Proteins of the matrix metalloproteinase (MMP) family are involved in the breakdown of extracellular matrix in normal physiological processes, such as embryonic development, reproduction, tissue remodeling, and disease processes, such as arthritis or metastasis. Most MMP's are secreted as inactive proproteins which are activated when cleaved by extracellular proteinases. Matrix metalloproteinase 9 (gelatinase B, 92kDa gelatinase, 92kDa type IV collagenase) (MMP9, synonyms: GELB, CLG4B) degrades collagens type IV and V. Studies in rhesus monkeys suggest that MMP9 is involved in IL-8-induced mobilization hematopoietic progenitor cells from bone marrow, and murine studies suggest a role in tumor-associated tissue remodeling. The pro-MMP9 is 92 kDa, and it can be detected a processed form of 68 kDa. This protein can exist as a dimer of 180 kDa (PMID:7492685).