Protein S100-A8

Also known as: Calgranulin-A, Calprotectin L1L subunit, Cystic fibrosis antigen, Leukocyte L1 complex light chain, Migration inhibitory factor-related protein 8, S100 calcium-binding protein A8, Urinary stone protein band A, S100A8, P05109

**Mechanism of Action** Protein S100-A8 (calgranulin A) is a member of the S100 family of calcium-binding proteins, predominantly expressed in neutrophils, monocytes, and epithelial cells. It forms heterodimers with S100-A9 (calprotectin) and, upon calcium binding, undergoes conformational changes that enable interaction with toll-like receptor 4 (TLR4) and receptor for advanced glycation end-products (RAGE). These interactions activate NF-κB and MAPK signaling pathways, promoting pro-inflammatory cytokine release (e.g., IL-1β, TNF-α) and leukocyte recruitment. Additionally, S100-A8 sequesters zinc and manganese, exerting antimicrobial effects by depriving pathogens of essential trace metals. **Key Research Findings** Experimental studies demonstrate that S100-A8 is upregulated in acute and chronic inflammatory conditions, including rheumatoid arthritis, inflammatory bowel disease, and sepsis. Elevated serum levels correlate with disease activity and serve as a biomarker for inflammation. In murine models, S100-A8 deficiency reduces neutrophil infiltration and tissue damage in sterile inflammation, while its overexpression exacerbates autoimmune responses. Zinc-binding capacity also links S100-A8 to regulation of matrix metalloproteinases and wound healing. Current research explores its role in cancer-associated inflammation, where it may promote tumor progression via RAGE signaling. **Clinical Relevance** S100-A8 is an experimental target for anti-inflammatory therapies, with inhibitors of its interaction with TLR4/RAGE under preclinical investigation. Calprotectin (S100-A8/A9) is already used clinically as a fecal biomarker for gastrointestinal inflammation. However, direct therapeutic modulation of S100-A8 remains investigational, with no approved drugs targeting this protein. Its dual role in host defense and chronic inflammation necessitates careful context-dependent evaluation. For research purposes only — not medical advice.

Key data

Mechanism of action

S100A8 is a calcium- and zinc-binding protein which plays a prominent role in the regulation of inflammatory processes and immune response. It can induce neutrophil chemotaxis and adhesion. Predominantly found as calprotectin (S100A8/A9) which has a wide plethora of intra- and extracellular functions. The intracellular functions include: facilitating leukocyte arachidonic acid trafficking and metabolism, modulation of the tubulin-dependent cytoskeleton during migration of phagocytes and activation of the neutrophilic NADPH-oxidase. Also participates in regulatory T-cell differentiation together with CD69 (PubMed:26296369). Activates NADPH-oxidase by facilitating the enzyme complex assembly at the cell membrane, transferring arachidonic acid, an essential cofactor, to the enzyme complex and S100A8 contributes to the enzyme assembly by directly binding to NCF2/P67PHOX. The extracellular functions involve pro-inflammatory, antimicrobial, oxidant-scavenging and apoptosis-inducing activities. Its pro-inflammatory activity includes recruitment of leukocytes, promotion of cytokine and chemokine production, and regulation of leukocyte adhesion and migration. Acts as an alarmin or a danger associated molecular pattern (DAMP) molecule and stimulates innate immune cells via binding to pattern recognition receptors such as Toll-like receptor 4 (TLR4) and receptor for advanced glycation endproducts (AGER). Binding to TLR4 and AGER activates the MAP-kinase and NF-kappa-B signaling pathways resulting in the amplification of the pro-inflammatory cascade. Has antimicrobial activity towards bacteria and fungi and exerts its antimicrobial activity probably via chelation of Zn(2+) which is essential for microbial growth. Can induce cell death via autophagy and apoptosis and this occurs through the cross-talk of mitochondria and lysosomes via reactive oxygen species (ROS) and the process involves BNIP3. Can regulate neutrophil number and apoptosis by an anti-apoptotic effect; regulates cell survival via ITGAM/ITGB and TLR4 and a signaling mechanism involving MEK-ERK. Its role as an oxidant scavenger has a protective role in preventing exaggerated tissue damage by scavenging oxidants. Can act as a potent amplifier of inflammation in autoimmunity as well as in cancer development and tumor spread. The iNOS-S100A8/A9 transnitrosylase complex directs selective inflammatory stimulus-dependent S-nitrosylation of GAPDH and probably multiple targets such as ANXA5, EZR, MSN and VIM by recognizing a [IL]-x-C-x-x-[DE] motif; S100A8 seems to contribute to S-nitrosylation site selectivity

Research & studies

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