Inhibition of RFX6 Suppresses the Invasive Ability of Tumor Cells Through the Notch Pathway and Affects Tumor Immunity in Hepatocellular Carcinoma

[High expression of DTX2 promotes proliferation, invasion and epithelial-mesenchymal transition of oxaliplatin-resistant colorectal cancer cells]

OBJECTIVES

To investigate the role of DTX2 in regulating biological behaviors of oxaliplatin-resistant colorectal cancer cells (CRC/OXA cells).

METHODS

CCK8 assay was used to determine the inhibition rate of oxaliplatin-treated CRC cells. A CRC/OXA cell line was constructed, in which DTX2 expression level was detected. The cells were transfected with a DTX2-shRNA plasmid or co-transfected with DTX2-shRNA and pcDNA-Notch2, and the changes in cell proliferation, migration and invasion ability were evaluated using plate cloning assay, scratch assay and Transwell invasion assay. The expression levels of Notch2, NICD and epithelial-mesenchymal transition (EMT) proteins of the transfected cells were detected with Western blotting. In a nude mouse model bearing SW620/OXA cell xenografts, the effects of DTX2 knockdown and Notch2 overexpression in the implanted cells on tumor growth and protein expressions were tested.

RESULTS

The IC50 of oxaliplatin was 6.00 μmol/L in SW620 cells and 8.00 μmol/L in LoVo cells. CRC/OXA cells showed a significantly increased expression of DTX2. DTX2 knockdown in CRC/OXA cells significantly inhibited cell proliferation, migration and invasion, and these effects were reversed by co-transfection of the cells with pcDNA-Notch2. DTX2 knockdown significantly reduced the expression levels of Notch2, NICD and vimentin proteins and increased E-cadherin expression in CRC/OXA cells, and co-transfection with pcDNA-Notch2 potently attenuated the changes in these proteins. In the tumor-bearing mice, DTX2 overexpression obviously promoted the growth of SW620/OXA cell xenograft, enhanced the protein expressions of Notch2, NICD and vimentin, and lowered the expression of E-cadherin.

CONCLUSIONS

High expression of DTX2 promotes proliferation, migration, invasion and EMT of CRC/OXA cells through the Notch2 signaling pathway, suggesting the potential of DTX2 as a target to improve the efficacy of oxaliplatin.

An integrative analysis to identify pancancer epigenetic biomarkers

Integrating and analyzing the pancancer data collected from different experiments is crucial for gaining insights into the common mechanisms in the molecular level underlying the development and progression of cancers. Epigenetic study of the pancancer data can provide promising results in biomarker discovery. The genes that are epigenetically dysregulated in different cancers are powerful biomarkers for drug-related studies. This paper identifies the genes having altered expression due to aberrant methylation patterns using differential analysis of TCGA pancancer data of 12 different cancers. We identified a comprehensive set of 115 epigenetic biomarker genes out of which 106 genes having pancancer properties. The correlation analysis, gene set enrichment, protein-protein interaction analysis, pancancer characteristics analysis, and diagnostic modeling were performed on these biomarkers to illustrate the power of this signature and found to be important in different molecular operations related to cancer. An accuracy of 97.56% was obtained on TCGA pancancer gene expression dataset for predicting the binary class tumor or normal. The source code and dataset of this work are available at https://github.com/panchamisuneeth/EpiPanCan.git.

Pan-cancer investigation of RFX family and associated genes identifies RFX8 as a therapeutic target in leukemia

Background

Several transcription factors and co-factors are encoded by the RFX (Regulatory Factor X) family (RFX1-8) and associated genes (RFXAP and RFXANK). Increasing evidence suggests that the RFX family and associated genes are involved in the development and progression of cancer. However, no prior research has focused on a multi-omic analysis of these genes to evaluate their role in tumor progression.

Methods

Using combined TCGA and GTEx pan-cancer data, we investigated the expression patterns and survival profiles of these ten genes. We then focused on RFX8 to analyze its clinicopathological and therapeutic features. Finally, we conducted experimental validation of RFX8 function in acute myeloid leukemia (AML).

