Intradomain Cleavage of Inhibitory Prodomain Is Essential to Protumorigenic Function of Membrane Type-1 Matrix Metalloproteinase (MT1-MMP) in Vivo*

Invasive cancers use pericellular proteolysis to breach the extracellular matrix and basement membrane barriers and invade the surrounding tissue. Proinvasive membrane type-1 matrix metalloproteinase (MT1-MMP) is the primary mediator of proteolytic events on the cancer cell surface. MT1-MMP is synthesized as a zymogen. The latency of MT1-MMP is maintained by its N-terminal inhibitory prodomain. In the course of MT1-MMP activation, the R108RKR111↓Y112 prodomain sequence is processed by furin. The intact prodomain released by furin alone, however, is a potent inhibitor of the emerging MT1-MMP enzyme. Evidence suggests that the prodomain undergoes intradomain cleavage at the PGD↓L50 site followed by the release of the degraded prodomain by furin cleavage that finalizes the two-step activation event. These cleavages, only if combined, cause the activation of MT1-MMP. The significance of the intradomain cleavage in the protumorigenic program of MT1-MMP, however, remained unidentified. To identify this important parameter, in our current study, we used the cells that expressed the wild-type prodomain-based fluorescent biosensor and the mutant biosensor with the inactivated PGD↓L50 cleavage site (L50D mutant) and also the cells with the enforced expression of the wild-type and L50D mutant MT1-MMP. Using cell-based tests, orthotopic breast cancer xenografts in mice, and genome-wide transcriptional profiling of cultured cells and tumor xenografts, we demonstrated that the intradomain cleavage of the PGD↓L50 sequence of the prodomain is essential for the protumorigenic function of MT1-MMP. Our results emphasize the importance of the intradomain cleavages resulting in the inactivation of the respective inhibitory prodomains not only for MT1-MMP but also for other MMP family members.