Receptor Extracellular Domain Research Articles

Development of an adrenocortical cell model of calcium signaling modulation to decipher the molecular mechanisms responsible for primary aldosteronism

Primary aldosteronism (PA) is the most frequent form of secondary hypertension. The identification of germline or somatic mutations in different genes coding for ion channels and defines PA as a channelopathy. These mutations promote activation of calcium signaling, the main trigger for aldosterone biosynthesis. The objective of our work was to elucidate, using chemogenetic tools, the molecular mechanisms underlying the development of PA by modulating sodium entry into the cells, mimicking some of known mutations identified in PA. We have developed an adrenocortical H295R-S2 cell line stably expressing a chimeric ion channel receptor formed by the extracellular ligand-binding domain of the α7 nicotinic acetylcholine receptor fused to the ion pore domain of the serotonin receptor 5HT3α and named α7-5HT3. Mutations have been introduced in the ligand-binding domain to allow only synthetic drugs to activate this channel receptor. Activation of α7-5HT3 by a specific drug, PSEM-817 leads to sodium entry into the cells. This cell line was characterized in terms of intracellular calcium concentrations, cell proliferation, aldosterone production, steroidogenic expression and electrophysiological properties. Treatment of α7-5HT3 expressing cells with increasing concentration of PSEM-817 (from 10-9 to 10-5 M) induced a significant increase in intracellular calcium concentrations, similarly to potassium (12 mM) or angiotensin II (10-8 M). This stimulation of calcium signaling did not affect cell proliferation, but was responsible for an increase in CYP11B2 expression and aldosterone production after 24 h of treatment. However, while increased intracellular calcium concentrations were observed starting from 10-8 M of PSEM-817, CYP11B2 expression and aldosterone production were only affected starting from 10-7 M, suggesting a dose-dependent effect. Finally, whereas cells were hyperpolarized in absence of stimulation (around −60 mV), PSEM-817 induced a strong depolarization, cells rising to a membrane potential around −10 mV. This cell line, in which we can modulate the intracellular calcium concentration “on demand”, is a useful tool for a better understanding of the alterations of intracellular ion balance and calcium signaling in the pathophysiology of PA.

Impact of EGFRA289T/Vmutation on relapse pattern in glioblastoma.

2046 Background: The prediction of the relapse pattern is an important issue in glioblastoma for personalized approach. Molecular factors, such as MGMT promoter methylation, influence relapse in- or out-field of the initial radiotherapy volume. Recently, a recurrent mutation located at position 289 of the extracellular domain of the epidermal growth factor receptor ( EGFRA289mut) has been associated with a more infiltrative phenotype in glioblastoma. The primary objective of the present study was to explore the impact of EGFRA289mut on the pattern of relapse after a chemo-radiotherapy based treatment of patients suffering from glioblastoma. Methods: An ancillary study from a monocentric prospective cohort of patients suffering from glioblastoma was conducted. All patients received radiotherapy and concomitant temozolomide. The population was divided into two groups according to EGFRA289 status (mutated versus wild-type). Primary endpoint was the overlap score (varying from 0 to 1) between initial irradiated tumor volume (Vinit) and relapse volume (Vr). Vinit was the initial 95% isodose of the radiotherapy and Vr was delineated using the enhanced MRI T1-weighted part of the relapse tumor. Secondary endpoints explored the impact of other EGFR extracellular mutations, EGFR amplification and EGFRvIII on the relapse pattern, as well as the impact of EGFRA289mut on survival. EGFR alterations were identified using next-generation sequencing or droplet-digital PCR based methods on formalin-fixed paraffin-embedded samples collected at initial diagnosis. Results: One hundred patients were included: 11% of the population had EGFRA289mut glioblastoma (n = 11/100). EGFRA289mut glioblastomas had a relapse pattern more marginal compared to EGFRA289wt glioblastomas: a mean overlap score Vinit/Vr of 0.78 was observed in the EGFRA289mut group versus 0.94 in the EGFRA289wt group (p = 0.021). The proportion of EGFR A289mut glioblastomas in the outfield relapse (overlap score < 0.8) has a trend to be higher than in the infield relapse (overlap score > 0.8): 25% (n = 2/8) versus 9.8% (n = 9/92) for the EGFRA289wt population, p = 0.21. Neither EGFR amplification nor EGFRvIII did influence overlap score Vinit/Vr. In our population, EGFRA289mut did not influence survival. Conclusions: EGFR A289mut influences the relapse pattern in a population of patients suffering from glioblastoma. The role of EGFRA289mut as a decision-making biomarker for personalized radiotherapy should now be investigated in dedicated clinical trial. Clinical trial information: NCT02617745.

