Long noncoding RNA HULC modulates abnormal lipid metabolism in hepatoma cells through an miR-9-mediated RXRA signaling pathway.

HULC is a long noncoding RNA overexpressed in hepatocellular carcinoma (HCC), but its functional contributions in this setting have not been determined. In this study, we explored the hypothesis that HULC contributes to malignant development by supporting abnormal lipid metabolism in hepatoma cells. HULC modulated the deregulation of lipid metabolism in HCC by activating the acyl-CoA synthetase subunit ACSL1. Immunohistochemical analysis of tissue microarrays revealed that approximately 77% (180/233) of HCC tissues were positive for ACSL1. Moreover, HULC mRNA levels correlated positively with ACSL1 levels in 60 HCC cases according to real-time PCR analysis. Mechanistic investigations showed that HULC upregulated the transcriptional factor PPARA, which activated the ACSL1 promoter in hepatoma cells. HULC also suppressed miR-9 targeting of PPARA mRNA by eliciting methylation of CpG islands in the miR-9 promoter. We documented the ability of HULC to promote lipogenesis, thereby stimulating accumulation of intracellular triglycerides and cholesterol in vitro and in vivo. Strikingly, ACSL1 overexpression that generates cholesterol was sufficient to enhance the proliferation of hepatoma cells. Further, cholesterol addition was sufficient to upregulate HULC expression through a positive feedback loop involving the retinoid receptor RXRA, which activated the HULC promoter. Overall, we concluded that HULC functions as an oncogene in hepatoma cells, acting mechanistically by deregulating lipid metabolism through a signaling pathway involving miR-9, PPARA, and ACSL1 that is reinforced by a feed-forward pathway involving cholesterol and RXRA to drive HULC signaling.

Cui M ，Xiao Z ，Wang Y ，Zheng M ，Song T ，Cai X ，Sun B ，Ye L ，Zhang X ... -  《-》

MiR-205 modulates abnormal lipid metabolism of hepatoma cells via targeting acyl-CoA synthetase long-chain family member 1 (ACSL1) mRNA.

The abnormal lipid metabolism is considered as a hallmarker of tumorigenesis. Liver is the central organ for metabolic homeostasis. Hence, the development of hepatocellular carcinoma (HCC) always exhibits alterations of metabolism. MicroRNAs emerge as key post-transcriptional modulators of gene expression in physiologic and pathologic states. Here, we aim to explore the mechanism of abnormal lipid metabolism of hepatoma cells. Previously, our group reported that miR-205 as a tumor suppressor was down-regulated in HCC. Therefore, we supposed that miR-205 might be involved in the event. Interestingly, in this study we uncover that miR-205 deregulates lipid metabolism in HCC through targeting acyl-CoA synthetase long-chain family member 1 (ACSL1) mRNA, which is an important and abundant lipid metabolism enzyme in liver. We identified that miR-205 was able to down-regulate ACSL1 via targeting its 3'UTR in the cells. Oil red O staining showed that miR-205 disordered the lipogenesis in hepatoma cells and anti-miR-205 resulted in the accumulation of triglyceride in the cells depending on ACSL1. Moreover, we validated that the low levels of miR-205 were negatively related to high levels of ACSL1 in clinical HCC tissues. The expression levels of ACSL1 and its metabolite triglyceride levels were remarkably increased in hepatitis B virus X protein (HBx)-induced liver cancer tissues from the HBx transgenic mice model. Thus, we conclude that miR-205-targeted ACSL1 may contribute to the abnormal lipid metabolism of liver cancer. Our finding provides new insights into the dysregulation of lipid metabolism in HCC mediated by miR-205 targeting ACSL1 mRNA.

Cui M ，Wang Y ，Sun B ，Xiao Z ，Ye L ，Zhang X ... -  《-》

Involvement of cholesterol in hepatitis B virus X protein-induced abnormal lipid metabolism of hepatoma cells via up-regulating miR-205-targeted ACSL4.

