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Updated: Mar 10, 2026
Enrichment of Extracellular Matrix Proteins from Tissues and Digestion into Peptides for Mass Spectrometry Analysis
Published on: July 23, 2015
An extracellular proteasome releases endostatin from human collagen XVIII
Maria L V Reiss-Pistilli1, Detlef Schuppan2, Madalena M S Barroso1
1Institute of Biomedical Sciences, Federal University of Rio de Janeiro, Rio de Janeiro, RJ, Brazil.
Abstract:
Endostatin is a potent anti-angiogenic and anti-tumor protein capable of regressing tumors without inducing acquired resistance. Since it is a fragment of the parental molecule, collagen XVIII, its endogenous production depends on the activity of a specific proteolytic enzyme. While such an enzyme has been described in mice, a human counterpart has not been identified so far. Here, we searched for this enzyme by using a fluorescence resonance energy transfer peptide containing the cleavage site of human collagen XVIII. We found that the cleavage activity was present in various murine and human tumor cells but not in untransformed cells. It was ascribed to a large protein complex identified as an extracellular form of proteasome 20S. Since circulating proteasome 20S has recently emerged as an important marker of tumor progression, the possibility of proteasomes controlling the production of angiostatic endostatin may inspire the development of new anticancer therapies.
Insights
Researchers identified proteasome 20S as the enzyme that produces endostatin, an anti-tumor protein. This discovery in tumor cells offers potential for new cancer therapies by targeting this pathway.
Area of Science:
- Biochemistry
- Oncology
- Molecular Biology
Background:
- Endostatin is a protein with potent anti-angiogenic and anti-tumor properties, derived from collagen XVIII.
- Its production relies on a specific proteolytic enzyme, which has been identified in mice but not humans.
- Identifying this enzyme is crucial for understanding endostatin's role in cancer and developing therapies.
Purpose of the Study:
- To identify the human enzyme responsible for cleaving collagen XVIII to produce endostatin.
- To investigate the presence and activity of this enzyme in tumor versus non-tumor cells.
- To explore the potential of targeting this enzymatic activity for cancer treatment.
Main Methods:
- Utilized a fluorescence resonance energy transfer (FRET) peptide assay designed to detect cleavage at the human collagen XVIII site.
- Assayed cleavage activity in various murine and human tumor cell lines, as well as untransformed cells.
- Characterized the identified enzyme complex through biochemical analysis.
Main Results:
- Discovered cleavage activity specific to the human collagen XVIII site in both murine and human tumor cells.
- Found no such cleavage activity in untransformed cells.
- Identified the enzyme responsible as an extracellular form of proteasome 20S.
Conclusions:
- Extracellular proteasome 20S acts as the enzyme that generates anti-angiogenic endostatin from collagen XVIII in tumor cells.
- The presence of this activity in tumor cells but not normal cells highlights its potential as a cancer-specific target.
- Targeting proteasome-mediated endostatin production could lead to novel therapeutic strategies against cancer.
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