A genome-scale CRISPR screen reveals factors regulating Wnt-dependent renewal of mouse gastric epithelial cells.

An ability to safely harness the powerful regenerative potential of adult stem cells for clinical applications is critically dependent on a comprehensive understanding of the underlying mechanisms regulating their activity. Epithelial organoid cultures accurately recapitulate many features of in vivo stem cell-driven epithelial renewal, providing an excellent ex vivo platform for interrogation of key regulatory mechanisms. Here, we employed a genome-scale clustered, regularly interspaced, short palindromic repeats (CRISPR) knockout (KO) screening assay using mouse gastric epithelial organoids to identify modulators of Wnt-driven stem cell-dependent epithelial renewal in the gastric mucosa. In addition to known Wnt pathway regulators, such as Apc, we found that KO of Alk, Bclaf3, or Prkra supports the Wnt independent self-renewal of gastric epithelial cells ex vivo. In adult mice, expression of these factors is predominantly restricted to non-Lgr5-expressing stem cell zones above the gland base, implicating a critical role for these factors in suppressing self-renewal or promoting differentiation of gastric epithelia. Notably, we found that Alk inhibits Wnt signaling by phosphorylating the tyrosine of Gsk3ß, while Bclaf3 and Prkra suppress regenerating islet-derived (Reg) genes by regulating the expression of epithelial interleukins. Therefore, Alk, Bclaf3, and Prkra may suppress stemness/proliferation and function as novel regulators of gastric epithelial differentiation.

Distinct Localization of Mature HGF from its Precursor Form in Developing and Repairing the Stomach.

Hepatocyte growth factor (HGF) is secreted as an inactive single-chain HGF (scHGF); however, only proteolytically processed two-chain HGF (tcHGF) can activate the MET receptor. We investigated the localization of tcHGF and activated/phosphorylated MET (pMET) using a tcHGF-specific antibody. In day 16.5 mouse embryos, total HGF (scHGF + tcHGF) was mainly localized in smooth muscle cells close to, but separate from, MET-positive epithelial cells in endodermal organs, including the stomach. In the adult stomach, total HGF was localized in smooth muscle cells, and tcHGF was mainly localized in the glandular base region. Immunostaining for pMET and Lgr5-driven green fluorescent protein (GFP) indicated that pMET localization overlapped with Lgr5+ gastric stem cells. HGF promoted organoid formation similar to EGF, indicating the potential for HGF to promote the survival and growth of gastric stem cells. pMET and tcHGF localizations changed during regeneration following gastric injury. These results indicate that MET is constantly activated in gastric stem cells and that the localization of pMET differs from the primary localization of precursor HGF but has a close relationship to tcHGF. Our results suggest the importance of the microenvironmental generation of tcHGF in the regulation of development, regeneration, and stem cell behavior.

Identification of FERM domain-containing protein 5 as a novel target of ß-catenin/TCF7L2 complex.

Deregulation of the canonical Wnt signaling pathway plays an important role in human tumorigenesis through the accumulation of ß-catenin and subsequent transactivation of TCF7L2. Although some of the consequences associated with the accumulated ß-catenin have been clarified, the comprehensive effect of activated ß-catenin/TCF7L2 transcriptional complex on tumorigenesis remains to be elucidated. To understand the precise molecular mechanisms underlying colorectal cancer, we searched for genes regulated by the complex in colorectal tumors. We performed expression profile analysis of HCT116 and SW480 colon cancer cells treated with ß-catenin siRNAs, and ChIP-sequencing using anti-TCF7L2 antibody. Combination of these data with public microarray data of LS174 cells with a dominant-negative form of TCF7L2 identified a total of 11 candidate genes. In this paper, we focused on FERM domain-containing protein 5 (FRMD5), and confirmed that it is regulated by both ß-catenin and TCF7L2. An additional reporter assay disclosed that a region in intron1 transcriptionally regulated the expression of FRMD5. ChIP assay also corroborated that TCF7L2 associates with this region. These data suggested that FRMD5 is a novel direct target of the ß-catenin/TCF7L2 complex.

Establishment and analysis of a novel mouse line carrying a conditional knockin allele of a cancer-specific FBXW7 mutation.

F-box and WD40 domain protein 7 (FBXW7) is a component of the SKP1-CUL1-F-box protein (SCF) complex that mediates the ubiquitination of diverse oncogenic target proteins. The exploration of FBXW7 mutations in human primary cancer has revealed three mutation hotspots at conserved arginine residues (Arg465, Arg479, and Arg505) in the WD40 domain, which are critical for substrate recognition. To study the function of human FBXW7 R465C , the most frequent mutation in human malignancies, we generated a novel conditional knockin mouse line of murine Fbxw7 R468C corresponding to human FBXW7 R465C . Systemic heterozygous knockin of the Fbxw7 R468C mutation resulted in perinatal lethality due to defects in lung development, and occasionally caused an eyes-open at birth phenotype and cleft palate. Furthermore, mice carrying liver-specific heterozygous and homozygous Fbxw7 R468C alleles cooperated with an oncogenic Kras mutation to exhibit bile duct hyperplasia within 8 months of birth and cholangiocarcinoma-like lesions within 8 weeks of birth, respectively. In addition, the substrates affected by the mutant Fbxw7 differed between the embryos, embryonic fibroblasts, and adult liver. This novel conditional knockin Fbxw7 R468C line should be useful to gain a more profound understanding of carcinogenesis associated with mutation of FBXW7.