Hepatitis B virus X protein (HBx) plays crucial roles in the development of hepatocellular carcinoma (HCC). The abnormal lipid metabolism is involved in the hepatocarcinogenesis. We previously reported that HBx suppressed miR-205 in hepatoma cells. In this study, we supposed that HBx-decreased miR-205 might contribute to the abnormal lipid metabolism according to the bioinformatics analysis. Interestingly, we showed that the expression levels of acyl-CoA synthetase long-chain family member 4 (ACSL4) were negatively associated with those of miR-205 in clinical HCC tissues. Then, we validated that miR-205 was able to inhibit the expression of ACSL4 at the levels of mRNA and protein through targeting its 3'UTR. Strikingly, we found that HBx was able to increase the levels of cellular cholesterol, a metabolite of ACSL4, in hepatoma cells, which could be blocked by miR-205 (or Triacsin C, an inhibitor of ACSL4). However, anti-miR-205 could increase the levels of cholesterol in the cells. Moreover, we demonstrated that the levels of cholesterol were increased in the liver of HBx transgenic mice in a time course manner. Functionally, oil red O staining revealed that HBx promoted lipogenesis in HepG2 cells, which could be abolished by miR-205 (or Triacsin C). However, anti-miR-205 was able to accelerate lipogenesis in the cells. Interestingly, the treatment with Triacsin C could remarkably block the role of anti-miR-205 in the event. Thus, we conclude that miR-205 is able to target ACSL4 mRNA. The HBx-depressed miR-205 is responsible for the abnormal lipid metabolism through accumulating cholesterol in hepatoma cells.

Cui M ，Xiao Z ，Sun B ，Wang Y ，Zheng M ，Ye L ，Zhang X ... -  《-》

A long noncoding RNA perturbs the circadian rhythm of hepatoma cells to facilitate hepatocarcinogenesis.

Clock circadian regulator (CLOCK)/brain and muscle arnt-like protein-1 (BMAL1) complex governs the regulation of circadian rhythm through triggering periodic alterations of gene expression. However, the underlying mechanism of circadian clock disruption in hepatocellular carcinoma (HCC) remains unclear. Here, we report that a long noncoding RNA (lncRNA), highly upregulated in liver cancer (HULC), contributes to the perturbations in circadian rhythm of hepatoma cells. Our observations showed that HULC was able to heighten the expression levels of CLOCK and its downstream circadian oscillators, such as period circadian clock 1 and cryptochrome circadian clock 1, in hepatoma cells. Strikingly, HULC altered the expression pattern and prolonged the periodic expression of CLOCK in hepatoma cells. Mechanistically, the complementary base pairing between HULC and the 5' untranslated region of CLOCK mRNA underlay the HULC-modulated expression of CLOCK, and the mutants in the complementary region failed to achieve the event. Moreover, immunohistochemistry staining and quantitative real-time polymerase chain reaction validated that the levels of CLOCK were elevated in HCC tissues, and the expression levels of HULC were positively associated with those of CLOCK in clinical HCC samples. In functional experiments, our data exhibited that CLOCK was implicated in the HULC-accelerated proliferation of hepatoma cells in vitro and in vivo. Taken together, our data show that an lncRNA, HULC, is responsible for the perturbations in circadian rhythm through upregulating circadian oscillator CLOCK in hepatoma cells, resulting in the promotion of hepatocarcinogenesis. Thus, our finding provides new insights into the mechanism by which lncRNA accelerates hepatocarcinogenesis through disturbing circadian rhythm of HCC.

Cui M ，Zheng M ，Sun B ，Wang Y ，Ye L ，Zhang X ... -  《NEOPLASIA》

The long noncoding RNA HULC promotes liver cancer by increasing the expression of the HMGA2 oncogene via sequestration of the microRNA-186.

The long noncoding RNA highly up-regulated in liver cancer (HULC) is aberrantly elevated in hepatocellular carcinoma (HCC), and this up-regulation is crucial for HCC pathogenesis. However, the underlying mechanism in HULC up-regulation is poorly understood. We hypothesized that HULC might modulate the oncogene high mobility group A2 (HMGA2) to promote hepatocarcinogenesis. Quantitative real-time PCR analysis showed that the expression levels of HULC were positively correlated with those of HMGA2 in clinical HCC tissues. Interestingly, we also observed that HULC could up-regulate HMGA2 in HCC cells. Mechanistically, we found that the microRNA-186 inhibited HMGA2 expression by targeting the 3'-untranslated region (3'-UTR) of HMGA2 mRNA. Strikingly, HULC acted as a competing noncoding RNA to sequester miR-186 and thereby relieved miR-186-mediated HMGA2 repression. Functionally, HMGA2 knockdown decreased the HULC-enhanced growth of HCC cells both in vitro and in vivo We conclude that the long noncoding RNA HULC increases HMGA2 expression by sequestering miR-186 post-transcriptionally and thereby promotes liver cancer growth, providing new insights into the mechanism by which HULC enhances hepatocarcinogenesis.

Wang Y ，Chen F ，Zhao M ，Yang Z ，Li J ，Zhang S ，Zhang W ，Ye L ，Zhang X ... -  《-》