The chemokine (C-X-C motif) ligand 1 (CXCL1) is a small peptide belonging to the CXC chemokine family that acts as a chemoattractant for several immune cells, especially neutrophils [5] [6] or other non-hematopoietic cells to the site of injury or infection and plays an important role in regulation of immune and inflammatory responses. It was previously called GRO1 oncogene, GROα, neutrophil-activating protein 3 (NAP-3) and melanoma growth stimulating activity, alpha (MGSA-α). CXCL1 was first cloned from a cDNA library of genes induced by platelet-derived growth factor (PDGF) stimulation of BALB/c-3T3 murine embryonic fibroblasts and named "KC" for its location in the nitrocellulose colony hybridization assay. [7] This designation is sometimes erroneously believed to be an acronym and defined as "keratinocytes-derived chemokine". Rat CXCL1 was first reported when NRK-52E (normal rat kidney-52E) cells were stimulated with interleukin-1β (IL-1β) and lipopolysaccharide (LPS) to generate a cytokine that was chemotactic for rat neutrophils, cytokine-induced neutrophil chemoattractant (CINC). [8] In humans, this protein is encoded by the gene CXCL1 [9] and is located on human chromosome 4 among genes for other CXC chemokines. [10]
CXCL1 exists as both monomer and dimer and both forms are able to bind chemokine receptor CXCR2. [11] However, CXCL1 chemokine is able to dimerize only at higher (micromolar) concentrations and its concentrations are only nanomolar or picomolar upon normal conditions, which means that the form of WT CXCL1 is more likely monomeric while dimeric CXCL1 is present only during infection or injury. CXCL1 monomer consists of three antiparallel β-strands followed by C- terminal α-helix and this α-helix together with the first β-strand are involved in forming a dimeric globular structure. [12]
Upon normal conditions, CXCL1 is not expressed constitutively. It's produced by a variety of immune cells such as macrophages, neutrophils and epithelial cells, [13] [14] or Th17 population. Moreover, its expression can be also induced indirectly by IL-1, TNF-α or IL-17 produced again by Th17 cells [15] and is triggered mainly by activation of NF-κB or C/EBPβ signaling pathways predominantly involved in inflammation and leading to production of other inflammatory cytokines. [15]
CXCL1 has a potentially similar role as interleukin-8 (IL-8/CXCL8). After binding to its receptor CXCR2, CXCL1 activates phosphatidylinositol-4,5-bisphosphate 3-kinase-γ (PI3Kγ)/Akt, MAP kinases such as ERK1/ERK2 or phospholipase-β (PLCβ) signaling pathways. CXCL1 is expressed at higher levels during inflammatory responses thus contributing to the process of inflammation. [16] CXCL1 is also involved in the processes of wound healing and tumorigenesis. [17] [18] [19]
CXCL1 has a role in angiogenesis and arteriogenesis [20] and thus has been shown to act in the process of tumor progression. The role of CXCL1 was described by several studies in the development of various tumors, such as breast cancer, gastric and colorectal carcinoma or lung cancer. [21] [22] [23] Also, CXCL1 is secreted by human melanoma cells, has mitogenic properties and is implicated in melanoma pathogenesis. [24] [25] [26]
CXCL1 plays a role in spinal cord development by inhibiting the migration of oligodendrocyte precursors. [11] CXCR2 receptor for CXCL1 is expressed in the brain and spinal cord by neurons and oligodendrocytes and during CNS pathologies such as Alzheimer's disease, multiple sclerosis and brain injury also by microglia. An initial study in mice showed evidence that CXCL1 decreased the severity of multiple sclerosis and may offer a neuro-protective function. [27] On the other hand, on the periphery, CXCL1 contributes to the release of prostaglandins and thus causes increased sensitivity to pain and drives nociceptive sensitization via recruitment of neutrophils to the tissue. Phosphorylation of ERK1/ERK2 kinases and activation of NMDA receptors leads to transcription of genes inducing chronic pain, such as c-Fos or cyclooxygenase-2 (COX-2). [16]
Chemokines, or chemotactic cytokines, are a family of small cytokines or signaling proteins secreted by cells that induce directional movement of leukocytes, as well as other cell types, including endothelial and epithelial cells. In addition to playing a major role in the activation of host immune responses, chemokines are important for biological processes, including morphogenesis and wound healing, as well as in the pathogenesis of diseases like cancers.
