Mmp9 encodes a member of the matrix metalloproteinase family of extracellular matrix-degrading enzymes that are involved in tissue remodeling, wound repair, progression of atherosclerosis and tumor invasion. The encoded preproprotein undergoes proteolytic processing to generate a mature, zinc-dependent endopeptidase enzyme that degrades collagens of type IV, V and XI, and elastin. Mice lacking the encoded protein exhibit an abnormal pattern of skeletal growth plate vascularization and ossification, reduced keratinocyte hyperproliferation at all neoplastic stages, a decreased incidence of invasive tumors, and resistance to experimental autoimmune encephalomyelitis.