Peptide Ligand Interaction with Maltose‐Binding Protein Tagged to the Calcitonin Gene‐Related Peptide Receptor: Inhibitory Roles of Receptor N‐Glycosylation

Calcitonin gene‐related peptide (CGRP) and adrenomedullin (AM) are peptide hormones and their receptors play a critical role in migraine progression and blood pressure control, respectively. CGRP and AM receptors are structurally related since they are the complex of the calcitonin receptor‐like receptor (CLR) with the different types of receptor activity‐modifying protein (RAMP); the CLR complex with RAMP1 is the CGRP receptor while the CLR complex with RAMP2 is the AM receptor. The extracellular domain (ECD) of CLR and RAMP provides a binding site for peptide ligands as reported in crystal structures. Several crystal structures of the CGRP and AM receptor ECD used maltose‐binding protein (MBP) as a tag protein to facilitate crystallization. Unexpectedly, the recent crystal structures of CGRP receptor ECD showed that the N‐terminal MBP tag located in proximity of the bound/mutated peptide ligands. The objective of the current study is to investigate potential chemical interaction between peptide ligands and the MBP tagged to the CGRP receptor ECD. Peptide ligand interaction with purified CGRP receptor ECD was evaluated with fluorescence polarization/anisotropy peptide binding assay with a fluorescent peptide probe. The results of the current study provided evidence that MBP N‐terminally tagged to the CGRP receptor ECD formed chemical interaction with mutated peptide ligands. Interestingly, N‐glycosylation of the CGRP receptor ECD was predicted to prevent MBP docking to the mutated peptide ligands. The N‐glycosylation of CLR ECD N123 was the most critical for inhibiting MBP interaction with the mutated peptide ligands. The MBP tag protein interaction was also dependent on the sequence of the peptide ligands. An endogenous CGRP fragment did not appear to interact with the MBP tag. In contrast to the CGRP receptor, the MBP tag was not involved in peptide ligand binding at AM receptor ECD. Here, I provided evidence that N‐glycosylation of the CGRP receptor ECD inhibited the MBP tag protein interaction suggesting an additional role of N‐glycosylation in the MBP‐tagged CGRP receptor ECD. This study reveals the importance of using a tag protein‐free CGRP receptor ECD for the accurate assessment of peptide ligand affinity.

Vertebrate Lonesome Kinase Phosphorylates EphB2 Receptors on an Extracellular Residue to Drive NMDA-Dependent Pain

EphB/ephrinB signaling plays a key role in synaptic function and is linked to several neuropathological conditions, including neuropathic pain. The EphB2 receptor tyrosine kinase is known to interact with N-Methyl-D-aspartate glutamate receptors (NMDAR), resulting in increased surface retention of NMDARs at the synapse and an enhancement of postsynaptic currents. As changes in NMDAR signaling have been heavily implicated in the development of both acute and chronic pain, targeting this receptor interaction may produce clinically relevant therapeutics. We have recently demonstrated that the phosphorylation of a tyrosine residue (Y504) on the extracellular domain of the EphB2 receptor is necessary and sufficient to induce its interaction with NMDARs and cause mechanical pain hypersensitivity. The kinase responsible for this phosphorylation is unknown. We hypothesized that Vertebrate Lonesome Kinase (VLK) may be the key effector. Since the phosphorylation site of interest is located on the extracellular face of the EphB2 receptor, a secreted tyrosine kinase like VLK is an ideal candidate. Our results provide strong support for our hypothesis that VLK drives pain via extracellular phosphorylation of EphBs. We show that intrathecal injection of VLK resulted in long-lasting mechanical hypersensitivity in mice. Additionally, the effects observed for VLK were dependent on kinase activity and entirely dependent upon NMDARs because they were blocked by AP-5. We also show evidence of VLK protein and mRNA expression in dorsal root ganglion and spinal cord neurons of both mice and humans. Our results provide evidence for the involvement of VLK in pain behaviors and spinal cord NMDAR signaling, and identify a completely unique extracellular kinase target for the alleviation of pain. Grant support from NIH grants NS111976 & NS115441.

