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.

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 was demonstrated to be closely linked with the development of HCC cells after diethylnitrosamine treatment. We identified the CL region as a dominant lobule for accumulation of hyperpolyploid hepatocytes and preneoplastic tumor foci formation. We also demonstrated that upregulation of Aurkb plays a critical role in promoting hyperpolyploidization. Increase of AURKB phosphorylation was detected on the midbody during cytokinesis, causing abscission failure and hyperpolyploidization. Pharmacological inhibition of AURKB dramatically reduced 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.

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.

MicroRNAs (miRNAs) are generated by a multiple steps process that post-transcriptionally regulate the expression of target genes. Dysregulation of miRNAs is linked to human diseases including the development of human cancer. Abrogation of cellular global miRNAs maturation has been proposed to promote tumorigenesis and cancer metastasis. Hypoxia stress is the major cause of dysregulation of miRNAs and promotes tumor angiogenesis, metastasis and tumorigenesis which is a pivotal factor to switch on the cellular oncogenic features during tumor progression. Although hypoxia stress regulates expression of a subset of miRNAs, the upstream regulators controlling miRNAs regulation under hypoxia remain unclear. This study demonstrates the molecular mechanism of post-translational regulation of Dicer under hypoxia. Our results show that knockdown of hypoxia inducible factor 1 alpha (HIF-1α) up-regulates Dicer expression in colorectal cancer (CRC) cells. Overexpression of HIF-1α enhances ubiquitination of Dicer and subsequently promotes it recognition by autophagic receptor for autophagy-lysosomal degradation. We also find that HIF-1α enhances cancer cell migration by regulating Dicer-regulated miRNAs. In conclusion, we demonstrated that HIF-1α down-regulated Dicer and abolishes miRNA biogenesis to enhance cancer cell migration. This study may provide a potential therapeutic direction that targets the dysregulated miRNAs in tumor hypoxia for patients with poor prognosis and metastatic CRC. Citation Format: Hui-Huang Lai, Yu-Jhen Lyu, Jie-Ning Li, Jen-Liang Su, Pai-Sheng Chen. Functional mechanism of hypoxia-inducible factor 1 alpha-mediated Dicer down-regulation. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 199. doi:10.1158/1538-7445.AM2015-199