NEIL3 promotes hepatoma epithelial-mesenchymal transition by activating the BRAF/MEK/ERK/TWIST signaling pathway.

Hepatocellular carcinoma (HCC) is among the most prevalent visceral neoplasms. So far, reliable biomarkers for predicting HCC recurrence in patients undergoing surgery are far from adequate. In the aim of searching for genetic biomarkers involved in HCC development, we performed analyses of cDNA microarrays and found that the DNA repair gene NEIL3 was remarkably overexpressed in tumors. NEIL3 belongs to the Fpg/Nei protein superfamily, which contains DNA glycosylase activity required for the base excision repair for DNA lesions. Notably, the other Fpg/Nei family proteins NEIL1 and NEIL2, which have the same glycosylase activity as NEIL3, were not elevated in HCC; NEIL3 was specifically induced to participate in HCC development independently of its glycosylase activity. Using RNA-seq and invasion/migration assays, we found that NEIL3 elevated the expression of epithelial-mesenchymal transition (EMT) factors, including the E/N-cadherin switch and the transcription of MMP genes, and promoted the invasion, migration, and stemness phenotypes of HCC cells. Moreover, NEIL3 directly interacted with the key EMT player TWIST1 to enhance invasion and migration activities. In mouse orthotopic HCC studies, NEIL3 overexpression also caused a prominent E-cadherin decrease, tumor volume increase, and lung metastasis, indicating that NEIL3 led to EMT and tumor metastasis in mice. We further found that NEIL3 induced the transcription of MDR1 (ABCB1) and BRAF genes through the canonical E-box (CANNTG) promoter region, which the TWIST1 transcription factor recognizes and binds to, leading to the BRAF/MEK/ERK pathway-mediated cell proliferation as well as anti-cancer drug resistance, respectively. In the HCC cohort, the tumor NEIL3 level demonstrated a high positive correlation with disease-free and overall survival after surgery. In conclusion, NEIL3 activated the BRAF/MEK/ERK/TWIST pathway-mediated EMT and therapeutic resistances, leading to HCC progression. Targeted inhibition of NEIL3 in HCC individuals with NEIL3 induction is a promising therapeutic approach. © 2022 The Pathological Society of Great Britain and Ireland.

Hyperpolyploidization of hepatocyte initiates preneoplastic lesion formation in the liver.

Hepatocellular carcinoma (HCC) is the most predominant primary malignancy in the liver. Genotoxic and genetic models have revealed that HCC cells are derived from hepatocytes, but where the critical region for tumor foci emergence is and how this transformation occurs are still unclear. Here, hyperpolyploidization of hepatocytes around the centrilobular (CL) region is demonstrated to be closely linked with the development of HCC cells after diethylnitrosamine treatment. We identify the CL region as a dominant lobule for accumulation of hyperpolyploid hepatocytes and preneoplastic tumor foci formation. We also demonstrate that upregulation of Aurkb plays a critical role in promoting hyperpolyploidization. Increase of AURKB phosphorylation is detected on the midbody during cytokinesis, causing abscission failure and hyperpolyploidization. Pharmacological inhibition of AURKB dramatically reduces nucleus size and tumor foci number surrounding the CL region in diethylnitrosamine-treated liver. Our work reveals an intimate molecular link between pathological hyperpolyploidy of CL hepatocytes and transformation into HCC cells.

TARBP2-mediated destabilization of Nanog overcomes sorafenib resistance in hepatocellular carcinoma.

Hepatocellular carcinoma (HCC) is a lethal human malignancy and a leading cause of cancer-related death worldwide. Patients with HCC are often diagnosed at an advanced stage, and the prognosis is usually poor. The multikinase inhibitor sorafenib is the first-line treatment for patients with advanced HCC. However, cases of primary or acquired resistance to sorafenib have gradually increased, leading to a predicament in HCC therapy. Thus, it is critical to investigate the mechanism underlying sorafenib resistance. Transactivation response element RNA-binding protein 2 (TARBP2) is a multifaceted miRNA biogenesis factor that regulates cancer stem cell (CSC) properties. The tumorigenicity and drug resistance of cancer cells are often enhanced due to the acquisition of CSC features. However, the role of TARBP2 in sorafenib resistance in HCC remains unknown. Our results demonstrate that TARBP2 is significantly downregulated in sorafenib-resistant HCC cells. The TARBP2 protein was destabilized through autophagic-lysosomal proteolysis, thereby stabilizing the expression of the CSC marker protein Nanog, which facilitates sorafenib resistance in HCC cells. In summary, here we reveal a novel miRNA-independent role of TARBP2 in regulating sorafenib resistance in HCC cells.

Role of Dicer in regulating oxaliplatin resistance of colon cancer cells.

