Binding in vitro of multiple cellular proteins to immunoglobulin heavy-chain enhancer DNA

Seven protein-binding sites on the immunoglobulin heavy-chain (IgH) enhancer element have been identified by exonuclease III protection and gel retardation assays. It appears that the seven sites bind a minimum of four separate proteins. Three of these proteins also bind to other enhancers or promoters, but one protein seems to recognize exclusively IgH enhancer sequences. A complex of four binding sites, recognized by different proteins, is located within one 80-base-pair region of IgH enhancer DNA. Close juxtaposition of enhancer proteins may allow protein-protein interactions or be part of a mechanism for modulating enhancer protein activity. All IgH enhancer-binding proteins identified in this study were found in extracts from nonlymphoid as well as lymphoid cells. These data provide the first direct evidence that multiple proteins bind to enhancer elements and that while some of these proteins recognize common elements of many enhancers, others have more limited specificities.

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A cell-based screening method using an intracellular antibody for discovering small molecules targeting the translocation protein LMO2

Science Advances ◽

10.1126/sciadv.abg1950 ◽

2021 ◽

Vol 7 (15) ◽

pp. eabg1950

Author(s):

Nicolas Bery ◽

Carole J.R. Bataille ◽

Angela Russell ◽

Angela Hayes ◽

Florence Raynaud ◽

...

Keyword(s):

Small Molecules ◽

Protein Interactions ◽

Binding Sites ◽

Screening Method ◽

Chromosomal Translocation ◽

Resonance Method ◽

Protein Protein Interactions ◽

Intracellular Antibody ◽

A Cell

Intracellular antibodies are tools that can be used directly for target validation by interfering with properties like protein-protein interactions. An alternative use of intracellular antibodies in drug discovery is developing small-molecule surrogates using antibody-derived (Abd) technology. We previously used this strategy with an in vitro competitive surface plasmon resonance method that relied on high-affinity antibody fragments to obtain RAS-binding compounds. We now describe a novel implementation of the Abd method with a cell-based intracellular antibody–guided screening method that we have applied to the chromosomal translocation protein LMO2. We have identified a chemical series of anti-LMO2 Abd compounds that bind at the same LMO2 location as the inhibitory anti-LMO2 intracellular antibody combining site. Intracellular antibodies could therefore be used in cell-based screens to identify chemical surrogates of their binding sites and potentially be applied to any challenging proteins, such as transcription factors that have been considered undruggable.

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Involvement of a second lymphoid-specific enhancer element in the regulation of immunoglobulin heavy-chain gene expression

Molecular and Cellular Biology ◽

10.1128/mcb.10.6.3155-3162.1990 ◽

1990 ◽

Vol 10 (6) ◽

pp. 3155-3162

Author(s):

T A Libermann ◽

M Lenardo ◽

D Baltimore

Keyword(s):

Binding Site ◽

Heavy Chain ◽

Critical Role ◽

Immunoglobulin Heavy Chain ◽

Lymphoid Cells ◽

Chain Gene ◽

Specific Expression ◽

Enhancer Activity ◽

Enhancer Element ◽

Dna Motif

To determine whether enhancer elements in addition to the highly conserved octamer (OCTA)-nucleotide motif are important for lymphoid-specific expression of the immunoglobulin heavy-chain (IgH) gene, we have investigated the effect of mutating the binding site for a putative additional lymphoid-specific transcription factor, designated NF-microB, in the murine IgH enhancer. We demonstrate that the NF-microB-binding site plays a critical role in the IgH enhancer, because mutation of the microB DNA motif decreased transcriptional activity of the IgH enhancer in cells of the B-cell lineage but not in nonlymphoid cells. This effect was comparable to or even stronger than the effect of a mutation in the OCTA site. Moreover, combined mutation of both microB and OCTA sites further reduced enhancer activity in lymphoid cells. Interestingly, alteration of either the microB or E3 site in a 70-base-pair fragment of the IgH enhancer that lacks the binding site for OCTA abolished enhancer activity in lymphoid cells completely. Nevertheless, a multimer of the microB motif alone showed no enhancer activity. DNase footprinting analysis corroborated the functional data showing that a lymphoid-specific protein binds to the microB DNA motif. Our results suggest that the microB element is a new crucial element important for lymphoid-specific expression of the IgH gene but that interaction with another enhancer element is essential for its activity.

