Extracellular proteolysis and turnover are core processes of tissue homeostasis. The predominant matrix-degrading
enzymes are members of the
Matrix Metalloproteinase (
MMP) family.
MMPs extensively degrade core matrix components in addition to processing a range of other factors in the extracellular, plasma membrane, and intracellular compartments. The proteolytic activity of
MMPs is modulated by the Tissue Inhibitors of
Metalloproteinases (TIMPs), a family of four multi-functional matrisome
proteins with extensively characterized
MMP inhibitory functions. Thus, a well-regulated balance between
MMP activity and TIMP levels has been described as critical for healthy tissue homeostasis, and this balance can be chronically disturbed in
pathological processes. The relationship between
MMPs and TIMPs is complex and lacks the constraints of a typical
enzyme-inhibitor relationship due to secondary interactions between various
MMPs (specifically
gelatinases) and TIMP family members. We illustrate a new complexity in this system by describing how MMP9 can cleave members of the TIMP family when in molar excess. Proteolytic processing of TIMPs can generate functionally altered
peptides with potentially novel attributes. We demonstrate here that all TIMPs are cleaved at their C-terminal tails by a molar excess of MMP9. This processing removes the N-glycosylation site for TIMP3 and prevents the TIMP2 interaction with latent proMMP2, a prerequisite for cell surface MMP14-mediated activation of proMMP2. TIMP2/4 are further cleaved producing ∼14 kDa N-terminal
proteins linked to a smaller C-terminal domain through residual
disulfide bridges. These cleaved TIMP2/4 complexes show perturbed
MMP inhibitory activity, illustrating that MMP9 may bear a particularly prominent influence upon the TIMP:
MMP balance in tissues.