the atomic level could be useful to design new inhibitors against such resistant pathogens. Hence, we carried out in vitro studies of APH from newly deposited multidrug-resistant organism Bacillus subtilis subsp. subtilis strain RK. Enzymatic modification studies of different aminoglycoside antibiotics along with purification and characterization revealed a novel class of APH, i.e., APH(5), with molecular weight 27kDa approximately. Biochemical analysis of virtually screened inhibitor ZINC71575479 by coupled spectrophotometric assay showed complete enzymatic inhibition of purified APH(5). In silico toxicity study comparison of ZINC71575479 with known inhibitor of APH, i.e., tyrphostin AG1478, predicted its acceptable values for 96h fathead minnow LC50, 48h Tetrahymena pyriformis IGC50, oral rat LD50, and developmental toxicity using different QSAR methodologies. Thus, the present study gives novel insight into the aminoglycoside resistance and inhibition mechanism of APH(5) by applying experimental and computational techniques synergistically.

The High Light Response in Arabidopsis Requires the Calcium Sensor Protein CAS, a Target of STN7- and STN8-Mediated Phosphorylation.

Reversible phosphorylation of thylakoid proteins contributes to photoacclimation responses in photosynthetic organisms, enabling the fine-tuning of light harvesting under changing light conditions and promoting the onset of photoprotective processes. However, the precise functional role of many of the described phosphorylation events on thylakoid proteins remains elusive. The calcium sensor receptor protein (CAS) has previously been indicated as one of the targets of the state transition kinase 8 (STN8). Here we show that in Arabidopsis thaliana, CAS is also phosphorylated by the state transition kinase 7 (STN7), as well as by another, so-far unknown, Ca2+-dependent kinase. Phosphoproteomics analysis and in vitro phosphorylation assays on CAS variants identified the phylogenetically conserved residues Thr-376, Ser-378, and Thr-380 as the major phosphorylation sites of the STN kinases. Spectroscopic analyses of chlorophyll fluorescence emission at 77K further showed that, while the cas mutant is not affected in state transition, it displays a persistent strong excitation of PSI under high light exposure, similar to the phenotype previously observed in other mutants defective in photoacclimation mechanisms. Together with the observation of a strong concomitant phosphorylation of light harvesting complex II (LHCII) and photosynthetic core proteins under high irradiance in the cas mutant this suggests a role for CAS in the STN7/STN8/TAP38 network of phosphorylation-mediated photoacclimation processes in Arabidopsis.

Rational creation and systematic analysis of cervical cancer kinase-inhibitor binding profile.

The kinase-regulatory cell signaling networks play a central role in the pathogenesis of human cervical cancer (hCC). However, only few kinase inhibitors have been successfully developed for treatment of this cancer to date. Considering that the active sites of protein kinases are highly conserved and small-molecule inhibitors should generally exhibit high promiscuity and broad specificity across the hCC-related kinase array, it is supposed that the established kinase targets of hCC can be targeted unexpectedly by certain noncognate kinase inhibitors. This provides a novel idea to practice the new uses for old drugs in anti-cancer chemotherapy. Here, we create a systematic kinase-inhibitor binding profile in a high-throughput manner by molecular docking and consensus scoring, where the kinases have been collected as therapeutic targets of hCC and the inhibitors are reversible, ATP-competitive and readily available. The docking/scoring scheme is tested rigorously with structure-solved and affinity-known kinase-inhibitor complex samples, which is later demonstrated to be effective in inferring unexpected inhibitor response to hCC-related kinases. Few promising kinase-inhibitor pairs are identified from the profile and tested experimentally at cellular and molecular levels. It is found that the kinase-inhibitor promiscuity is a common phenomenon but only few can interaction effectively and inhibit potently. In addition, the high-scoring inhibitors generally exhibit good suppressing potency on hCC cell viability as compared to those low-scoring ones, imparting that the created profile can well reflect the tumor cytotoxicity of noncognate kinase inhibitors. A further kinase assay suggests that the ErbB family kinases are the potential targets of these high-scoring inhibitors, with noncognate inhibitory activity up to nanomolar level. Structure analysis reveals that the nonbonded interactions of potent noncogante kinase-inhibitor binding can divided into a polar tail and a nonpolar lobe, which confer specificity and stability to the binding, respectively.

Mg2+ regulation of kinase signaling and immune function.

