β-catenin coordinates with Jup and the TCF1/GATA6 axis to regulate human embryonic stem cell fate

β-catenin mediates endodermal commitment of human ES cells via distinct transactivation functions

BACKGROUND

β-catenin, acting as the core effector of canonical Wnt signaling pathway, plays a pivotal role in controlling lineage commitment and the formation of definitive endoderm (DE) during early embryonic development. Despite extensive studies using various animal and cell models, the β-catenin-centered regulatory mechanisms underlying DE formation remain incompletely understood, partly due to the rapid and complex cell fate transitions during early differentiation.

RESULTS

In this study, we generated new CTNNB1-/- human ES cells (hESCs) using CRISPR-based insertional gene disruption approach and systematically rescued the DE defect in these cells by introducing various truncated or mutant forms of β-catenin. Our analysis showed that a truncated β-catenin lacking both N- and C-terminal domains (ΔN148C) could robustly rescue the DE formation, whereas hyperactive β-catenin mutants with S33Y mutation or N-terminal deletion (ΔN90) had limited ability to induce DE lineage. Notably, the ΔN148C mutant exhibited significant nuclear translocation that was positively correlated with successful DE rescue. Transcriptomic analysis further uncovered that two weak β-catenin mutants lacking the C-terminal transactivation domain (CTD) activated primitive streak (PS) genes, whereas the hyperactive β-catenin mutants activated mesoderm genes.

CONCLUSION

Our study uncovered an unconventional regulatory function of β-catenin through weak transactivation, indicating that the levels of β-catenin activity determine the lineage bifurcation from mesendoderm into endoderm and mesoderm.

DSC2 suppresses the growth of gastric cancer through the inhibition of nuclear translocation of γ-catenin and PTEN/PI3K/AKT signaling pathway

BACKGROUND

Globally, gastric cancer (GC) is still a major leading cause of cancer-associated deaths. Downregulated desmocollin2 (DSC2) is considered to be closely related to tumor progression. However, the underlying mechanisms of DSC2 in GC progression require further exploration.

METHOD

We initially constructed different GC cells based on DSC2 contents, established the mouse tumor xenografts, and subsequently performed clonal formation, MTT, Caspase-3 activity, and sperm DNA fragmentation assays to detect the functions of DSC2 in GC growth. Subsequently, we performed western blot, Co-IP, and immunofluorescence assays to investigate the underlying mechanisms through pretreatment with PI3K inhibitor, LY294002, and its activator, recombinant human insulin-like growth factor I (IGF1).

RESULT

DSC2 could significantly inhibit the viability of GC cells at both in vitro and in vivo levels. The underlying mechanism may be that DSC2 binds the γ-catenin to decrease its nuclear level, thereby downregulating the anti-apoptotic factor BCL-2 expression and upregulating the pro-apoptotic factor P53 expression, which adjusts the PTEN/PI3K/AKT signaling pathway to promote the cancer cell apoptosis.

CONCLUSIONS

Our finding suggests that DSC2 might be a potential therapeutic target for the treatment of cancers, most especially GC.

DSC2 Suppresses the Metastasis of Gastric Cancer through Inhibiting the BRD4/Snail Signaling Pathway and the Transcriptional Activity of β-Catenin

Downregulated DSC2 involved in the metastasis of cancers. Unfortunately, its role on the development of gastric cancer (GC) and the potential mechanisms remain unclear. Bioinformatics analysis, Western blot, qRT-PCR, and immunohistochemistry were performed to detect the DSC2 levels of human GC and normal stomach tissues. The role of DSC2 and the downstream signaling in gastric carcinogenesis were explored by using GC specimens, GC cells with different DSC2 expression, inhibitors, and mouse metastasis models. We found that the level of DSC2 decreased significantly in GC tissues and cells. Recovered DSC2 inhibited the invasion and migration of GC cells both in culture and in xenografts. Mechanistically, DSC2 could not only decrease Snail level and nuclear BRD4 level by forming DSC2/BRD4, but also inhibit nuclear translocation of β-catenin. We concluded that DSC2 inhibited the metastasis of GC, and the underlying mechanisms were closely related to the regulation on nuclear translocation of BRD4 and β-catenin. Our results suggest that DSC2 may serve as a novel therapeutic target for GC.

