The chemokine X-factor: Structure-function analysis of the CXC motif at CXCR4 and ACKR3

Cryo-EM structure of monomeric CXCL12-bound CXCR4 in the active state

CXCR4 binding of its endogenous agonist CXCL12 leads to diverse functions, including bone marrow retention of hematopoietic progenitors and cancer metastasis. However, the structure of the CXCL12-bound CXCR4 remains unresolved despite available structures of CXCR4 in complex with antagonists. Here, we present the cryoelectron microscopy (cryo-EM) structure of the CXCL12-CXCR4-Gi complex at an overall resolution of 2.65 Å. CXCL12 forms a 1:1 stoichiometry complex with CXCR4, following the two-site model. The first 8 amino acids of mature CXCL12 are crucial for CXCR4 activation by forming polar interactions with minor sub-pocket residues in the transmembrane binding pocket. The 3.2-Å distance between V3 of CXCL12 and the "toggle switch" W6.48 marks the deepest insertion among all chemokine-receptor pairs, leading to conformational changes of CXCR4 for G protein activation. These results, combined with functional assays and computational analysis, provide the structural basis for CXCR4 activation by CXCL12.

The chemokine Cxcl14 regulates interneuron differentiation in layer I of the somatosensory cortex

Spontaneous and sensory-evoked activity sculpts developing circuits. Yet, how these activity patterns intersect with cellular programs regulating the differentiation of neuronal subtypes is not well understood. Through electrophysiological and in vivo longitudinal analyses, we show that C-X-C motif chemokine ligand 14 (Cxcl14), a gene previously characterized for its association with tumor invasion, is expressed by single-bouquet cells (SBCs) in layer I (LI) of the somatosensory cortex during development. Sensory deprivation at neonatal stages markedly decreases Cxcl14 expression. Additionally, we report that loss of function of this gene leads to increased intrinsic excitability of SBCs-but not LI neurogliaform cells-and augments neuronal complexity. Furthermore, Cxcl14 loss impairs sensory map formation and compromises the in vivo recruitment of superficial interneurons by sensory inputs. These results indicate that Cxcl14 is required for LI differentiation and demonstrate the emergent role of chemokines as key players in cortical network development.

The role of proinflammatory cytokines and CXC chemokines (CXCL1-CXCL16) in the progression of prostate cancer: insights on their therapeutic management

Reproductive cancers are malignancies that develop in the reproductive organs. One of the leading cancers affecting the male reproductive system on a global scale is prostate cancer (PCa). The negative consequences of PCa metastases endure and are severe, significantly affecting mortality and life quality for those who are affected. The association between inflammation and PCa has captured interest for a while. Inflammatory cells, cytokines, CXC chemokines, signaling pathways, and other elements make up the tumor microenvironment (TME), which is characterized by inflammation. Inflammatory cytokines and CXC chemokines are especially crucial for PCa development and prognosis. Cytokines (interleukins) and CXC chemokines such as IL-1, IL-6, IL-7, IL-17, TGF-β, TNF-α, CXCL1-CXCL6, and CXCL8-CXCL16 are thought to be responsible for the pleiotropic effects of PCa, which include inflammation, progression, angiogenesis, leukocyte infiltration in advanced PCa, and therapeutic resistance. The inflammatory cytokine and CXC chemokines systems are also promising candidates for PCa suppression and immunotherapy. Therefore, the purpose of this work is to provide insight on how the spectra of inflammatory cytokines and CXC chemokines evolve as PCa develops and spreads. We also discussed recent developments in our awareness of the diverse molecular signaling pathways of these circulating cytokines and CXC chemokines, as well as their associated receptors, which may one day serve as PCa-targeted therapies. Moreover, the current status and potential of theranostic PCa therapies based on cytokines, CXC chemokines, and CXC receptors (CXCRs) are examined.

