The effect of MMP-12 cleavage on mCXCL2 and 3 in vitro chemotactic activity. Silver-stained 15% Tris-Tricine SDS-PAGE gels of the appropriate full-length or cleaved chemokines used in the chemotaxis assay are shown. Black vertical line indicates part of gel removed for presentation purposes. PMNs isolated from murine bone marrow chemoattracted toward full-length mCXCL2(1-73) (A) and mCXCL3(1-73) (B) in a transwell cell migration assay. However, mCXCL2(1-73) and mCXCL3(1-73) incubated with MMP-12 overnight lost all chemotactic activity toward PMNs, as did the synthetic analog of MMP-12-proteolyzed mCXCL3(7-73). This demonstrates that the MMP-12 cleavage in the CXC-receptor binding ELR motif is an inactivating one. However, using a synthetic analog of MMP-12 cleaved mCXCL5(5-92) as a positive control, we also demonstrate enhancement of PMN chemotaxis after MMP-12 activity on this chemokine alone. Data are presented as the ratio of cells migrated toward chemokine compared with buffer control (chemotactic index); standard error bars are shown. *, **, Student t test values (P < .05 and .01, respectively).