The WNT signaling pathway is a critical mediator of tissue homeostasis and repair, and frequently co-opted during tumor development. Almost all colorectal cancers (CRC) demonstrate hyperactivation of the WNT pathway, which in many cases is believed to be the initiating and driving event. In this short review, we provide a focused overview of recent developments in our understanding of the WNT pathway in CRC, describe new research tools that are enabling a deeper understanding of WNT biology, and outline ongoing efforts to target this pathway therapeutically.

Colorectal cancer (CRC) is a leading cause of death, yet facile preclinical models that mimic the natural stages of CRC progression are lacking. Through the orthotopic engraftment of colon organoids we describe a broadly usable immunocompetent CRC model that recapitulates the entire adenoma-adenocarcinoma-metastasis axis in vivo. The engraftment procedure takes less than 5 minutes, shows efficient tumor engraftment in 2/3 mice, and can be achieved using organoids derived from GEMMs, wild type organoids engineered ex vivo, or from patient-derived human CRC organoids. In this model, we describe the genotype and time-dependent progression of CRCs from adenocarcinoma (6 weeks), to local disseminated disease (11–12 weeks) and spontaneous metastasis (>20 weeks). Further, we use the system to show that loss of dysregulated Wnt signaling is critical for the progression of disseminated CRCs. Thus, our approach provides a fast and flexible means to produce tailored CRC mouse models for genetic studies and pre-clinical investigation.

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Summary Mixed Lineage Leukemia (MLL) fusion proteins cause oncogenic transformation of hematopoietic cells by constitutive recruitment of elongation factors to HOX promoters, resulting in over-expression of target genes. The structural basis of transactivation by MLL fusion partners remains undetermined. We show that the ANC1 Homology Domain (AHD) of AF9, one of the most common MLL translocation partners, is intrinsically disordered and recruits multiple transcription factors through coupled folding and binding. We determined the structure of the AF9 AHD in complex with the elongation factor AF4, and show that aliphatic residues which are conserved in each of the AF9 binding partners form an integral part of the hydrophobic core of the complex. NMR relaxation measurements show AF9 retains significant dynamic behavior which may facilitate exchange between disordered partners. We propose that AF9 functions as a signaling hub which regulates transcription through dynamic recruitment of co-factors in normal hematopoiesis and in acute leukemia.

The majority of colorectal cancers (CRCs) show hyperactivated WNT signaling due to inactivating mutations in the APC tumor suppressor. Genetically restoring Apc suppresses WNT and induces rapid and sustained tumor regression, implying that re-engaging this endogenous tumor suppressive mechanism may be an effective therapeutic strategy. Here, using new animal models, human cell lines, and ex vivo organoid cultures, we show that Tankyrase (TNKS) inhibition can control WNT hyperactivation and provide long-term tumor control in vivo, but that effective responses are critically dependent on how APC is disrupted. Mutant APC proteins truncated within the Mutation Cluster Region (MCR) region physically engage the destruction complex and suppress the WNT transcriptional program, while early APC truncations (i.e. Apc Min) show limited interaction with AXIN1 and β-catenin, and do not respond to TNKS blockade. Together, this work shows that TNKS inhibition, like APC restoration, can reestablish endogenous control of WNT/β-catenin signaling, but that APC genotype is a crucial determinant of this response.