Chr21 protein-protein interactions: enrichment in proteins involved in intellectual disability, autism, and late-onset Alzheimer's disease.

Down syndrome (DS) is caused by human chromosome 21 (HSA21) trisomy. It is characterized by a poorly understood intellectual disability (ID). We studied two mouse models of DS, one with an extra copy of the <i>Dyrk1A</i> gene (189N3) and the other with an extra copy of the mouse Chr16 syntenic region (Dp(16)1Yey). RNA-seq analysis of the transcripts deregulated in the embryonic hippocampus revealed an enrichment in genes associated with chromatin for the 189N3 model, and synapses for the Dp(16)1Yey model. A large-scale yeast two-hybrid screen (82 different screens, including 72 HSA21 baits and 10 rebounds) of a human brain library containing at least 10⁷ independent fragments identified 1,949 novel protein-protein interactions. The direct interactors of HSA21 baits and rebounds were significantly enriched in ID-related genes (<i>P</i>-value &lt; 2.29 × 10^-8). Proximity ligation assays showed that some of the proteins encoded by HSA21 were located at the dendritic spine postsynaptic density, in a protein network at the dendritic spine postsynapse. We located HSA21 DYRK1A and DSCAM, mutations of which increase the risk of autism spectrum disorder (ASD) 20-fold, in this postsynaptic network. We found that an intracellular domain of DSCAM bound either DLGs, which are multimeric scaffolds comprising receptors, ion channels and associated signaling proteins, or DYRK1A. The DYRK1A-DSCAM interaction domain is conserved in <i>Drosophila</i> and humans. The postsynaptic network was found to be enriched in proteins associated with ARC-related synaptic plasticity, ASD, and late-onset Alzheimer's disease. These results highlight links between DS and brain diseases with a complex genetic basis.

Discovery of a putative blood-based protein signature associated with response to ALK tyrosine kinase inhibition.

BACKGROUND: ALK tyrosine kinase inhibition has become a mainstay in the clinical management of ALK fusion positive NSCLC patients. Although ALK mutations can reliably predict the likelihood of response to ALK tyrosine kinase inhibitors (TKIs) such as crizotinib, they cannot reliably predict response duration or intrinsic/extrinsic therapeutic resistance. To further refine the application of personalized medicine in this indication, this study aimed to identify prognostic proteomic biomarkers in ALK fusion positive NSCLC patients to crizotinib. METHODS: Twenty-four patients with advanced NSCLC harboring ALK fusion were administered crizotinib in a phase IV trial which included blood sampling prior to treatment. Targeted proteomics of 327 proteins using MRM-MS was used to measure plasma levels at baseline (including pre-treatment and early treatment blood samples) and assess potential clinical association. RESULTS: Patients were categorized by duration of response: long-term responders [PFS ≥ 24 months (n = 7)], normal responders [3 < PFS < 24 months (n = 10)] and poor responders [PFS ≤ 3 months (n = 5)]. Several proteins were identified as differentially expressed between long-term responders and poor responders, including DPP4, KIT and LUM. Next, using machine learning algorithms, we evaluated the classification potential of 40 proteins. Finally, by integrating the different analytic methods, we selected 22 proteins as potential candidates for a blood-based prognostic signature of response to crizotinib in NSCLC patients harboring ALK fusion. CONCLUSION: In conjunction with ALK mutation, the expression of this proteomic signature may represent a liquid biopsy-based marker of long-term response to crizotinib in NSCLC. Expanding the utility of prognostic biomarkers of response duration could influence choice of therapy, therapeutic sequencing, and potentially the need for alternative or combination therapy.Trial registration ClinicalTrials.gov, NCT02041468. Registered 22 January 2014, https://clinicaltrials.gov/ct2/show/NCT02041468?term=NCT02041468&rank=1.

HENA, heterogeneous network-based data set for Alzheimer's disease.

