S100A2 (S100 calcium binding protein A2)

	The S100A2 gene spans a total region of 4723 bp (NM_005978.3) consisting of three exons. Exon 1 is untranslated, exon 2 codes for the N-terminal 47 amino acids and exon 3 codes for the C-terminal 50 amino acids.
Description	The nucleotide sequence and genomic organization of the S100A2 gene was originally described by Wicki et al. (1997), using a normal and a tumorigenic breast epithelial cell line. The structure of S100A2 was originally deduced by the analysis of cDNA from a positive genomic clone from an EMBL-3 SP6/T7 human female peripheral blood leukocyte genomic library (Clontech, no. HL 1111j). The human S100A2 gene is located next to the S100A4 locus on chromosome 1q21.3 within a cluster of S100 genes (Wolf et al., 2011), and part of the epidermal differentiation complex (Wolf et al., 2011). The S100A2 gene spans a total region of 4723 bp (NM_005978.3) consisting of three exons. The three-exon-structure contains the coding sequence within exons two and three, reflecting the common composition of S100 genes. Exon 1 is untranslated, exon 2 codes for the N-terminal 47 amino acids and exon 3 codes for the C-terminal 50 amino acids. The S100A2 gene has a total length of 4723 bp and seven splice variants, which can be categorized into five variants with protein product and two transcripts without an open-reading frame. Four of the variants contain the three-exon structure with the coding sequences in exon 2 and exon 3, while also sharing identical protein sequences only differing in their untranslated 5' region (Wolf et al., 2011).
Transcription	The S100A2 mRNA product length, including the poly-adenylate stretch, is 970 bp (NM_005978.3). The S100A2 gene has an open-reading frame of 294 nucleotides encoding for a protein of 97 amino acid residues with a molecular mass of 11,117 kDa (NM_005969.1; see below). Wicki et al. (1997) identified an enhancer element in the promoter region necessary for the transcription of the S100A2 gene. This enhancer element is active in both orientations and either upstream or downstream of the reporter gene, and is both necessary and sufficient for transcription of the gene (Wicki et al., 1997).

Note	The S100A2 gene encodes for a protein of 97 amino acid residues, with a molecular mass of 11,117 kDa (P29034; UniProtKB).
	The protein structure and amino acid sequence of S100A2 (human). Modified from Wolf et al., Amino Acids, 2011.
Description	S100A2 is a member of the S100 family of calcium-binding proteins. The S100A2 gene encodes for a protein of 98 amino acid residues, with a molecular mass of 11,117 kDa (P29034; UniProtKB). S100 proteins are a family of low-molecular weight (9-12 kD), calcium-binding proteins that initiate a number of cellular processes such as cell division, motility, secretion, protein synthesis, and membrane permeability through both calcium dependent and independent mechanism. Greater than twenty five different S100 proteins have so far been identified with many mapping closely together on chromosome 1q21. S100A2 calcium-binding protein is characterized by four helices, two distinct calcium-binding EF-hand motifs, a central hinge region and C- and N-terminal variable domains. S100 proteins are found in the cytoplasm as preassembled dimers. A potential role for S100 proteins in cancer originated from observations that the evolutionarily conserved gene cluster containing S100 genes on human chromosome 1q21 underwent several rearrangements during tumour development.
Expression	S100A2 appears to be tissue specific as it is expressed in many normal and tumour tissues. Expression of S100A2 occurs in normal breast, lung, kidney, prostate, skin and oral squamous cell tissue, with loss of expression observed in associated carcinomas suggesting a putative tumour suppressor role; while in some malignant tissues, such as pancreatic, esophageal, gastric, papillary and follicular thyroid, some subsets of lung cancer and non-small cell lung cancer high expression of S100A2 is associated with poor prognosis and increased metastases. Clearly, expression of S100A2 is not ubiquitous for all tissues and there is evidently an element of tissue-specific expression.
Localisation	S100A2 is primarily localised in the nucleus with translocation to the cytoplasm evident in a number of tissue types.
Function	Little is known about S100A2 function and its potential contribution as either a tumour suppressor or contributor to tumorigenesis and metastases. Upon calcium binding a conformational change occurs exposing a target protein recognition site. Once in the calcium-activated state each monomer can interact with one target protein. In this state the S100 proteins act as calcium sensors and play a role in protein phosphorylation, enzyme activation via phosphorylation, inflammation, cellular contraction and relaxation by regulating cytoskeletal constituents including actin and myosin, and nuclear transcription promoting cell proliferation and differentiation.
Homology	Close relation to S100A4 has been confirmed by sequence analysis. Both proteins share over 60% amino acid sequence identity (Glenney et al., 1989).

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