Results

RFX5 and RFXANK showed higher expression levels, while RFX6 showed lower expression levels in most types of cancer, with RFX8 being the most upregulated in LAML. RFX2 and RFXAP demonstrated prognostic significance in eight types of cancer, and RFX8 showed significance in six types of cancer. The expression of these ten genes exhibited specific characteristics in immune subtypes, tumor microenvironment, and stemness. The expression of RFX8 was correlated with various tumor stages, microsatellite instability (MSI), tumor mutation burden (TMB), immune cell infiltration, and immune-checkpoint expression. Additionally, RFX8 was found to regulate tumorigenesis and sensitivity to chelerythrine in AML.

Conclusions

Our work delineated the landscape of the RFX family and associated genes in the pan-cancer context and the specific role of RFX8 in AML. These findings might offer cues for further investigations of these genes in cancer biology.

DTX2 promotes glioma development via regulation of HLTF

BACKGROUND

Human Deltex 2 (DTX2) is a ubiquitin E3 ligase that functions as an oncogene and has been shown to participate in many human cancers. However, the role of DTX2 in glioma progression has remained obscure. In this study, we explore the mechanism underlying the function of DTX2 in glioma progression.

METHODS

The associations between DTX2 expression and clinical characteristics of glioma were determined by bioinformatic analysis of data from The Cancer Genome Atlas and Human Protein Atlas. The expression of DTX2 in glioma tissues was detected using immunohistochemistry and western blotting. Lentivirus-mediated gene knockdown and overexpression were used to determine the effects of DTX2 and helicase-like transcription element (HLTF) on glioma cell proliferation and migration with CCK-8, cell colony formation, transwell, and wound healing assays; flow cytometry in vitro; and animal models in vivo. The interaction of the DTX2 and HLTF proteins was verified by immunoprecipitation assay and confocal microscopy.

RESULTS

DTX2 was highly expressed in glioma samples, and this was correlated with worse overall survival. Silencing of DTX2 suppressed glioma cell viability, colony formation, and migration and induced cell apoptosis. In vitro ubiquitination assays confirmed that DTX2 could downregulate HLTF protein levels by increasing ubiquitination of the HLTF protein. We also observed that HLTF inhibited proliferation and migration of glioma cells. Subcutaneous xenografts with DTX2-overexpressing U87 cells showed significantly increased tumor volumes and weights.

CONCLUSIONS

We have identified DTX2/HLTF as a new axis in the development of glioma that could serve as a prognostic or therapeutic marker.

RFX6 facilitates aerobic glycolysis-mediated growth and metastasis of hepatocellular carcinoma through targeting PGAM1

BACKGROUND

Hepatocellular carcinoma (HCC) cells undergo reprogramming of glucose metabolism to support uncontrolled proliferation, of which the intrinsic mechanism still merits further investigation. Although regulatory factor X6 (RFX6) is aberrantly expressed in different cancers, its precise role in cancer development remains ambiguous.

METHODS

Microarrays of HCC tissues were employed to investigate the expression of RFX6 in tumour and adjacent non-neoplastic tissues. Functional assays were employed to explore the role of RFX6 in HCC development. Chromatin immunoprecipitation, untargeted metabolome profiling and sequencing were performed to identify potential downstream genes and pathways regulated by RFX6. Metabolic assays were employed to investigate the effect of RFX6 on glycolysis in HCC cells. Bioinformatics databases were used to validate the above findings.

RESULTS

HCC tissues exhibited elevated expression of RFX6. High RFX6 expression represented as an independent hazard factor correlated to poor prognosis in patients with HCC. RFX6 deficiency inhibited HCC development in vitro and in vivo, while its overexpression exerted opposite functions. Mechanistically, RFX6 bound to the promoter area of phosphoglycerate mutase 1 (PGAM1) and upregulated its expression. The increased PGAM1 protein levels enhanced glycolysis and further promoted the development of HCC.

