Two subtypes of colorectal tumor with distinct molecular features in familial adenomatous polyposis

C8orf48 inhibits the tumorigenesis of colorectal cancer by regulating the MAPK signaling pathway

AIMS

Colorectal cancer (CRC) is a leading cause of cancer-related death globally. Thus, in this study, we aimed to investigate chromosome 8 open reading frame 48 (C8orf48) as a biomarker for early detection of CRC.

MAIN METHODS

RNA expression and methylation profiles were downloaded from The Cancer Genome Atlas (TCGA) database. Cell proliferation, migration and invasion assays were performed to confirm the function of C8orf48 in CRC cells. Dual-luciferase reporter assay was used to identify that C8orf48 was the direct target of miR-556. Genomics of Drug Sensitivity in Cancer (GDSC) database, gene set enrichment analysis (GSEA) and western blot analysis were performed to explore the mechanism of C8orf48.

KEY FINDINGS

we found that C8orf48 is down-regulated in clinical samples of CRC tissues. Enrichment analysis showed that C8orf48 is associated with methylation biomarkers in CRC, and TCGA database confirmed that the methylation of C8orf48 is up-regulated in the early stage of CRC. We further revealed that the overexpression of C8orf48 decreased CRC cell proliferation, migration and invasion. Luciferase reporter indicated that C8orf48 was the direct target of the oncogene miR-556. Additionally, we used GDSC database, GSEA database and western blot analysis to demonstrate that C8orf48 plays a suppressor role in CRC by inhibiting MAPK signaling pathway.

SIGNIFICANCE

C8orf48 was identified as a biomarker for early detection of CRC for the first time, and might provide novel information for CRC prediction and therapy.

Clinicopathologic and Molecular Characteristics of Familial Adenomatous Polyposis-associated Traditional Serrated Adenoma

Colorectal carcinogenesis in familial adenomatous polyposis (FAP) follows a conventional adenoma-carcinoma sequence. However, previous studies have also reported the occurrence of traditional serrated adenomas (TSAs) in patients with FAP. In the present study, we analyzed the clinicopathologic and molecular features of 37 TSAs from 21 FAP patients. Histologically, the majority of FAP-associated TSAs showed typical cytology and slit-like serration; however, ectopic crypt formation was infrequent. Next-generation sequencing and Sanger sequencing identified KRAS and BRAF V600E mutations in 18 (49%) and 14 (38%) TSAs, respectively. Somatic APC mutations were detected in 26 lesions (84% of analyzed cases). Three lesions had BRAF non-V600E mutations, and 2 of them had a concurrent KRAS mutation. Seven TSAs (19%) were associated with a precursor polyp, 6 with a hyperplastic polyp, and 1 with a sessile serrated lesion, and all of them showed the BRAF V600E mutation. Additional sequencing analysis of 4 TSAs with a precursor polyp showed that the BRAF V600E mutation was shared between the TSA and precursor components, but APC mutations were exclusive to the TSA component in all the analyzed lesions. None of the lesions showed the high CpG island methylation phenotype. These results indicate that FAP-associated TSAs frequently have KRAS or BRAF mutations, similar to sporadic cases, and second-hit somatic APC mutations are commonly involved in their tumorigenesis as in other FAP-associated tumors. Although progression to adenocarcinoma is likely rare, tumorigenesis via the serrated pathway occurs in patients with FAP.

Solid pseudopapillary neoplasms of the pancreas are dependent on the Wnt pathway

Solid pseudopapillary neoplasms (SPNs) are rare and relatively indolent tumors of the pancreas. While primary SPNs can be surgically resected, there are currently no therapies available for patients with advanced stage disease. Given that these tumors frequently carry CTNNB1 hotspot (recurrently mutated loci in a gene) mutations resulting in β‐catenin nuclear accumulation, it has been speculated that the Wnt pathway may be a driver in this disease. Here, we present a comprehensive “multi‐omics” study where the genome, transcriptome, and methylome of SPNs were analyzed. We found that SPNs are characterized by a low‐complexity genome where somatic mutations in CTNNB1, present in 100% of the cases, are the only actionable genomic lesions. Compared to more common subtypes of pancreatic tumors (adenocarcinomas and pancreatic neuroendocrine tumors), SPNs show high expression levels of genes belonging to the Wnt pathway. Their methylome was consistent with an epithelial cell origin and a general upregulation of Wnt pathway genes. Clinical studies to evaluate the exquisite sensitivity of SPNs to inhibitors of the Wnt pathway are warranted.

The frequency of promoter DNA hypermethylation is decreased in colorectal neoplasms of familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is an inherited disorder characterized by numerous colorectal adenomatous polyps with predisposition to the development of colorectal cancer (CRC). Here, we conducted genome-wide DNA methylation analysis of FAP neoplasms, including seven cancer samples and 16 adenoma samples, using an Infinium 450K BeadArray. As controls for sporadic colorectal neoplasms and mucosae, we used Infinium 450k data from 297 CRC samples, 45 colorectal adenoma samples, and 37 normal mucosa samples with reference to The Cancer Genome Atlas and other databases. Unsupervised two-way hierarchical clustering analysis of FAP and sporadic CRC/adenoma revealed that CRC was classified into four DNA methylation epigenotypes (MEs): high-ME (HME), intermediate-ME (IME), low-ME (LME), and normal-like ME (NME). Five FAP neoplasms (two cancer and three adenoma) were clustered with IME, whereas 18 FAP neoplasms (five cancer and 13 adenoma) were clustered into NME. IME FAP neoplasms significantly correlated with KRAS mutations, similar to sporadic CRC. Within IME cases, however, aberrant DNA methylation was significantly less frequent in FAP neoplasms than sporadic neoplasms, and these unmethylated genes included WNT family genes and several types of oncogenes. In summary, FAP neoplasms were classified into at least two molecular subtypes, i.e., NME in the majority of cases showing mostly no aberrant methylation and IME in some cases accompanied by KRAS mutations but less frequent aberrant DNA methylation than sporadic neoplasms, suggesting that FAP may follow a tumorigenesis pathway different from that of sporadic CRC.

Niclosamide is a potential therapeutic for familial adenomatosis polyposis by disrupting Axin-GSK3 interaction

The epithelial-mesenchymal transition (EMT) is implicated in tumorigenesis and cancer progression, and canonical Wnt signaling tightly controls Snail, a key transcriptional repressor of EMT. While the suppression of canonical Wnt signaling and EMT comprises an attractive therapeutic strategy, molecular targets for small molecules reverting Wnt and EMT have not been widely studied. Meanwhile, the anti-helminthic niclosamide has been identified as a potent inhibitor of many oncogenic signaling pathways although its molecular targets have not yet been clearly identified. In this study, we show that niclosamide directly targets Axin-GSK3 interaction, at least in part, resulting in suppression of Wnt/Snail-mediated EMT. In vitro and in vivo, disruption of Axin-GSK3 complex by niclosamide induces mesenchymal to epithelial reversion at nM concentrations, accompanied with suppression of the tumorigenic potential of colon cancer. Niclosamide treatment successfully attenuates Snail abundance while increasing E-cadherin abundance in xenograft tumor. Notably, oral administration of niclosamide significantly suppressed adenoma formation in an APC-MIN mice model, indicating that niclosamide is an effective therapeutic for familial adenomatosis polyposis (FAP) patients. In this study, we identified a novel target to control the canonical Wnt pathway and Snail-mediated EMT program, and discovered a repositioned therapeutics for FAP patients.