Nuclear Localization And Biological Function Of Matrix Metalloproteinase-2

Matrix metalloproteinases (MMPs) are zinc-dependent proteases that are involved in intra- and extra-cellular matrix remodeling associated with developmental processes and disease progression. Several MMPs including MMP-2 have been found in the nucleus. The biological functions and substrates of nuclear MMPs are mostly unknown. We hypothesize that MMP-2 is present in the nucleus under physiological conditions but increases during oxidative stress to proteolyse structural and DNA repair proteins. Lamin A/C, a possible nuclear MMP-2 target, is an intermediate filament protein that provides structural support to the nuclear envelope. Cytosolic, membrane and nuclear fractions were extracted from blood-free, isolated rat hearts. Western blots for MMP-2, lamin A/C (nuclear marker), SERCA2 (membrane marker) and GAPDH (cytosol marker) were used to demonstrate fraction purity. This showed that the nuclear fraction was free of cytosolic and membrane contamination and MMP-2 was detected in all three fractions. MMP-2 activity (by gelatin zymography) showed that nuclear MMP-2 activity was lowest compared to that in the cytosolic and membrane fractions. The presence of nuclear MMP-2 was examined by immunofluorescence confocal microscopy in HT1080 fibrosarcoma cells. Recombinant lamin A/C was proteolysed into 50 and 25 kDa fragments by incubation with MMP-2 (0.5h, 37oC) in vitro and this was blocked by the MMP inhibitor o-phenanthroline. MMP-2 is present in highly purified nuclear fractions obtained from rat hearts and in the nuclei of HT1080 cells. Ongoing experiments will determine the colocalization of MMP-2 with nuclear bodies, its nuclear substrates and therefore its function within nuclei. Support: CIHR.