Alzheimer's disease and other types of dementia are the top cause for disabilities in later life and various types of experiments have been performed to understand the underlying mechanisms of the disease with the aim of coming up with potential drug targets. These experiments have been carried out by scientists working in different domains such as proteomics, molecular biology, clinical diagnostics and genomics. The results of such experiments are stored in the databases designed for collecting data of similar types. However, in order to get a systematic view of the disease from these independent but complementary data sets, it is necessary to combine them. In this study we describe a heterogeneous network-based data set for Alzheimer's disease (HENA). Additionally, we demonstrate the application of state-of-the-art graph convolutional networks, i.e. deep learning methods for the analysis of such large heterogeneous biological data sets. We expect HENA to allow scientists to explore and analyze their own results in the broader context of Alzheimer's disease research.

Structural insights into the functional versatility of an FHA domain protein in mycobacterial signaling.

Forkhead-associated (FHA) domains are modules that bind to phosphothreonine (pThr) residues in signaling cascades. The FHA-containing mycobacterial protein GarA is a central element of a phosphorylation-dependent signaling pathway that redirects metabolic flux in response to amino acid starvation or cell growth requirements. GarA acts as a phosphorylation-dependent ON/OFF molecular switch. In its nonphosphorylated ON state, the GarA FHA domain engages in phosphorylation-independent interactions with various metabolic enzymes that orchestrate nitrogen flow, such as 2-oxoglutarate decarboxylase (KGD). However, phosphorylation at the GarA N-terminal region by the protein kinase PknB or PknG triggers autoinhibition through the intramolecular association of the N-terminal domain with the FHA domain, thus blocking all downstream interactions. To investigate these different FHA binding modes, we solved the crystal structures of the mycobacterial upstream (phosphorylation-dependent) complex PknB-GarA and the downstream (phosphorylation-independent) complex GarA-KGD. Our results show that the phosphorylated activation loop of PknB serves as a docking site to recruit GarA through canonical FHA-pThr interactions. However, the same GarA FHA-binding pocket targets an allosteric site on nonphosphorylated KGD, where a key element of recognition is a phosphomimetic aspartate. Further enzymatic and mutagenesis studies revealed that GarA acted as a dynamic allosteric inhibitor of KGD by preventing crucial motions in KGD that are necessary for catalysis. Our results provide evidence for physiological phosphomimetics, supporting numerous mutagenesis studies using such approaches, and illustrate how evolution can shape a single FHA-binding pocket to specifically interact with multiple phosphorylated and nonphosphorylated protein partners.

GmZPR3d Interacts with GmHD-ZIP III Proteins and Regulates Soybean Root and Nodule Vascular Development.

Fabaceans produce two major classes of symbiotic nodules: the indeterminate type characterized by a persistent meristem, and the determinate type that lacks a persistent meristem. The class III homeodomain leucine zipper (HD-ZIP III) transcription factor family influence development of multiple lateral organs and meristem maintenance, but their role in determinate nodule development is not known. HD-ZIP III protein activity is post-translationally regulated by members of the small leucine zipper protein (ZPR) family in arabidopsis. We characterized the ZPR gene family in soybean and evaluated their ability to interact with two key members of GmHD-ZIP III family through yeast two-hybrid assays. GmZPR3d displayed the strongest interaction with GmHD-ZIP III-2 among the different pairs evaluated. GmHD-ZIP III-1, -2, and GmZPR3d showed overlapping expression patterns in the root stele and in nodule parenchyma tissues. Over-expression of GmZPR3d resulted in ectopic root secondary xylem formation, and enhanced expression of vessel-specific master switch genes in soybean. The nodules in ZPR3d over-expressing roots were larger in size, had a relatively larger central zone and displayed increased nodule vascular branching. The results from this study point to a key role for GmZPR3d in soybean root and nodule development.

LPS-Induced Inflammation Abolishes the Effect of DYRK1A on IkB Stability in the Brain of Mice.

