Capns1 regulates usp1 stability and stem cells maintenance
Calpains are a family of calcium-related cysteine-proteases that are involved in a wide number of cellular processes. The ubiquitous calpains, micro- and milli-calpain, are heterodimers composed of catalytic subunits and a common regulatory subunit, encoded by CAPNS1. We identified USP1 deubiquitinase as a CAPNS1-interacting protein. USP1 is a key modulator of DNA repair, partly through deubiquitination of its known targets FANCD2 and PCNA. Usp1 knockout mice have a severe phenotype and die soon after birth. Usp1−/− cells are defective in FANCD2 focus formation and are hypersensitive to DNA damage. PCNA ubiquitination is higher in USP1-depleted cells than in control cells, thus leading to recruitment of error-prone, translesion DNA synthesis (TLS) polymerases and the consequent increase in mutation rate. USP1 promotes inhibitor of DNA binding (ID) protein stability and stem cell-like characteristics in osteosarcoma and is required for normal skeletogenesis. We found that 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/Ccdh1, 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. Our data suggest 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.
EUT Edizioni Università di Trieste
Francesca Cataldo and Francesca Demarchi, Capns1 regulates usp1 stability and stem cells maintenance, in S. Passamonti, S. Gustincich, T. Lah Turnšek, B. Peterlin, R. Pišot, P. Storici (Eds.), Cross-border Italy-Slovenia biomedical research: are we ready for horizon 2020? Conference proceedings with an analysis of innovation management and knowledge transfer potential for a smart specialization strategy. Trieste, EUT Edizioni Università di Trieste, 2014, pp. 251-255