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STIM2
Stromal interaction molecule 2 (STIM2) is a protein that in humans is encoded by the ''STIM2'' gene.〔(【引用サイトリンク】 url = http://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=57620 )〕
This gene is a member of the stromal interaction molecule (STIM) family which comprises only two members together with its homologue STIM1, and likely arose from a common ancestral gene. They encode type 1 transmembrane proteins that are located in the sarco/endoplasmic reticulum (SR / ER) into the cell. Alternative translation initiation from an AUG and a non-AUG (UUG) start site results in the production of two different STIM2 isoforms.
Both members of the STIM family were identified in 2005 as free-calcium (Ca2+) sensors which participate in a mechanism of Ca2+ entry into the cell referred to as store-operated Ca2+ entry (SOCE). Many cellular processes and signaling pathways are started by previous release of Ca2+ stored in subcellular organelles, which needs of a continuous refilling. SOCE is considered the mechanism of store refilling and an essential mechanism of Ca2+ signaling in non-electrically excitable cells. While STIM1 triggers SOCE, research on STIM2 function suggests a major role as feedback regulator that stabilizes basal cytosolic and S/ER Ca2+ concentration (). STIM2 detects small decreases in Ca2+ content stored in the S/ER, switches to the activated state and interacts with so called store-operated Ca2+ (SOC) channels located in the plasma membrane, such as Orai or TRPC channels, allowing SOCE. Although the functional role of STIM2 has been elusive for many years, studies performed in 2009-2010 on murine models suggested that STIM2 participates in processes of the development and functioning of many cell types, including smooth muscle myoblasts, cells of the immune system and neurons, and is involved in tumorigenesis, the development of autoimmune diseases and mechanisms of neuronal damage after transient ischemic conditions.
== Gene ==
In 2001, ''STIM2'' was identified as a new human homologue of the ''STIM1'' gene, representing the second member of a two-gene family in vertebrates.〔 The ''STIM2'' gene contains 12 exons and 11 introns located on the human chromosome 4p15.1, and on the large arm of the mouse chromosome 5, close to the centromere. The members of ''STIM'' family most probably have evolved from a single gene in lower multicellular eukaryotes into two related genes in vertebrates, since human ''STIM1'' and ''STIM2'' as well as ''Drosophila melanogaster'' ''Stim'' (''D-Stim'') have a conserved genomic organization. The D-STIM protein of 570 aas exhibits equal similarity to both STIM1 (33% identical; 50% of amino acid sequence conserved) and STIM2 (31% identical; 46% of amino acid sequence conserved). Unicellular eukaryotes such as ''Monosiga brevicollis'', a unicellular choanoflagellate has been reported to have a STIM-like gene, however no ''STIM''-like genes have been identified in prokaryotes. No additional STIM-like proteins have been identified until now in vertebrates.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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