Nucleolar Matrix Metalloproteinase‐2 Regulates rRNA Transcription

Abstract

Gene expression in eukaryotic cells is a tightly regulated process, from pre‐transcriptional through post‐transcriptional stages. A major control point in gene expression is ribosome synthesis, since it executes mRNA translation and also regulates their stability. Genes encoding ribosomal proteins and ribosomal RNA (rRNA) are physically located and transcribed in specialized structures within the nucleus known as nucleoli. We previously reported that the protease matrix metalloproteinase‐2 (MMP‐2) was located inside the nucleus but its role there remains elusive.Confocal microscopy studies in our lab showed an accumulation of MMP‐2 in nucleoli in U‐2OS human osteosarcoma cells, suggesting a role in rRNA transcription. We found that MMP‐2 co‐localizes with nucleoli markers fibrillarin and nucleophosmin, and is located in active rRNA transcription sites within nucleoli of U‐2OS cells pulsed with 5‐fluorouridine (5‐FU).Chromatin immunoprecipitation (ChIP) assays showed an enrichment of MMP‐2 in the rRNA gene promoter region. We also found evidence of MMP‐2‐mediated proteolysis of purified histones (H1, H2A, H2B, H3 and H4), in a concentration‐dependent manner. Interestingly, we identified histone H3 to be the most susceptible to MMP‐2 activity and found at least one MMP‐ 2 cleavage site in the N‐terminal tail of histone H3.The N‐terminal tail of histone H3 is the location of a large number of known post‐translational modifications that are involved in the regulation of DNA relaxation and transcription, RNA splicing and DNA repair. Emerging evidence indicates that one of the mechanisms behind this is the proteolytic removal of the N‐terminal tail of histone H3 by a yet uncharacterized protease. Therefore, we sought to elucidate if nucleolar MMP‐2 has proteolytic activity on recombinant histone H3. We incubated MMP‐2 immunoprecipitated from isolated nucleoli with recombinant histone H3, in presence or absence of the MMP‐2 preferring inhibitor ARP‐100. Our data revealed that nucleolar MMP‐2 has proteolytic activity on histone H3 and is sensitive to ARP‐ 100.The involvement of MMP‐2 in rRNA gene expression in the nucleolus is a major novel mechanism by which intracellular may MMP‐2 regulate cell function via histone proteolysis.Support or Funding InformationCanadian Institutes of Health Research (CIHR) grants FDN‐143299 (to RS) and MOP‐119515 (to MH)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.