Project description:Hepatocytes are highly polarized epithelia. Loss of hepatocyte polarity is associated with various liver diseases, including cholestasis. However, the molecular underpinnings of hepatocyte polarization remain poorly understood. Previously, we have shown that loss of β-catenin at adherens junctions (AJs) is compensated by β-catenin and dual loss of both catenins in dual knockouts (DKO) in mice liver leads to progressive intrahepatic cholestasis. However, the clinical relevance of this observation, and further phenotypic characterization of the phenotype, is important. Here, we identify simultaneous loss of β- and γ-catenin in a subset of liver samples from patients of progressive familial intrahepatic cholestasis and primary sclerosing cholangitis. Hepatocytes in DKO mice exhibited defect in apical-basolateral localization of polarity proteins, impaired bile canaliculi formation, and loss of microvilli. Loss of polarity in DKO livers manifested as epithelial-to-mesenchymal transition, increased hepatocyte proliferation, and suppression of hepatocyte differentiation, which was associated with up-regulation of TGFβ signaling and repression of Hnf4α expression and activity. In conclusion, concomitant loss of the two catenins in the liver may be playing a pathogenic role in subsets of cholangiopathies. Our findings also support a previously unknown role β- and γ-catenin in the maintenance of hepatocyte polarity. Improved understanding of the regulation of hepatocyte polarization processes by β and γ-catenin could potentially benefit development of new therapies for cholestasis.
Project description:ß-catenin is part of the cell-cell adhesion complex, where it plays a structural role but is also the key effector of the Wnt pathway, where it is endowed with a transcriptional regulatory activity. Oncogenic mutations of ß-catenin are present in about one third of hepatocellular carcinoma. In most tumors, ß-catenin mutations are heterozygous meaning that mutated and wild-type proteins co-exist in tumor cells. We address here the interplay between wild-type and mutated ß-catenins in liver tumor cells. We have designed a RNA interference strategy in HepG2 cells that allows uncoupling of the two functions of ß-catenin in the same cellular background: nuclear/transcriptional activity, a function almost exclusively mediated by the mutated ß-catenin, and membrane/structural activity, which is mediated by the degradable WT ß-catenin.
Project description:Background & Aims Hepatocytes differentiated from human embryonic stem cells (hESCs) have the potential to overcome the shortage of primary hepatocytes for clinical use and drug development. Many strategies for this process have been reported, but the functionality of the resulting cells is incomplete. We hypothesize that the functionality of hPSC-derived hepatocytes might be improved by making the differentiation method more similar to normal in vivo hepatic development. Methods We tested combinations of growth factors and small molecules targeting candidate signaling pathways culled from the literature to identify optimal conditions for differentiation of hESCs to hepatocytes, using qRT-PCR for stage-specific markers to identify the best conditions. Immunocytochemistry was then used to validate the selected conditions. Finally, induction of expression of metabolic enzymes in terminally differentiated cells was used to assess the functionality of the hESC-derived hepatocytes. Results Optimal differentiation of hESCs was attained using a 5-stage protocol. After initial induction of definitive endoderm (stage 1), we showed that inhibition of the WNT/β-catenin pathway during the 2nd and 3rd stages of differentiation was required to specify first posterior foregut, and then hepatic gut cells. In contrast, during the 4th stage of differentiation, we found that activation of the WNT/β-catenin pathway allowed generation of proliferative bipotent hepatoblasts, which then were efficiently differentiated into hepatocytes in the 5th stage by dual inhibition of TGF-β and NOTCH signaling. Conclusion Here, we show that stage-specific regulation of the WNT/β-catenin pathway results in improved differentiation of hESCs to functional hepatocytes.
