Abstract
Hepatocyte nuclear factor 4α (HNF4α) controls the expression of liver-specific protein-coding genes. However, some microRNAs are also modulated by HNF4α, and it is not known whether they are direct targets of HNF4α and whether they influence hepatic function. In this study, we found that HNF4α regulates microRNAs, indicated by marked down-regulation of miR-194 and miR-192 (miR-194/192) in liver-specific Hnf4a-null (Hnf4aΔH) mice. Transactivation of the shared miR-194/192 promoter was dependent on HNF4α expression, indicating that miR-194/192 is a target gene of HNF4α. Screening of potential mRNAs targeted by miR-194/192 revealed that expression of genes involved in glucose metabolism (glycogenin 1 (Gyg1)), cell adhesion and migration (activated leukocyte cell adhesion molecule (Alcam)), tumorigenesis and tumor progression (Rap2b and epiregulin (Ereg)), protein SUMOylation (Sumo2), epigenetic regulation (Setd5 and Cullin 4B (Cln4b)), and the epithelial-mesenchymal transition (moesin (Msn)) was up-regulated in Hnf4aΔH mice. Moreover, we also found that miR-194/192 binds the 3'-UTR of these mRNAs. siRNA knockdown of HNF4α suppressed miR-194/192 expression in human hepatocellular carcinoma (HCC) cells and resulted in up-regulation of their mRNA targets. Inhibition and overexpression experiments with miR-194/192 revealed that Gyg1, Setd5, Sumo2, Cln4b, and Rap2b are miR-194 targets, whereas Ereg, Alcam, and Msn are miR-192 targets. These findings reveal a novel HNF4α network controlled by miR-194/192 that may play a critical role in maintaining the hepatocyte-differentiated state by inhibiting expression of genes involved in dedifferentiation and tumorigenesis. These insights may contribute to the development of diagnostic markers for early HCC detection, and targeting of the miR-194/192 pathway could be useful for managing HCC.
Highlights
Hepatocyte nuclear factor 4␣ (HNF4␣) controls the expression of liver-specific protein-coding genes
These findings reveal a novel HNF4␣ network controlled by miR-194/192 that may play a critical role in maintaining the hepatocyte-differentiated state by inhibiting expression of genes involved in dedifferentiation and tumorigenesis
Direct transcriptional repression by HNF4␣ itself could be considered as a mechanism by which these mRNAs are reduced in Hnf4a⌬H mice, another possibility is the involvement of microRNAs that could be under direct transcriptional control of HNF4␣. miRNAs are small non-coding RNAs involved in various physiological functions such as development, differentiation, inflammation, and tumorigenesis through their ability to down-regulate protein-coding gene expression by binding to target mRNAs and either promoting mRNA degradation or inhibiting mRNA translation [14, 15]. miRNAs have important roles in liver diseases such as viral hepatitis, steatohepatitis, liver fibrosis, polycystic liver disease, and hepatocellular carcinoma (HCC) [16, 17]
Summary
Hepatocyte nuclear factor 4␣ (HNF4␣) controls the expression of liver-specific protein-coding genes. Inhibition and overexpression experiments with miR-194/192 revealed that Gyg, Setd, Sumo, Cln4b, and Rap2b are miR-194 targets, whereas Ereg, Alcam, and Msn are miR-192 targets These findings reveal a novel HNF4␣ network controlled by miR-194/192 that may play a critical role in maintaining the hepatocyte-differentiated state by inhibiting expression of genes involved in dedifferentiation and tumorigenesis. These insights may contribute to the development of diagnostic markers for early HCC detection, and targeting of the miR-194/192 pathway could be useful for managing HCC. The HNF4␣–miR-194/192 pathway could be a novel HNF4␣ cascade and a candidate for early detection of HCC and development of anti-HCC drugs
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