title: CAPNS1 regulates USP1 stability and maintenance of genome integrity.
abstract: Calpains regulate a wide spectrum of biological functions, including migration, adhesion, apoptosis, secretion, and autophagy, through the modulating cleavage of specific substrates. Ubiquitous microcalpain (μ-calpain) and millicalpain (m-calpain) are heterodimers composed of catalytic subunits encoded, respectively, by CAPN1 and CAPN2 and a regulatory subunit encoded by CAPNS1. Here we show that calpain is required for the stability of the deubiquitinating enzyme USP1 in several cell lines. USP1 modulates DNA replication polymerase choice and repair by deubiquitinating PCNA. The ubiquitinated form of the USP1 substrate PCNA is stabilized in CAPNS1-depleted U2OS cells and mouse embryonic fibroblasts (MEFs), favoring polymerase-η loading on chromatin and increased mutagenesis. USP1 degradation directed by the cell cycle regulator APC/C(cdh1), which marks USP1 for destruction in the G1 phase, is upregulated in CAPNS1-depleted cells. USP1 stability can be rescued upon forced expression of calpain-activated Cdk5/p25, previously reported as a cdh1 repressor. These data suggest that calpain stabilizes USP1 by activating Cdk5, which in turn inhibits cdh1 and, consequently, USP1 degradation. Altogether these findings point to a connection between the calpain system and the ubiquitin pathway in the regulation of DNA damage response and place calpain at the interface between cell cycle modulation and DNA repair.
authors.affiliation: LNCIB Laboratorio Nazionale Consorzio Interuniversitario Biotecnologie AREA Science Park-Padriciano, Trieste, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Cataldo
authors.forename: Leticia Y
authors.initials: LY
authors.lastname: Peche
authors.forename: Enio
authors.initials: E
authors.lastname: Klaric
authors.forename: Claudio
authors.initials: C
authors.lastname: Brancolini
authors.forename: Michael P
authors.initials: MP
authors.lastname: Myers
authors.forename: Francesca
authors.initials: F
authors.lastname: Demarchi
authors.forename: Claudio
authors.initials: C
authors.lastname: Schneider
mesh_terms: D025601:Adenomatous Polyposis Coli Protein; D000818:Animals; D015703:Antigens, CD; D017209:Apoptosis; D029681:Arabidopsis Proteins; D015820:Cadherins / Q000037:antagonists & inhibitors; D002154:Calpain / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002465:Cell Movement; D000090266:Chromobox Protein Homolog 5; D051360:Cyclin-Dependent Kinase 5 / Q000378:metabolism; D004249:DNA Damage; D004260:DNA Repair; D004259:DNA-Directed DNA Polymerase; D010450:Endopeptidases / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000378:metabolism; D064570:Ubiquitin-Specific Proteases; D054875:Ubiquitination; D000099270:Y-Family DNA Polymerases
chemical_list: D025601:Adenomatous Polyposis Coli Protein; D015703:Antigens, CD; D029681:Arabidopsis Proteins; D015820:Cadherins; D002154:Calpain; D000090266:Chromobox Protein Homolog 5; D051360:Cyclin-Dependent Kinase 5; D004259:DNA-Directed DNA Polymerase; D010450:Endopeptidases; D009419:Nerve Tissue Proteins; D064570:Ubiquitin-Specific Proteases; C555337:APC protein, human; C000715594:CBX5 protein, human; C513384:CDH1 protein, human; C118136:TPPP protein, human; C495905:CDK5 protein, human; C112338:Rad30 protein; D000099270:Y-Family DNA Polymerases; C579228:USP1 protein, human; C579227:Usp1 protein, mouse; C449000:m-calpain; C527669:CAPNS1 protein, human