Multiplex Detection of Fluorescent Chemokine Binding to CXC Chemokine Receptors by NanoBRET

NanoLuc-mediated bioluminescence resonance energy transfer (NanoBRET) has gained popularity for its ability to homogenously measure ligand binding to G protein-coupled receptors (GPCRs), including the subfamily of chemokine receptors. These receptors, such as ACKR3, CXCR4, CXCR3, play a crucial role in the regulation of the immune system, are associated with inflammatory diseases and cancer, and are seen as promising drug targets. The aim of this study was to optimize NanoBRET-based ligand binding to NLuc-ACKR3 and NLuc-CXCR4 using different fluorescently labeled chemokine CXCL12 analogs and their use in a multiplex NanoBRET binding assay of two chemokine receptors at the same time. The four fluorescent CXCL12 analogs (CXCL12-AZD488, -AZD546, -AZD594, -AZD647) showed high-affinity saturable binding to both NLuc-ACKR3 and NLuc-CXCR4, with relatively low levels of non-specific binding. Additionally, the binding of all AZDye-labeled CXCL12s to Nluc receptors was inhibited by pharmacologically relevant unlabeled chemokines and small molecules. The NanoBRET binding assay for CXCL10-AZD488 binding to Nluc-CXCR3 was also successfully established and successfully employed for the simultaneous measurement of the binding of unlabeled small molecules to NLuc-CXCR3 and NLuc-CXCR4. In conclusion, multiplexing the NanoBRET-based competition binding assay is a promising tool for testing unlabeled (small) molecules against multiple GPCRs simultaneously.

Regulating Chemokine-Receptor Interactions through the Site-Specific Bioorthogonal Conjugation of Photoresponsive DNA Strands

Oligonucleotide conjugation has emerged as a versatile molecular tool for regulating protein activity. A state-of-the-art labeling strategy includes the site-specific conjugation of DNA, by employing bioorthogonal groups genetically incorporated in proteins through unnatural amino acids (UAAs). The incorporation of UAAs in chemokines has to date, however, remained underexplored, probably due to their sometimes poor stability following recombinant expression. In this work, we designed a fluorescent stromal-derived factor-1β (SDF-1β) chemokine fusion protein with a bioorthogonal functionality amenable for click reactions. Using amber stop codon suppression, p-azido-L-phenylalanine was site-specifically incorporated in the fluorescent N-terminal fusion partner, superfolder green fluorescent protein (sfGFP). Conjugation to single-stranded DNAs (ssDNA), modified with a photocleavable spacer and a reactive bicyclononyne moiety, was performed to create a DNA-caged species that blocked the receptor binding ability. This inhibition was completely reversible by means of photocleavage of the ssDNA strands. The results described herein provide a versatile new direction for spatiotemporally regulating chemokine-receptor interactions, which is promising for tissue engineering purposes.

The Chemokine, CCL20, and Its Receptor, CCR6, in the Pathogenesis and Treatment of Psoriasis and Psoriatic Arthritis

Background

Chemokines represent a superfamily of immune-modulatory small protein molecules that regulate leukocyte migration to inflammatory sites through their chemoattractant and cell signaling properties. This review focuses on the immunological functions of the CCR6 chemokine receptor and is chemokine ligand, CCL20, that contribute to it role in inflammation in human psoriasis.

Methods

Peer-reviewed relevant articles are searched and selected from 2000 to 2022 using the search engines including PubMed and Google Scholar.

Results

After selectively reviewing and evaluating over seventy articles, a comprehensive overview on the immunology of CCL20-CCR6 axis in psoriasis and psoriatic arthritis, the X-ray crystal structures of CCL20 monomers, and the potential of developing clinical therapies targeting this axis is summarized.

Conclusions

Over the past decade, preclinical studies carried out in animal models of psoriasis involving agents targeting CCL20-CCR6 axis have yielded promising results. Other studies that this axis may play a role in a number of other autoimmune diseases, including rheumatoid arthritis, suggesting a rationale for further investigation into this key signaling/migratory pathway.

