APC mutations disrupt ß-catenin destruction complex condensates organized by Axin phase separation.

The Wnt/ß-catenin pathway is critical to maintaining cell fate decisions. Recent study showed that liquid-liquid-phase separation (LLPS) of Axin organized the ß-catenin destruction complex condensates in a normal cellular state. Mutations inactivating the APC gene are found in approximately 80% of all human colorectal cancer (CRC). However, the molecular mechanism of the formation of ß-catenin destruction complex condensates organized by Axin phase separation and how APC mutations impact the condensates are still unclear. Here, we report that the ß-catenin destruction complex, which is constructed by Axin, was assembled condensates via a phase separation process in CRC cells. The key role of wild-type APC is to stabilize destruction complex condensates. Surprisingly, truncated APC did not affect the formation of condensates, and GSK 3ß and CK1α were unsuccessfully recruited, preventing ß-catenin phosphorylation and resulting in accumulation in the cytoplasm of CRCs. Besides, we propose that the phase separation ability of Axin participates in the nucleus translocation of ß-catenin and be incorporated and concentrated into transcriptional condensates, affecting the transcriptional activity of Wnt signaling pathway.

Targeted deep sequencing reveals APC mutations as predictors of overall survival in Chinese colorectal patients receiving adjuvant chemotherapy.

Objective: Targeted deep sequencing was used to characterize the mutational spectrum of APC in Chinese colorectal tumors in comparison to that in Caucasians from The Cancer Genome Atlas (TCGA) and to investigate whether APC mutations can predict overall survival in CRC patients receiving adjuvant chemotherapy.Methods: A total of 315 Chinese CRC patients including 241 stage II/III patients receiving fluorouracil-based adjuvant chemotherapy were included in this study. Next generation sequencing was carried out to detect somatic mutations on all APC exons. The associations between APC mutations and overall survival were determined by the Cox proportional hazards model.Results:APC was mutated in 221 of 315 colorectal tumors (70.2%). Chinese CRC had a much higher frequency of missense mutations (16.2% vs. 2.4%), but a lower frequency of nonsense (41.0% vs. 54.2%) and frameshift mutations (10.5% vs. 18.4%) than Caucasian CRC. Among stage II/III patients receiving fluorouracil-based adjuvant chemotherapy, APC mutations showed a significant association with worse survival (HR = 1.69; 95% CI, 1.10-2.62; p = .0179). Of the mutation types, frameshift mutations conferred the highest risk of death (HR = 2.88; 95% CI, 1.54-5.37; p =.0009). Among individual mutation sites, Arg232Ter, the most frequent mutation in Chinese CRC, exhibited the strongest negative impact on survival (HR = 2.65; 95% CI, 1.16-6.03; p =.0202).Conclusion:APC overall mutation was an independent predictor for overall survival of stage II/III CRC patients receiving fluorouracil-based chemotherapy.

Multiple pilomatrixomas in a survivor of WNT-activated medulloblastoma leading to the discovery of a germline APC mutation and the diagnosis of familial adenomatous polyposis.

Because children diagnosed with WNT-activated medulloblastoma have a 10-year overall survival rate of 95%, active long-term follow-up is critically important in reducing mortality from other causes. Here, we describe an 11-year-old adopted female who developed multiple pilomatrixomas 3 years after diagnosis of WNT-activated medulloblastoma, an unusual finding that prompted deeper clinical investigation. A heterozygous germline APC gene mutation was discovered, consistent with familial adenomatous polyposis. Screening endoscopy revealed numerous precancerous polyps that were excised. This case highlights the importance of long-term follow-up of pediatric cancer survivors, including attention to unexpected symptoms, which might unveil an underlying cancer predisposition syndrome.

Colorectal cancer in patients of advanced age is associated with increased incidence of BRAF p.V600E mutation and mismatch repair deficiency.