Mg2+ is required at micromolar concentrations as a cofactor for ATP, enzymatic reactions, and other biological processes. We show that decreased extracellular Mg2+ reduced intracellular Mg2+ levels and impaired the Ca2+ flux, activation marker up-regulation, and proliferation after T cell receptor (TCR) stimulation. Reduced Mg2+ specifically impairs TCR signal transduction by IL-2-inducible T cell kinase (ITK) due to a requirement for a regulatory Mg2+ in the catalytic pocket of ITK. We also show that altered catalytic efficiency by millimolar changes in free basal Mg2+ is an unrecognized but conserved feature of other serine/threonine and tyrosine kinases, suggesting a Mg2+ regulatory paradigm of kinase function. Finally, a reduced serum Mg2+ concentration in mice causes an impaired CD8+ T cell response to influenza A virus infection, reduces T cell activation, and exacerbates morbidity. Thus, Mg2+ directly regulates the active site of specific kinases during T cell responses, and maintaining a high serum Mg2+ concentration is important for antiviral immunity in otherwise healthy animals.

Kinase Atlas: Druggability Analysis of Potential Allosteric Sites in Kinases

The inhibition of kinases has been pursued by the pharmaceutical industry for over 20 years. While the locations of the sites that bind type II and III inhibitors at or near the adenosine 5'-triphosphate binding sites are well defined, the literature describes 10 different regions that were reported as regulatory hot spots in some kinases and thus are potential target sites for type IV inhibitors. Kinase Atlas is a systematic collection of binding hot spots located at the above ten sites in 4910 structures of 376 distinct kinases available in the Protein Data Bank. The hot spots are identified by FTMap, a computational analogue of experimental fragment screening. Users of Kinase Atlas ( https://kinase-atlas.bu.edu ) may view summarized results for all structures of a particular kinase, such as which binding sites are present and how druggable they are, or they may view hot spot information for a particular kinase structure of interest.

Targeting Dynamic ATP-Binding Site Features Allows Discrimination between Highly Homologous Protein Kinases.

ATP-competitive inhibitors that demonstrate exquisite selectivity for specific members of the human kinome have been developed. Despite this success, the identification of highly selective inhibitors is still very challenging, and it is often not possible to rationally engineer selectivity between the ATP-binding sites of kinases, especially among closely related family members. Src-family kinases (SFKs) are a highly homologous family of eight multidomain, nonreceptor tyrosine kinases that play general and specialized roles in numerous cellular processes. The high sequence and functional similarities between SFK members make it hard to rationalize how selectivity can be gained with inhibitors that target the ATP-binding site. Here, we describe the development of a series of inhibitors that are highly selective for the ATP-binding sites of the SFKs Lyn and Hck over other SFKs. By biochemically characterizing how these selective ATP-competitive inhibitors allosterically influence the global conformation of SFKs, we demonstrate that they most likely interact with a binding pocket created by the movement of the conformationally flexible helix αC in the ATP-binding site. With a series of sequence swap experiments, we show that sensitivity to this class of selective inhibitors is due to the identity of residues that control the conformational flexibility of helix αC rather than any specific ATP-binding site interactions. Thus, the ATP-binding sites of highly homologous kinases can be discriminated by targeting heterogeneity within conformationally flexible regions.

Hematopoietic cytokines mediate resistance to targeted therapy in FLT3-ITD acute myeloid leukemia

AbstractActivating mutations in Fms-like tyrosine kinase 3 (FLT3) occur in ∼30% of adult cases of acute myeloid leukemia (AML). Selective second- and third-generation FLT3 inhibitors have shown significant clinical activity in patients with relapsed FLT3-mutant AML. However, clearance of FLT3-mutant clones does not consistently occur, and disease will progress in most patients after an initial response. This scenario challenges the model of FLT3-mutant AML being oncogene addicted, and it suggests that redundant signaling pathways regulate AML cell survival after FLT3 inhibition. We show that primary FLT3-mutant AML cells escape apoptosis induced by FLT3 inhibition in vitro in the presence of cytokines produced normally in the bone marrow, particularly granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-3 (IL-3). Despite reactivating canonical FLT3-signaling pathways, GM-CSF and IL-3 maintain cell survival without rescuing proliferation. Cytokine-mediated resistance through GM-CSF and IL-3 is dependent on JAK kinase, STAT5, and proviral integration site of Moloney murine leukemia virus (PIM) but not MAPK or mammalian target of rapamycin signaling. Cotreatment with FLT3 inhibitors and inhibitors of JAK or PIM kinases blocks GM-CSF and IL-3 rescue of cell survival in vitro and in vivo. Altogether, these data provide a strong rationale for combination therapy with FLT3 inhibitors to potentially improve clinical responses in AML.

