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.

Differential functions of calpain 1 during epithelial cell death and adipocyte differentiation in mammary gland involution

“…The results of the present study and previously published data in other models [24,35] suggest that CAPN1 might have different targets in the nuclear compartment of mammary gland cells during involution. Therefore we studied the possible role of CAPN1 in chromatin organization in whole mammary tissue.…”

“…The calpain system has been reported previously to have a role in the nucleus of different cell types [14,23,24]. Since we have already demonstrated calpain translocation to the mitochondria and lysosomes during weaning, we investigated the possible role of these proteases in the nuclear compartment.…”

Calcium influx-mediated translocation ofm-calpain induces Ku80 cleavage and enhances the Ku80-related DNA repair pathway

“…To verify the identity of the enzyme that cleaved nuclear Ku80, we treated the cells with calpeptin prior to treatment with 0.75 μM ionomycin since a previous study had reported that m -calpain was translocated from the cytosol to the nucleus after activation by calcium [ 24 ]. Calpeptin is a well-known, cell-permeable calpain inhibitor and synthetic peptidomimetic aldehyde moiety-conteining molecule.…”

“…Although the induction of DNA damage is the main treatment for cancer, it can promote carcinogenesis by damaging normal cells, to which the majority of the adverse effects of anticancer therapy are attributed. Moreover, the DNA process is easily affected by cell cycle-related proteins and apoptosis regulators [ 23 , 24 ]; therefore, it is very important to control DNA damage and to repair it properly in order to minimize side effects.…”

“…Translocated m -calpain proteolyzes topoisomerase I, which produces DNA topological problems during the cell cycle. The relaxation activity of topoisomerase I is greater when it is truncated by m -calpain [ 24 ]. Calpains belong to the family of calcium-dependent cytoplasmic cysteine proteases; due to the high calcium level in cancer cells resulting from the low buffering system, calpains are easily activated to process toward survival [ 25 – 29 ].…”