Endothelial Regulation of Microvascular Growth and Stability by Ang‐Tie and VEGF Signaling Pathways: A Mechanistic Computational Systems Biology Model

The Angiopoietin‐Tie (Ang‐Tie) pathway is a key signaling pathway regulating vascular stability and permeability, and it significantly intersects and crosstalk with the vascular endothelial growth factor (VEGF) signaling pathway, a major signaling pathway regulating angiogenesis and vascular permeability. Disrupted Ang‐Tie and VEGF signaling is linked to vascular dysfunction related to cancer, systemic inflammation, cardiovascular disease, and diabetic macular edema. Ang‐Tie pathway is regulated by various molecular mechanisms, including ligand‐receptor interactions, receptor multimerization, binding of co‐receptor Tie1, inhibition by vascular endothelial protein tyrosine phosphatase (VE‐PTP), receptor extracellular domain shedding, junctional localization, trafficking, and turnover. VEGF pathway is regulated by ligand binding, homo‐ and heterodimerization of VEGF receptors VEGFR1 and VEGFR2, interaction with neuropilin, thrombospondin‐1/CD47, receptor internalization, recycling, and degradation. Ang‐Tie and VEGF signaling pathways also share crosstalk mechanisms and integrative downstream signaling through phosphoinositide 3‐kinases (PI3K)/Akt, sphingosine‐dependent Erk activation, Src sequestration via RhoA/mDia, and calcium cycling, forming a complex reaction network that requires an integrative model to study the signaling outcomes on a systems level. The present study uses a mechanistic computational model of the Ang‐Tie and VEGF signaling pathways, their regulatory mechanisms, crosstalk, and integrative downstream signaling to quantitatively characterize the molecular control of vascular growth, permeability, and stability by endothelial cells. The model captures and reproduces key experimental observations of the Ang‐Tie/VEGF signaling network with detailed molecular mechanisms. The model significantly expands our previous computational models of the Ang‐Tie signaling pathway [1,2] and integrates our systems biology understanding of the VEGF pathway and their crosstalk. The model serves as a platform for quantitatively predicting the signaling outcome of varying ligand concentrations and receptor expressions in physiological and pathological conditions, identifying molecular mechanisms and targets for therapeutic interventions targeting the signaling network, and simulating the effects of drugs and their combinations on the signaling outcome on a network level.

Triazole Modified Tetraiodothyroacetic Acid Conjugated to Polyethylene Glycol, a Thyrointegrin αvβ3 Antagonist as a Radio- and Chemo-Sensitizer in Pancreatic Cancer.

Thyroid hormone L thyroxine stimulates pancreatic carcinoma cell proliferation via thyrointegrin αvβ3 receptors, and antagonist tetraiodothyroacetic acid (tetrac) inhibits cancer cell growth. Chemically modified bis-triazole-tetrac conjugated with polyethylene glycol (P-bi-TAT) has higher binding affinity to αvβ3 receptors compared to tetrac. We investigated the antiproliferation effect of P-bi-TAT in pancreatic cancer cells (SUIT2) and its radio- and chemo-sensitizing roles in a mouse model of pancreatic cancer. P-bi-TAT treatment increased tumor-targeted radiation-induced cell death and decreased tumor size. P-bi-TAT acted as a chemo-sensitizer and enhanced the 5-fluorouracil (5FU) effect in decreasing pancreatic tumor weight compared to 5FU monotherapy. Withdrawal of treatment continued the tumor regression; however, the 5FU group showed tumor regrowth. The mechanisms of the anti-cancer activity of P-bi-TAT on SUIT2 cells were assessed by microarray experiments, and genome-wide profiling identified significant alterations of 1348 genes’ expression. Both down-regulated and up-regulated transcripts suggest that a molecular interference at the signaling pathway-associated gene expression is the prevalent mode of P-bi-TAT anti-cancer activity. Our data indicate that non-cytotoxic P-bi-TAT is not only an anti-cancer agent but also a radio-sensitizer and chemo-sensitizer that acts on the extracellular domain of the cell surface αvβ3 receptor.