Genetic alterations in Japanese extrahepatic biliary tract cancer.

Biliary tract cancer (BTC) is one of the most devastating types of malignant neoplasms worldwide. However, the mechanisms underlying the development and progression of BTC remain unresolved. BTC includes extrahepatic bile duct carcinoma (EBDC), gallbladder carcinoma (GBC) and ampulla of Vater carcinoma (AVC), named according to the location of the tumor. Although genetic alterations of intrahepatic cholangiocarcinoma have been investigated, those of EBDC, GBC and AVC have not yet been fully understood. The present study analyzed somatic mutations of 50 cancer-associated genes in 27 Japanese BTC cells, including: 11 EBDC, 14 GBC and 2 AVC. Next-generation sequencing using an Ion AmpliSeq Cancer Panel identified a total of 44 somatic mutations across 14 cancer-associated genes. Among the 44 mutations, 42 were judged as pathological mutations. Frequent mutations were identified in tumor protein 53 (TP53) (14/27), SMAD family member 4 (SMAD4) (6/27), phosphatidylinositol-4,5-bisphosphate 3-kinase, catalytic subunit α (PIK3CA) (6/27), and Kirsten rat sarcoma (KRAS) (6/27); no significant differences were identified between EBDC and GBC tissues. Notably, the frequency of the PIK3CA mutation was higher when compared with previous reports. This result may suggest that the activation of the PIK3CA-protein kinase B signaling pathway, in addition to the abrogation of p53, SMAD4 and RAS mitogen-activated protein kinase may have a crucial role in the carcinogenesis of Japanese BTC. These findings may be useful for the development of personalized therapies for BTC.

A novel mouse model of intrahepatic cholangiocarcinoma induced by liver-specific Kras activation and Pten deletion.

Intrahepatic cholangiocarcinoma (ICC) is an aggressive malignancy with poor prognosis and its incidence is increasing worldwide. Recently, several types of cells have been considered as the origin of ICC, namely cholangiocytes, liver progenitor cells, and hepatocytes. Here, we have established a novel mouse model of ICC by liver-specific Kras activation and Pten deletion. An activating mutation of Kras in combination with deletion of Pten was introduced in embryonic hepatic bipotential progenitor cells (so-called hepatoblasts) and mature hepatocytes using the Cre-loxP system. As a result, liver-specific Kras activation and homozygous Pten deletion cooperated to induce ICCs exclusively. In contrast, Kras activation in combination with heterozygous Pten deletion induced both ICCs and HCCs, whereas Kras activation alone resulted in HCCs but not ICCs. Furthermore, a cell-lineage visualization system using tamoxifen-inducible Cre-loxP demonstrated that the ICCs did not originate from hepatocytes but from cholangiocytes. Our data suggest that mice carrying liver-specific Kras activation in combination with homozygous Pten deletion should be useful for the investigation of therapeutic strategies for human ICC.

Molecular profiles of high-grade and low-grade pseudomyxoma peritonei.

Pseudomyxoma peritonei (PMP) is a rare disease exhibiting a distinct clinical feature caused by cancerous cells that produce mucinous fluid in the abdominal cavity. PMPs originate most frequently from the appendix and less frequently from the ovary. This disease can range from benign to malignant, and histologically, PMP is classified into two types: disseminated peritoneal adenomucinosis (DPAM) representing the milder phenotype, and peritoneal mucinous adenocarcinomas (PMCA) representing the aggressive phenotype. Although histological classification is clinically useful, the pathogenesis of PMP remains largely unknown. To elucidate the molecular mechanisms underlying PMP, we analyzed 18 PMP tumors comprising 10 DPAMs and 8 PMCAs. DNA was extracted from tumor and matched non-tumorous tissues, and was sequenced using Ion AmpliSeq Cancer Panel containing 50 cancer-related genes. Analysis of the data identified a total of 35 somatic mutations in 10 genes, and all mutations were judged as pathological mutations. Mutations were frequently identified in KRAS (14/18) and GNAS (8/18). Interestingly, TP53 mutations were found in three of the eight PMCAs, but not in the DPAMs. PIK3CA and AKT1 mutations were also identified in two PMCAs, but not in the DPAMs. These results suggested that KRAS and/or GNAS mutations are common genetic features of PMP, and that mutations in TP53 and/or genes related to the PI3K-AKT pathway may render malignant properties to PMP. These findings may be useful for the understanding of tumor characteristics, and facilitate the development of therapeutic strategies.