Restricting food availability to the active period restores rhythmic activation of aortic NOS3 in high fat diet fed mice

Timing of food intake increases the risk for cardiometabolic disease. A chronic high fat diet (HFD) leads to endothelial dysfunction with loss of nitric oxide (NO) signaling in mice. Both endothelial function and vascular resistance display circadian variation with endothelial‐dependent relaxation and NO signaling peaking during the active period, while vascular resistance peaks shortly after waking. We hypothesized that HFD leads to a loss of circadian rhythm in endothelial NO synthase (NOS3) activation that is restored by restricting food availability to the active period. Mice (male 8‐week old, C57BL/6J) were given normal diet (ND; 10% fat) or HFD (45% fat) for 20 weeks ad libitum. Restricted feeding (RF; food availability only during the active phase) was enforced in half the mice during the final 2 weeks of feeding. Aortae were harvested at 4‐hour intervals over a 24‐hour period (ZT0 at 7AM; ZT12 at 7PM). NOS3 (total and phosphorylation at serine 1177 (pNOS3(S1177)) was assessed by Western blotting. NOS3 expression was unchanged with time in all 4 groups. In mice on ad libitum ND, pNOS3(S1117) expression displayed a diurnal variation with peak expression at ZT17. HFD mice displayed a significantly blunted amplitude and an earlier acrophase of the diurnal rhythm in pNOS3(S1117) expression by cosinor analysis (amplitude: HFD: 1.4±0.4 rdu; ND: 4.8±0.6 rdu, n=3, p=0.01; acrophase: HFD: 10.3±1.6 hrs, ND: 15.7±1.4 hrs, n=3, p=0.06). RF with HFD restored the acrophase of the pNOS3(S1177) rhythm (HFD: 10.3±1.6 rdu; HFD+RF: 16.4±1.4 rdu, n=3, p=0.04). To further examine the mechanism of NOS3 activation, we determined the expression of AMP kinase (AMPK), Akt kinase (Akt), and phosphorylation sites on each kinase at ZT5 and ZT17. Interestingly, RF in HFD mice significantly increased pAMPK(T172) abundance at ZT17 (n=4–5, p=0.02) compared to ad libitum HFD mice. Expression of AMPK, Akt, and Akt phosphorylation sites were unaffected by RF on ND or HFD. We further examined the 24 hour mean arterial pressure (MAP), heart rate (HR), and locomotor activity by telemetry. MAP was similar in all 4 groups (n=5–6, ND: 113±1 m Hg; ND+RF: 109±4 mmHg; HFD: 118±3 mmHg; HFD+RF: 114±2 mmHg). HR was increased with HFD and reduced in mice exposed to HFD+RF similar to ND mice (n=5–6, p<0.05). Locomotor activity was significantly decreased in HFD and HFD+RF mice compared to ND (n=5–6, p<0.05). In summary, aortic NOS3 activation displays a rhythm peaking during the active period at ZT17. HFD depresses the rhythm of aortic NOS3 activation, while RF restores the rhythm with an associated activation of AMP kinase at ZT17. We propose that time restricted feeding may lower the incidence of vascular disease through maintenance of rhythmic vascular NOS3 activation.Support or Funding InformationSupported by T32 DK007545 to PP, an AHA pre‐doctoral fellowship (18PRE33990345) to DZ, P01 HL069999 to JSP and DMP, and P01 HL136267 to JSP, EWI, and DMP.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Targeting MAPK phosphorylation of Connexin43 provides neuroprotection in stroke.

Connexin43 (Cx43) function is influenced by kinases that phosphorylate specific serine sites located near its C-terminus. Stroke is a powerful inducer of kinase activity, but its effect on Cx43 is unknown. We investigated the impact of wild-type (WT) and knock-in Cx43 with serine to alanine mutations at the protein kinase C (PKC) site Cx43S368A, the casein kinase 1 (CK1) sites Cx43S325A/328Y/330A, and the mitogen-activated protein kinase (MAPK) sites Cx43S255/262/279/282A (MK4) on a permanent middle cerebral artery occlusion (pMCAO) stroke model. We demonstrate that MK4 transgenic animals exhibit a significant decrease in infarct volume that was associated with improvement in behavioral performance. An increase in astrocyte reactivity with a concomitant decrease in microglial reactivity was observed in MK4 mice. In contrast to WT, MK4 astrocytes displayed reduced Cx43 hemichannel activity. Pharmacological blockade of Cx43 hemichannels with TAT-Gap19 also significantly decreased infarct volume in WT animals. This study provides novel molecular insights and charts new avenues for therapeutic intervention associated with Cx43 function.