Colorectal carcinoma (CRC) is one of the most common malignant tumors, and its main cause of death is tumor metastasis. RNA N6-methyladenosine (m6A) is an emerging regulatory mechanism for gene expression and methyltransferase-like 3 (METTL3) participates in tumor progression in several cancer types. However, its role in CRC remains unexplored. Western blot, quantitative real-time PCR (RT-qPCR) and immunohistochemical (IHC) were used to detect METTL3 expression in cell lines and patient tissues. Methylated RNA immunoprecipitation sequencing (MeRIP-seq) and transcriptomic RNA sequencing (RNA-seq) were used to screen the target genes of METTL3. The biological functions of METTL3 were investigated in vitro and in vivo. RNA pull-down and RNA immunoprecipitation assays were conducted to explore the specific binding of target genes. RNA stability assay was used to detect the half-lives of the downstream genes of METTL3. Using TCGA database, higher METTL3 expression was found in CRC metastatic tissues and was associated with a poor prognosis. MeRIP-seq revealed that SRY (sex determining region Y)-box 2 (SOX2) was the downstream gene of METTL3. METTL3 knockdown in CRC cells drastically inhibited cell self-renewal, stem cell frequency and migration in vitro and suppressed CRC tumorigenesis and metastasis in both cell-based models and PDX models. Mechanistically, methylated SOX2 transcripts, specifically the coding sequence (CDS) regions, were subsequently recognized by the specific m6A “reader”, insulin-like growth factor 2 mRNA binding protein 2 (IGF2BP2), to prevent SOX2 mRNA degradation. Further, SOX2 expression positively correlated with METTL3 and IGF2BP2 in CRC tissues. The combined IHC panel, including “writer”, “reader”, and “target”, exhibited a better prognostic value for CRC patients than any of these components individually. Overall, our study revealed that METTL3, acting as an oncogene, maintained SOX2 expression through an m6A-IGF2BP2-dependent mechanism in CRC cells, and indicated a potential biomarker panel for prognostic prediction in CRC.

/pdf/mettl3-facilitates-tumor-progression-via-an-m6a-igf2bp2-2nnkw8tmbu.pdf

METTL3 facilitates tumor progression via an m6A-IGF2BP2-dependent mechanism in colorectal carcinoma

Abstract Cancer arises from a multitude of disorders resulting in loss of differentiation and a stem cell-like phenotype characterized by uncontrolled growth. Polycomb Group (PcG) proteins are members of multiprotein complexes that are highly conserved throughout evolution. Historically, they have been described as essential for maintaining epigenetic cellular memory by locking homeotic genes in a transcriptionally repressed state. What was initially thought to be a function restricted to a few target genes, subsequently turned out to be of much broader relevance, since the main role of PcG complexes is to ensure a dynamically choregraphed spatio-temporal regulation of their numerous target genes during development. Their ability to modify chromatin landscapes and refine the expression of master genes controlling major switches in cellular decisions under physiological conditions is often misregulated in tumors. Surprisingly, their functional implication in the initiation and progression of cancer may be either dependent on Polycomb complexes, or specific for a subunit that acts independently of other PcG members. In this review, we describe how misregulated Polycomb proteins play a pleiotropic role in cancer by altering a broad spectrum of biological processes such as the proliferation-differentiation balance, metabolism and the immune response, all of which are crucial in tumor progression. We also illustrate how interfering with PcG functions can provide a powerful strategy to counter tumor progression. 

/pdf/mechanisms-of-polycomb-group-protein-function-in-cancer-34gjjjcv.pdf

Mechanisms of Polycomb group protein function in cancer

Acidosis is a significant feature of the tumor microenvironment in glioma, and it is closely related to multiple biological functions of cancer stem cells. Here, we found that the self-renewal ability, the mitochondrial activity and ATP production were elevated in stem cell-like glioma cells (SLCs) under acidic microenvironment, which promoted and maintained the stemness of SLCs. Under acidosis, 25-hydroxy vitamin D3-24-hydroxylase (CYP24A1) was upregulated and catalyzed the fast degradation of 1α,25(OH)2D3. We further revealed that the active form of vitamin D (1α,25(OH)2D3) could inhibit the expression of stemness markers, attenuate acidosis-induced increase of self-renewal ability and mitochondrial respiration in stem cell-like glioma cells. Our study indicates that the acidosis–CYP24A1–vitamin D pathway may be a key regulator of the cancer stem cell phenotype in malignant glioma and point out the potential value for the utilization of vitamin D to target cancer stem cells and to restrain the growth of malignant glioma in the future.