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Norstictic acid is a selective allosteric transcriptional regulator

10.1101/2021.03.26.437253 ◽

2021 ◽

Author(s):

Julie M Garlick ◽

Steven M Sturlis ◽

Paul A Bruno ◽

Joel A Yates ◽

Amanda Peiffer ◽

...

Keyword(s):

Binding Site ◽

Protein Interactions ◽

Binding Sites ◽

Triple Negative ◽

Transcriptional Coactivator ◽

Protein Protein Interactions ◽

Ppi Networks ◽

Binding Surface ◽

Inhibitor Discovery

Inhibitors of transcriptional protein-protein interactions (PPIs) have high value both as tools and for therapeutic applications. The PPI network mediated by the transcriptional coactivator Med25, for example, regulates stress-response and motility pathways and dysregulation of the PPI networks contributes to oncogenesis and metastasis. The canonical transcription factor binding sites within Med25 are large (~900 square angstroms) and have little topology, and thus do not present an array of attractive small-molecule binding sites for inhibitor discovery. Here we demonstrate that the depsidone natural product norstictic acid functions through an alternative binding site to block Med25-transcriptional activator PPIs in vitro and in cell culture. Norstictic acid targets a binding site comprised of a highly dynamic loop flanking one canonical binding surface and in doing so, it both orthosterically and allosterically alters Med25-driven transcription in a patient-derived model of triple negative breast cancer. These results highlight the potential of Med25 as a therapeutic target as well as the inhibitor discovery opportunities presented by structurally dynamic loops within otherwise challenging proteins.

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Involvement of a second lymphoid-specific enhancer element in the regulation of immunoglobulin heavy-chain gene expression.

Molecular and Cellular Biology ◽

10.1128/mcb.10.6.3155 ◽

1990 ◽

Vol 10 (6) ◽

pp. 3155-3162 ◽

Cited By ~ 23

Author(s):

T A Libermann ◽

M Lenardo ◽

D Baltimore

Keyword(s):

Binding Site ◽

Heavy Chain ◽

Critical Role ◽

Immunoglobulin Heavy Chain ◽

Lymphoid Cells ◽

Chain Gene ◽

Specific Expression ◽

Enhancer Activity ◽

Enhancer Element ◽

Dna Motif

To determine whether enhancer elements in addition to the highly conserved octamer (OCTA)-nucleotide motif are important for lymphoid-specific expression of the immunoglobulin heavy-chain (IgH) gene, we have investigated the effect of mutating the binding site for a putative additional lymphoid-specific transcription factor, designated NF-microB, in the murine IgH enhancer. We demonstrate that the NF-microB-binding site plays a critical role in the IgH enhancer, because mutation of the microB DNA motif decreased transcriptional activity of the IgH enhancer in cells of the B-cell lineage but not in nonlymphoid cells. This effect was comparable to or even stronger than the effect of a mutation in the OCTA site. Moreover, combined mutation of both microB and OCTA sites further reduced enhancer activity in lymphoid cells. Interestingly, alteration of either the microB or E3 site in a 70-base-pair fragment of the IgH enhancer that lacks the binding site for OCTA abolished enhancer activity in lymphoid cells completely. Nevertheless, a multimer of the microB motif alone showed no enhancer activity. DNase footprinting analysis corroborated the functional data showing that a lymphoid-specific protein binds to the microB DNA motif. Our results suggest that the microB element is a new crucial element important for lymphoid-specific expression of the IgH gene but that interaction with another enhancer element is essential for its activity.

