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.

The unique structural and functional features of CXCL12

The CXC chemokine CXCL12 is an important factor in physiological and pathological processes, includingembryogenesis, hematopoiesis, angiogenesis and inflammation, because it activates and/or induces migration ofhematopoietic progenitor and stem cells, endothelial cells and most leukocytes. Therefore, CXCL12 activity istightly regulated at multiple levels. CXCL12 has the unique property of existing in six splice variants in humans,each having a specific tissue distribution and in vivo activity. Controlled splice variant transcription and mRNAstability determine the CXCL12 expression profile. CXCL12 fulfills its functions in homeostatic and pathologicalconditions by interacting with its receptors CXC chemokine receptor 4 (CXCR4) and atypical chemokine receptor 3(ACKR3) and by binding to glycosaminoglycans (GAGs) in tissues and on the endothelium to allow a properpresentation to passing leukocytes. Homodimerizaton and heterodimerization of CXCL12 and its receptors can altertheir signaling activity, as exemplified by the synergy between CXCL12 and other chemokines in leukocyte migrationassays. Receptor binding may also initiate CXCL12 internalization and its subsequent removal from theenvironment. Furthermore, CXCL12 activity is regulated by posttranslational modifications. Proteolytic removal ofNH2- or COOH-terminal amino acids, citrullination of arginine residues by peptidyl arginine deiminases or nitrationof tyrosine residues reduce CXCL12 activity. This review summarizes the interactions of CXCL12 with the cellularenvironment and discusses the different levels of CXCL12 activity regulation.

Neutrophil chemoattractant receptors in health and disease: double-edged swords

Neutrophils are frontline cells of the innate immune system.These effector leukocytes are equipped with intriguing antimicrobial machinery and consequently display high cytotoxic potential.Accurate neutrophil recruitment is essential to combat microbes and to restore homeostasis,for inflammation modulation and resolution,wound healing and tissue repair.After fulfilling the appropriate effector functions,however,dampening neutrophil activation and infiltration is crucial to prevent damage to the host.In humans,chemoattractant molecules can be categorized into four biochemical families,i.e.,chemotactic lipids,formyl peptides,complement anaphylatoxins and chemokines.They are critically involved in the tight regulation of neutrophil bone marrow storage and egress and in spatial and temporal neutrophil trafficking between organs.Chemoattractants function by activating dedicated heptahelical G protein-coupled receptors(GPCRs).In addition,emerging evidence suggests an important role for atypical chemoattractant receptors(ACKRs)that do not couple to G proteins in fine-tuning neutrophil migratory and functional responses.The expression levels of chemoattractant receptors are dependent on the level of neutrophil maturation and state of activation,with a pivotal modulatory role for the(inflammatory)environment.Here,we provide an overview of chemoattractant receptors expressed by neutrophils in health and disease.Depending on the(patho)physiological context,specific chemoattractant receptors may be up-or downregulated on distinct neutrophil subsets with beneficial or detrimental consequences,thus opening new windows for the identification of disease biomarkers and potential drug targets.

Ferritin acts as a target site for the snowdrop lectin （GNA） in the midgut of the cotton leafworm Spodoptera littoralis

The snowdrop lectin GNA （Galanthus nivalis agglutinin） has been shown to possess insecticidal activity to a range of economically important insect pests. However, the precise mechanism of insecticidal action of GNA against insects remains unknown. In this investigation, we attempted to purify and identify receptor（s） responsible for binding of GNA in the larval midgut of a major lepidopteran pest （the cotton leafworm, Spodoptera littoralis） to better understand its mode of action. Therefore, cytoplasmic as well as membrane proteins from 800 larval midguts were chromatographed on a column with immobilized GNA. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the proteins eluted from the GNA column followed by sequencing of the GNA-binding proteins and BLAST analyses revealed that the N-terminal sequences of a 24 kDa polypeptide purified from the cytoplasmic and membrane protein fraction revealed sequence similarity to sequences encoding heavy chain homologs of ferritin from Manduca sexta （76% sequence identity）, Calpodes ethlius （80% sequence identity） and Bombyx mori （61% sequence identity）. Furthermore, the N-terminal sequence of a 31 kDa polypeptide from the membrane protein fraction showed sequence similarity to a light chain homolog of ferritin from Manduca sexta （88% sequence identity）.