Cholesterol-rich membrane microdomains modulate Wnt/β-catenin morphogen gradient during Xenopus development

GBA1-dependent membrane glucosylceramide reprogramming promotes liver cancer metastasis via activation of the Wnt/β-catenin signalling pathway

The effect of glucosylceramide (GlcCer) reprogramming on liver cancer metastasis remains poorly understood. In this study, we demonstrated that the protein expression of GBA1, which catalyses the conversion of GlcCer to ceramide, was downregulated in liver cancer tissue. A clinical relevance analysis revealed that low expression of GBA1 was associated with the metastatic potential of liver cancer cells. Furthermore, loss- and gain-of-function studies confirmed that low expression of GBA1 promoted metastasis of liver cancer both in vitro and in vivo. Mechanistic studies indicated that low expression of GBA1 enhanced the metastatic ability of liver cancer by promoting the epithelial-mesenchymal transition (EMT), in which Wnt signalling pathway is involved. In the plasma membrane (PM), GBA1-dependent GlcCer reprogramming increased LRP6 location in the PM leading to an interaction between GlcCer and LRP6, subsequently promoting LRP6 phosphorylation at Ser1490, and finally activating the Wnt/β-catenin signalling pathway. To our knowledge, this is the first time to be found that GlcCer interacted with a protein. In addition, the results of mass spectrometry indicated that GlcCer d18:1/18:0 was the most notably increased studied species in the PM when GBA1 was downregulated, suggesting that GlcCer d18:1/18:0 may be the major functional lipid that promotes GBA1-dependent liver cancer metastasis. Thus, GBA1-mediated GlcCer reprogramming in the PM promotes metastasis of liver cancer via activation of the Wnt/β-catenin signalling pathway, upregulation of GBA1 may be a potential therapeutic strategy to combat liver cancer metastasis.

A Novel Long Non-Coding RNA lnc030 Maintains Breast Cancer Stem Cell Stemness by Stabilizing SQLE mRNA and Increasing Cholesterol Synthesis

Cancer stem cells (CSCs) are considered the roots of cancer metastasis and recurrence (CSCs), due in part to their self-renewal and therapy resistance properties. However, the underlying mechanisms for the regulation of CSC stemness are poorly understood. Recently, increasing evidence shows that long non-coding RNAs (lncRNAs) are critical regulators for cancer cell function in various malignancies including breast cancer, but how lncRNAs regulate the function of breast cancer stem cells (BCSCs) remains to be determined. Herein, using lncRNA/mRNA microarray assays, a novel lncRNA (named lnc030) is identified, which is highly expressed in BCSCs in vitro and in vivo, as a pivotal regulator in maintaining BCSC stemness and promoting tumorigenesis. Mechanistically, lnc030 cooperates with poly(rC) binding protein 2(PCBP2) to stabilize squalene epoxidase (SQLE) mRNA, resulting in an increase of cholesterol synthesis. The increased cholesterol in turn actives PI3K/Akt signaling, which governs BCSC stemness. In summary, these findings demonstrate that a new, lnc030-based mechanism for regulating cholesterol synthesis and stemness properties of BCSCs. The lnc030-SQLE-cholesterol synthesis pathway may serve as an effective therapeutic target for BCSC elimination and breast cancer treatment.

Roles of two types of heparan sulfate clusters in Wnt distribution and signaling in Xenopus

Wnt proteins direct embryonic patterning, but the regulatory basis of their distribution and signal reception remain unclear. Here, we show that endogenous Wnt8 protein is distributed in a graded manner in Xenopus embryo and accumulated on the cell surface in a punctate manner in association with “N-sulfo-rich heparan sulfate (HS),” not with “N-acetyl-rich HS”. These two types of HS are differentially clustered by attaching to different glypicans as core proteins. N-sulfo-rich HS is frequently internalized and associated with the signaling vesicle, known as the Frizzled/Wnt/LRP6 signalosome, in the presence of Wnt8. Conversely, N-acetyl-rich HS is rarely internalized and accumulates Frzb, a secreted Wnt antagonist. Upon interaction with Frzb, Wnt8 associates with N-acetyl-rich HS, suggesting that N-acetyl-rich HS supports Frzb-mediated antagonism by sequestering Wnt8 from N-sulfo-rich HS. Thus, these two types of HS clusters may constitute a cellular platform for the distribution and signaling of Wnt8.

Wnt proteins mediate embryonic development but how protein localization and patterning is regulated is unclear. Here, the authors show that distinct structures with different heparan sulfate modifications (‘N-sulfo-rich’ and ‘N-acetyl-rich’) regulate cellular localization and signal transduction of Wnt8 in Xenopus.

NRAGE induces β-catenin/Arm O-GlcNAcylation and negatively regulates Wnt signaling

The Wnt pathway is crucial for animal development, as well as tumor formation. Understanding the regulation of Wnt signaling will help to elucidate the mechanism of the cell cycle, cell differentiation and tumorigenesis. It is generally accepted that in response to Wnt signals, β-catenin accumulates in the cytoplasm and is imported into the nucleus where it recruits LEF/TCF transcription factors to activate the expression of target genes. In this study, we report that human NRAGE, a neurotrophin receptor p75 (p75NTR) binding protein, markedly suppresses the expression of genes activated by the Wnt pathway. Consistent with this finding, loss of function of NRAGE by RNA interference (RNAi) activates the Wnt pathway. Moreover, NRAGE suppresses the induction of axis duplication by microinjected β-catenin in Xenopus embryos. To our surprise, NRAGE induces nuclear localization of β-catenin and increases its DNA binding ability. Further studies reveal that NRAGE leads to the modification of β-catenin/Arm with O-linked beta-N-acetylglucosamine (O-GlcNAc), and failure of the association between β-catenin/Arm and pygopus(pygo) protein, which is required for transcriptional activation of Wnt target genes. Therefore, our findings suggest a novel mechanism for regulating Wnt signaling.