S100 calcium-binding protein A9 (S100A9) also known as migration inhibitory factor-related protein 14 (MRP14) or calgranulin B is a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

that in humans is encoded by the ''S100A9''

gene In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protei ...

. The proteins

S100A8 S100 calcium-binding protein A8 (S100A8) is a protein that in humans is encoded by the ''S100A8'' gene. It is also known as calgranulin A. The proteins S100A8 and S100A9 form a heterodimer called calprotectin. The protein encoded by this ge ...

and S100A9 form a

heterodimer In biochemistry, a protein dimer is a macromolecular complex or multimer formed by two protein monomers, or single proteins, which are usually non-covalently bound. Many macromolecules, such as proteins or nucleic acids, form dimers. The word ...

called calprotectin.

Function

S100A9 is a member of the S100 family of proteins containing 2

EF hand The EF hand is a helix–loop–helix structural domain or ''motif'' found in a large family of calcium-binding proteins. The EF-hand motif contains a helix–loop–helix topology, much like the spread thumb and forefinger of the human hand, in ...

calcium-binding motifs. S100 proteins are localized in the

cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...

and/or nucleus of a wide range of cells, and involved in the regulation of a number of cellular processes such as cell cycle progression and differentiation. S100 genes include at least 13 members which are located as a cluster on chromosome 1q21. This protein may function in the inhibition of casein kinase. MRP14 complexes with MRP-8 (

), another member of the S100 family of calcium-modulated proteins; together, MRP8 and MRP14 regulate myeloid cell function by binding to Toll-like receptor 4 ( TLR4) and the receptor for advanced glycation end products. Intracellular S100A9 alters mitochondrial homeostasis within

neutrophils Neutrophils are a type of phagocytic white blood cell and part of innate immunity. More specifically, they form the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. Their functions vary in different ...

. As a result, neutrophils lacking S100A9 produce higher levels of mitochondrial superoxide and undergo elevated levels of suicidal NETosis in response to bacterial pathogens. Furthermore, S100A9-deficient mice are protected from systemic ''

Staphylococcus aureus ''Staphylococcus aureus'' is a Gram-positive spherically shaped bacterium, a member of the Bacillota, and is a usual member of the microbiota of the body, frequently found in the upper respiratory tract and on the skin. It is often posi ...

'' infections with lower bacterial burdens in the heart, which suggests an organ-specific function for S100A9.

Clinical significance

Altered expression of the S100A9 protein is associated with the disease

cystic fibrosis Cystic fibrosis (CF) is a genetic disorder inherited in an autosomal recessive manner that impairs the normal clearance of Sputum, mucus from the lungs, which facilitates the colonization and infection of the lungs by bacteria, notably ''Staphy ...

. MRP-8/14 broadly regulates vascular inflammation and contributes to the biological response to vascular injury by promoting

leukocyte White blood cells (scientific name leukocytes), also called immune cells or immunocytes, are cells of the immune system that are involved in protecting the body against both infectious disease and foreign entities. White blood cells are genera ...

recruitment. MRP-8/14 also regulates vascular insults by controlling

neutrophil Neutrophils are a type of phagocytic white blood cell and part of innate immunity. More specifically, they form the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. Their functions vary in differe ...

and

macrophage Macrophages (; abbreviated MPhi, φ, MΦ or MP) are a type of white blood cell of the innate immune system that engulf and digest pathogens, such as cancer cells, microbes, cellular debris and foreign substances, which do not have proteins that ...

accumulation,

cytokine Cytokines () are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are produced by a broad range of cells, including immune cells like macrophages, B cell, B lymphocytes, T cell, T lymphocytes ...

production, and SMC proliferation. The above study has shown therefore the deficiency of MRP-8 and MRP-14 reduces neutrophil- and monocyte-dependent vascular inflammation and attenuates the severity of diverse vascular injury responses in vivo. MRP-8/14 may be a useful biomarker of platelet and inflammatory disease activity in atherothrombosis and may serve as a novel target for therapeutic intervention. Also, the platelet transcriptome reveals quantitative differences between acute and stable coronary artery disease. MRP-14 expression increases before ST-segment-elevation myocardial infarction, (STEMI), and increasing plasma concentrations of MRP-8/14 among healthy individuals predict the risk of future cardiovascular events. S100A9 (myeloid-related protein 14, MRP 14 or calgranulin B) has been implicated in the abnormal differentiation of myeloid cells in the stroma of cancer, and to leukemia progression. This contributes to creating an overall immunosuppressive microenvironment that may contribute to the inability of a protective or therapeutic cellular immune response to be generated by the tumor-bearing host. Outside of malignancy, S100A9 in association with its dimerization partner,

(MRP8 or calgranulin A) signals for lymphocyte recruitment in sites of inflammation. S100A9/A8 (synonyma: Calgranulin A/B; Calprotectin) are also regarded as marker proteins for a number of inflammatory diseases in humans, especially in rheumatoid arthritis and

inflammatory bowel disease Inflammatory bowel disease (IBD) is a group of inflammatory conditions of the colon and small intestine, with Crohn's disease and ulcerative colitis (UC) being the principal types. Crohn's disease affects the small intestine and large intestine ...

(IBD). Myeloid-related protein (MRP)-8 is an inflammatory protein found in several mucosal secretions. In cervico-vaginal secretions MRP-8 can stimulate HIV production; and thus might be involved in sexual transmission of HIV, as well as other sexually transmitted diseases (STD). In Vitro studies have shown that HIV-inducing of recombinant MRP-8 can increase HIV expression by up to 40-fold.

Animal studies

A S100A9

knockout mouse A knockout mouse, or knock-out mouse, is a genetically modified mouse (''Mus musculus'') in which researchers have inactivated, or " knocked out", an existing gene by replacing it or disrupting it with an artificial piece of DNA. They are importan ...

has (a mouse mutant, that is deficient of S100A9) been constructed. This mouse is fertile, viable and healthy. However, expression of S100A8 protein, the dimerization partner of S100A9, is also absent in these mice in differentiated myeloid cells. This mouse line has been used to study the role of S100A9 and S100A8 in a number of experimental inflammatory conditions.

Function

Clinical significance

Animal studies

See also

References

Further reading