''For the ICAO airport code see Candle Lake Airpark, for the diradical compound see Dichlorocarbene.'' The chemokine (C-C motif) ligand 2 (CCL2) is also referred to as monocyte chemoattractant protein 1 (MCP1) and small inducible cytokine A2. CCL2 is a small

cytokine Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm. Cytokines have been shown to be involved in au ...

that belongs to the CC

chemokine 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 additi ...

family. CCL2 tightly regulates cellular mechanics and thereby recruits

monocyte Monocytes are a type of leukocyte or white blood cell. They are the largest type of leukocyte in blood and can differentiate into macrophages and conventional dendritic cells. As a part of the vertebrate innate immune system monocytes also ...

s, memory T cells, and dendritic cells to the sites of

inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molec ...

produced by either tissue injury or

infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable di ...

Genomics

In the human genome, CCL2 and many other CC chemokines are located on chromosome 17 (17q11.2-q21.1). The gene span is 1,927 bases and the CCL2 gene resides on the Watson (plus) strand. The CCL2 gene has three

exon An exon is any part of a gene that will form a part of the final mature RNA produced by that gene after introns have been removed by RNA splicing. The term ''exon'' refers to both the DNA sequence within a gene and to the corresponding sequen ...

s and two

intron An intron is any Nucleic acid sequence, nucleotide sequence within a gene that is not expressed or operative in the final RNA product. The word ''intron'' is derived from the term ''intragenic region'', i.e. a region inside a gene."The notion of ...

s. The CCL2

protein precursor A protein precursor, also called a pro-protein or pro-peptide, is an inactive protein (or peptide) that can be turned into an active form by post-translational modification, such as breaking off a piece of the molecule or adding on another molecule ...

contains a signal peptide of 23

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...

s. In turn, the mature CCL2 is 76 amino acids long. The CCL2 predicted weight is 11.025 kiloDaltons (kDa).

Population genetics

In humans, the levels of CCL2 can vary considerably. In the white people of European descent, the multivariable-adjusted heritability of CCL2 concentrations is as much as 0.37 in the blood plasma and 0.44 - in the serum.

Molecular biology

CCL2 is a monomeric

polypeptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. ...

, with a

molecular weight A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bio ...

of approximately 13-15 kDa depending on levels of

glycosylation Glycosylation is the reaction in which a carbohydrate (or ' glycan'), i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule (a glycosyl acceptor) in order to form a glycoconjugate. In biology (but not al ...

. CCL2 is anchored in the plasma membrane of endothelial cells by glycosaminoglycan side chains of proteoglycans. CCL2 is primarily secreted by

macrophage Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer ce ...

s and

dendritic cell Dendritic cells (DCs) are antigen-presenting cells (also known as ''accessory cells'') of the mammalian immune system. Their main function is to process antigen material and present it on the cell surface to the T cells of the immune system. Th ...

s. Platelet derived growth factor is a major inducer of CCL2 gene. CCR2 and CCR4 are two cell surface receptors that bind CCL2. CCL2 exhibits a chemotactic activity for monocytes and basophils. However, it does not attract neutrophils or eosinophils. After deletion of the N-terminal residue, CCL2 loses its attractivity for basophils and becomes a chemoattractant of eosinophils. Basophils and mast cells that are treated with CCL2 release their granules to the intercellular space. This effect can be also potentiated by a pre-treatment with IL-3 or even by other cytokines. CCL2 augments monocyte anti-tumor activity and it is essential for formation of granulomas. CCL2 protein become a CCR2 antagonist when it is cleaved by

metalloproteinase A metalloproteinase, or metalloprotease, is any protease enzyme whose catalytic mechanism involves a metal. An example is ADAM12 which plays a significant role in the fusion of muscle cells during embryo development, in a process known as myo ...

MMP-12. CCL2 can be found at the sites of tooth eruption and bone degradation. In the bone, CCL2 is expressed by mature osteoclasts and

osteoblast Osteoblasts (from the Greek language, Greek combining forms for "bone", ὀστέο-, ''osteo-'' and βλαστάνω, ''blastanō'' "germinate") are cell (biology), cells with a single Cell nucleus, nucleus that synthesize bone. However, in the p ...

s and it is under control of nuclear factor κB (NFκB). In the human osteoclasts, CCL2 and RANTES (regulated on activation normal T cell expressed and secreted). Both MCP-1 and RANTES induce formation of TRAP-positive, multinuclear cells from M-CSF-treated monocytes in the absence of RANKL, but produced osteoclasts that lacked cathepsin K expression and resorptive capacity. It is proposed that CCL2 and RANTES act as

autocrine Autocrine signaling is a form of cell signaling in which a cell secretes a hormone or chemical messenger (called the autocrine agent) that binds to autocrine receptors on that same cell, leading to changes in the cell. This can be contrasted with p ...

loop in human osteoclast differentiation. The CCL2 chemokine is also expressed by neurons, astrocytes and microglia. The expression of CCL2 in neurons is mainly found in the cerebral cortex, globus pallidus, hippocampus, paraventricular and supraoptic hypothalamic nuclei, lateral hypothalamus, substantia nigra, facial nuclei, motor and spinal trigeminal nuclei, gigantocellular reticular nucleus and in Purkinje cells in the cerebellum.

