CTSK Gene (Cathepsin K)
Key regulator of bone resorption and extracellular matrix degradation
Gene Information Card
| Symbol | CTSK |
|---|---|
| Full Name | cathepsin K |
| Gene Type | protein-coding |
| Chromosomal Location | 1q21.3 |
| NCBI Gene ID | 1513 ncbi.nlm.nih.gov/gene/1513 |
| Ensembl ID | ENSG00000143387 |
| UniProt ID | P43235 |
| OMIM ID | 601105 |
| HGNC ID | 2536 |
| Aliases | CTSO2, CTSO1, CTSO, PKND, MGC23107 |
Description
The CTSK gene encodes cathepsin K, a lysosomal cysteine protease predominantly expressed in osteoclasts. It plays a critical role in bone resorption by degrading collagen type I and other matrix proteins. Mutations in CTSK cause pycnodysostosis, an autosomal recessive skeletal dysplasia characterized by short stature, osteosclerosis, and bone fragility. Cathepsin K is also implicated in osteoporosis, arthritis, and certain cancers.
Disease Associations
| Disease category | Pathophysiological mechanism | Genomic evidence |
|---|---|---|
| Pycnodysostosis | Loss-of-function mutations in CTSK impair bone resorption, leading to osteosclerosis and skeletal abnormalities. | OMIM #265800 |
| Osteoporosis | Increased cathepsin K activity contributes to excessive bone resorption; inhibitors are being developed as therapeutics. | NCBI Gene, PubMed |
| Osteoarthritis | Elevated cathepsin K expression in cartilage and synovium promotes matrix degradation. | PubMed |
Expression Profile
Tissue Expression
| Tissue | nTPM | level |
|---|---|---|
| Bone marrow | 0.0 | Not detected |
| Spleen | 0.0 | Not detected |
| Lung | 0.0 | Not detected |
| Thyroid | 0.0 | Not detected |
| Testis | 0.0 | Not detected |
| Ovary | 0.0 | Not detected |
| Small intestine | 0.0 | Not detected |
| Colon | 0.0 | Not detected |
| Kidney | 0.0 | Not detected |
| Liver | 0.0 | Not detected |
| Heart | 0.0 | Not detected |
| Skeletal muscle | 0.0 | Not detected |
| Adipose tissue | 0.0 | Not detected |
| Breast | 0.0 | Not detected |
| Prostate | 0.0 | Not detected |
| Bladder | 0.0 | Not detected |
| Cervix | 0.0 | Not detected |
| Endometrium | 0.0 | Not detected |
| Fallopian tube | 0.0 | Not detected |
| Vagina | 0.0 | Not detected |
| Skin | 0.0 | Not detected |
| Blood | 0.0 | Not detected |
| Lymph node | 0.0 | Not detected |
| Tonsil | 0.0 | Not detected |
| Bone | 0.0 | Not detected |
| Cartilage | 0.0 | Not detected |
| Synovial fluid | 0.0 | Not detected |
| Salivary gland | 0.0 | Not detected |
| Esophagus | 0.0 | Not detected |
| Stomach | 0.0 | Not detected |
| Duodenum | 0.0 | Not detected |
| Pancreas | 0.0 | Not detected |
| Gallbladder | 0.0 | Not detected |
| Adrenal gland | 0.0 | Not detected |
| Pituitary gland | 0.0 | Not detected |
| Brain | 0.0 | Not detected |
| Cerebellum | 0.0 | Not detected |
| Spinal cord | 0.0 | Not detected |
| Retina | 0.0 | Not detected |
| Optic nerve | 0.0 | Not detected |
| Heart muscle | 0.0 | Not detected |
| Smooth muscle | 0.0 | Not detected |
| Placenta | 0.0 | Not detected |
| Umbilical cord | 0.0 | Not detected |
| Amniotic fluid | 0.0 | Not detected |
| Fetal brain | 0.0 | Not detected |
| Fetal liver | 0.0 | Not detected |
| Fetal lung | 0.0 | Not detected |
| Fetal kidney | 0.0 | Not detected |
| Fetal heart | 0.0 | Not detected |
| Fetal muscle | 0.0 | Not detected |
| Fetal skin | 0.0 | Not detected |
| Fetal bone | 0.0 | Not detected |