Interleukin 8 is a chemokine produced by macrophages and other cell types such as epithelial cells, airway smooth muscle cells and endothelial cells. Endothelial cells store IL-8 in their storage vesicles, the Weibel–Palade bodies. In humans, the interleukin-8 protein is encoded by the CXCL8 gene. IL-8 is initially produced as a precursor peptide of 99 amino acids which then undergoes cleavage to create several active IL-8 isoforms. In culture, a 72 amino acid peptide is the major form secreted by macrophages.
Macrophage Inflammatory Proteins (MIP) belong to the family of chemotactic cytokines known as chemokines. In humans, there are two major forms, MIP-1α and MIP-1β, renamed CCL3 and CCL4 respectively, since 2000. However, other names are sometimes encountered in older literature, such as LD78α, AT 464.1 and GOS19-1 for human CCL3 and AT 744, Act-2, LAG-1, HC21 and G-26 for human CCL4. Other macrophage inflammatory proteins include MIP-2, MIP-3 and MIP-5.
Interleukin 17 family is a family of pro-inflammatory cystine knot cytokines. They are produced by a group of T helper cell known as T helper 17 cell in response to their stimulation with IL-23. Originally, Th17 was identified in 1993 by Rouvier et al. who isolated IL17A transcript from a rodent T-cell hybridoma. The protein encoded by IL17A is a founding member of IL-17 family. IL17A protein exhibits a high homology with a viral IL-17-like protein encoded in the genome of T-lymphotropic rhadinovirus Herpesvirus saimiri. In rodents, IL-17A is often referred to as CTLA8.
Chemokine ligand 1 (CCL1) is also known as small inducible cytokine A1 and I-309 in humans. CCL1 is a small glycoprotein that belongs to the CC chemokine family.
Chemokine ligand 9 (CXCL9) is a small cytokine belonging to the CXC chemokine family that is also known as monokine induced by gamma interferon (MIG). The CXCL9 is one of the chemokine which plays role to induce chemotaxis, promote differentiation and multiplication of leukocytes, and cause tissue extravasation.
Chemokine ligand 2 (CXCL2) is a small cytokine belonging to the CXC chemokine family that is also called macrophage inflammatory protein 2-alpha (MIP2-alpha), Growth-regulated protein beta (Gro-beta) and Gro oncogene-2 (Gro-2). CXCL2 is 90% identical in amino acid sequence as a related chemokine, CXCL1. This chemokine is secreted by monocytes and macrophages and is chemotactic for polymorphonuclear leukocytes and hematopoietic stem cells. The gene for CXCL2 is located on human chromosome 4 in a cluster of other CXC chemokines. CXCL2 mobilizes cells by interacting with a cell surface chemokine receptor called CXCR2.
Chemokine ligand 3 (CXCL3) is a small cytokine belonging to the CXC chemokine family that is also known as GRO3 oncogene (GRO3), GRO protein gamma (GROg) and macrophage inflammatory protein-2-beta (MIP2b). CXCL3 controls migration and adhesion of monocytes and mediates its effects on its target cell by interacting with a cell surface chemokine receptor called CXCR2. More recently, it has been shown that Cxcl3 regulates cell autonomously the migration of the precursors of cerebellar granule neurons toward the internal layers of cerebellum, during the morphogenesis of cerebellum. Moreover, if the expression of Cxcl3 is reduced in cerebellar granule neuron precursors, this highly enhances the frequency of the medulloblastoma, the tumor of cerebellum. In fact, the reduced expression of Cxcl3 forces the cerebellar granule neuron precursors to remain at the surface of the cerebellum, where they highly proliferate under the stimulus of Sonic hedgehog, becoming target of transforming insults. Remarkably, the treatment with CXCL3 completely prevents the growth of medulloblastoma lesions in a Shh-type mouse model of medulloblastoma. Thus, CXCL3 is a target for medulloblastoma therapy. Cxcl3 is directly regulated transcriptionally by BTG2
C-X-C motif chemokine 5 is a protein that in humans is encoded by the CXCL5 gene.
