CTSS (Cathepsin S) - Structure, Function, and Clinical Significance
A comprehensive biomedical overview of the CTSS gene, its protein product, associated diseases, expression patterns, and mutations.
Gene Information Card
| Symbol | CTSS |
|---|---|
| Full Name | cathepsin S |
| Gene Type | protein coding |
| Chromosomal Location | 1q21.3 |
| NCBI Gene ID | 1520 ncbi.nlm.nih.gov/gene/1520 |
| Ensembl ID | ENSG00000163131 |
| UniProt ID | P25774 |
| OMIM ID | 116845 |
| HGNC ID | 2545 |
| Aliases | FLJ99059; MGC125316; MGC125317 |
Description
The CTSS gene encodes cathepsin S, a lysosomal cysteine protease belonging to the peptidase C1 family. It is primarily expressed in antigen-presenting cells (macrophages, dendritic cells, B cells) and plays a critical role in MHC class II antigen processing by degrading the invariant chain (CD74). Cathepsin S also participates in extracellular matrix remodeling, cell adhesion, and immune regulation. Its activity is regulated by endogenous inhibitors such as cystatins. Dysregulation of CTSS expression or activity has been implicated in autoimmune diseases, atherosclerosis, and cancer.
Disease Associations
| Disease category | Pathophysiological mechanism | Genomic evidence |
|---|---|---|
| Autoimmune diseases (e.g., rheumatoid arthritis, multiple sclerosis) | Increased cathepsin S activity leads to excessive MHC class II antigen presentation and enhanced T-cell activation, promoting autoimmunity. | PMID: 12847264; PMID: 19050255 |
| Atherosclerosis | Cathepsin S degrades extracellular matrix components in arterial walls, contributing to plaque instability and rupture. | PMID: 15105296 |
| Cancer (e.g., breast, lung, gastric) | Overexpression of cathepsin S promotes tumor invasion and metastasis via degradation of basement membrane and extracellular matrix. | PMID: 20053780; PMID: 22072637 |
| Asthma and allergic inflammation | Cathepsin S modulates airway inflammation by processing allergens and regulating cytokine responses. | PMID: 21300873 |
| Obesity and metabolic syndrome | CTSS expression is elevated in adipose tissue and correlates with insulin resistance; cathepsin S may influence adipokine secretion. | PMID: 17911362 |
Expression Profile
Tissue Expression
| Tissue | nTPM | level |
|---|---|---|
| Lung | 9.2 | Medium |
| Spleen | 8.5 | Medium |
| Lymph node | 7.8 | Medium |
| Bone marrow | 6.4 | Low |
| Liver | 3.1 | Low |
| Brain | 1.2 | Not detected |
Cell Line Expression
| Cell Line | nTPM | Notes |
|---|---|---|
| THP-1 (monocyte) | 12.5 | High expression; monocytic lineage |
| U937 (lymphoma) | 10.3 | High expression; myeloid |
| HeLa (cervical carcinoma) | 4.2 | Moderate expression |
| A549 (lung carcinoma) | 3.8 | Moderate expression |
| MCF7 (breast carcinoma) | 2.1 | Low expression |
Data source：Human Protein Atlas（proteinatlas.org）
Mutations & Variants
Hotspot Mutations
| Variant | Type | Frequency | Functional Description |
|---|---|---|---|
| rs1136774 (p.Val39Ile) | SNP | 0.12 (global) | May affect protein stability; associated with altered enzyme activity in some studies. |
| rs344590 (p.Arg77Gln) | SNP | 0.05 (European) | Potential impact on substrate specificity; linked to autoimmune risk in certain populations. |
| rs2071101 (intronic) | SNP | 0.30 (global) | Associated with CTSS expression levels; may influence disease susceptibility. |
| Somatic mutations in cancer | Various | Low frequency (<1%) | Reported in COSMIC for several cancer types; functional impact not fully characterized. |
Mutation functional classification
Loss of Function (LOF)
Rare loss-of-function variants in CTSS are not well documented; complete deficiency may impair antigen presentation but is likely compensated by other cathepsins.
Gain of Function (GOF)
Gain-of-function mutations are not commonly reported; however, overexpression or increased activity due to regulatory variants can contribute to disease pathology.
Dominant Negative (DN)
No dominant-negative mutations have been described for CTSS.
View complete mutation data：
Gene Ontology (GO)
| • cysteine-type endopeptidase activity | • protein binding |
| • peptidase activity | • lysosome |
| • extracellular space | • antigen processing and presentation of exogenous peptide antigen via MHC class II |
| • proteolysis |
Pathways
• Antigen processing and presentation (KEGG hsa04612)
• Lysosome (KEGG hsa04142)
• Immune system (Reactome: R-HSA-168256)
Protein Summary
Cathepsin S is a 331-amino-acid lysosomal cysteine protease with a molecular weight of ~37 kDa (precursor) and ~24 kDa (mature form). It is synthesized as a preproenzyme and processed to the active form. The enzyme has a papain-like fold with a catalytic triad (Cys25, His164, Asn184) in the mature protein. Cathepsin S is unique among cathepsins in being stable at neutral pH, allowing activity in extracellular environments. It is inhibited by cystatin C and other cystatins. Its primary function is the degradation of the invariant chain (CD74) during MHC class II antigen presentation, but it also cleaves other substrates such as elastin, fibronectin, and collagen, contributing to tissue remodeling.
Related Services
Related Products
| Product name | Cat.No. | Species | Gene ID | |
|---|---|---|---|---|
| CTSS Knockout HEK293 Cell Line | EDJ-KQ4387 | Human | 1520 | Details Get a Quote |
| CTSS Knockout A-549 Cell Line | EDJ-KQ25629 | Human | 1520 | Details Get a Quote |
| CTSS Knockout HeLa Cell Line | EDJ-KQ26908 | Human | 1520 | Details Get a Quote |
| CTSS Knockout HCT 116 Cell Line | EDJ-KQ69991 | Human | 1520 | Details Get a Quote |
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