/pdf/acidosis-enhances-the-self-renewal-and-mitochondrial-1xxzp57vr1.pdf

Acidosis enhances the self-renewal and mitochondrial respiration of stem cell-like glioma cells through CYP24A1-mediated reduction of vitamin D

The acidic tumor microenvironment provides an energy source driving malignant tumor progression. Adaptation of cells to an acidic environment leads to the emergence of cancer stem cells. The expression of the vitamin D receptor (VDR) is closely related to the initiation and development of colorectal carcinoma (CRC), but its regulatory mechanism in CRC stem cells is still unclear. Our study revealed that acidosis reduced VDR expression by downregulating peroxisome proliferator-activated receptor delta (PPARD) expression. Overexpression of VDR effectively suppressed the stemness and oxaliplatin resistance of cells in acidosis. The nuclear export signal in VDR was sensitive to acidosis, and VDR was exported from the nucleus. Chromatin immunoprecipitation (ChIP) and assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) analyses showed that VDR transcriptionally repressed SRY-box 2 (SOX2) by binding to the vitamin D response elements in the promoter of SOX2, impairing tumor growth and drug resistance. We demonstrated that a change in the acidic microenvironment combined with overexpression of VDR substantially restricted the occurrence and development of CRC in vivo. These findings reveal a new mechanism by which acidosis could affect the stemness of CRC cells by regulating the expression of SOX2 and show that abnormal VDR expression leads to ineffective activation of vitamin D signaling, resulting in a lack of efficacy of vitamin D in antineoplastic process.

/pdf/vdr-sox2-signaling-promotes-colorectal-cancer-stemness-and-43fe188pdy.pdf

VDR–SOX2 signaling promotes colorectal cancer stemness and malignancy in an acidic microenvironment

Gliomas account for approximately 80% of primary malignant tumors in the central nervous system. Despite aggressive therapy, the prognosis of patients remains extremely poor. Glioma stem cells (GSCs) which considered as the potential target of therapy for their crucial role in therapeutic resistance and tumor recurrence, are believed to be key factors for the disappointing outcome. Here, we took advantage of GSCs as the cell model to perform high-throughput drug screening and the old antibiotic, clofoctol, was identified as the most effective compound, showing reduction of colony-formation and induction of apoptosis of GSCs. Moreover, growth of tumors was inhibited obviously in vivo after clofoctol treatment especially in primary patient-derived xenografts (PDXs) and transgenic xenografts. The anticancer mechanisms demonstrated by analyzing related downstream genes and discovering the targeted binding protein revealed that clofoctol exhibited the inhibition of GSCs by upregulation of Kruppel-like factor 13 (KLF13), a tumor suppressor gene, through clofoctol's targeted binding protein, Upstream of N-ras (UNR). Collectively, these data demonstrated that induction of KLF13 expression suppressed growth of gliomas and provided a potential therapy for gliomas targeting GSCs. Importantly, our results also identified the RNA-binding protein UNR as a drug target.

/pdf/the-antibiotic-clofoctol-suppresses-glioma-stem-cell-12759bj6zp.pdf

The antibiotic clofoctol suppresses glioma stem cell proliferation by activating KLF13

Polycomb group (PcG) proteins play an important role in development and stem cell maintenance, and their dysregulation have been closely linked to oncogenesis and cancer stem cell phenotypes. Here, we found that nervous system polycomb 1 (NSPc1) was highly expressed in stem cell-like glioma cells (SLCs). Knockdown of NSPc1 in SLCs resulted in impaired neurosphere formation and self-renewal abilities, down-regulated expression of stemness markers such as NESTIN, CD133 and SOX2, and decreased capacity to propagate subcutaneous xenografts. In contrast, glioma cells overexpressing NSPc1 exhibited a stem cell-like phenotype, up-regulated expression of stemness markers NESTIN, CD133 and SOX2, and an enhanced capacity to propagate subcutaneous xenografts. Furthermore, we identified that NSPc1 epigenetically repressed the expression of retinol dehydrogenase 16 (RDH16) by directly binding to a region upstream (-1073 to -823) of the RDH16 promoter. Next, we confirmed that RDH16 is a stemness suppressor that partially rescues SLCs from the NSPc1-induced increase in neurosphere formation. Finally, we showed that ATRA partly reversed the NSPc1-induced stemness enhancement in SLCs, through mechanisms correlated with an ATRA-dependent decrease in the expression of NSPc1. Thus, our results demonstrate that NSPc1 promotes cancer stem cell self-renewal by repressing the synthesis of ATRA via targeting RDH16 and may provide novel targets for glioma treatment in the future.

NSPc1 promotes cancer stem cell self-renewal by repressing the synthesis of all-trans retinoic acid via targeting RDH16 in malignant glioma

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NSPc1 promotes cancer stem cell self-renewal by repressing the synthesis of all-trans retinoic acid via targeting RDH16 in malignant glioma