lncRNA SNHG9 enhances liver cancer stem cell self-renewal and tumorigenicity by negatively regulating PTEN expression via recruiting EZH2.

Abstract

Liver cancer stem cell (CSC) self-renewal and tumorigenesis are important causes of hepatocellular carcinoma (HCC) recurrence. We purposed to investigate the function of long noncoding RNA small nucleolar RNA host gene 9 (SNHG9) in liver CSC self-renewal and tumorigenesis in this study. Flow cytometry was carried out to separate CD133⁺ Populations and CD133^- Populations from HCC cell lines. A combination of CD133⁺ cells and Matrigel matrix was subcutaneously injected to create the NOD-SCID mouse xenograft tumor model. Colony formation test and spheroids formation assay were carried out to clarify the impact of SNHG9 on the self-renewal of liver CSCs. RNA immunoprecipitation, RNA-pull down, and chromatin immunoprecipitation were performed on CD133⁺ cells to elucidate the mechanism of SNHG9 regulating PTEN expression. We found that SNHG9 was highly expressed in HCC clinical samples, HCC cells, and CD133⁺ cells. In vitro, interference with SNHG9 prevented the formation of colonies and spheroids in liver CSC cells and primary HCC cells. In vivo, interference with SNHG9 reduced the tumor volume and weight. SNHG9 could bind to EZH2, and SNHG9 interference suppressed EZH2 recruitment and H3K27me3 levels in the PTEN promoter region. In addition, SNHG9 inhibition promoted PTEN expression while having little impact on EZH2 levels. Interference with SNHG9 inhibited liver CSC self-renewal and tumorigenesis by up-regulating PTEN levels. In conclusion, by binding to EZH2, SNHG9 down-regulated PTEN levels, promoting liver CSC self-renewal and tumor formation, and exacerbating HCC progression.