Introduction: The highest incidence of colorectal cancer (CRC) is in patients diagnosed at 80 years or older highlighting a need for understanding the clinical and molecular features of these tumors. Methods. In this retrospective cohort study, 544 CRCs underwent next generation sequencing and mismatch repair (MMR) evaluation. Molecular and clinical features were compared between 251 patients with traditional-onset CRC (50-69 years at diagnosis) and 60 with late-onset CRC (>80 years at diagnosis). Results: Late-onset CRC showed a significantly higher rate of right-sided tumors (82% vs 35%), MMR deficiency (35% vs. 8%) and BRAF p.V600E mutations (35% vs. 8%) and a significantly lower rate of stage IV disease (15% vs 28%) and APC mutations (52% vs. 78%). Association of these features with advanced age was supported by stratifying patients into 6 age groups (<40, 40-49, 50-59, 60-69, 70-79 and >80 years). However, the age-related rise in MMR deficient (dMMR) CRC was only seen in the female patients with an incidence of 48% (vs. 10% in the male patient) in the >80y group. In addition, BRAF p.V600E was significantly enriched in MMR deficient CRC of advanced age (67% in late-onset CRC). Categorizing CRC by mutational profiling, late-onset CRC revealed a significantly higher rate of dMMR/BRAF + APC - (18% vs. 2.0%), dMMR/BRAF - APC - (8.3% vs. 1.2%) and MMR proficient (pMMR)/BRAF + APC - (12% vs. 4.0%) as compared to traditional-onset CRC. Discussion: In summary, there was a higher rate of dMMR and BRAF p.V600E in late-onset CRC, independently or in combination. The higher incidence of dMMR in late-onset CRC in females is most likely predominantly driven by BRAF p.V600E induced hypermethylation. Prospective studies with treatment plans designed specifically for these older patients are warranted to improve their outcomes.

Intestinal Apc-inactivation induces HSP25 dependency.

The majority of colorectal cancers (CRCs) present with early mutations in tumor suppressor gene APC. APC mutations result in oncogenic activation of the Wnt pathway, which is associated with hyperproliferation, cytoskeletal remodeling, and a global increase in mRNA translation. To compensate for the increased biosynthetic demand, cancer cells critically depend on protein chaperones to maintain proteostasis, although their function in CRC remains largely unexplored. In order to investigate the role of molecular chaperones in driving CRC initiation, we captured the transcriptomic profiles of murine wild type and Apc-mutant organoids during active transformation. We discovered a strong transcriptional upregulation of Hspb1, which encodes small heat shock protein 25 (HSP25). We reveal an indispensable role for HSP25 in facilitating Apc-driven transformation, using both in vitro organoid cultures and mouse models, and demonstrate that chemical inhibition of HSP25 using brivudine reduces the development of premalignant adenomas. These findings uncover a hitherto unknown vulnerability in intestinal transformation that could be exploited for the development of chemopreventive strategies in high-risk individuals.

Multiple roles of Adenomatous Polyposis Coli gene in Wnt Signalling - a Computational Model.

The Adenomatous Polyposis Coli (APC) gene is a multifunctional gene that plays a major role in regulating the Wnt signalling pathway. The Wnt pathway, when activated by Wnt signalling molecules, initiates cell division. Mutation of APC disrupts the regulation and causes continuous activation of the Wnt pathway even in the absence of Wnt signals, thus causing uncontrolled cell proliferation. APC regulates the Wnt pathway by controlling the formation of the nuclear complex ß-catenin/TCF that initiates the transcription of the Wnt target genes. There are at least five mechanisms by which APC can regulate the formation of the ß-catenin/TCF complex: This paper presents a computational model for the Wnt pathway that explicitly includes the above five roles of APC in regulating ß-catenin/TCF formation. We use this computational model to perform in-silico experiments to study the effect of different functional losses of APC on the level of ß-catenin/TCF complex. The simulations also demonstrate the different outcomes that could be expected when the system is governed by different hypotheses.