Fbw7 and p53 cooperatively suppress advanced and chromosomally unstable intestinal cancer.

Colorectal cancer (CRC) remains a major cause of cancer mortality worldwide. Murine models have yielded critical insights into CRC pathogenesis, but they often fail to recapitulate advanced-disease phenotypes, notably metastasis and chromosomal instability (CIN). New models are thus needed to understand disease progression and to develop therapies. We sought to model advanced CRC by inactivating two tumor suppressors that are mutated in human CRCs, the Fbw7 ubiquitin ligase and p53. Here we report that Fbw7 deletion alters differentiation and proliferation in the gut epithelium and stabilizes oncogenic Fbw7 substrates, such as cyclin E and Myc. However, Fbw7 deletion does not cause tumorigenesis in the gut. In contrast, codeletion of both Fbw7 and p53 causes highly penetrant, aggressive, and metastatic adenocarcinomas, and allografts derived from these tumors form highly malignant adenocarcinomas. In vitro evidence indicates that Fbw7 ablation promotes genetic instability that is suppressed by p53, and we show that most Fbw7⁻/⁻; p53⁻/⁻ carcinomas exhibit a CIN⁺ phenotype. We conclude that Fbw7 and p53 synergistically suppress adenocarcinomas that mimic advanced human CRC with respect to histopathology, metastasis, and CIN. This model thus represents a novel tool for studies of advanced CRC as well as carcinogenesis associated with ubiquitin pathway mutations.

Identification of a disease-defining gene fusion in epithelioid hemangioendothelioma.

Integrating transcriptomic sequencing with conventional cytogenetics, we identified WWTR1 (WW domain-containing transcription regulator 1) (3q25) and CAMTA1 (calmodulin-binding transcription activator 1) (1p36) as the two genes involved in the t(1;3)(p36;q25) chromosomal translocation that is characteristic of epithelioid hemangioendothelioma (EHE), a vascular sarcoma. This WWTR1/CAMTA1 gene fusion is under the transcriptional control of the WWTR1 promoter and encodes a putative chimeric transcription factor that joins the amino terminus of WWTR1, a protein that is highly expressed in endothelial cells, in-frame to the carboxyl terminus of CAMTA1, a protein that is normally expressed only in brain. Thus, CAMTA1 expression is activated inappropriately through a promoter-switch mechanism. The gene fusion is present in virtually all EHEs tested but is absent from all other vascular neoplasms, demonstrating it to be a disease-defining genetic alteration. A sensitive and specific break-apart fluorescence in situ hybridization assay was also developed to detect the translocation and will assist in the evaluation of this diagnostically challenging neoplasm. The chimeric WWTR1/CAMTA1 transcription factor may represent a therapeutic target for EHE and offers the opportunity to shed light on the functions of two poorly characterized proteins.