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Synthesis of Novel Suramin Analogs With Anti-Proliferative Activity via FGF1 and FGFRD2 Blockade

Frontiers in Chemistry ◽

10.3389/fchem.2021.764200 ◽

2022 ◽

Vol 9 ◽

Author(s):

Nuzhat Parveen ◽

Yan-Liang Lin ◽

Ruey-Hwang Chou ◽

Chung-Ming Sun ◽

Chin Yu

Keyword(s):

Cell Proliferation ◽

Protein Interactions ◽

Binding Sites ◽

Proliferative Activity ◽

Three Dimensional ◽

Cancer Cell Line ◽

Protein Protein Interactions ◽

Docking Simulations ◽

Three Dimensional Models

A promising approach in cancer therapy is the inhibition of cell proliferation using small molecules. In this study, we report the synthesis of suramin derivatives and their applications. We used NMR spectroscopy and docking simulations to confirm binding sites and three-dimensional models of the ligand-protein complex. The WST-1 assay was used to assess cell viability and cell proliferation in vitro to evaluate the inhibition of protein–protein interactions and to investigate the anti-proliferative activities in a breast cancer cell line. All the suramin derivatives showed anti-proliferative activity by blocking FGF1 binding to its receptor FGFRD2. The dissociation constant was measured by fluorescence spectroscopy. The suramin compound derivatives synthesized herein show potential as novel therapeutic agents for their anti-proliferative activity via the inhibition of protein–protein interactions. The cytotoxicity of these suramin derivatives was lower than that of the parent suramin compound, which may be considered a significant advancement in this field. Thus, these novel suramin derivatives may be considered superior anti-metastasis molecules than those of suramin.

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In Silico Evaluation of Cyclophilin Inhibitors as Potential Treatment for SARS-CoV-2

Open Forum Infectious Diseases ◽

10.1093/ofid/ofab189 ◽

2021 ◽

Author(s):

Kyle Laurie ◽

David Holcomb ◽

Jacob Kames ◽

Anton A Komar ◽

Michael DiCuccio ◽

...

Keyword(s):

Protein Interactions ◽

Cyclophilin A ◽

Coagulation Factors ◽

Mortality Rates ◽

Protein Protein Interactions ◽

Protein Activity ◽

N Protein ◽

Isomerase Activity ◽

Coagulation Proteins

Abstract The advent of SARS-CoV-2 provoked researchers to propose multiple antiviral strategies to improve patients' outcomes. Studies provide evidence that Cyclosporine A (CsA) decreases SARS-CoV-2 replication in vitro, and decreases mortality rates of COVID-19 patients. CsA binds Cyclophilins, which isomerize prolines, affecting viral protein activity. We investigated the proline composition from various Coronavirus proteomes to identify proteins that may critically rely on cyclophilin’s peptidyl-proline isomerase activity and found the Nucleocapsid (N) protein significantly depends on Cyclophilin A (CyPA). We modeled CyPA and N protein interactions to demonstrate the N protein as a potential indirect therapeutic target of CsA, which we propose may impede coronavirus replication by obstructing nucleocapsid folding. Finally, we analyzed literature and protein-protein interactions, finding evidence that, by inhibiting CyPA, CsA may impact coagulation proteins and hemostasis. Despite CsA’s promising antiviral characteristics, the interactions between cyclophilins and coagulation factors emphasize risk stratification for COVID patients with thrombosis dispositions.

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Probing the 14-3-3 Isoform-Specificity Profile of Interactions Stabilized by Fusicoccin A

10.26434/chemrxiv.12052869.v1 ◽

2020 ◽

Author(s):

James Frederich ◽

Ananya Sengupta ◽

Josue Liriano ◽

Ewa A. Bienkiewicz ◽

Brian G. Miller

Keyword(s):

Protein Interactions ◽

Neurological Diseases ◽

Adapter Proteins ◽

Protein Protein Interactions ◽

Specific Expression ◽

Individual Client ◽

Isoform Specificity ◽

Fusicoccin A

Fusicoccin A (FC) is a fungal phytotoxin that stabilizes protein–protein interactions (PPIs) between 14-3-3 adapter proteins and their phosphoprotein interaction partners. In recent years, FC has emerged as an important chemical probe of human 14-3-3 PPIs implicated in cancer and neurological diseases. These previous studies have established the structural requirements for FC-induced stabilization of 14-3-3·client phosphoprotein complexes; however, the effect of different 14-3-3 isoforms on FC activity has not been systematically explored. This is a relevant question for the continued development of FC variants because there are seven distinct isoforms of 14-3-3 in humans. Despite their remarkable sequence and structural similarities, a growing body of experimental evidence supports both tissue-specific expression of 14-3-3 isoforms and isoform-specific functions <i>in vivo</i>. Herein, we report the isoform-specificity profile of FC <i>in vitro</i>using recombinant human 14-3-3 isoforms and a focused library of fluorescein-labeled hexaphosphopeptides mimicking the C-terminal 14-3-3 recognition domains of client phosphoproteins targeted by FC in cell culture. Our results reveal modest isoform preferences for individual client phospholigands and demonstrate that FC differentially stabilizes PPIs involving 14-3-3s. Together, these data provide strong motivation for the development of non-natural FC variants with enhanced selectivity for individual 14-3-3 isoforms.

