The cystatin superfamily encompasses proteins that contain multiple cystatin-like sequences. Some of the members are active cysteine protease inhibitors, while others have lost or perhaps never acquired this inhibitory activity. There are three inhibitory families in the superfamily, including the type 1 cystatins (stefins), type 2 cystatins and the kininogens. The type 2 cystatin proteins are a class of cysteine proteinase inhibitors found in a variety of human fluids and secretions, where they appear to provide protective functions. This gene encodes a cystatin from the type 2 family, which is down-regulated in metastatic breast tumor cells as compared to primary tumor cells. Loss of expression is likely associated with the progression of a primary tumor to a metastatic phenotype.[7]
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Thiesse M, Millar SJ, Dickinson DP (1994). "The human type 2 cystatin gene family consists of eight to nine members, with at least seven genes clustered at a single locus on human chromosome 20". DNA Cell Biol. 13 (2): 97–116. doi:10.1089/dna.1994.13.97. PMID8179826.
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Schagdarsurengin U, Pfeifer GP, Dammann R (2007). "Frequent epigenetic inactivation of cystatin M in breast carcinoma". Oncogene. 26 (21): 3089–94. doi:10.1038/sj.onc.1210107. PMID17099723. S2CID20497160.