CONCLUSIONS

RFX6 acted as a novel driver for HCC development by promoting aerobic glycolysis, disclosing the potential of the RFX6-PGAM1 axis for therapeutic targeting.

The DTX Protein Family: An Emerging Set of E3 Ubiquitin Ligases in Cancer

Until recently, Deltex (DTX) proteins have been considered putative E3 ligases, based on the presence of an E3 RING domain in their protein coding sequence. The human DTX family includes DTX1, DTX2, DTX3, DTX3L and DTX4. Despite the fact that our knowledge of this class of E3-ubiquitin ligases is still at an early stage, our understanding of their role in oncogenesis is beginning to unfold. In fact, recently published studies allow us to define specific biological scenarios and further consolidate evidence-based working hypotheses. According to the current evidence, all DTX family members are involved in the regulation of Notch signaling, suggesting a phylogenetically conserved role in the regulation of this pathway. Indeed, additional evidence reveals a wider involvement of these proteins in other signaling complexes and cancer-promoting mechanisms beyond NOTCH signaling. DTX3, in particular, had been known to express two isoform variants (DTX3a and DTX3b). The recent identification and cloning of a third isoform variant in cancer (DTX3c), and its specific involvement in EphB4 degradation in cancer cells, sheds further light on this group of proteins and their specific role in cancer. Herein, we review the cumulative knowledge of this family of E3 Ubiquitin ligases with a specific focus on the potential oncogenic role of DTX isoforms in light of the rapidly expanding findings regarding this protein family's cellular targets and regulated signaling pathways. Furthermore, using a comparative and bioinformatic approach, we here disclose a new putative motif of a member of this family which may help in understanding the biological and contextual differences between the members of these proteins.

Glycolysis-related gene dihydrolipoamide acetyltransferase promotes poor prognosis in hepatocellular carcinoma through the Wnt/β-catenin and PI3K/Akt signaling pathways

Background

Recent research suggests that dihydrolipoamide acetyltransferase (DLAT), which is a copper-induced cell death-related gene, is involved in multiple biological events in tumors. This study sought to investigate the relationship between DLAT and hepatocellular carcinoma (HCC).

Methods

In the Cancer Genome Atlas (TCGA) database, we first identified the differentially expressed gene (i.e., DLAT), then confirmed DLAT expression, and found a link between it and the prognosis of HCC patients. An internal validation nomogram was built based on a multivariate Cox regression analysis. Data from the Tumor Immune Estimation Resource (TIMER) database was used to examine the association between DLT and immunological cells. A gene set enrichment analysis (GSEA) was conducted to investigate the probable mechanism of action. Finally, in vitro cytological research was conducted to further examin the involvement of DLAT in HCC-related unfavorable biological events.

Results

The database screenings showed that DLAT was a differentially expressed molecule; that is, DLAT was more highly expressed in the cancer tissues than normal tissues. TCGA results and Kaplan-Meier-plotter data sets showed that HCC patients with reduced DLAT expression had greater disease-specific survival (DSS), overall survival (OS), and progression-free interval (PFI). The prediction model had a concordance index of 0.659 (0.614-0.704), which indicates high accuracy. According to the TIMER database, tumor cells in the HCC microenvironment may be able to bypass the immune system due to the expression of DLAT. The in vitro cytological tests showed that DLAT knockdown significantly decreased the proliferation and invasion of the HCC cells. It also inhibited the activity of the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/protein kinase B (Akt) and Wnt/β-catenin signaling pathways.

Conclusions

Decreased DLAT expression significantly prolongs the OS, PFI, and DSS of HCC patients. DLAT may be employed as a new predictive biomarker for HCC, and may be linked to the immune system in HCC patients. The tumor microenvironment (TME) may have a significant effect on the ability of tumor cells to evade the immune system. The PI3K/Akt and Wnt/β-catenin signaling pathways may affect the prognosis of HCC by interfering with DLAT. Given these findings, HCC may be an ideal target for the development of anti-cancer therapies.