DOC-2/DAB2 interactive protein destabilizes c-Myc to impair the growth and self-renewal of colon tumor-repopulating cells

Synthetic Retinoid Sulfarotene Selectively Inhibits Tumor-Repopulating Cells of Intrahepatic Cholangiocarcinoma via Disrupting Cytoskeleton by P-Selectin/PSGL1 N-Glycosylation Blockage

Intrahepatic cholangiocarcinoma (ICC) is a highly lethal malignancy that currently lacks effective clinical treatments. Eliminating stem cell-like cancer cells is an extremely promising but challenging strategy for treating ICC. A recently developed synthetic retinoid, sulfarotene, abrogates proliferation, and induces apoptosis of tumor-repopulating cells (TRCs) that exhibit stem cell-like properties, yet its effect and underlying mechanisms remain elusive in ICC. It is found that although 5-fluorouracil, cisplatin, pemigatinib, and gemcitabine all inhibit ICC-TRCs, sulfarotene demonstrates superior efficacy. Sulfarotene induces retinoic acid receptor alpha (RARɑ) translocation from the cytoplasm to the nucleus, suppressing P-selectin expression at the transcriptional level. Moreover, it directly interacts with fucosyltransferase 8 (FUT8), inhibiting the core fucosylation of P-selectin glycoprotein ligand 1 (PSGL1). These actions collectively inhibit ICC-TRCs via destroying PSGL1-regulated cytoskeleton. The findings provide a strategy of inhibiting P-selectin/PSGL1 interaction and altering PSGL1 glycosylation pattern to compromise the cytoskeletal integrity and eliminate ICC-TRCs.

SET facilitates immune escape of microsatellite stability colorectal cancer by inhibiting c-Myc degradation

Microsatellite stability (MSS) colorectal cancer (CRC) exhibits a low mutation load and poor immunogenicity, contributing to immune escape of tumor cells and less benefit from immune checkpoint blockade (ICB) treatment. The mechanisms underlying immunotherapeutic resistance in MSS CRC remain to be elucidated. Here, we identified that nuclear proto-oncogene SET is significantly higher expressed in MSS CRC compared to microsatellite instability (MSI) CRC and facilitates immune escape of MSS CRC. Mechanistically, SET represses the expression of C-C motif chemokine ligand 5 (CCL5) and upregulates mismatch repair (MMR) proteins expression in a c-Myc-dependent manner, which inhibits infiltration and migration of CD8+ T cells to tumor tissues and results in low immunogenicity in MSS CRC. In addition, we found that SET impairs ubiquitination and proteasomal degradation of c-Myc by disrupting the interaction between E3 ligase FBXW7 and c-Myc. Moreover, SET inhibition enhances the response to immunotherapy in MSS CRC in vivo. Overall, this study reveals the critical roles and posttranslational regulatory mechanism of SET in immune escape and highlights the SET/c-Myc axis as a potential target for immunotherapy of MSS CRC that have implications for targeting a unique aspect of this disease.

CircFAM114A2 Suppresses Cell Proliferation, Migration, and Invasion of Colorectal Cancer Through Sponging miR-647 to Upregulate DAB2IP Expression

BACKGROUND

Increasing evidence had proved that some circular RNA (circRNA) exerted critical roles in tumors progression by functioning as "microRNAs (miRNAs) sponges" to regulate their targeted genes.

METHODS

circFAM114A2 and miR-647 expression was measured in CRC tissues and cells by quantitative real-time polymerase chain reaction (qRT-PCR), and the prognostic value of circFAM114A2 evaluated by Kaplan-Meier survival curve. Subsequently, wounding healing and transwell assays were performed to assess cell proliferation, migration, and invasion. RNA pull-down and dual-luciferase reporter assays were used to confirm the interactions between circFAM114A2, miR-647, and DAB2IP.

RESULTS

CircFAM114A2 was notably downregulated in CRC tissues and cells, and low circFAM114A2 expression indicated the poor prognosis of CRC patients. Next, overexpression of circFAM114A2 suppressed CRC cells proliferation, migration, and invasion in vitro and impede CRC tumor growth in vivo. Mechanically, circFAM114A2 competitively bound to miR-647 and upregulated its target gene DAB2IP expression in CRC cells.

