The Ubiquitin Ligase TRAIP: Double-Edged Sword at the Replisome.

In preparation for cell division, the genome must be copied with high fidelity. However, replisomes often encounter obstacles, including bulky DNA lesions caused by reactive metabolites and chemotherapeutics, as well as stable nucleoprotein complexes. Here, we discuss recent advances in our understanding of TRAIP, a replisome-associated E3 ubiquitin ligase that is mutated in microcephalic primordial dwarfism. In interphase, TRAIP helps replisomes overcome DNA interstrand crosslinks and DNA-protein crosslinks, whereas in mitosis it triggers disassembly of all replisomes that remain on chromatin. We describe a model to explain how TRAIP performs these disparate functions and how they help maintain genome integrity.

Comprehensive analysis of chromothripsis in 2,658 human cancers using whole-genome sequencing.

Chromothripsis is a mutational phenomenon characterized by massive, clustered genomic rearrangements that occurs in cancer and other diseases. Recent studies in selected cancer types have suggested that chromothripsis may be more common than initially inferred from low-resolution copy-number data. Here, as part of the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium of the International Cancer Genome Consortium (ICGC) and The Cancer Genome Atlas (TCGA), we analyze patterns of chromothripsis across 2,658 tumors from 38 cancer types using whole-genome sequencing data. We find that chromothripsis events are pervasive across cancers, with a frequency of more than 50% in several cancer types. Whereas canonical chromothripsis profiles display oscillations between two copy-number states, a considerable fraction of events involve multiple chromosomes and additional structural alterations. In addition to non-homologous end joining, we detect signatures of replication-associated processes and templated insertions. Chromothripsis contributes to oncogene amplification and to inactivation of genes such as mismatch-repair-related genes. These findings show that chromothripsis is a major process that drives genome evolution in human cancer.

Emi1 maintains genomic integrity during zebrafish embryogenesis and cooperates with p53 in tumor suppression.

A growing body of evidence indicates that early mitotic inhibitor 1 (Emi1) is essential for genomic stability, but how this function relates to embryonic development and cancer pathogenesis remains unclear. We have identified a zebrafish mutant line in which deficient emi1 gene expression results in multilineage hematopoietic defects and widespread developmental defects that are p53 independent. Cell cycle analyses of Emi1-depleted zebrafish or human cells showed chromosomal rereplication, and metaphase preparations from mutant zebrafish embryos revealed rereplicated, unsegregated chromosomes and polyploidy. Furthermore, EMI1-depleted mammalian cells relied on topoisomerase II alpha-dependent mitotic decatenation to progress through metaphase. Interestingly, the loss of a single emi1 allele in the absence of p53 enhanced the susceptibility of adult fish to neural sheath tumorigenesis. Our results cast Emi1 as a critical regulator of genomic fidelity during embryogenesis and suggest that the factor may act as a tumor suppressor.