Matrix metalloproteinase-2 (MMP-2) is produced as a zymogen, which is subsequently activated by membrane-type 1 metalloproteinase (MT1-MMP). The objectives of the present study were to clone bovine MT1-MMP and to investigate its expression in the corpus luteum. Corpora lutea were harvested from nonlactating dairy cows on Days 4, 10, and 16 of the estrous cycle (Day 0 = estrus; n = 3 for each age). The bovine MT1-MMP cDNA contained an open reading frame of 1749 base pairs, which encoded a predicted protein of 582 amino acids. Northern blotting revealed no differences (P > 0.05) in MT1-MMP mRNA levels between any ages of corpora lutea. Western blotting demonstrated that two species of MT1-MMP, the latent form ( approximately 63 kDa) and the active form ( approximately 60 kDa), were present in corpora lutea throughout the estrous cycle. Active MT1-MMP was lower (P < 0.05) in early stages of the corpus luteum than the mid and late stages, where MMP-2 activity, as revealed by gelatin zymography, was also elevated. Furthermore, immunohistochemistry revealed that MT1-MMP was localized in endothelial, large luteal, and fibroblast cells of the corpus luteum at different stages. Taken together, the differential expression and localization of MT1-MMP in the corpus luteum suggest that it may have multiple functions throughout the course of the estrous cycle, including activation of pro-MMP-2.