Clinical importance

CCL2 is implicated in pathogeneses of several diseases characterized by

monocytic Monocytes are a type of leukocyte or white blood cell. They are the largest type of leukocyte in blood and can differentiate into macrophages and conventional dendritic cells. As a part of the vertebrate innate immune system monocytes also infl ...

infiltrates, such as

psoriasis Psoriasis is a long-lasting, noncontagious autoimmune disease characterized by raised areas of abnormal skin. These areas are red, pink, or purple, dry, itchy, and scaly. Psoriasis varies in severity from small, localized patches to comple ...

rheumatoid arthritis Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and hands are inv ...

and

atherosclerosis Atherosclerosis is a pattern of the disease arteriosclerosis in which the wall of the artery develops abnormalities, called lesions. These lesions may lead to narrowing due to the buildup of atheromatous plaque. At onset there are usually no s ...

. Administration of anti-CCL2 antibodies in a model of

glomerulonephritis Glomerulonephritis (GN) is a term used to refer to several kidney diseases (usually affecting both kidneys). Many of the diseases are characterised by inflammation either of the glomeruli or of the small blood vessels in the kidneys, hence the ...

reduces infiltration of macrophages and T cells, reduces crescent formation, as well as scarring and renal impairment. CCL2 is involved in the neuroinflammatory processes that takes place in the various diseases of the central nervous system (CNS), which are characterized by neuronal degeneration. CCL2 expression in

glial cells Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cells in the central nervous system (brain and spinal cord) and the peripheral nervous system that do not produce electrical impulses. They maintain homeostasis, form myel ...

is increased in epilepsy, brain ischemia Alzheimer's disease

experimental autoimmune encephalomyelitis Experimental autoimmune encephalomyelitis, sometimes experimental allergic encephalomyelitis (EAE), is an animal model of brain inflammation. It is an inflammatory demyelinating disease of the central nervous system (CNS). It is mostly used with r ...

(EAE), and

traumatic brain injury A traumatic brain injury (TBI), also known as an intracranial injury, is an injury to the brain caused by an external force. TBI can be classified based on severity (ranging from mild traumatic brain injury TBI/concussionto severe traumatic br ...

. Hypomethylation of CpG sites within the CCL2 promoter region is affected by high levels of blood glucose and TG, which increase CCL2 levels in the blood serum. The later plays an important role in the vascular complications of type 2 diabetes. CCL2 induces amylin expression through

ERK1 Mitogen-activated protein kinase 3, also known as p44MAPK and ERK1, is an enzyme that in humans is encoded by the ''MAPK3'' gene. Function The protein encoded by this gene is a member of the mitogen-activated protein kinase (MAP kinase) famil ...

/ ERK2/ JNK- AP1 and

NF-κB Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) is a protein complex that controls transcription of DNA, cytokine production and cell survival. NF-κB is found in almost all animal cell types and is involved in cellular ...

related signaling pathways independent of CCR2. Amylin upregulation by CCL2 contributes to the elevation of the plasma amylin and insulin resistance in obesity.

Adipocyte Adipocytes, also known as lipocytes and fat cells, are the cells that primarily compose adipose tissue, specialized in storing energy as fat. Adipocytes are derived from mesenchymal stem cells which give rise to adipocytes through adipogenesis. I ...

s secrete various

adipokine The adipokines, or adipocytokines (Greek ', fat; ', cell; and ', movement) are cytokines (cell signaling proteins) secreted by adipose tissue. Some contribute to an obesity-related low-grade state of inflammation or to the development of metabolic ...

s that may be involved in the negative cross-talk between adipose tissue and skeletal muscle. CCL2 impairs insulin signaling in skeletal muscle cells via ERK1/2 activation at doses similar to its physiological plasma concentrations (200 pg/mL), but does not involve activation of the NF-κB pathway. CCL2 significantly reduced insulin-stimulated glucose uptake in myocytes. CCL2 may represent a molecular link in the negative cross-talk between adipose tissue and skeletal muscle assigning a completely novel important role to CCL2 besides inflammation. Incubation of HL-1

cardiomyocyte Cardiac muscle (also called heart muscle, myocardium, cardiomyocytes and cardiac myocytes) is one of three types of vertebrate muscle tissues, with the other two being skeletal muscle and smooth muscle. It is an involuntary, striated muscle ...

s and human myocytes with oxidized-LDL induced the expression of BNP and CCL2 genes, while native LDL (N-LDL) had no effect. Treatment with melatonin in old mice with age related liver inflammation decreased the mRNA expression of TNF-α,

IL-1β Interleukin-1 beta (IL-1β) also known as leukocytic pyrogen, leukocytic endogenous mediator, mononuclear cell factor, lymphocyte activating factor and other names, is a cytokine protein that in humans is encoded by the ''IL1B'' gene."Catabolin ...

, HO ( HO-1 and HO-2),

iNOS Nitric oxide synthases () (NOSs) are a family of enzymes catalyzing the production of nitric oxide (NO) from L-arginine. NO is an important cellular signaling molecule. It helps modulate vascular tone, insulin secretion, airway tone, and perista ...

, CCL2, NF-κB1, NF-κB2 and NKAP in old male mice. The protein expression of TNF-α,

was also decreased and IL-10 increased with melatonin treatment. Exogenous administration of

melatonin Melatonin is a natural product found in plants and animals. It is primarily known in animals as a hormone released by the pineal gland in the brain at night, and has long been associated with control of the sleep–wake cycle. In vertebrat ...

was able to reduce inflammation.

Genomics

Population genetics

Molecular biology

Clinical importance

References

External links

Further reading