Matrix metalloproteinase-2 mediates ribosomal RNA transcription by cleaving nucleolar histones

Cell proliferation and survival require continuous ribosome biogenesis and protein synthesis. Genes encoding ribosomal RNA (rRNA) are physically located in a specialized substructure within the nucleus known as the nucleolus, which has a central role in the biogenesis of ribosomes. Matrix metalloproteinase-2 (MMP-2) was previously detected in the nucleus. However, its role there is elusive. Herein we report that MMP-2 resides within the nucleolus to regulate rRNA transcription. MMP-2 is enriched at the promoter region of rRNA gene repeats and its inhibition downregulates pre-rRNA transcription. The N-terminal tail of histone H3 is clipped by MMP-2 in the nucleolus and thereby enhances rRNA transcription. Knocking down/out MMP-2 or inhibiting its activity reduces both rRNA transcription and cellular proliferation. In addition to the known extracellular roles of MMP-2 in tumour growth, our data reveal a novel epigenetic mechanism whereby intranucleolar MMP-2 regulates cell proliferation through histone proteolysis and facilitation of rRNA transcription.