Cathepsin K mRNA and protein expression in prostate cancer progression

J Bone Miner Res. 2003 Feb;18(2):222-30. doi: 10.1359/jbmr.2003.18.2.222.


Prostate cancer (CaP) is the most commonly diagnosed malignancy in men and is often associated with bone metastases, which cause much of the morbidity associated with CaP. Lesions associated with CaP generally exhibit increased bone formation and resorption. Increased bone resorption may release factors from the extracellular matrix that contribute to tumor growth. Cathepsin K (cat K) is a cysteine protease that exhibits strong degradative activity against the extracellular matrix and is involved in osteoclast-mediated bone destruction. In this study, we analyzed the expression of cat K in CaP cell lines and patient samples. Cat K message was detected in CaP cell lines by reverse transcription-polymerase chain reaction (RT-PCR) and in primary CaP and metastases by in situ hybridization. Immunohistochemistry revealed variable expression of cat K in primary CaP samples, as well as nonosseous metastases, whereas expression in bone metastases was significantly higher than in primary CaP, and normal prostate tissues were negative. Cat K protein was detected in CaP cell lines by Western blotting after immunoprecipitation. Cat K enzymatic activity was also detected in CaP cell lines by a fluorogenic assay and by an assay for degradation of collagen type I. Increased levels of NTx, a marker of bone matrix degradation mediated primarily by cat K, were also detected in sera of patients with CaP bone metastases. We hypothesize that CaP-expressed cat K may contribute to the invasive potential of CaP, while increased expression in bone metastases is consistent with a role in matrix degradation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Blotting, Western
  • Bone Resorption
  • Cathepsin K
  • Cathepsins / metabolism*
  • Collagen / metabolism
  • Collagen Type I / metabolism
  • Cysteine Endopeptidases / metabolism
  • Disease Progression
  • Electrophoresis, Polyacrylamide Gel
  • Enzyme-Linked Immunosorbent Assay
  • Humans
  • Immunohistochemistry
  • In Situ Hybridization
  • Male
  • Neoplasm Metastasis
  • Precipitin Tests
  • Prostatic Neoplasms / metabolism*
  • Prostatic Neoplasms / pathology
  • RNA, Messenger / metabolism*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Tumor Cells, Cultured


  • Collagen Type I
  • RNA, Messenger
  • Collagen
  • Cathepsins
  • Cysteine Endopeptidases
  • CTSK protein, human
  • Cathepsin K