Glycans that regulate Notch signaling in the intestine.

Intestinal homeostasis is key to the maintenance of good health. The small intestine plays important roles in absorption, digestion, hormonal and immune functions. Crypt base columnar (CBC) stem cells residing at the bottom of crypts are nurtured by Paneth cells, and together create the stem cell niche, the foundation of intestinal homeostasis. CBC stem cells replicate to replenish their number, or differentiate into a variety of epithelial cells with specialized functions. Notch signaling is a cell-cell signaling pathway that regulates both the proliferation and differentiation of CBC stem cells. NOTCH1 and NOTCH2 stimulated by canonical Notch ligands DLL1 and DLL4 mediate Notch signaling in the intestine that, in concert with other signaling pathways including the WNT and BMP pathways, determines cell fates. Importantly, interactions between Notch receptors and canonical Notch ligands are regulated by O-glycans linked to Ser/Thr in epidermal growth factor-like (EGF) repeats of the Notch receptor extracellular domain (NECD). The O-glycans attached to NECD are key regulators of the strength of Notch signaling. Imbalances in Notch signaling result in altered cell fate decisions and may lead to cancer in the intestine. In this review, we summarize the impacts of mutations in Notch pathway members on intestinal development and homeostasis, with a focus on the glycosyltransferases that transfer O-glycans to EGF repeats of NOTCH1, NOTCH2, DLL1 and DLL4.

Tumor in the Crossfire: Inhibiting TGF-β to Enhance Cancer Immunotherapy.

Cancer immunotherapy using monoclonal antibodies targeting immune checkpoints has undoubtedly revolutionized the cancer treatment landscape in the last decade. Immune checkpoint inhibitors can elicit long-lasting, previously unheard-of responses in a number of tumor entities. Yet, even in such tumors as metastatic melanoma and non-small cell-lung cancer, in which immune checkpoint inhibition has become the first-line treatment of choice, only a minority of patients will benefit considerably from these treatments. This has been attributed to a number of factors, including an immune-suppressive tumor microenvironment (TME). Using different modalities to break these barriers is of utmost importance to expand the population of patients that benefit from immune checkpoint inhibition. The multifunctional cytokine transforming growth factor-β (TGF-β) has long been recognized as an immune-suppressive factor in the TME. A considerable number of drugs have been developed to target TGF-β, yet most of these have since been discontinued. The combination of anti–TGF-β agents with immune checkpoint inhibitors now has the potential to revive this target as a viable immunomodulatory therapeutic approach. Currently, a limited number of small molecular inhibitor and monoclonal antibody candidates that target TGF-β are in clinical development in combination with the following immune checkpoint inhibitors: SRK 181, an antibody inhibiting the activation of latent TGF-β1; NIS 793, a monoclonal antibody targeting TGF-β; and SHR 1701, a fusion protein consisting of an anti-PD-L1 monoclonal antibody fused with the extracellular domain of human TGF-β receptor II. Several small molecular inhibitors are also in development and are briefly reviewed: LY364947, a pyrazole-based small molecular inhibitor of the serine-threonine kinase activity of TGFβRI; SB-431542, an inhibitor targeting several TGF-β superfamily Type I activin receptor-like kinases as well as TGF-β1-induced nuclear Smad3 localization; and galunisertib, an oral small molecular inhibitor of the TGFβRI kinase. One of the most advanced agents in this area is bintrafusp alfa, a bifunctional fusion protein composed of the extracellular domain of TGF-β receptor II fused to a human IgG1 mAb blocking PD-L1. Bintrafusp alfa is currently in advanced clinical development and as an agent in this space with the most clinical experience, is a focused highlight of this review.