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Identification and Biochemical Characterization of High Mobility Group Protein 20A as a Novel Ca2+/S100A6 Target

Biomolecules ◽

10.3390/biom11040510 ◽

2021 ◽

Vol 11 (4) ◽

pp. 510

Author(s):

Maho Yamamoto ◽

Rina Kondo ◽

Haruka Hozumi ◽

Seita Doi ◽

Miwako Denda ◽

...

Keyword(s):

Protein Interactions ◽

Biochemical Characterization ◽

S100 Protein ◽

High Mobility ◽

Dependent Manner ◽

Protein Signaling ◽

Protein Protein Interactions ◽

High Mobility Group Protein ◽

Pulldown Assay

During screening of protein-protein interactions, using human protein arrays carrying 19,676 recombinant glutathione s-transferase (GST)-fused human proteins, we identified the high-mobility protein group 20A (HMG20A) as a novel S100A6 binding partner. We confirmed the Ca2+-dependent interaction of HMG20A with S100A6 by the protein array method, biotinylated S100A6 overlay, and GST-pulldown assay in vitro and in transfected COS-7 cells. Co-immunoprecipitation of S100A6 with HMG20A from HeLa cells in a Ca2+-dependent manner revealed the physiological relevance of the S100A6/HMG20A interaction. In addition, HMG20A has the ability to interact with S100A1, S100A2, and S100B in a Ca2+-dependent manner, but not with S100A4, A11, A12, and calmodulin. S100A6 binding experiments using various HMG20A mutants revealed that Ca2+/S100A6 interacts with the C-terminal region (residues 311–342) of HMG20A with stoichiometric binding (HMG20A:S100A6 dimer = 1:1). This was confirmed by the fact that a GST-HMG20A mutant lacking the S100A6 binding region (residues 311–347, HMG20A-ΔC) failed to interact with endogenous S100A6 in transfected COS-7 cells, unlike wild-type HMG20A. Taken together, these results identify, for the first time, HMG20A as a target of Ca2+/S100 proteins, and may suggest a novel linkage between Ca2+/S100 protein signaling and HMG20A function, including in the regulation of neural differentiation.

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Ways into Understanding HIF Inhibition

Cancers ◽

10.3390/cancers13010159 ◽

2021 ◽

Vol 13 (1) ◽

pp. 159

Author(s):

Tina Schönberger ◽

Joachim Fandrey ◽

Katrin Prost-Fingerle

Keyword(s):

Protein Interactions ◽

Target Genes ◽

Protein Protein Interactions ◽

Low Oxygen ◽

Drug Candidates ◽

Open Questions ◽

Wide Range ◽

Hif Pathway

Hypoxia is a key characteristic of tumor tissue. Cancer cells adapt to low oxygen by activating hypoxia-inducible factors (HIFs), ensuring their survival and continued growth despite this hostile environment. Therefore, the inhibition of HIFs and their target genes is a promising and emerging field of cancer research. Several drug candidates target protein–protein interactions or transcription mechanisms of the HIF pathway in order to interfere with activation of this pathway, which is deregulated in a wide range of solid and liquid cancers. Although some inhibitors are already in clinical trials, open questions remain with respect to their modes of action. New imaging technologies using luminescent and fluorescent methods or nanobodies to complement widely used approaches such as chromatin immunoprecipitation may help to answer some of these questions. In this review, we aim to summarize current inhibitor classes targeting the HIF pathway and to provide an overview of in vitro and in vivo techniques that could improve the understanding of inhibitor mechanisms. Unravelling the distinct principles regarding how inhibitors work is an indispensable step for efficient clinical applications and safety of anticancer compounds.

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