MMP-9 sheds the beta2 integrin subunit (CD18) from macrophages

Area of Science:

• Immunology
• Proteomics
• Biochemistry

Background:

• Activated macrophages are key immune cells and a primary source of matrix metalloproteinase-9 (MMP-9).
• MMP-9 is a gelatinase involved in extracellular matrix degradation and cellular signaling.

Purpose of the Study:

• To identify cellular substrates of MMP-9 using proteomics.
• To investigate the role of MMP-9 in the shedding of transmembrane proteins, specifically beta(2) integrin.

Main Methods:

• Subtractive proteomics comparing wild-type and M9A macrophages (expressing autoactivating pro-MMP-9).
• Two-dimensional liquid chromatography and tandem mass spectrometry to identify proteins in conditioned medium.
• Biochemical assays and peptide substrate mapping to confirm MMP-9 cleavage sites on beta(2) integrin.

Main Results:

• Proteomics identified 467 proteins; subtractive analysis yielded 18 candidate MMP-9 substrates.
• Beta(2) integrin (CD18) and amyloid precursor protein (APP) were confirmed as MMP-9 substrates.
• MMP-9 specifically cleaved beta(2) integrin at residues Ala(705)-Ile(706), leading to its shedding.

Conclusions:

• Subtractive proteomics combined with peptide mapping is effective for identifying proteolytic substrates.
• MMP-9 plays a significant role in the shedding and regulation of beta(2) integrin.
• These findings suggest novel functions for MMP-9 in immune regulation and cell surface protein turnover.