Signal Transduction of C-Terminal Phosphorylation Regions for Equine Luteinizing Hormone/Chorionic Gonadotropin Receptor (eLH/CGR).

This study aimed to investigate the signal transduction of phosphorylation sites at the carboxyl (C)-terminal region of equine luteinizing hormone/chorionic gonadotropin receptor (eLH/ CGR). The eLH/CGR has a large extracellular domain of glycoprotein hormone receptors within the G protein-coupled receptors. We constructed a mutant (eLH/CGR-t656) of eLH/ CGR, in which the C-terminal cytoplasmic tail was truncated at the Phe656 residue, through polymerase chain reaction. The eLH/CGR-t656 removed 14 potential phosphorylation sites in the intracellular C-terminal region. The plasmids were transfected into Chinese hamster ovary (CHO)-K1 and PathHunter Parental cells expressing β-arrestin, and agonist-induced cAMP responsiveness was analyzed. In CHO-K1 cells, those expressing eLH/CGR-t656 were lower than those expressing eLH/CGR wild-type (eLH/CGR-wt). The EC50 of the eLH/ CGR-t656 mutant was approximately 72.2% of the expression observed in eLH/CGR-wt. The maximal response in eLH/CGR-t656 also decreased to approximately 43% of that observed in eLH/CGR-wt. However, in PathHunter Parental cells, cAMP activity and maximal response of the eLH/CGR-t656 mutant were approximately 173.5% and 100.8%, respectively, of that of eLH/CGR-wt. These results provide evidence that the signal transduction of C-terminal phosphorylation in eLH/CGR plays a pivotal role in CHO-K1 cells. The cAMP level was recovered in PathHunter Parental cells expressing β-arrestin. We suggest that the signal transduction of the C-terminal region phosphorylation sites is remarkably different depending on the cells expressing β-arrestin in CHO-K1 cells.

The Changing Landscape of Systemic Treatment for Cervical Cancer: Rationale for Inhibition of the TGF-β and PD-L1 Pathways.

Cervical cancer is one of the most common and lethal cancers among women worldwide. Treatment options are limited in patients with persistent, recurrent, or metastatic cervical cancer, with <20% of women living >5 years. Persistent human papillomavirus (HPV) infection has been implicated in almost all cases of cervical cancer. HPV infection not only causes normal cervical cells to transform into cancer cells, but also creates an immunosuppressive environment for cancer cells to evade the immune system. Recent clinical trials of drugs targeting the PD-(L)1 pathway have demonstrated improvement in overall survival in patients with cervical cancer, but only 20% to 30% of patients show overall survival benefit beyond 2 years, and resistance to these treatments remains common. Therefore, novel treatment strategies targeting HPV infection–associated factors are currently being evaluated in clinical trials. Bintrafusp alfa is a first-in-class bifunctional fusion protein composed of the extracellular domain of the TGF-βRII receptor (a TGF-β “trap”) fused to a human immunoglobulin G1 monoclonal antibody that blocks PD-L1. Early clinical trials of bintrafusp alfa have shown promising results in patients with advanced cervical cancer.

Targeting insulin-like growth factor-1 receptor (IGF1R) for brain delivery of biologics.

The blood-brain barrier (BBB) prevents the majority of drugs from crossing into the brain and reaching neurons. To overcome this challenge, safe and non-invasive technologies targeting receptor-mediated pathways have been developed. In this study, three single-domain antibodies (sdAbs; IGF1R3, IGF1R4, and IGF1R5) targeting the extracellular domain of the human insulin-like growth factor-1 receptor (IGF1R), generated by llama immunization, showed enhanced transmigration across the rat BBB model (SV-ARBEC) in vitro. The rate of brain uptake of these sdAbs fused to mouse Fc (sdAb-mFc) in vivo was estimated using the fluorescent in situ brain perfusion (ISBP) technique followed by optical brain imaging and distribution volume evaluation. Compared to the brains perfused with the negative control A20.1-mFc, the brains perfused with anti-IGF1R sdAbs showed a significant increase of the total fluorescence intensity (~2-fold, p<.01) and the distribution volume (~4-fold, p<.01). The concentration curve for IGF1R4-mFc demonstrated a linear accumulation plateauing at approximately 400µg (~1µM), suggesting a saturable mechanism of transport. Capillary depletion and mass spectrometry analyses of brain parenchyma post-ISBP confirmed the IGF1R4-mFc brain uptake with ~25% of the total amount being accumulated in the parenchymal fraction in contrast to undetectable levels of A20.1-mFc after a 5-min perfusion protocol. Systemic administration of IGF1R4-mFc fused with the non-BBB crossing analgesic peptide galanin (2 and 5mg/kg) induced a dose-dependent suppression of thermal hyperalgesia in the Hargreaves pain model. In conclusion, novel anti-IGF1R sdAbs showed receptor-mediated brain uptake with pharmacologically effective parenchymal delivery of non-permeable neuroactive peptides.

