LncRNA NBR2 Inhibits Tumor Growth By Regulating Autophagy In Hepatocellular Carcinoma

Background and aims: Lnc RNAs(long non-coding RNAs)are transcripts longer than 200 nucleotides,constituting a large portion of the mammalian transcriptome.More than half of the human lnc RNA genes overlap or neighbor with known protein-coding genes.In addition,more and more studies have shown that lnc RNA is closely related to the occurrence of tumors,and lnc RNA plays an important role in the regulation of autophagy.Autophagy is a conserved catabolic process involving the formation of a vesicle termed autophagosome,which encapsulates cytoplasm and organelles and then fuses with lysosomes to form autolysosomes,thus degrading the contents of the vesicle.Autophagy can regulate the proliferation and apoptosis of liver cells in different contexts,but its role in hepatocellular carcinoma is controversial.NBR2(neighbor of BRCA1 gene 2)is a non–protein coding gene that resides adjacent to tumor suppressor gene BRCA1.In addition,NBR2 has been identified as a lnc RNA that is induced by glucose deprivation.However,its potential biological function in hepatocellular carcinoma has remained unexplored.And the relationship between NBR2 and autophagy and the effect on hepatocellular carcinoma have not been researched yet.This study aimed to explore the function of NBR2 and to verify that NBR2 inhibits tumorigenesis by regulating autophagy in hepatocellular carcinoma.Methods: Functional analysis of lnc RNA on HCC proliferation and autophagy was performed both in vitro and in vivo.Autophagic activity was estimated by Western blot for autophagic marker proteins and by transmission electron microscopy(TEM).Transfection of m RFP-GFP-LC3 adenovirus was applied to observe autophagic flux.Cell proliferation was examined by CCK8,clone formation assays and Ed U proliferation assay.Cell cycle was analyzed by flow cytometry.Migration and invasion were detected by transwell assays and wound healing assay.The signaling pathway that regulates autophagy was investigated by Western blot.Results The study found that NBR2 expression levels are generally downregulated in liver cancer cell lines.In patients with advanced liver cancer(stage ?-?),the overall survival rate of patients with low expression of NBR2 was significantly lower than that of patients with high expression of NBR2.In addition,NBR2 can inhibit the proliferation of HCC cells in vitro and in vivo,and also inhibit the invasion and migration of liver cancer cells in vitro.We further found that silencing NBR2 induces cytoprotective autophagy to promote HCC cell proliferation in vitro,and blocking autophagy can impair the growth of HCC cells induced by silencing NBR2.At the same time,it was found that all the variables in the experiment did not affect the expression level of Atg7,indicating that NBR2 regulates autophagy of HCC cells through Beclin 1 but not Atg7.Therefore,we hypothesized that NBR2 may regulate autophagy in a Beclin 1-dependent manner in hepatocarcinoma and inhibit autophagic flow of hepatoma cells.Conclusion NBR2 can significantly inhibit the proliferation and metastasis of hepatoma cells,and can regulate autophagy in hepatoma cells.Further studies have found that down-regulation of NBR2 can promote hepatoma cell proliferation by inducing cytoprotective autophagy.