The E3-ligases SCF(Ppa) and APC/C(Cdh1) co-operate to regulate CENP-A(CID) 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 SCF(Ppa) and APC/C(Cdh1). We show that SCF(Ppa) 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 SCF(Ppa)-mediated degradation but not from APC/C(Cdh1)-mediated degradation. These results suggest that, whereas SCF(Ppa) 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.