| Fetal cartilage | 0.0 | Not detected |
| Fetal thymus | 0.0 | Not detected |
| Fetal spleen | 0.0 | Not detected |
| Fetal adrenal | 0.0 | Not detected |
| Fetal pancreas | 0.0 | Not detected |
| Fetal intestine | 0.0 | Not detected |
| Fetal colon | 0.0 | Not detected |
| Fetal kidney | 0.0 | Not detected |
| Fetal lung | 0.0 | Not detected |
| Fetal heart | 0.0 | Not detected |
| Fetal muscle | 0.0 | Not detected |
| Fetal skin | 0.0 | Not detected |
| Fetal bone | 0.0 | Not detected |
| Fetal cartilage | 0.0 | Not detected |
| Fetal thymus | 0.0 | Not detected |
| Fetal spleen | 0.0 | Not detected |
| Fetal adrenal | 0.0 | Not detected |
| Fetal pancreas | 0.0 | Not detected |
| Fetal intestine | 0.0 | Not detected |
| Fetal colon | 0.0 | Not detected |
Cell Line Expression
| Cell Line | nTPM | Notes |
|---|---|---|
| Osteoclasts | High | Primary site of expression; essential for bone resorption. |
| Macrophages | Moderate | Expressed in activated macrophages; involved in inflammation. |
| Fibroblasts | Low | Induced under certain pathological conditions. |
| Breast cancer cells | Variable | Overexpressed in some breast cancer cell lines; associated with metastasis. |
Data source：Human Protein Atlas（proteinatlas.org）
Mutations & Variants
Hotspot Mutations
| Variant | Type | Frequency | Functional Description |
|---|---|---|---|
| c.830C>T (p.Thr277Ile) | Missense | Rare | Loss of function; associated with pycnodysostosis. |
| c.746G>A (p.Arg249Gln) | Missense | Rare | Loss of function; associated with pycnodysostosis. |
| c.1A>G (p.Met1Val) | Start loss | Rare | Loss of function; associated with pycnodysostosis. |
| c.121_122delCT (p.Leu41Valfs*19) | Frameshift | Rare | Loss of function; associated with pycnodysostosis. |
Mutation functional classification
Loss of Function (LOF)
Most CTSK mutations are loss-of-function, leading to pycnodysostosis due to impaired bone resorption.
Gain of Function (GOF)
No gain-of-function mutations have been reported in CTSK.
Dominant Negative (DN)
No dominant-negative mutations have been described for CTSK.
View complete mutation data：
Gene Ontology (GO)
| • cysteine-type endopeptidase activity | • proteolysis |
| • collagen catabolic process | • bone resorption |
| • lysosome | • extracellular matrix disassembly |
Pathways
• Osteoclast differentiation (KEGG hsa04380)
• Lysosome (KEGG hsa04142)
Protein Summary
Cathepsin K is a 329-amino acid lysosomal cysteine protease with a molecular weight of approximately 37 kDa. It is synthesized as a zymogen and activated by proteolytic cleavage. The enzyme has a unique ability to cleave collagen type I at multiple sites, making it essential for bone resorption. Its activity is regulated by pH and specific inhibitors such as cystatin C. Cathepsin K is a target for therapeutic inhibition in osteoporosis.
Related Services
Related Products
| Product name | Cat.No. | Species | Gene ID | |
|---|---|---|---|---|
| CTSK Knockout HEK293 Cell Line | EDJ-KQ3610 | Human | 1513 | Details Get a Quote |
| CTSK Knockout A-549 Cell Line | EDJ-KQ25529 | Human | 1513 | Details Get a Quote |
| CTSK Knockout HCT 116 Cell Line | EDJ-KQ25530 | Human | 1513 | Details Get a Quote |
| CTSK Knockout HeLa Cell Line | EDJ-KQ25531 | Human | 1513 | Details Get a Quote |
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