Down syndrome is characterized by premature aging and dementia with neurological features that mimic those found in Alzheimer's disease. This pathology in Down syndrome could be related to inflammation, which plays a role in other neurodegenerative diseases. We previously found a link between the NFkB pathway, long considered a prototypical proinflammatory signaling pathway, and the dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A). DYRK1A is associated with early onset of Alzheimer's disease in Down syndrome patients. Here, we sought to determine the role of DYRK1A on regulation of the NFkB pathway in the mouse brain. We found that over-expression of Dyrk1A (on a C57BL/6J background) stabilizes IκBα protein levels by inhibition of calpain activity and increases cytoplasmic p65 sequestration in the mouse brain. In contrast, Dyrk1A-deficient mice (on a CD1 background) have decreased IκBα protein levels with an increased calpain activity and decreased cytoplasmic p65 sequestration in the brain. Taken together, our results demonstrate a role of DYRK1A in regulation of the NFkB pathway. However, decreased IκBα and DYRK1A protein levels associated with an increased calpain activity were found in the brains of mice over-expressing Dyrk1A after lipopolysaccharide treatment. Although inflammation induced by lipopolysaccharide treatment has a positive effect on calpastatin and a negative effect on DYRK1A protein level, a positive effect on microglial activation is maintained in the brains of mice over-expressing Dyrk1A.

Bidirectional Allosteric Communication between the ATP-Binding Site and the Regulatory PIF Pocket in PDK1 Protein Kinase.

Allostery is a phenomenon observed in many proteins where binding of a macromolecular partner or a small-molecule ligand at one location leads to specific perturbations at a site not in direct contact with the region where the binding occurs. The list of proteins under allosteric regulation includes AGC protein kinases. AGC kinases have a conserved allosteric site, the phosphoinositide-dependent protein kinase 1 (PDK1)-interacting fragment (PIF) pocket, which regulates protein ATP-binding, activity, and interaction with substrates. In this study, we identify small molecules that bind to the ATP-binding site and affect the PIF pocket of AGC kinase family members, PDK1 and Aurora kinase. We describe the mechanistic details and show that although PDK1 and Aurora kinase inhibitors bind to the conserved ATP-binding site, they differentially modulate physiological interactions at the PIF-pocket site. Our work outlines a strategy for developing bidirectional small-molecule allosteric modulators of protein kinases and other signaling proteins.

Use of a fluorescent ATP analog to probe the allosteric conformational change in the active site of the protein kinase PDK1.

There is growing interest in exploring allosteric sites on proteins for drug discovery. At the center of the regulation of many protein kinases from the AGC family there is an allosteric site termed "PIF-pocket." The regulated binding of a C-terminal region of the kinase to the PIF-pocket, within the small lobe of the catalytic core, modulates the activity of AGC kinases. Small compounds that bind to the PIF-pocket can mimic its physiological mechanism of regulation and modulate the kinase activity in vitro, e.g., small compounds can activate the phosphoinositide-dependent protein kinase 1 (PDK1). Compounds binding to an allosteric site on a protein kinase may produce conformational changes at the ATP-binding site within the active site of the kinase domain. We here describe a fluorescent method using the ATP analog TNP-ATP that allows evaluating the allosteric conformational changes at the ATP-binding site of PDK1 triggered by small compounds binding to the PIF-pocket.

Allosteric regulation of protein kinase PKCζ by the N-terminal C1 domain and small compounds to the PIF-pocket.

Protein kinases are key mediators of cellular signaling, and therefore, their activities are tightly controlled. AGC kinases are regulated by phosphorylation and by N- and C-terminal regions. Here, we studied the molecular mechanism of inhibition of atypical PKCζ and found that the inhibition by the N-terminal region cannot be explained by a simple pseudosubstrate inhibitory mechanism. Notably, we found that the C1 domain allosterically inhibits PKCζ activity and verified an allosteric communication between the PIF-pocket of atypical PKCs and the binding site of the C1 domain. Finally, we developed low-molecular-weight compounds that bind to the PIF-pocket and allosterically inhibit PKCζ activity. This work establishes a central role for the PIF-pocket on the regulation of PKCζ and allows us to envisage development of drugs targeting the PIF-pocket that can either activate or inhibit AGC kinases.

Structure and allosteric effects of low-molecular-weight activators on the protein kinase PDK1.

