Identification of interleukin-8 converting enzyme as cathepsin L

Biochim Biophys Acta. 2003 Jun 26;1649(1):30-9. doi: 10.1016/s1570-9639(03)00152-3.


IL-8 is produced by various cells, and the NH(2)-terminal amino acid sequence of IL-8 displays heterogeneity among cell types. The mature form of IL-8 has 72 amino acids (72IL-8), while a precursor form (77IL-8) of IL-8 has five additional amino acids to the 72IL-8 NH(2)-terminal. However, it has been unclear how IL-8 is processed to yield the mature form. In this study, converting enzyme was purified as a single 31-kDa band on silver-stained polyacrylamide gel from 160 l of cultured fibroblast supernatant by sequential chromatography. NH(2)-terminal amino acid sequence analysis revealed a sequence, EAPRSVDWRE, which was identified as a partial sequence of cathepsin L. Polyclonal antibodies raised against cathepsin L recognized the purified converting enzyme on Western blot. Moreover, human hepatic cathepsin L cleaved 77IL-8 between Arg(5) and Ser(6), which is the same cleavage site as the putative converting enzyme, resulting in 72IL-8 formation. These data indicate that the converting enzyme of the partially purified fraction of the human fibroblast culture supernatant was cathepsin L. Furthermore, 72IL-8 was sevenfold more potent than 77IL-8 in a neutrophil chemotaxis assay. These results show that cathepsin L is secreted from human fibroblasts in response to external stimuli and plays an important role in IL-8 processing in inflammatory sites.

MeSH terms

  • Blotting, Western
  • Cathepsin L
  • Cathepsins / isolation & purification
  • Cathepsins / metabolism*
  • Cells, Cultured
  • Chemotaxis / drug effects
  • Chromatography, High Pressure Liquid / methods
  • Culture Media
  • Cysteine Endopeptidases
  • Fibroblasts / enzymology
  • Fibroblasts / metabolism
  • Humans
  • Interleukin-8 / metabolism*
  • Interleukin-8 / pharmacology
  • Liver / enzymology
  • Neutrophils / cytology
  • Neutrophils / drug effects
  • Protein Precursors / metabolism
  • Protein Processing, Post-Translational


  • Culture Media
  • Interleukin-8
  • Protein Precursors
  • Cathepsins
  • Cysteine Endopeptidases
  • CTSL protein, human
  • Cathepsin L