Inactivation of lncRNA HOTAIRM1 caused by histone methyltransferase RIZ1 accelerated the proliferation and invasion of liver cancer.

Abstract

Liver cancer is the second most common cause of cancer death, causing more than 700,000 deaths every year. It has been demonstrated that Long non-coding RNA (LncRNA) plays an important regulatory role in a series of diseases. However, the regulatory mechanism of LncRNAs in liver cancer has not been fully elucidated. The purpose of this study was to explore the interaction of lncRNA HOTAIRM1 and aberrant histone modification in liver cancer. qRT-PCR was used to detect the expression levels of RIZ1 and miR-125b in liver cancer cells. Cell proliferation was measured using the CCK8 assay. ChIP-Real-time PCR confirmed the binding site of the promoter of HOTAIRM1 by H3K9me1. The direct target of HOTAIRM1 and miR-125b in liver cancer cells was measured by a luciferase reporter assay. Cell proliferation was detected by Cell Counting Kit-8 (CCK8). Cell invasion was measured by transwell assays and cell migration was detected by wound healing assay. The expression level of RIZ1 and miR-125b was upregulated, and HOTAIRM1 was downregulated in liver cancer cells. Transwell and CCK-8 assay showed that RIZ1 expression is associated with the proliferation, invasion and migration of liver cancer cells, silencing of RIZ1 inhibited cell proliferation, migration, and invasion in HEPG2 and HCC-LM3 cells. RIZ1 interference could significantly inhibit H3K9me1 expression. H3K9me1 protein can bind to HOTAIRM1 promoter directly. Furthermore, the bioinformatics prediction and luciferase assay demonstrated that miR-125b can interact with HOTAIRM1 by direct binding. HOTAIRM1 down-expression promoted HEPG2 cell growth and metastasis, which was further strengthened following the co-transfection of miR-125b. Furthermore, overexpressed HOTAIRM1 inhibited HCC-LM3 cell growth and metastasis and a complete reversal of the results seen when transfected with miR-125b. For the first time, we found that RIZ1 was upregulated in liver cancer cells and RIZ1-mediated H3K9me1 enrichment on the HOTAIRM1 promoter regulated the growth and metastasis of liver cancer cells by targeting miR-125b, which could further accelerate tumor proliferation, migration and invasion. It may serve as a therapeutic marker for liver cancer treatment.