The E3-ligases SCFPpa and APC/CCdh1 co-operate to regulate CENP-ACID expression across the cell cycle

Centromere identity is determined by the specific deposition of CENP-A, a histone H3 variant localizing exclusively at centromeres. Increased CENP-A expression, which is a frequent event in cancer, causes mislocalization, ectopic kinetochore assembly and genomic instability. Proteolysis regulates CENP-A expression and prevents its misincorporation across chromatin. How proteolysis restricts CENP-A localization to centromeres is not well understood. Here we report that, in Drosophila, CENP-A(CID) expression levels are regulated throughout the cell cycle by the combined action of SCFPpa and APC/C-Cdh1. We show that SCFPpa regulates CENP-A(CID) expression in G1 and, importantly, in S-phase preventing its promiscuous incorporation across chromatin during replication. In G1, CENP-A(CID) expression is also regulated by APC/C-Cdh1. We also show that Cal1, the specific chaperone that deposits CENP-A(CID) at centromeres, protects CENP-A(CID) from SCFPpa-mediated degradation but not from APC/C-Cdh1-mediated degradation. These results suggest that, whereas SCFPpa targets the fraction of CENP-A(CID) that is not in complex with Cal1, APC/C-Cdh1 mediates also degradation of the Cal1-CENP-A(CID) complex and, thus, likely contributes to the regulation of centromeric CENP-A(CID) deposition.