Cathepsin K

Cathepsin K, abbreviated CTSK, is an enzyme that in humans is encoded by the CTSK gene.

Function

The protein encoded by this gene is a lysosomal cysteine protease involved in bone remodeling and resorption. This protein, which is a member of the peptidase C1 protein family, is expressed predominantly in osteoclasts.

Cathepsin K is a protease, which is defined by its high specificity for kinins, that is involved in bone resorption. The enzyme's ability to catabolize elastin, collagen, and gelatin allow it to break down bone and cartilage. This catabolic activity is also partially responsible for the loss of lung elasticity and recoil in emphysema. Cathepsin K inhibitors, such as odanacatib, show great potential in the treatment of osteoporosis. Cathepsin K is degraded by Cathepsin S, called Controlled Cathepsin Cannibalism.

Cathepsin K expression is stimulated by inflammatory cytokines that are released after tissue injury.

Clinical significance

Cathepsin K is also expressed in a significant fraction of human breast cancers, where it could contribute to tumor invasiveness. Mutations in this gene are the cause of pycnodysostosis, an autosomal recessive disease characterized by osteosclerosis and short stature.

Merck has a Cathepsin K inhibitor in Phase 3 clinical trials by the name of Odanacatib for an expected indication of osteoporosis. Velcura Therapeutics, Inc. has also developded a highly selective cathepsin K inhibitor named VEL-0230 and has been tested in human, rat, equine clinical trials.

Additional images

• Osteoclast1.jpg

  Osteoclast

External links

• The MEROPS online database for peptidases and their inhibitors: C01.036
• Cathepsin K at the US National Library of Medicine Medical Subject Headings (MeSH)