Chemokine ligand 14 (CXCL14) is a small cytokine belonging to the CXC chemokine family that is also known as BRAK. Mature CXCL14 has many of the conserved features of the CXC chemokine subfamily but has some differences too, such as a shorter N-terminus and five extra amino acids in the region between its third and fourth cysteines. CXCL14 is constitutively expressed at high levels in many normal tissues, where its cellular source is thought to be fibroblasts. However, it is reduced or absent from most cancer cells. This chemokine is chemotactic for monocytes and can activate these cells in the presence of an inflammatory mediator called prostaglandin-E2 (PGE2). It is also a potent chemoattractant and activator of dendritic cells, is implicated in homing of these cells, and can stimulate the migration of activated NK cells. CXCL14 also inhibits angiogenesis, possibly as a result of its ability to block endothelial cell chemotaxis. The gene for CXCL14 contains four exons and is located on chromosome 5 in humans.
CXC chemokine receptors are integral membrane proteins that specifically bind and respond to cytokines of the CXC chemokine family. They represent one subfamily of chemokine receptors, a large family of G protein-linked receptors that are known as seven transmembrane (7-TM) proteins, since they span the cell membrane seven times. There are currently six known CXC chemokine receptors in mammals, named CXCR1 through CXCR6.
Chemokine ligand 6 (CXCL6) is a small cytokine belonging to the CXC chemokine family that is also known as granulocyte chemotactic protein 2 (GCP-2). As its former name suggests, CXCL6 is a chemoattractant for neutrophilic granulocytes. It elicits its chemotactic effects by interacting with the chemokine receptors CXCR1 and CXCR2. The gene for CXCL6 is located on human chromosome 4 in a cluster with other CXC chemokine genes.
Chemokine ligand 17 (CXCL17) is a small cytokine belonging to the CXC chemokine family that has been identified in humans and mice. CXCL17 attracts dendritic cells and monocytes and is regulated in tumors. It is also known as VEGF co-regulated chemokine 1 (VCC-1) and dendritic cell- and monocyte-attracting chemokine-like protein (DMC). This chemokine is constitutively expressed in the lung. The gene for human CXCL17 is located on chromosome 19.
Interleukin 8 receptor, beta is a chemokine receptor. IL8RB is also known as CXCR2, and CXCR2 is now the IUPHAR Committee on Receptor Nomenclature and Drug classification-recommended name.
Interleukin 8 receptor, alpha is a chemokine receptor. This name and the corresponding gene symbol IL8RA have been replaced by the HGNC approved name C-X-C motif chemokine receptor 1 and the approved symbol CXCR1. It has also been designated as CD181. The IUPHAR Committee on Receptor Nomenclature and Drug Classification use the HGNC recommended name, CXCR1.
Chemokine receptor 6 also known as CCR6 is a CC chemokine receptor protein which in humans is encoded by the CCR6 gene. CCR6 has also recently been designated CD196. The gene is located on the long arm of Chromosome 6 (6q27) on the Watson (plus) strand. It is 139,737 bases long and encodes a protein of 374 amino acids.
Interleukin-17A is a protein that in humans is encoded by the IL17A gene. In rodents, IL-17A used to be referred to as CTLA8, after the similarity with a viral gene.
Chemorepulsion is the directional movement of a cell away from a substance. Of the two directional varieties of chemotaxis, chemoattraction has been studied to a much greater extent. Only recently have the key components of the chemorepulsive pathway been elucidated. The exact mechanism is still being investigated, and its constituents are currently being explored as likely candidates for immunotherapies.
Interleukin 17F (IL-17F) is signaling protein that is in human is encoded by the IL17F gene and is considered a pro-inflammatory cytokine. This protein belongs to the interleukin 17 family and is mainly produced by the T helper 17 cells after their stimulation with interleukin 23. However, IL-17F can be also produced by a wide range of cell types, including innate immune cells and epithelial cells.
Ann Richmond is the Ingram Professor of Cancer Research at the Vanderbilt-Ingram Cancer Center and professor of Pharmacology and Dermatology at Vanderbilt University.