title: Cathepsin H indirectly regulates morphogenetic protein-4 (BMP-4) in various human cell lines.
abstract: BACKGROUND
  Cathepsin H is a cysteine protease considered to play a major role in tumor progression, however, its precise function in tumorigenesis is unclear. Cathepsin H was recently proposed to be involved in processing of bone morphogenetic protein 4 (BMP-4) in mice. In order to clarify whether cathepsin H also regulates BMP-4 in humans, its impact on BMP-4 expression, processing and degradation was investigated in prostate cancer (PC-3), osteosarcoma (HOS) and pro-monocytic (U937) human cell lines.
  
  
  METHODS
  BMP-4 expression was founded to be regulated by cathepsin H using PCR array technology and confirmed by real time PCR. Immunoassays including Western blot and confocal microscopy were used to evaluate the influence of cathepsin H on BMP-4 processing.
  
  
  RESULTS
  In contrast to HOS, the expression of BMP-4 mRNA in U937 and PC3 cells was significantly decreased by cathepsin H. The different regulation of BMP-4 synthesis could be associated with the absence of the mature 28 kDa cathepsin H form in HOS cells, where only the intermediate 30 kDa form was observed. No co-localization of BMP-4 and cathepsin H was observed in human cell lines and the multistep processing of BMP-4 was not altered in the presence of specific cathepsin H inhibitor. Isolated cathepsin H does not cleave mature recombinant BMP-4, neither with its amino- nor its endopeptidase activity.
  
  
  CONCLUSIONS
  Our results exclude direct proteolytic processing of BMP-4 by cathepsin H, however, they provide support for its involvement in the regulation of BMP-4 expression.
authors.affiliation: Department of Pharmaceutical Biology, Faculty of Pharmacy, University of Ljubljana, Ljubljana, Slovenia.
authors.forename: Matija
authors.initials: M
authors.lastname: Rojnik
authors.forename: Zala
authors.initials: Z
authors.lastname: Jevnikar
authors.forename: Bojana
authors.initials: B
authors.lastname: Mirkovic
authors.forename: Damjan
authors.initials: D
authors.lastname: Janes
authors.forename: Nace
authors.initials: N
authors.lastname: Zidar
authors.forename: Danijel
authors.initials: D
authors.lastname: Kikelj
authors.forename: Janko
authors.initials: J
authors.lastname: Kos