CONCLUSION

Our results indicated that circFAM114A2/miR-647/DAP2IP axis played an important role in CRC progression, suggesting that circFAM114A2 might be a novel therapeutic target in patients with CRC.

An update on the tumor-suppressive functions of the RasGAP protein DAB2IP with focus on therapeutic implications

The dynamic crosstalk between tumor and stromal cells is a major determinant of cancer aggressiveness. The tumor-suppressor DAB2IP (Disabled homolog 2 interacting protein) plays an important role in this context, since it modulates cell responses to multiple extracellular inputs, including inflammatory cytokines and growth factors. DAB2IP is a RasGAP and negatively controls Ras-dependent mitogenic signals. In addition, it modulates other major oncogenic pathways, including TNFα/NF-κB, WNT/β-catenin, PI3K/AKT, and androgen receptor signaling. In line with its tumor-suppressive role, DAB2IP is frequently inactivated in cancer by transcriptional and post-transcriptional mechanisms, including promoter methylation, microRNA-mediated downregulation, and protein-protein interactions. Intriguingly, some observations suggest that downregulation of DAB2IP in cells of the tumor stroma could foster establishment of a pro-metastatic microenvironment. This review summarizes recent insights into the tumor-suppressive functions of DAB2IP and the consequences of its inactivation in cancer. In particular, we explore potential approaches aimed at reactivating DAB2IP, or augmenting its expression levels, as a novel strategy in cancer treatment. We suggest that reactivation or upregulation of DAB2IP would concurrently attenuate multiple oncogenic pathways in both cancer cells and the tumor microenvironment, with implications for improved treatment of a broad spectrum of tumors.

Expression Pattern of DAB Adaptor Protein 2 in Left- and Right-Side Colorectal Carcinoma

Left-sided and right-sided colorectal cancer (L-CRC and R-CRC) have relatively different clinical pictures and pathophysiological backgrounds. The aim of this study was to investigate the presence of DAB adapter protein 2 (DAB2) as a potential molecular mechanism that contributes to this diversity in terms of malignancy and responses to therapy. The expression of the suppressor gene DAB2 in colon cancer has already been analyzed, but its significance has not been fully elucidated. Archived samples from 34 patients who underwent colon cancer surgery were included in this study, with 13 patients with low-grade CRC and 21 with high-grade CRC. Twenty of the tumors were R-CRC, while 14 were L-CRC. DAB2 expression was analyzed immunohistochemically in the tumor tissue and the colon resection margin was used as a control. Tumors were divided into L-CRC and R-CRC, with splenic flexure as the cutoff point for each side. The results showed that R-CRC had lower DAB2 protein expression compared to L-CRC (p = 0.01). High-grade tumors had reduced DAB2 expression compared to low-grade tumors (p = 0.02). These results are consistent with the analysis of DAB2 gene expression data that we exported from the TCGA Colon and Rectal Cancer Study (COADREAD). In 736 samples of colon cancer, lower DAB2 gene expression was found in R-CRC compared to L-CRC (p < 0.0001). DAB2 gene expression was significantly higher in the sigmoid colon than in the cecum and ascending colon (p < 0.01). The analysis confirmed a lower expression of the DAB2 in tumors with positive microsatellite instability (p < 0.001). In conclusion, DAB2 has a role in the biological differences between R-CRC and L-CRC and its therapeutic and diagnostic potential needs to be further examined.

Identification and Validation of a Potential Stemness-Associated Biomarker in Hepatocellular Carcinoma

Background

Cancer stem cells (CSCs) are typically related to metastasis, recurrence, and drug resistance in malignant tumors. However, the biomarker and mechanism of CSCs need further exploration. This study is aimed at comprehensively depicting the stemness characteristics and identify a potential stemness-associated biomarker in hepatocellular carcinoma (HCC).