Refer analysis of α1β2γ2 GABA type a receptor suggests a slight phase shift between principal and complementary subunits at the extracellular domain upon channel activation

GABAa receptors are pentameric ligand gated ion channels and play a key role in synaptic inhibiton. Recently, structures of this receptor were revealed in closed and desensitized but not in the open state. However, the molecular mechanisms of the activation process remain elusive. We have made an attempt to address this issue by applying the REFER (φ-value) analysis which provides information on sequential movements of channel’s structural elements upon opening. Single-channel recordings from WT and selected single point mutants of the extracellular domain and interface of the α1β2γ2 receptor were performed and modeling was used to optimize the rate constants to determine the φ values.

Role of JAK2/STAT3 Signaling Pathway in the Tumorigenesis, Chemotherapy Resistance, and Treatment of Solid Tumors: A Systemic Review.

Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) pathway is a common signaling pathway used to transduce signals from the extracellular to the intracellular (nucleus) upon the binding of cytokines and growth factors to the extracellular domain of specific cell surface receptors. This signaling pathway is tightly regulated and has a multitude of biological functions such as cell proliferation, differentiation, and apoptosis. Besides, the regulated JAK2/STAT3 signaling plays a crucial role in embryonic development, hemopoiesis, and controlling the immune system. Conversely, aberrantly activated JAK2/STAT3 is frequently detected in varieties of tumors and involved in oncogenesis, angiogenesis, and metastasis of many cancer diseases that are usually refractory to the standard chemotherapy. However, the JAK3/STAT3 pathway recently emerged interestingly as a new site for the development of novel anti-tumor agents and becomes a promising therapeutic target in the treatment of many solid malignancies. Herein, this review aimed to provide insight into the JAK2/STAT3 pathway, in the hope to gain an understanding of its potential role in the pathogenesis, progression, chemotherapy resistance, and cancer therapy of solid tumors.

Peptide ligand interaction with maltose-binding protein tagged to the calcitonin gene-related peptide receptor: The inhibitory role of receptor N-glycosylation

Calcitonin gene-related peptide (CGRP) and adrenomedullin (AM) are peptide hormones and their receptors play a critical role in migraine progression and blood pressure control, respectively. CGRP and AM receptors are structurally related since they are the complex of the calcitonin receptor-like receptor (CLR) with the different types of receptor activity-modifying protein (RAMP). Several crystal structures of the CGRP and AM receptor extracellular domain (ECD) used maltose-binding protein (MBP) as a tag protein to facilitate crystallization. Unexpectedly, the recent crystal structures of CGRP receptor ECD showed that the N-terminal tag MBP located in proximity of bound/mutated peptide ligands. This study provided evidence that MBP N-terminally tagged to the CGRP receptor ECD formed chemical interaction with the mutated peptide ligands. Interestingly, N-glycosylation of the CGRP receptor ECD was predicted to prevent MBP docking to the mutated peptide ligands. I found that the N-glycosylation of CLR ECD N123 was the most critical for inhibiting MBP interaction with the mutated peptide ligands. The MBP tag protein interaction was also dependent on the sequence of the peptide ligands. In contrast to the CGRP receptor, the MBP tag was not involved in peptide ligand binding at AM receptor ECD. Here, I provided evidence that N-glycosylation of the CGRP receptor ECD inhibited the tag protein interaction suggesting an additional function of N-glycosylation in the MBP-fused CGRP receptor ECD. This study reveals the importance of using tag protein-free versions of the CGRP receptor for the accurate assessment of peptide binding affinity.