β-catenin links cell seeding density to global gene expression during mouse embryonic stem cell differentiation

Although cell density is known to affect numerous biological processes including gene expression and cell fate specification, mechanistic understanding of what factors link cell density to global gene regulation is lacking. Here, we reveal that the expression of thousands of genes in mouse embryonic stem cells (mESCs) is affected by cell seeding density and that low cell density enhances the efficiency of differentiation. Mechanistically, β-catenin is localized primarily to adherens junctions during both self-renewal and differentiation at high density. However, when mESCs differentiate at low density, β-catenin translocates to the nucleus and associates with Tcf7l1, inducing co-occupied lineage markers. Meanwhile, Esrrb sustains the expression of pluripotency-associated genes while repressing lineage markers at high density, and its association with DNA decreases at low density. Our results provide new insights into the previously neglected but pervasive phenomenon of density-dependent gene regulation.

Human Pluripotent Stem Cell-Derived Endoderm for Modeling Development and Clinical Applications

The liver, lung, pancreas, and digestive tract all originate from the endoderm germ layer, and these vital organs are subject to many life-threatening diseases affecting millions of patients. However, primary cells from endodermal organs are often difficult to grow in vitro. Human pluripotent stem cells thus hold great promise for generating endoderm cells and their derivatives as tools for the development of new therapeutics against a variety of global healthcare challenges. Here we describe recent advances in methods for generating endodermal cell types from human pluripotent stem cells and their use for disease modeling and cell-based therapy.

Simvastatin promotes endothelial dysfunction by activating the Wnt/β‑catenin pathway under oxidative stress

Atherosclerosis is a major pathogenic factor in patients with cardiovascular diseases, and endothelial dysfunction (ED) plays a primary role in its occurrence and development. Simvastatin is a lipid‑lowering drug, which is commonly used to prevent or treat risk factors of cardiovascular diseases with a significant anti‑atherogenic effect. However, its impact on endothelial cells under conditions of oxidative stress and broader mechanisms of action remain unclear. The present study evaluated the effect of simvastatin on human umbilical vein endothelial cells (HUVECs) under oxidative stress with H2O2, and the associated mechanisms. At a high dose (1 µM), simvastatin exacerbated H2O2‑induced endothelial cell dysfunction. Moreover, inhibition of the Wnt/β‑catenin pathway by salinomycin significantly suppressed the simvastatin‑associated HUVEC dysfunction. Western blot analysis further demonstrated that simvastatin promoted the phosphorylation of low‑density lipoprotein receptor‑related protein 6 (LRP6) and activated the Wnt/β‑catenin pathway. Simvastatin also activated endoplasmic reticulum (ER) stress, which was reversed by salinomycin treatment. Based on these results, it was hypothesized that simvastatin may promote ER stress by facilitating LRP6 phosphorylation and the subsequent activation of the Wnt/β‑catenin pathway, thereby enhancing H2O2‑induced ED. Therefore, high‑dose simvastatin treatment could have potential toxic side effects, indicating the need for close clinical management, monitoring and patient selection.

Targeting AMP-activated kinase impacts hepatocellular cancer stem cells induced by long-term treatment with sorafenib

Hepatocellular carcinoma (HCC) is the third leading cause of cancer death worldwide. HCC treatment is hindered by the frequent emergence of chemoresistance to the multikinase inhibitor sorafenib, which has been related to the presence of cancer stem cells (CSCs) that self‐renew and often escape therapy. The key metabolic sensor AMP‐activated kinase (AMPK) has recently been recognized as a tumour growth regulator. In this study, we aimed to elucidate the role of AMPK in the development of a stem cell phenotype in HCC cells. To this end, we enriched the CSC population in HCC cell lines that showed increased expression of drug resistance (ALDH1A1, ABCB1A) and stem cell (CD133, Nanog, Oct4, alpha fetoprotein) markers and demonstrated their stemness phenotype. These cells were refractory to sorafenib‐induced cell death. We report that sorafenib‐resistant cells had lower levels of total and phosphorylated AMPK as well as its downstream substrate, ACC, compared with the parental cells. Interestingly, AMPK knockdown with siRNA or inhibition with dorsomorphin increased the expression of stem cell markers in parental cells and blocked sorafenib‐induced cell death. Conversely, the upregulation of AMPK, either by transfection or by pharmacological activation with A‐769662, decreased the expression of ALDH1A1, ABCB1A, CD133, Nanog, Oct4, and alpha fetoprotein, and restored sensitivity to sorafenib. Analysis of the underlying mechanism points to hypoxia‐inducible factor HIF‐1α as a regulator of stemness. In vivo studies in a xenograft mouse model demonstrated that stem‐like cells have greater tumourigenic capacity. AMPK activation reduced xenograft tumour growth and decreased the expression of stem cell markers. Taken together, these results indicate that AMPK may serve as a novel target to overcome chemoresistance in HCC.

