- Human pathology

Home > A. Molecular pathology > cathepsin-K


Thursday 7 January 2021



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


- Germline mutations cause sclerosing osteochondrodysplasia pycnodysostosis, a rare autosomal recessive skeletal dysplasia characterized by abnormal bone and tooth development.


- Positive staining - normal cells

  • fibroblasts (skin, lung, J Am Acad Dermatol 2012;66:e89),
  • osteoclasts
  • Intervertebral disc (Arthritis Res Ther 2011;13:R140)
  • Skin: stratum corneum, mature sebaceous cells, outer root sheath of hair follicles (J Eur Acad Dermatol Venereol 2013;27:e128)

- tumors

- Negative staining

  • Endothelium
  • Most carcinomas (Am J Clin Pathol 2013;139:151)