Colorectal cancer (CRC) is a major health problem due to its high mortality rate. The incidence of CRC is increasing in young individuals. Oxaliplatin (OXA) is an approved third-generation drug and is used for first-line chemotherapy in CRC. Although current standard chemotherapy improves the overall survival of CRC patients, an increasing number of reports of OXA resistance in CRC therapy indicates that resistance has become an urgent problem in clinical applications. Dicer is a critical enzyme involved in miRNA maturation. The expression of Dicer has been reported to be involved in the resistance to various drugs in cancer. In the present study, we aimed to investigate the role of Dicer in OXA resistance in CRC. We found that OXA treatment inhibited Dicer expression through decreasing the protein stability. OXA-induced Dicer protein degradation occurred through both proteasomal and lysosomal proteolysis, while the CHIP E3 ligase was involved in OXA-mediated Dicer ubiquitination and degradation. We established stable OXA-resistant clones from CRC cells, and observed that the CHIP E3 ligase was decreased, along with the increased Dicer expression in OXA-resistant cells. Knockdown of Dicer resensitized CRC cells to OXA treatment. In this study, we have revealed the role of miRNA biogenesis factors in OXA resistance in CRC cells.

Dual mechanism of DICER downregulation facilitates cancer metastasis.

Although downregulation of DICER - a critical enzyme in microRNA (miRNA) maturation - reportedly promotes cancer metastasis, understanding of its upstream regulators remains limited. Our recent study demonstrated a noncanonical oncogenic effect of hypoxia-inducible factor-1α (HIF-1α), which directly binds with DICER to promote PARKIN-mediated autophagic-lysosomal proteolysis and consequently suppresses miRNA biogenesis, facilitating metastasis.

HIF-1α promotes autophagic proteolysis of Dicer and enhances tumor metastasis.

HIF-1α, one of the most extensively studied oncogenes, is activated by a variety of microenvironmental factors. The resulting biological effects are thought to depend on its transcriptional activity. The RNAse enzyme Dicer is frequently downregulated in human cancers, which has been functionally linked to enhanced metastatic properties; however, current knowledge of the upstream mechanisms regulating Dicer is limited. In the present study, we identified Dicer as a HIF-1α-interacting protein in multiple types of cancer cell lines and different human tumors. HIF-1α downregulated Dicer expression by facilitating its ubiquitination by the E3 ligase Parkin, thereby enhancing autophagy-mediated degradation of Dicer, which further suppressed the maturation of known tumor suppressors, such as the microRNA let-7 and microRNA-200b. Consequently, expression of HIF-1α facilitated epithelial-mesenchymal transition (EMT) and metastasis in tumor-bearing mice. Thus, this study uncovered a connection between oncogenic HIF-1α and the tumor-suppressive Dicer. This function of HIF-1α is transcription independent and occurs through previously unrecognized protein interaction-mediated ubiquitination and autophagic proteolysis.

A novel application of E1A in combination therapy with EGFR-TKI treatment in breast cancer.

Epidermal growth factor receptor (EGFR) is commonly overexpressed in breast cancer and is associated with poor clinical outcomes; however, an increasing number of patients have shown a poor effective response to EGFR tyrosine kinase inhibitors (EGFR-TKI). Here, we found that AXL expression was positively correlated with poor progression in breast cancer patients. Suppression of AXL by an anti-tumor protein, E1A, enhanced EGFR-TKI (gefitinib, erlotinib and lapatinib) sensitization, resulting in significant inhibition of tumor growth in breast cancer cells. Additionally, AXL overexpression dramatically impaired E1A-mediated EGFR-TKI sensitization. These findings show that downregulation of AXL expression by E1A contributes to sensitization to EGFR-TKI in breast cancer, suggesting that combinatorial therapy of AXL inhibitors or E1A gene therapy with EGFR-TKI may be a potential therapeutic strategy for treatment of breast cancer patients.

Novel peptides suppress VEGFR-3 activity and antagonize VEGFR-3-mediated oncogenic effects.

Vascular endothelial growth factor receptor 3 (VEGFR-3) supports tumor lymphangiogenesis. It was originally identified as a lymphangiogenic factor expressed in lymphatic endothelial cells. VEGFR-3 was detected in advanced human malignancies and correlated with poor prognosis. Our previous studies show that activation of the VEGF-C/VEGFR-3 axis promotes cancer metastasis and is associated with clinical progression in patients with lung cancer, indicating that VEGFR-3 is a potential target for cancer therapy. In this study, we developed eight peptides targeting VEGFR-3. Two peptides strongly inhibited the kinase activity of VEGFR-3 and suppressed VEGF-C-mediated invasion of cancer cells. Moreover, these peptides abolished VEGF-C-induced drug resistance and tumor initiating cell formation. This study demonstrates the therapeutic potential of VEGFR-3-targeting peptides.