Membrane type 4 matrix metalloproteinase (MMP17) has tumor necrosis factor-alpha convertase activity but does not activate pro-MMP2

Membrane type 4 matrix metalloproteinase (MT4-MMP) shows the least sequence homology to the other MT-MMPs, suggesting a distinct function for this pro tein. We have isolated a complete cDNA corresponding to the mouse homologue which includes the signal peptide and a complete pro-domain, features that were lacking from the human form originally isolated. Mouse MT4-MMP (mMT4- MMP) expressed in COS-7 cells is located at the cell surface but does not s how ability to activate pro-MMP2. The pro-catalytic domain was expressed in Escherichia coli as insoluble inclusions and active enzyme recovered after refolding. Activity of the isolated catalytic domain against synthetic pep tides commonly used for MMP enzyme assays could be inhibited by TIMP1, -2, and -3. The recombinant mMT4-MMP catalytic domain was also unable to activa te pro-MMP2 and was very poor at hydrolyzing components of the extracellula r matrix with the exception of fibrinogen and fibrin. mMT4-MMP was able to hydrolyze efficiently a peptide consisting of the pro-tumor necrosis factor alpha (TNF alpha) cleavage site, a glutathione S-transferase-proTNF alpha fusion protein, and was found to shed pro-TNF alpha when co-transfected in COS-7 cells. MT4-MMP was detected by Western blot in monocyte/macrophage ce ll lines which in combination with its fibrinolytic and TNF alpha-convertin g activity suggests a role in inflammation.