Protein phosphorylation transduces a large set of intracellular signals. One mechanism by which phosphorylation mediates signal transduction is by prompting conformational changes in the target protein or interacting proteins. Previous work described an allosteric site mediating phosphorylation-dependent activation of AGC kinases. The AGC kinase PDK1 is activated by the docking of a phosphorylated motif from substrates. Here we present the crystallography of PDK1 bound to a rationally developed low-molecular-weight activator and describe the conformational changes induced by small compounds in the crystal and in solution using a fluorescence-based assay and deuterium exchange experiments. Our results indicate that the binding of the compound produces local changes at the target site, the PIF binding pocket, and also allosteric changes at the ATP binding site and the activation loop. Altogether, we present molecular details of the allosteric changes induced by small compounds that trigger the activation of PDK1 through mimicry of phosphorylation-dependent conformational changes.

3,5-Diphenylpent-2-enoic acids as allosteric activators of the protein kinase PDK1: structure-activity relationships and thermodynamic characterization of binding as paradigms for PIF-binding pocket-targeting compounds.

The modulation of protein kinase activities by low molecular weight compounds is a major goal of current pharmaceutical developments. In this line, important efforts are directed to the development of drugs targeting the conserved ATP binding site. However, there is very little experience on targeting allosteric, regulatory sites, different from the ATP binding site, in protein kinases. Here we describe the synthesis, cell-free activation potency, and calorimetric binding analysis of 3,5-diphenylpent-2-enoic acids and derivatives as allosteric modulators of the phosphoinositide-dependent kinase-1 (PDK1) catalytic activity. Our SAR results combined with thermodynamic binding analyses revealed both favorable binding enthalpy and entropy and confirmed the PIF-binding pocket of PDK1 as a druggable site. In conclusion, we defined the minimal structural requirements for compounds to bind to the PIF-binding pocket and to act as allosteric modulators and identified two new lead structures (12Z and 13Z) with predominating binding enthalpy.

Allosteric activation of the protein kinase PDK1 with low molecular weight compounds.

Organisms rely heavily on protein phosphorylation to transduce intracellular signals. The phosphorylation of a protein often induces conformational changes, which are responsible for triggering downstream cellular events. Protein kinases are themselves frequently regulated by phosphorylation. Recently, we and others proposed the molecular mechanism by which phosphorylation at a hydrophobic motif (HM) regulates the conformation and activity of many members of the AGC group of protein kinases. Here we have developed specific, low molecular weight compounds, which target the HM/PIF-pocket and have the ability to allosterically activate phosphoinositide-dependent protein kinase 1 (PDK1) by modulating the phosphorylation-dependent conformational transition. The mechanism of action of these compounds was characterized by mutagenesis of PDK1, synthesis of compound analogs, interaction-displacement studies and isothermal titration calorimetry experiments. Our results raise the possibility of developing drugs that target the AGC kinases via a novel mode of action and may inspire future rational development of compounds with the ability to modulate phosphorylation-dependent conformational transitions in other proteins.

Tissue-specific and inducible Cre-mediated recombination in the gut epithelium.

We generated two complementary systems for Cre-mediated recombination of target genes in the mouse digestive epithelium and tested them with a Cre-reporter mouse strain. Cre was expressed under the control of a 9 kb regulatory region of the murine villin gene (vil-Cre). Genetic recombination was initiated at embryonic day (E) 9 in the visceral endoderm, and by E12.5 in the entire intestinal epithelium, but not in other tissues. Cre expression was maintained throughout adulthood. Furthermore, transgenic mice bearing a tamoxifen-dependent Cre recombinase (vil-Cre-ERT2) expressed under the control of the villin promoter were created to perform targeted spatiotemporally controlled somatic recombination. After tamoxifen treatment, recombination was detectable throughout the digestive epithelium. The recombined locus persisted for 60 days after tamoxifen administration, despite rapid intestinal cell renewal, indicating that epithelial progenitor cells had been targeted. The villin-Cre and villin-Cre-ERT2 mice provide valuable tools for studies of cell lineage allocation and gene function in the developing and adult intestine.