title: Calcium-induced cleavage of DNA topoisomerase I involves the cytoplasmic-nuclear shuttling of calpain 2.
abstract: Important to the function of calpains is temporal and spatial regulation of their proteolytic activity. Here, we demonstrate that cytoplasm-resident calpain 2 cleaves human nuclear topoisomerase I (hTOP1) via Ca(2+)-activated proteolysis and nucleoplasmic shuttling of proteases. This proteolysis of hTOP1 was induced by either ionomycin-caused Ca(2+) influx or addition of Ca(2+) in cellular extracts. Ca(2+) failed to induce hTOP1 proteolysis in calpain 2-knockdown cells. Moreover, calpain 2 cleaved hTOP1 in vitro. Furthermore, calpain 2 entered the nucleus upon Ca(2+) influx, and calpastatin interfered with this process. Calpain 2 cleavage sites were mapped at K(158) and K(183) of hTOP1. Calpain 2-truncated hTOP1 exhibited greater relaxation activity but remained able to interact with nucleolin and to form cleavable complexes. Interestingly, calpain 2 appears to be involved in ionomycin-induced protection from camptothecin-induced cytotoxicity. Thus, our data suggest that nucleocytoplasmic shuttling may serve as a novel type of regulation for calpain 2-mediated nuclear proteolysis.
authors.affiliation: Department and Graduate Institute of Microbiology, College of Medicine, Taipei, Taiwan.
authors.forename: Shang-Min
authors.initials: SM
authors.lastname: Chou
authors.forename: Ting-Hsiang
authors.initials: TH
authors.lastname: Huang
authors.forename: Hsiang-Chin
authors.initials: HC
authors.lastname: Chen
authors.forename: Tsai-Kun
authors.initials: TK
authors.lastname: Li
mesh_terms: D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000494:pharmacology; D002154:Calpain / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002166:Camptothecin / Q000633:toxicity; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000201:enzymology / Q000378:metabolism; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D006801:Humans; D015759:Ionomycin / Q000494:pharmacology; D008969:Molecular Sequence Data; D010447:Peptide Hydrolases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism; D000097796:Nucleolin
chemical_list: D002118:Calcium; D002135:Calcium-Binding Proteins; D002154:Calpain; D002166:Camptothecin; D004264:DNA Topoisomerases, Type I; D015759:Ionomycin; D010447:Peptide Hydrolases; D010750:Phosphoproteins; D016601:RNA-Binding Proteins; D000097796:Nucleolin; C033668:calpastatin; C569870:CAPN2 protein, human