LncRNA SAMD12-AS1 promotes cell proliferation and inhibits apoptosis by interacting with NPM1

Qi Liu,Dandan Qi,Fang Zhang,Wenjia Chai,Ningning Liu,Qilin Shangguan,Xin Ye,Xin Zhao,Zhiwei Li,Xiaomei Tong

doi:10.1038/s41598-019-48116-1

Abstract

Chronic hepatitis B virus infection is a major risk factor for hepatocellular carcinoma. HBV infection affects lncRNA expression in infected cells, but the detailed mechanism and biological significance are not yet clear. In this study, we focused on exploring the function of the HBV-upregulated lncRNA SAMD12-AS1 in cell proliferation. We found that there is a higher level of SAMD12-AS1 expression in tumors than in adjacent nontumorous liver tissues. We showed that ectopic expression of SAMD12-AS1 promotes cell growth and blocks apoptosis, while knockdown of SAMD12-AS1 inhibits cell proliferation and enhances etoposide-induced apoptosis. Using RNA immunoprecipitation and mass spectrometry, we determined that SAMD12-AS1 interacts with NPM1 and confirmed that SAMD12-AS1(1-350) is required for the interaction with NPM1. As it is known that NPM1 interacts with the E3 ligase HDM2 and reduces HDM2-mediated p53 degradation, we examined whether SAMD12-AS1 can affect p53 stability. Overexpression of SAMD12-AS1 caused a reduction in p53 protein levels by shortening its half-life. Conversely, knockdown of SAMD12-AS1 prolonged the half-life of p53. We further demonstrated that SAMD12-AS1 increased the interaction of HDM2 and p53 and enhanced p53 ubiquitination. Our findings reveal that HBV-upregulated SAMD12-AS1 regulates cell proliferation and apoptosis via the NPM1-HDM2-p53 axis.

Highlights

Chronic hepatitis B (CHB) virus infection is the leading cause of hepatocellular carcinoma (HCC) and affects more than 250 million individuals1,2
We identified 38 Long noncoding RNAs (lncRNAs) that were upregulated in HepG2-4D14 cells20
SAMD12-AS1 is located in the same locus as SAMD12 on chromosome 8 (Fig. 1a). Quantitative RT-PCR (qRT-PCR) data showed that SAMD12-AS1 was upregulated in HepG2-4D14 cells compared with HepG2 cells, which is consistent with the RNA-Seq data20 (Fig. 1b)

Summary

Introduction

Chronic hepatitis B (CHB) virus infection is the leading cause of hepatocellular carcinoma (HCC) and affects more than 250 million individuals. HBV inhibits TGF-β-induced apoptosis by upregulating Smad to downregulate TGF-β signaling and promote tumor development. LncRNA-HEIH was identified as a highly expressed lncRNA in HBV-related HCC and acts as an oncogenic lncRNA that promotes tumor progression. The HBV-encoded HBx suppresses the expression of lncRNA-Dreh, which functions as a tumor suppressor. It has been found that HBx increases lncRNA UCA1 transcription to promote HCC progression. We analyzed differentially expressed lncRNAs between HBV-negative (HepG2) and HBV-positive (HepG2-4D14) cells and identified a series of HBV-associated lncRNAs, including lnc-HUR1, which promotes cell growth and tumorigenesis by inhibiting p53 transcriptional activity. We show that HBV-encoded HBx enhances SAMD12-AS1 transcription. Functional analyses indicate that SAMD12-AS1 promotes cell proliferation and inhibits apoptosis. Our study reveals that HBx-upregulated SAMD12-AS1 reduces p53 stability through the NPM1-HDM2-p53 axis, which in turn affects cell proliferation and apoptosis

Methods

Results

Conclusion