Dual inhibition of TGF-β and PD-L1: a novel approach to cancer treatment.

Transforming growth factor‐β (TGF‐β) and programmed death ligand 1 (PD‐L1) initiate signaling pathways with complementary, nonredundant immunosuppressive functions in the tumor microenvironment (TME). In the TME, dysregulated TGF‐β signaling suppresses antitumor immunity and promotes cancer fibrosis, epithelial‐to‐mesenchymal transition, and angiogenesis. Meanwhile, PD‐L1 expression inactivates cytotoxic T cells and restricts immunosurveillance in the TME. Anti‐PD‐L1 therapies have been approved for the treatment of various cancers, but TGF‐β signaling in the TME is associated with resistance to these therapies. In this review, we discuss the importance of the TGF‐β and PD‐L1 pathways in cancer, as well as clinical strategies using combination therapies that block these pathways separately or approaches with dual‐targeting agents (bispecific and bifunctional immunotherapies) that may block them simultaneously. Currently, the furthest developed dual‐targeting agent is bintrafusp alfa. This drug is a first‐in‐class bifunctional fusion protein that consists of the extracellular domain of the TGF‐βRII receptor (a TGF‐β ‘trap’) fused to a human immunoglobulin G1 (IgG1) monoclonal antibody blocking PD‐L1. Given the immunosuppressive effects of the TGF‐β and PD‐L1 pathways within the TME, colocalized and simultaneous inhibition of these pathways may potentially improve clinical activity and reduce toxicity.

The pseudokinase domain in receptor guanylyl cyclases.

Cyclic GMP is produced by enzymes called guanylyl cyclases, of which the membrane-associated forms contain an intracellular pseudokinase domain that allosterically regulates the C-terminal guanylyl cyclase domain. Ligand binding to the extracellular domain of these single transmembrane-spanning domain receptors elicits an increase in cGMP levels in the cell. The pseudokinase domain (or kinase-homology domain) in these receptors appears to be critical for ligand-mediated activation. While the pseudokinase domain does not possess kinase activity, biochemical evidence indicates that the domain can bind ATP and thereby allosterically regulate the catalytic activity of these receptors. The pseudokinase domain also appears to be the site of interaction of regulatory proteins, as seen in the retinal guanylyl cyclases that are involved in visual signal transduction. In the absence of structural information on the pseudokinase-guanylyl cyclase domain organization of any member of this family of receptors, biochemical evidence has provided clues to the physical interaction of the pseudokinase and guanylyl cyclase domain. An α-helical linker region between the pseudokinase domain and the guanylyl cyclase domain regulates the basal activity of these receptors in the absence of a stimulatory ligand and is important for stabilizing the structure of the pseudokinase domain that can bind ATP. Here, we present an overview of salient features of ATP-mediated regulation of receptor guanylyl cyclases and describe biochemical approaches that allow a clearer understanding of the intricate interplay between the pseudokinase domain and catalytic domain in these proteins.

Synthesis of the extracellular domain of GLP-1R by chemical and biotechnological approaches.

The extracellular domain of the glucagon-like peptide-1 receptor, GLP-1R, is responsible for the binding of GLP-1, and a handful of additional agonists (such as exenatide, lixisenatide, and liraglutide) used daily for treating type II diabetes mellitus. Lead discovery and optimization, however, require binding studies, which, in turn, necessitate the total synthesis of GLP-1R, comprising 108 residues. A protein domain of 10–15 kDa size could be obtained either by expression in E. coli or by ligating solid-phase peptide synthesis (SPPS)-made fragments. However, direct overexpression fails to give a properly folded protein, as GLP-1R forms an inclusion body, which fails to refold due to improper disulfide pairing. Several bacterial strains, constructs, and fusion partners were probed and it was found that only co-expression with MBP gave a 3D-fold allowing the native disulfide bond pattern formation. Some fusion partners can act as covalently linked or in situ chaperones for guiding the refolding of GLP-1R toward success. Therefore, the bottleneck to preparing GPCR extracellular domains is the correct pairing of the Cys residues. As a proof-of-concept model, nGLP1-R was made by SPPS to form the purified full-length polypeptide chain, subjected to self-guided or spontaneous Cys pairing. However, the formation of correct SS-pairs was lagging behind any protocol in use support, and the bottleneck of large-scale protein production relies on the risky step of proper refolding, which is sometimes possible only if a suitable fusion partner effectively helps and catalysis of the correct disulfide formation.

