Matrix metalloproteinase (MMP)-3 is a protease involved in cancer progression and tissue remodeling. Using immunofluorescence and immunoelectron microscopy, we identified nuclear localization of MMP-3 in several cultured cell types and in human liver tissue sections. Western blot analysis of nuclear extracts revealed two immunoreactive forms of MMP-3 at 35 and 45 kd, with the 35-kd form exhibiting caseinolytic activity. By transient transfection, we expressed active MMP-3 fused to the enhanced green fluorescent protein (EGFP/aMMP-3) in Chinese hamster ovary cells. We showed that EGFP/aMMP-3 translocates into the nucleus. A functional nuclear localization signal was demonstrated by the loss of nuclear translocation after site-directed mutagenesis of a putative nuclear localization signal and by the ability of the MMP-3 nuclear localization signal to drive a heterologous protein into the nucleus. Finally, expression by Chinese hamster ovary cells of EGFP/aMMP-3 induced a twofold increase of apoptosis rate, compared with EGFP/pro-MMP-3, which does not translocate to the nucleus. Increased apoptosis was abolished by site-directed mutagenesis of the catalytic site of MMP-3 or by using the MMP inhibitor GM6001. This study elucidates for the first time the mechanisms of nuclear localization of a MMP and shows that nuclear MMP-3 can induce apoptosis via its catalytic activity.

BackgroundThe P140 phosphopeptide issued from the spliceosomal U1-70K small nuclear ribonucleoprotein protein displays protective properties in MRL/lpr lupus-prone mice. It binds both major histocompatibility class II (MHCII) and HSC70/Hsp73 molecules. P140 peptide increases MRL/lpr peripheral blood lymphocyte apoptosis and decreases autoepitope recognition by T cells.ObjectiveTo explore further the mode of action of P140 peptide on HSC70+ antigen-presenting cells.MethodsP140 biodistribution was monitored in real time using an imaging system and by fluorescence and electron microscopy. Fluorescence activated cell sorting and Western blotting experiments were used to evaluate the P140 effects on autophagic flux markers.ResultsP140 fluorescence accumulated especially in the lungs and spleen. P140 peptide reduced the number of peripheral and splenic T and B cells without affecting these cells in normal mice. Remaining MRL/lpr B cells responded normally to mitogens. P140 peptide decreased the expression levels of HSC70/Hsp73 chaperone and stable MHCII dimers, which are both increased in MRL/lpr splenic B cells. It impaired refolding properties of chaperone HSC70. In MRL/lpr B cells, it increased the accumulation of the autophagy markers p62/SQSTM1 and LC3-II, consistent with a downregulated lysosomal degradation during autophagic flux.ConclusionThe study results suggest that after P140 peptide binding to HSC70, the endogenous (auto)antigen processing might be greatly affected in MRL/lpr antigen-presenting B cells, leading to the observed decrease of autoreactive T-cell priming and signalling via a mechanism involving a lysosomal degradation pathway. This unexpected mechanism might explain the beneficial effect of P140 peptide in treated MRL/lpr mice.

The design and construction of biomimetic self-assembling systems is a challenging yet potentially highly rewarding endeavour that contributes to the development of new biomaterials, catalysts, drug-delivery systems and tools for the manipulation of biological processes. Significant progress has been achieved by engineering self-assembling DNA-, protein- and peptide-based building units. However, the design of entirely new, completely non-natural folded architectures that resemble biopolymers ('foldamers') and have the ability to self-assemble into atomically precise nanostructures in aqueous conditions has proved exceptionally challenging. Here we report the modular design, formation and structural elucidation at the atomic level of a series of diverse quaternary arrangements formed by the self-assembly of short amphiphilic α-helicomimetic foldamers that bear proteinaceous side chains. We show that the final quaternary assembly can be controlled at the sequence level, which permits the programmed formation of either discrete helical bundles that contain isolated cavities or pH-responsive water-filled channels with controllable pore diameters.