The transcription factor TFCP2L1 induces expression of distinct target genes and promotes self-renewal of mouse and human embryonic stem cells

TFCP2L1 (transcription factor CP2-like 1) is a transcriptional regulator critical for maintaining mouse and human embryonic stem cell (ESC) pluripotency. However, the direct TFCP2L1 target genes are uncharacterized. Here, using gene overexpression, immunoblotting, quantitative real-time PCR, ChIP, and reporter gene assays, we show that TFCP2L1 primarily induces estrogen-related receptor β (Esrrb) expression that supports mouse ESC identity and also selectively enhances Kruppel-like factor 4 (Klf4) expression and thereby promotes human ESC self-renewal. Specifically, we found that in mouse ESCs, TFCP2L1 binds directly to the Esrrb gene promoter and regulates its transcription. Esrrb knockdown impaired Tfcp2l1's ability to induce interleukin 6 family cytokine (leukemia inhibitory factor)-independent ESC self-renewal and to reprogram epiblast stem cells to naïve pluripotency. Conversely, Esrrb overexpression blocked differentiation induced by Tfcp2l1 down-regulation. Moreover, we identified Klf4 as a direct TFCP2L1 target in human ESCs, bypassing the requirement for activin A and basic fibroblast growth factor in short-term human ESC self-renewal. Enforced Klf4 expression recapitulated the self-renewal-promoting effect of Tfcp2l1, whereas Klf4 knockdown eliminated these effects and caused loss of colony-forming capability. These findings indicate that TFCP2L1 functions differently in naïve and primed pluripotency, insights that may help elucidate the different states of pluripotency.

Dual ablation of β- and γ-catenin: Critical regulators of junctions and their functions

The duality of β- and γ–catenin during liver injury has not been defined. It’s well known that loss of β-catenin plays a critical role in overall liver health and is a major component of adherens junctions (AJ). Further, γ-catenin has been shown to regulate β-catenin and vice-versa. In this excellent manuscript, the authors investigated the effects of knocking out both β- and γ–catenin creating a β-;γ-catenin-double knockout (DKO). The result of this interbreeding revealed a model that is reminiscent of early childhood cholestatic liver diseases (CLD) like Progressive Familial Intrahepatic Cholestasis (PFIC). The authors provide both in vivo and in vitro data to demonstrate the important role of these catenin genes in the regulation of hepatocyte-junctions. The experiments show partially redundant function of catenin’s at hepatocyte AJ in regulating tight junctions (TJ) and contributing to a disrupted blood-bile barrier. Further, concomitant hepatic loss of β- and γ-catenin disrupts structural and functional integrity of AJ and TJ via transcriptional and posttranslational mechanisms. Overall, these studies shed important light on junctional protein dysregulation during CLD.

Tfcp2l1 safeguards the maintenance of human embryonic stem cell self-renewal

Tfcp2l1 is a transcription factor critical for mouse embryonic stem cell (mESC) maintenance. However, its role in human ESCs (hESCs) remains unclear. Here, we investigated the role of Tfcp2l1 in controlling hESC activity and showed that Tfcp2l1 is functionally important in the maintenance of hESC identity. Tfcp2l1 expression is highly enriched in hESCs and dramatically decreases upon differentiation. Forced expression of Tfcp2l1 promoted hESC self-renewal. Functional analysis of the mutant forms of Tfcp2l1 revealed that both the CP2- and SAM-like domains are indispensable for Tfcp2l1 to maintain the undifferentiated state of hESCs. Notably, the CP2-like domain is closely related to the suppression of definitive endoderm and mesoderm commitment. Accordingly, knockdown of Tfcp2l1 significantly induced differentiation preferentially into definitive endoderm and mesoderm. Further studies found that inhibition of Wnt/β-catenin signaling pathway by IWR1 is able to eliminate the differentiation caused by Tfcp2l1 downregulation. Taken together, these findings reveal the unique and crucial role of Tfcp2l1 in the determination of hESC fate and will expand our understanding of the self-renewal and differentiation circuitry in hESCs.