The propeptide domain of membrane type 1-matrix metalloproteinase acts as an intramolecular chaperone when expressed in trans with the mature sequence in COS-l cells

It has been assumed that cleavage of the N-terminal propeptide domain of me mbrane type-1 matrix metalloproteinase (MT1-MMP) is required for enzyme fun ction, We recently demonstrated that the propeptide domain of MT1-MMP is no t cleaved and actually is required for function of the membrane-bound enzym e in transfected COS-1 cells (Cao, J., Drews, M., Lee, H. M., Conner, C., B ahou, W. F., and Zucker, S. (1998) J. Biol. Chem. 273, 34745-34752). In thi s report, we have inserted the cDNA encoding the signal and propeptide sequ ences of MT1-MMP (MT1-109) and the cDNA encoding propeptide-deleted mature MT1-MMP (MT Delta pro) in expression vectors that were then transfected int o matrix metalloproteinase-deficient COS-1 cells. Co-expression of both the mature sequence and the prosequence of MT1-MMP as independent polypeptides (in trans) in COS-1 cells resulted in reconstitution of MT1-MMP function i n terms of facilitating I-125-labeled tissue inhibitor of metalloproteinase 2 binding to transfected cells and subsequent activation of progelatinase A. Transfection of cells with either cDNA alone resulted in non-functional cells, These results are consistent with the propeptide sequence of MT1-MMP functioning as an intramolecular chaperone involved in protein folding and trafficking to the cell surface.