Computational analysis of fusion protein of anti-HER2 scFv and alpha luffin: A new immunotoxin protein for HER2 positive cancers

The present study deals with the computational design and analysis of a novel fusion protein based on a single chain variable fragment that binds to the extracellular domain of human epidermal growth factor receptor 2 (HER2) in breast cancer cells. Alpha luffin, a small ribosome inactivating protein (RIP), was attached to the anti-HER2 antibody fragment. I-TASSER modeling provided the full-length structure of the fusion protein. Molecular docking evaluated the molecular interactions of the complementarity-determining regions of designed fusion protein to HER2. Energy minimization and molecular dynamics simulations were conducted to refine the complexes. RMSD plot revealed reasonable stability of the fusion protein during the simulation. The free binding energy profile of complexes affirmed a favorable binding affinity of proteins in complex with HER2 using molecular mechanics Poisson-Boltzmann surface area (G-MMPBSA) algorithm. In general, this approach looks promising in the development of new fusion proteins in terms of immunotoxins with appropriate cytotoxicity.

New treatment for myelodysplastic syndromes: luspatercept and oral hypomethylating agents

Several novel myelodysplastic syndromes (MDS) treatment drugs are being developed, and luspatercept and oral hypomethylating medicines have already been licensed in the United States and other countries. Luspatercept is a ligand trap that inhibits SMAD2/3 signals by combining the extracellular domain of the activin type IIA receptor with the human immunoglobulin G1 Fc domain. In the phase 2 study for low-risk MDS, the hematological improvement-erythroid (HI-E) was found in 63% of patients, and in the phase 3 study for transfusion-dependent low-risk MDS with ring sideroblasts, 38% of patients achieved transfusion independence. A combination of oral decitabine with oral cedazuridine, an inhibitor of cytidine deaminase, which metabolizes decitabine, demonstrated pharmacological equivalence with intravenous decitabine and has overall response rates of 60% and 43% for high-risk MDS in phase 2 and 3 trials, respectively. Furthermore, oral azacitidine and its combination with oral cedazuridine have been under development.

The insulin receptor discovery is 50 years old - A review of achieved progress

The isolation of insulin from the pancreas and its purification to a degree permitting its safe administration to type 1 diabetic patients were accomplished 100 years ago at the University of Toronto by Banting, Best, Collip and McLeod and constitute undeniably one of the major medical therapeutic revolutions, recognized by the attribution of the 1923 Nobel Prize in Physiology or Medicine to Banting and McLeod. The clinical spin off was immediate as well as the internationalization of insulin's commercial production. The outcomes regarding basic research were much slower, in particular regarding the molecular mechanisms of insulin action on its target cells. It took almost a half-century before the determination of the tri-dimensional structure of insulin in 1969 and the characterization of its cell receptor in 1970-1971. The demonstration that the insulin receptor is in fact an enzyme named tyrosine kinase came in the years 1982-1985, and the crystal structure of the intracellular kinase domain 10 years later. The crystal structure of the first intracellular kinase substrate (IRS-1) in 1991 paved the way for the elucidation of the intracellular signalling pathways but it took 15 more years to obtain the complete crystal structure of the extracellular receptor domain (without insulin) in 2006. Since then, the determination of the structure of the whole insulin-receptor complex in both the inactive and activated states has made considerable progress, not least due to recent improvement in the resolution power of cryo-electron microscopy. I will here review the steps in the development of the concept of hormone receptor, and of our knowledge of the structure and molecular mechanism of activation of the insulin receptor.