TAILS N-Terminomics and Proteomics Show Protein Degradation Dominates over Proteolytic Processing by Cathepsins in Pancreatic Tumors

Cell Rep. 2016 Aug 9;16(6):1762-1773. doi: 10.1016/j.celrep.2016.06.086. Epub 2016 Jul 28.


Deregulated cathepsin proteolysis occurs across numerous cancers, but in vivo substrates mediating tumorigenesis remain ill-defined. Applying 8-plex iTRAQ terminal amine isotopic labeling of substrates (TAILS), a systems-level N-terminome degradomics approach, we identified cathepsin B, H, L, S, and Z in vivo substrates and cleavage sites with the use of six different cathepsin knockout genotypes in the Rip1-Tag2 mouse model of pancreatic neuroendocrine tumorigenesis. Among 1,935 proteins and 1,114 N termini identified by TAILS, stable proteolytic products were identified in wild-type tumors compared with one or more different cathepsin knockouts (17%-44% of 139 cleavages). This suggests a lack of compensation at the substrate level by other cathepsins. The majority of neo-N termini (56%-83%) for all cathepsins was consistent with protein degradation. We validated substrates, including the glycolytic enzyme pyruvate kinase M2 associated with the Warburg effect, the ER chaperone GRP78, and the oncoprotein prothymosin-alpha. Thus, the identification of cathepsin substrates in tumorigenesis improves the understanding of cathepsin functions in normal physiology and cancer.

Keywords: ECM; TAILS degradomics; cysteine cathepsins; degradation; lysosomal hydrolases; pancreatic neuroendocrine cancer; proteases; proteolytic processing; proteomics; substrate discovery.

MeSH terms

  • Animals
  • Carcinogenesis / metabolism
  • Cathepsins / metabolism*
  • Endoplasmic Reticulum Chaperone BiP
  • Heat-Shock Proteins / metabolism
  • Mice, Transgenic
  • Oncogene Proteins / metabolism
  • Pancreatic Neoplasms / metabolism*
  • Protein Processing, Post-Translational
  • Proteome / metabolism*
  • Proteomics / methods
  • Substrate Specificity / physiology


  • Endoplasmic Reticulum Chaperone BiP
  • Heat-Shock Proteins
  • Hspa5 protein, mouse
  • Oncogene Proteins
  • Proteome
  • Cathepsins