Project description:Up to 41% of hepatocellular carcinomas (HCCs) result from activating mutations in the CTNNB1 gene encoding β-catenin. β-catenin has dual cellular functions as a component of the Wnt signaling pathway and adherens junctions. HCC-associated CTNNB1 mutations stabilize the β-catenin protein, leading to nuclear and/or cytoplasmic localization of β-catenin and downstream activation of Wnt target genes. In patient HCC samples, β-catenin nuclear and cytoplasmic localization are typically patchy, even among HCC with highly active CTNNB1 mutations. The functional and clinical relevance of this heterogeneity in β-catenin activation are not well understood. To define mechanisms of β-catenin-driven HCC initiation, we generated a Cre-lox system that enabled switching on activated β-catenin in 1) a small number of hepatocytes in early development; or 2) the majority of hepatocytes in later development or adulthood. We discovered that switching on activated β-catenin in a subset of larval hepatocytes was sufficient to drive HCC initiation. To determine the role of Wnt/β-catenin signaling heterogeneity later in hepatocarcinogenesis, we performed RNA-seq analysis of zebrafish β-catenin-driven HCC. Ingenuity Pathway Analysis of differentially expressed genes in the Cre-lox HCC model revealed that “Cancer” and “Liver Tumor” categories were significantly altered, indicating transcriptional similarities with human HCC and other vertebrate HCC models. At the single-cell level, 2.9% to 15.2% of hepatocytes from zebrafish β-catenin-driven HCC expressed two or more of the Wnt target genes axin2, mtor, glula, myca, and wif1, indicating focal activation of Wnt signaling in established tumors. Thus, heterogeneous β-catenin activation drives HCC initiation and persists throughout hepatocarcinogenesis.
Project description:Up to 41% of hepatocellular carcinomas (HCCs) result from activating mutations in the CTNNB1 gene encoding β-catenin. β-catenin has dual cellular functions as a component of the Wnt signaling pathway and adherens junctions. HCC-associated CTNNB1 mutations stabilize the β-catenin protein, leading to nuclear and/or cytoplasmic localization of β-catenin and downstream activation of Wnt target genes. In patient HCC samples, β-catenin nuclear and cytoplasmic localization are typically patchy, even among HCC with highly active CTNNB1 mutations. The functional and clinical relevance of this heterogeneity in β-catenin activation are not well understood. To define mechanisms of β-catenin-driven HCC initiation, we generated a Cre-lox system that enabled switching on activated β-catenin in 1) a small number of hepatocytes in early development; or 2) the majority of hepatocytes in later development or adulthood. We discovered that switching on activated β-catenin in a subset of larval hepatocytes was sufficient to drive HCC initiation. To determine the role of Wnt/β-catenin signaling heterogeneity later in hepatocarcinogenesis, we performed RNA-seq analysis of zebrafish β-catenin-driven HCC. Ingenuity Pathway Analysis of differentially expressed genes in the Cre-lox HCC model revealed that “Cancer” and “Liver Tumor” categories were significantly altered, indicating transcriptional similarities with human HCC and other vertebrate HCC models. At the single-cell level, 2.9% to 15.2% of hepatocytes from zebrafish β-catenin-driven HCC expressed two or more of the Wnt target genes axin2, mtor, glula, myca, and wif1, indicating focal activation of Wnt signaling in established tumors. Thus, heterogeneous β-catenin activation drives HCC initiation and persists throughout hepatocarcinogenesis.
Project description:In nucleated cells, β-catenin, the key downstream effector of this pathway, is a dual function protein, regulating the coordination of gene transcription and cell–cell adhesion. The specific role of β-catenin in the anucleate platelet however remains elusive. Here, we performed a label-free quantitative proteomic analysis of β-catenin immunoprecipitates from human platelets identifying 9 co-immunoprecipitating proteins. GO biological pathway analysis revealed a significant enrichment of specific functional terms including 'cell adhesion', 'cell junction organization' and ‘adherens junction organization'. Our bioinformatics data suggests that human platelet β-catenin may be involved in facilitating cell adhesion and cell junctions. We found three proteins co-immunoprecipitating with β-catenin under both resting and activated conditions, four proteins under resting condition only and two proteins under activated condition only.
Project description:O-GlcNAc is a dynamic post-translational modification on thousands of intracellular proteins, it regulates protein functions and is involved in many metabolic diseases. Using a dual-specificity aptamer, we targeted the O-GlcNAc transferase (OGT) to endogenous β-catenin and specifically increased O-GlcNAcylation of β-catenin. To study how O-GlcNAcylation of β-catenin regulates the transcriptome, we performed RNA sequencing on HEK293T cells expressing individual (Ctrl.) or dual-specificity aptamers. We found that O-GlcNAcylation of β-catenin shifts the transcriptome in a Wnt-dependent manner: it repressed the expression of about 100 genes in the absence of Wnt, while it activated the expression of these genes when Wnt signaling was turned on.
Project description:The liver has a remarkable capacity to regenerate, which is sustained by the ability of hepatocytes to act as facultative stem cells that, while normally quiescent, re-enter the cell cycle upon injury. In rodents, growth factor signaling is indispensable, whereas Wnt/β-catenin is not required for effective tissue repair. However, molecular networks controlling human liver regeneration remain unclear.