Matrix metalloproteinase 3 (MMP-3), also known as stromelysin 1 and progelatinase, is encoded by the MMP3 gene. The expression of MMP3 is mainly regulated at the transcriptional level, where gene promoters respond to a variety of stimuli including growth factors, cytokines, carcinogens and proto-oncogene products. MMP-3 degrade II, III, IV, IX and X collagen, proteoglycan, fibronectin, laminin, and elastin. In addition, MMP-3 can also activate other MMPs such as MMP-1, MMP-7 and MMP-9, so MMP-3 plays a key role in connective tissue remodeling. This enzyme is involved in wound repair, atherosclerotic progression, and tumor initiation. Studies of MMP-3 wild type and gene knockout in mice have shown that MMP-3 increases the permeability of the blood-brain barrier after traumatic injury. Nuclear MMP-3 works as a transcription factor and protease.