Expression of Three Membrane-type Matrix Metalloproteinases (MT-MMPs) in Rat Vascular Smooth Muscle Cells and Characterization of MT3-MMPs with and without Transmembrane Domain

Matrix metalloproteinases (MMPs) produced by rat smooth muscle cells (SMCs) were investigated. SMCs expressed three kinds of membrane-type MMP, MT1-MMP, MT2-MMP, and MT3-MMP, and the MT-MMP expression was stimulated by the presence of serum. MT3-MMP was characterized further by cloning its cDNA. A rat MT3-MMP cDNA encoding 607 amino acids and a cDNA for its transmembrane domainless variant MT3-MMP-del were cloned from a rat SMC cDNA library; a human MT3-MMP cDNA was cloned from a fetal brain cDNA library. Human brain MT3-MMP was similar but not identical to the previously reported human placenta MT3-MMP (94.4% homology). When the MT3-MMP cDNA was expressed in COS-7 cells, endogenous progelatinase A was processed to the mature form. The transfection of rat MT3-MMP-del efficiently converted progelatinase A to the intermediate form but not to the mature one, indicating that the transmembrane domain is important for the complete processing of progelatinase A to maturation. Both MT3-MMP-del and MT3-MMP hydrolyzed gelatin and casein, indicating their broad substrate specificity. Results of experiments with a synthetic MMP inhibitor suggested that MT3-MMP-del and MT3-MMP are rapidly degraded immediately after maturation. The present study suggests that multiple forms of MMPs including MT3-MMP are involved in the matrix remodeling of blood vessels.