Methods

The data of HCC patients from The Cancer Genome Atlas (TCGA) were collected and divided based on the mRNA expression-based stemness index (mRNAsi) in this study. Weighted gene coexpression network analysis (WGCNA) and the protein-protein interaction (PPI) network were performed, and the genes were screened through the Cytoscape software. Then, we constructed a prognostic expression signature using the multivariable Cox analysis and verified using the GEO and ICGC databases. Even more importantly, we used the three-dimensional (3D) fibrin gel to enrich the tumor-repopulating cells (TRCs) to validate the expression of the signature in CSCs by quantitative RT-PCR.

Results

mRNAsi was significantly elevated in tumor and high-mRNAsi score was associated with poor overall survival in HCC. The positive stemness-associated (blue) module with 737 genes were screened based on WGCNA, and Budding uninhibited by benzimidazoles 1 (BUB1) was identified as the hub gene highly related to stemness in HCC. Then, the prognostic value and stemness characteristics were well validated in the ICGC and GSE14520 cohorts. Further analysis showed the expression of BUB1 was elevated in TRCs.

Conclusion

BUB1, as a potential stemness-associated biomarker, could serve as a therapeutic CSCs-target and predicted the clinical outcomes of patients with HCC.

microRNA-1266-5p directly targets DAB2IP to enhance oncogenicity and metastasis in oral cancer

Background/purpose

Oral cancer has been recognized as one of the most common malignancies worldwide and ranks the fifth leading cause of cancer death in Taiwan. A variety of studies have demonstrated that microRNAs are involved in the regulation of the hallmarks of oral carcinogenesis. Nevertheless, the effect of miR-1266-5p on the tumorigenesis of oral cancer has not been investigated, and not to mention, its functional role in oral cancer.

Materials and methods

The upregulation of miR-1266-5p in SASVO3 and SASM5 cells was identified by RNA-Seq and examined by qRT-PCR analysis. The phenotypic assays including proliferation activity, migration capacity, invasion, wound healing, and colony-forming abilities were conducted in oral cancer cells after knockdown of miR-1266-5p. Luciferase reporter and western blotting were used to validate DAB2IP was a direct target of miR-1266-5p in oral cancer.

Results

We identified that miR-1266-5p was significantly overexpressed in highly tumorigenic SASVO3 cells and metastatic SASM5 cells. qRT-PCR revealed that miR-1266 significantly increased upregulated in oral cancer and lymph node metastatic tissues compared to normal counterparts We found that downregulation of miR-1266-5p inhibited the proliferation and clonogenicity capacities of SASVO3 cells. Knockdown of miR-1266-5p also inhibited migration/invasion and self-renewal abilities in SASM5 cells. Moreover, we validated miR-1266-5p directly bound to the 3′UTR of DAB2IP in oral cancer cells. We found that DAB2IP knockdown reversed the inhibitory effects of self-renewal and migration mediated by silencing of miR-1266-5p.

Conclusion

miR-1266 functions as a biomarker in oral cancer patients, and downregulation of miR-1266 may ameliorate the oncogenic and metastasis potential of oral cancer by targeting DAB2IP.

DOC-2/DAB2 interactive protein destabilizes c-Myc to impair the growth and self-renewal of colon tumor-repopulating cells

Colorectal carcinoma (CRC) remains a huge challenge in clinical treatment due to tumor metastasis and recurrence. Stem cell-like colon tumor-repopulating cells (TRCs) are a subpopulation of cancer cells with highly tumorigenic and chemotherapy resistant properties. The core transcription factor c-Myc is essential for maintaining cancer stem-like cell phenotypes, yet its roles and regulatory mechanisms remain unclear in colon TRCs. We report that elevated c-Myc protein supported formation and growth of TRC spheroids. The tumor suppressor DOC-2/DAB2 interactive protein (DAB2IP) suppressed c-Myc expression to inhibit TRC expansion and self-renewal. Particularly, DAB2IP disrupted c-Myc stability through glycogen synthase kinase 3β/protein phosphatase 2A-B56α-mediated phosphorylation and dephosphorylation cascade on c-Myc protein, leading to its eventual degradation through the ubiquitin-proteasome pathway. The expression of DAB2IP was negatively correlated with c-Myc in CRC specimens. Overall, our results improved mechanistic insight into how DAB2IP suppressed TRC growth and self-renewal.