Cathepsin K

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

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

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

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

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

Merck has a Cathepsin K inhibitor in Phase 3 clinical trials by the name of is_associated_with::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.