Nuclear Localization and Biological Function of Matrix Metalloproteinase‐2

Abstract

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.