Abstract
In recent years, long noncoding RNAs (lncRNAs) have been demonstrated to be important tumor-associated regulatory factors. LncRNA growth arrest-specific transcript 5 (Gas5) acts as an anti-oncogene in most cancers. Whether Gas5 acts as an oncogene or anti-oncogene in hepatocellular carcinoma (HCC) remains unclear. In the present study, the expression and role of Gas5 in HCC were investigated in vitro and in vivo. Lower expression levels of Gas5 were determined in HCC tissues and cells by quantitative reverse transcription-polymerase chain reaction. Overexpressed Gas 5 lentiviral vectors were constructed to analyze their influence on cell viability, migration, invasion, and apoptosis. Fluorescence in situ hybridization was used to identify the subcellular localization of Gas5. Protein complexes that bound to Gas5 were isolated from HepG2 cells through pull-down experiments and analyzed by mass spectrometry. A series of novel Gas5-interacting proteins were identified and bioinformatics analysis was carried out. These included ribosomal proteins, proteins involved in protein folding, sorting, and transportation in the ER, some nucleases and protein enzymes involved in gene transcription, translation, and other proteins with various functions.78 kDa glucose-regulated protein (GRP78) was identified as a direct target of Gas5 by Rip-qPCR and Western blot analysis assay. Gas5 inhibited HepG2 cell growth and induced cell apoptosis via upregulating CHOP to activate the ER stress signaling pathway. Further studies indicated that the knockdown of CHOP by shRNA partially reversed Gas5-mediated apoptosis in HepG2 cells. Magnetic resonance imaging showed that the ectopic expression of Gas5 inhibited the growth of HCC in nude mice. These findings suggest that Gas5 functions as a tumor suppressor and induces apoptosis through activation of ER stress by targeting the CHOP signal pathway in HCC.