The Ubiquitin-Ligase APC-Cdh1 Is Required for Maintaining Genomic Stability and Is Transcriptional Repressed by AML1/ETO.

Accurate DNA replication and chromosome segregation is essential during cell division in order to provide genomic stability and avoid malignant growth. We found that ubiquitin-dependent proteolytic cell cycle control by the E3-ubiquitin-ligase anaphase-promoting complex (APC) activated by Cdh1 (APC-Cdh1) is required for maintaining genomic integrity and viability in proliferating human cells. Lentiviral-delivered stable expression of short hairpins targeted against Cdh1 causes an apoptotic phenotype associated with p53-stabilization and p53-dependent transcriptional up-regulation of the cyclin-dependent kinase inhibitor p21. Cdh1-depleted cells enter mitosis delayed compared to controls suggesting the activation of a DNA-damage checkpoint in S- and G2-phase. Depletion of Cdh1 leads to premature accumulation of cyclin A2 and cyclin B1 in G1- and S-phase. This may interfere with loading of pre-replication-complexes onto origins of replication in G1 and cause chromosomal instability when cells progress into mitosis. In addition, stabilization of the Cdh1 target Aurora A at physiological levels is sufficient to cause centrosome overduplication and subsequent polyploidization in Cdh1 and p53 deficient cells. Genetic instability is a hallmark of cancer cells and deregulation of APC-Cdh1 may be involved, since we observe downregulation of Cdh1 in t(8;21) acute myeloid leukemia. Moreover, expression of AML1/ETO in an inducible system leads to downregulation of Cdh1 indicating transcriptional repression of Cdh1 by AML1/ETO. Consistent with these data AML1/ETO positive cell lines show numerical chromosomal aberrations. Thus, disruption of the central mitotic control machinery leads to genetic instability by several mechanisms and the APC may be an important suppressor of tumor progression in AML1/ETO positive leukemia.