Mitomycin C modulates intracellular matrix metalloproteinase-9 expression and affects corneal fibroblast migration

Mitomycin C (MMC) is often used to prevent postoperative corneal haze and subconjunctival fibrosis in ocular surgery. It also affects the motility and viability of the residual ocular cells, including corneal stromal cells. Extracellular matrix metalloproteinase-9 (MMP-9) contributes to the promotion of cell movement in macrophage and cancer cells, but the intracellular role of MMP-9 remained unclear. Herein, we illustrated the novel role of intracellular MMP-9 in MMC-suppressed cell migration using isolated human corneal fibroblasts (HCFs). In HCFs, MMC enhanced intracellular MMP-9 at transcriptional and protein levels. Using co-immunoprecipitation analysis, we confirmed that MMC enhanced the association between intracellular MMP-9 and inactive FAK/paxillin (PXN) complexes, i.e. PXN without phospho-tyrosine 118 (pY118) and FAK without phospho-tyrosine 397 (pY397). To verify the role of intracellular MMP-9 in migration, its gene was directly isolated from HCFs and highly expressed in HCFs by a lentivirus-based pseudovirus system with encephalomyocarditis virus (EMCV)-driven enhanced green fluorescent protein (GFP) as the MMP-9-IG-versus IG-expressing cells. Compared with the IG-expressing cells, higher intracellular MMP-9 expression in the MMP-9-IG expressing HCFs proliferated and migrated more slowly. Phosphorylation of FAK at Y397 and PXN at both Y31 and Y118 were significantly less in the MMP-9-IG expressing HCFs. These suggested that MMC-upregulated intracellular MMP-9 clutched inactive FAK/PXN complexes at focal adhesion sites to form a new "inactive" trimer, prohibited FAK/PXN complexes phosphorylation and retarded corneal fibroblast migration.