The chemokines CXCL8 and CXCL12: molecular and functional properties, role in disease and efforts towards pharmacological intervention

Chemokines are an indispensable component of our immune system through the regulation of directional migration and activation of leukocytes. CXCL8 is the most potent human neutrophil-attracting chemokine and plays crucial roles in the response to infection and tissue injury. CXCL8 activity inherently depends on interaction with the human CXC chemokine receptors CXCR1 and CXCR2, the atypical chemokine receptor ACKR1, and glycosaminoglycans. Furthermore, (hetero)dimerization and tight regulation of transcription and translation, as well as post-translational modifications further fine-tune the spatial and temporal activity of CXCL8 in the context of inflammatory diseases and cancer. The CXCL8 interaction with receptors and glycosaminoglycans is therefore a promising target for therapy, as illustrated by multiple ongoing clinical trials. CXCL8-mediated neutrophil mobilization to blood is directly opposed by CXCL12, which retains leukocytes in bone marrow. CXCL12 is primarily a homeostatic chemokine that induces migration and activation of hematopoietic progenitor cells, endothelial cells, and several leukocytes through interaction with CXCR4, ACKR1, and ACKR3. Thereby, it is an essential player in the regulation of embryogenesis, hematopoiesis, and angiogenesis. However, CXCL12 can also exert inflammatory functions, as illustrated by its pivotal role in a growing list of pathologies and its synergy with CXCL8 and other chemokines to induce leukocyte chemotaxis. Here, we review the plethora of information on the CXCL8 structure, interaction with receptors and glycosaminoglycans, different levels of activity regulation, role in homeostasis and disease, and therapeutic prospects. Finally, we discuss recent research on CXCL12 biochemistry and biology and its role in pathology and pharmacology.

CXC Chemokines in the Pathogenesis of Pulmonary Disease and Pharmacological Relevance

Chemokines and their receptors play important roles in the pathophysiology of many diseases by regulating the cellular migration of major inflammatory and immune players. The CXC motif chemokine subfamily is the second largest family, and it is further subdivided into ELR motif CXC (ELR+) and non-ELR motif (ELR-) CXC chemokines, which are effective chemoattractants for neutrophils and lymphocytes/monocytes, respectively. These chemokines and their receptors are expected to have a significant impact on a wide range of lung diseases, many of which have inflammatory or immunological underpinnings. As a result, manipulations of this subfamily of chemokines and their receptors using small molecular agents and other means have been explored for potential therapeutic benefit in the setting of several lung pathologies. Furthermore, encouraging preclinical data has necessitated the progression of a few of these drugs into clinical trials in order to make the most effective use of interventions in the development of viable targeted therapeutics. The current review presents the understanding of the roles of CXC ligands (CXCLs) and their cognate receptors (CXCRs) in the pathogenesis of several lung diseases such as allergic rhinitis, COPD, lung fibrosis, lung cancer, pneumonia, and tuberculosis. The potential therapeutic benefits of pharmacological or other CXCL/CXCR axis manipulations are also discussed.

Gene Structure Analysis of Chemokines and Their Receptors in Allotetraploid Frog, Xenopus laevis

Chemokines, relatively small secreted proteins, are involved in cell migration and function in various biological events, including immunity, morphogenesis, and disease. Due to their nature, chemokines tend to be a target of hijacking of immunity by virus and therefore show an exceptionally high mutation rate. Xenopus laevis is considered an excellent model to investigate the effect of whole-genome duplication for gene family evolution. Because its allotetraploidization occurred around 17–18 million years ago, ancestral subgenomes L and S were well conserved. Based on the gene model of human and diploid frog Xenopus tropicalis, we identified 52 chemokine genes and 26 chemokine receptors in X. laevis. The retention rate of the gene in the X. laevis L and S subgenomes was 96% (45/47) and 68% (32/47), respectively. We conducted molecular phylogenetic analysis and found clear orthologies in all receptor genes but not in the ligand genes, suggesting rapid divergences of the ligand. dN/dS calculation demonstrated that dN/dS ratio greater than one was observed in the four ligand genes, cxcl8b.1.S, cxcl18.S, ccl21.S, and xcl1.L, but nothing in receptor genes. These results revealed that the whole-genome duplication promotes diversification of chemokine ligands in X. laevis while conserving the genes necessary for homeostasis, suggesting that selective pressure also supports a rapid divergence of the chemokines in amphibians.