CST5

What is CST5 protein?

CST5 (cystatin D) gene is a protein coding gene which situated on the short arm of chromosome 20 at locus 20p11. CST5 is a protein belonging to the cystic protease inhibitor family, members of which are widely present in various organisms and have the function of inhibiting the activity of cystic protease. CST5, in particular, is a secretory type of cystic protease inhibitor found primarily in human saliva and tears, but may also be present in other body fluids and secretions. It contains a signaling peptide, a mature protein region, and a possible glycosylation site. Its structural features include a typical cystic protease inhibitor domain that is critical for its inhibitory activity. The CST5 protein is consisted of 142 amino acids and its molecular mass is approximately 16.1 kDa.

What is the function of CST5 protein?

The primary function of CST5 is as an inhibitor of proteases, particularly cystic proteases such as feline hepsin, cathepsin L and cathepsin S. This inhibition plays an important role in maintaining the balance of cathepasome and preventing tissue damage and inflammation. CST5 expression is regulated by a variety of factors, including the vitamin D metabolite 1α, 25-dihydroxyvitamin D3 (1α,25(OH)2D3). Studies have shown that 1α,25(OH)2D3 can induce the expression of CST5, which may be involved in the regulation of cell proliferation and antitumor activity.

CST5 Related Signaling Pathway

CST5 is an endogenous cysteine protease inhibitor, which is mainly involved in the regulation of proteolysis in cells. It inhibits the activity of the target protease by forming a tight complex with it. In signaling, CST5 can affect a variety of pathways, including cell proliferation, differentiation, apoptosis, and immune regulation. For example, CST5 can regulate the MAPK, NF-κB and PI3K/Akt signaling pathways by inhibiting cysteine protease, thereby affecting the growth and survival of tumor cells. In addition, CST5 may also be involved in the regulation of inflammatory responses and immune responses, as it is able to influence T cell function and cytokine production.

CST5 Related Diseases

CST5 is associated with cerebral amyloid angiopathy, a disease that affects blood vessels in the brain, causing blood vessel walls to thin and amyloid deposits to form, increasing the risk of bleeding in the brain. Studies have shown that CST5 is an ultra-early inflammatory biomarker for traumatic brain injury. Levels of CST5 change rapidly after a TBI occurs, which may help diagnose the severity of TBI and identify patients at risk of developing secondary damage. CST5 is associated with the endochondral ossification pathway, which may affect the normal development and maintenance of bones and is associated with diseases of the skeletal system. In addition, it may be associated with autoimmune diseases, certain types of cancer, and chronic infections.

Fig1. Multifaceted roles of CST5 in breast cancer progression. (Paloma Ordóñez-Morán, 2010)

Bioapplications of CST5

In the field of sports medicine and occupational health, CST5 testing can be used to assess the risk of brain injury in athletes and people engaged in high-risk occupations, as well as to monitor their recovery from potential brain injuries. As a biomarker, CST5 can also be used in forensic and toxicological studies to detect and evaluate possible brain injury conditions, such as in cases of trauma, substance abuse, or other conditions that may lead to brain injury.

CST5 is considered to be an ultra-early inflammatory biomarker for traumatic brain injury. Levels of CST5 change rapidly after a TBI occurs, which may help diagnose the severity of TBI and identify patients at risk of developing secondary damage. This application has important implications for improving clinical interventions, especially in emergency situations, to enable rapid diagnosis and assessment of the condition of patients with TBI.

Case Study 1: Gemma Ferrer-Mayorga, 2015

Cystatin D is an inhibitor of lysosomal and secreted cysteine proteases. Strikingly, cystatin D has been found to inhibit proliferation, migration, and invasion of colon carcinoma cells indicating tumor suppressor activity that is unrelated to protease inhibition. This study demonstrates that a proportion of cystatin D locates within the cell nucleus at specific transcriptionally active chromatin sites. Consistently, transcriptomic analysis show that cystatin D alters gene expression, including that of genes encoding transcription factors such as RUNX1, RUNX2, and MEF2C in HCT116 cells. In concordance with transcriptomic data, quantitative proteomic analysis identified 292 proteins differentially expressed in cystatin D-expressing cells involved in cell adhesion, cytoskeleton, and RNA synthesis and processing. Furthermore, using cytokine arrays we found that cystatin D reduces the secretion of several protumor cytokines such as fibroblast growth factor-4, CX3CL1/fractalkine, neurotrophin 4 oncostatin-M, pulmonary and activation-regulated chemokine/CCL18, and transforming growth factor B3.

Fig1. Western blot analysis showing the presence of cystatin D in both cytoplasm (C) and nuclear (N) fractions of mock- and CST5-transfected SW480-ADH and HCT116 cells.

Fig2. Western blot analysis (20 μg of total cell extracts) of the expression in HCT116-CST5 and HCT116-Mock cells of several proteins selected from the transcriptomic or proteomic analyses.

Case Study 2: Silvia Alvarez-Díaz, 2009

The active vitamin D metabolite 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] has wide but not fully understood antitumor activity. A previous transcriptomic analysis of 1alpha,25(OH)2D3 action on human colon cancer cells revealed cystatin D (CST5), which encodes an inhibitor of several cysteine proteases of the cathepsin family, as a candidate target gene. This study reports that 1alpha,25(OH)2D3 induced vitamin D receptor (VDR) binding to, and activation of, the CST5 promoter and increased CST5 RNA and protein levels in human colon cancer cells. In cells lacking endogenous cystatin D, ectopic cystatin D expression inhibited both proliferation in vitro and xenograft tumor growth in vivo. Furthermore, cystatin D inhibited migration and anchorage-independent growth, antagonized the Wnt/beta-catenin signaling pathway, and repressed c-MYC expression. Cystatin D repressed expression of the epithelial-mesenchymal transition inducers SNAI1, SNAI2, ZEB1, and ZEB2 and, conversely, induced E-cadherin and other adhesion proteins.

Fig3. Immunofluorescence analysis of cystatin D induction.

Fig4. Western blot analysis showing changes in E-cadherin, c-MYC, and LEF-1 proteins in cystatin D–expressing cells.

CST5 has several biochemical functions, for example, cysteine-type endopeptidase inhibitor activity,protein binding. Some of the functions are cooperated with other proteins, some of the functions could acted by CST5 itself. We selected most functions CST5 had, and list some proteins which have the same functions with CST5. You can find most of the proteins on our site.

CST5 has direct interactions with proteins and molecules. Those interactions were detected by several methods such as yeast two hybrid, co-IP, pull-down and so on. We selected proteins and molecules interacted with CST5 here. Most of them are supplied by our site. Hope this information will be useful for your research of CST5.