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Gene Review

CTSO  -  cathepsin O

Homo sapiens

Synonyms: CTSO1, Cathepsin O
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Disease relevance of CTSO

  • The cathepsin O cDNA was expressed in Escherichia coli, and after purification and refolding, the recombinant protein was able to degrade the synthetic peptides benzyloxycarbonyl-Phe-Arg-7-amido-4- methylcoumarin and benzyloxycarbonyl-Arg-Arg-7-amido-4-methylcoumarin widely used as substrates for cysteine proteinases [1].

High impact information on CTSO

  • Cathepsin O proteolytic activity was abolished by trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane (E-64), an inhibitor of this subclass of proteolytic enzymes, thus providing additional evidence that the isolated cDNA codes for an authentic cysteine proteinase [1].
  • Chromosomal localization of CTSO revealed that it maps to chromosome 4q31-q32, which is a unique location for all cysteine proteinases mapped to date [2].
  • The gene (HGMW-approved symbol CTSO) is composed of eight coding exons and seven introns and spans more than 30 kb [2].
  • Based on its high homology to OC2, we have named the human enzyme cathepsin O. Cathepsin O mRNA was identified as a single approximately 1.7 kb transcript in cultures of 15-day-old monocyte-derived macrophages, but was not expressed in human monocytes or alveolar macrophages [3].
  • When transfected into COS-7 cells, cathepsin O displayed potent endoprotease activity against fibrinogen at acid pH [3].

Associations of CTSO with chemical compounds

  • A newly synthesized artificial vitamin B6 derivative, a pridoxal propionate derivative, CLIK-164, showed selective inhibition of cathepsin O/K [4].

Analytical, diagnostic and therapeutic context of CTSO

  • Human cathepsin O. Molecular cloning from a breast carcinoma, production of the active enzyme in Escherichia coli, and expression analysis in human tissues [1].
  • Northern blot analysis of poly(A)+ RNAs isolated from a variety of human tissues demonstrated that cathepsin O is expressed in all examined tissues, which is consistent with a putative role of this protein as a proteolytic enzyme involved in normal cellular protein degradation and turnover [1].


  1. Human cathepsin O. Molecular cloning from a breast carcinoma, production of the active enzyme in Escherichia coli, and expression analysis in human tissues. Velasco, G., Ferrando, A.A., Puente, X.S., Sánchez, L.M., López-Otín, C. J. Biol. Chem. (1994) [Pubmed]
  2. Genomic structure and chromosomal localization of the human cathepsin O gene (CTSO). Santamaría, I., Pendás, A.M., Velasco, G., López-Otín, C. Genomics (1998) [Pubmed]
  3. Molecular cloning of human cathepsin O, a novel endoproteinase and homologue of rabbit OC2. Shi, G.P., Chapman, H.A., Bhairi, S.M., DeLeeuw, C., Reddy, V.Y., Weiss, S.J. FEBS Lett. (1995) [Pubmed]
  4. Inhibition of cathepsin activities by vitamin B6 derivatives. Matsui, A., Tsuzuki, H., Murata, E., Tada, Y., Asao, T., Katunuma, N. Biofactors (2000) [Pubmed]
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