LncRNA NEAT1 suppresses cellular senescence in hepatocellular carcinoma via KIF11-dependent repression of CDKN2A.

BACKGROUND: Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related deaths worldwide. Therapeutic options for advanced HCC are limited, which is due to a lack of full understanding of pathogenesis. Cellular senescence is a state of cell cycle arrest, which plays important roles in the pathogenesis of HCC. Mechanisms underlying hepatocellular senescence are not fully understood. LncRNA NEAT1 acts as an oncogene and contributes to the development of HCC. Whether NEAT1 modulates hepatocellular senescence in HCC is unknown. METHODS: The role of NEAT1 and KIF11 in cellular senescence and tumor growth in HCC was assessed both in vitro and in vivo. RNA pulldown, mass spectrometry, Chromatin immunoprecipitation (ChIP), luciferase reporter assays, RNA FISH and immunofluorescence (IF) staining were used to explore the detailed molecular mechanism of NEAT1 and KIF11 in cellular senescence of HCC. RESULTS: We found that NEAT1 was upregulated in tumor tissues and hepatoma cells, which negatively correlated with a senescence biomarker CDKN2A encoding p16INK4a and p14ARF proteins. NEAT1 was reduced in senescent hepatoma cells induced by doxorubicin (DOXO) or serum starvation. Furthermore, NEAT1 deficiency caused senescence in cultured hepatoma cells, and protected against the progression of HCC in a mouse model. During senescence, NEAT1 translocated into cytosol and interacted with a motor protein KIF11, resulting in KIF11 protein degradation and subsequent increased expression of CDKN2A in cultured hepatoma cells. Furthermore, KIF11 knockdown caused senescence in cultured hepatoma cells. Genetic deletion of Kif11 in hepatocytes inhibited the development of HCC in a mouse model. CONCLUSIONS: Conclusively, NEAT1 overexpression reduces senescence and promotes tumor progression in HCC tissues and hepatoma cells, whereas NEAT1 deficiency causes senescence and inhibits tumor progression in HCC. This is associated with KIF11-dependent repression of CDKN2A. These findings lay the foundation to develop potential therapies for HCC by inhibiting NEAT1 and KIF11 or inducing senescence.

MUC13 promotes intrahepatic cholangiocarcinoma progression via EGFR/PI3K/AKT pathways.

BACKGROUND & AIMS: Mucin 13 (MUC13) is reportedly overexpressed in human malignancies. However, the clinicopathological and biological significance of MUC13 in human intrahepatic cholangiocarcinoma (iCCA) remain unclear. The aim of this study was to define the role of MUC13 in the progression of iCCA. METHODS: Expression levels of MUC13 in human iCCA samples were evaluated by immunohistochemistry, western blot, and real-time PCR. In vitro and in vivo experiments were used to assess the effect of MUC13 on iCCA cell growth and metastasis. Crosstalk between MUC13 and EGFR/PI3K/AKT signaling was analyzed by molecular methods. The upstream regulatory effects of MUC13 were evaluated by Luciferase and DNA methylation assays. RESULTS: MUC13 was overexpressed in human iCCA specimens and iCCA cells. MUC13 overexpression positively correlated with clinicopathological characteristics of iCCA, such as vascular invasion and lymph node metastasis, and was independently associated with poor survival. Results from loss-of-function and gain-of-function experiments suggested that knockdown of MUC13 attenuated, while overexpression of MUC13 enhanced, the proliferation, motility, and invasiveness of iCCA cells in vitro and in vivo. Mechanistically, we found that the phosphatidylinositol 3-kinase-AKT signal pathway and its downstream effectors, such as tissue inhibitor of metalloproteinases 1 and matrix metallopeptidase 9, were required for MUC13-mediated tumor metastasis of iCCA. MUC13 interacted with epidermal growth factor receptor (EGFR) and subsequently activated the EGFR/PI3K/AKT signaling pathway by promoting EGFR dimerization and preventing EGFR internalization. We also found that MUC13 was directly regulated by miR-212-3p, whose downregulation was related to aberrant CpG hypermethylation in the promoter area. CONCLUSIONS: These findings suggest that aberrant hypermethylation-induced downregulation of miR-212-3p results in overexpression of MUC13 in iCCA, leading to metastasis via activation of the EGFR/PI3K/AKT signaling pathway. LAY SUMMARY: Mucin 13 overexpression has been implicated in the development of malignancies, although its role in intrahepatic cholangiocarcinoma has not been studied. Herein, we show that mucin 13 plays a critical role in intrahepatic cholangiocarcinoma. Mucin 13 could have therapeutic value both as a prognostic marker and as a treatment target.