Epigenetic regulation of MicroRNA-122 by peroxisome proliferator activated receptor-gamma and hepatitis b virus X protein in hepatocellular carcinoma cells

Abstract

MiR-122, a pivotal liver specific miRNA, has been implicated in several liver diseases including hepatocellular carcinoma (HCC) and hepatitis C and B viral infection. This study aimed to explore epigenetic regulation of miR-122 in human hepatocellular carcinoma (HCC) cells and to examine the effect of hepatitis C virus (HCV) and hepatitis B virus (HBV). We performed microRNA microarray analysis and identified miR-122 as the most up-regulated miRNA (6-fold) in human hepatocellular cancer cells treated with 5′aza-2′deoxycytidine (5-Aza-CdR, DNA methylation inhibitor) and 4-phenylbutyric acid (PBA, histone deacetylation inhibitor). Real-time PCR analysis verified significant upregulation of miR-122 by 5′aza and PBA in HCC cells, and to a lesser extent in primary hepatocytes. Peroxisome proliferator activated receptor-gamma (PPARγ) and retinoid X receptor alpha (RXRα) complex was found to be associated with the DR1 and DR2 consensus site in the miR-122 gene promoter which enhanced miR-122 gene transcription. 5-Aza-CdR and PBA treatment increased the association of PPARγ/RXRα, but decreased the association of its co-repressors (N-CoR and SMRT), with the miR-122 DR1 and DR2 motifs. The aforementioned DNA-protein complex also contains SUV39H1, a H3K9 histone methyl transferase, which downregulates miR-122 expression. Our findings establish a novel role of the PPARγ binding complex for epigenetic regulation of miR-122 in human HCC cells. Moreover, we show that hepatitis B virus X protein (HBX) binds PPARγ and inhibits the transcription of miR-122, whereas hepatitis C viral particles exhibited no significant effect; these findings provide mechanistic insight into reduction of miR-122 in patients with HBV but not with HCV infection.

Decreased Expression of Hepatocyte Nuclear Factor 4α (Hnf4α)/MicroRNA-122 (miR-122) Axis in Hepatitis B Virus-associated Hepatocellular Carcinoma Enhances Potential Oncogenic GALNT10 Protein Activity

“…The level of miR-122 is decreased in patients with HBV infection (42), but the mechanism underlying is not fully elucidated. Song et al (43,44) reported that HBx conferred epigenetic down-regulation of miR-122 by peroxisome proliferator-activated receptor-␥⅐ retinoid X receptor ␣ complex through interaction with the co-repressors and H3K9 histone methyltransferase (SUV39H1) in HCC cells. In addition, Li et al (45) reported that HBV mRNAs act as sponges to bind and sequester endogenous miR-122 to facilitate HBV replication.…”

Inflammation-Induced Expression and Secretion of MicroRNA 122 Leads to Reduced Blood Levels of Kidney-Derived Erythropoietin and Anemia

“…MiR-122 expression was also shown to be epigenetically regulated by the PPARγ/RXRa complex 12 . Additionally, miR-122 is regulated by Rev-ErbA alpha suggesting that miR-122 is a circadian metabolic regulator 13 .…”

Antitumor function of microRNA-122 against hepatocellular carcinoma

“…The promoter region of miR-122 is hypermethylated in HCC cells, but not in human primary hepatocytes [31]. The treatment of HCC cells with a demethylating agent, 5-Aza-2 0 deoxycytidine (5-Aza-Cd), significantly increases the gene expression of miR-122 [37]. Moreover, in HCC cells, a H3K9 histone methyl transferase down-regulates the gene expression of miR-122 by inhibiting PPARc/RXRa-mediated promoter activity, which is cancelled by cotreatment with 5-Aza-Cd and histone deacetylase inhibitor [37].…”