A Novel Long Non-Coding RNA (Ctcflos) Modulates Glucocorticoid Receptor-Mediated Induction of Hepatic Phosphoenolpyruvate Carboxykinase in Mice

Abstract Background Phosphoenolpyruvate carboxykinase (Pck1) is a key enzyme that catalyzes an irreversible step of hepatic gluconeogenesis; however, the mechanism underlying Pck1 regulation is not fully understood. This study aims to identify a lncRNA that regulates transcription of the Pck1 gene. Methods The precise structures of five different hepatic Ctcflos isotypes were identified through rapid amplification of cDNA ends in the mouse liver. The expression level of hepatic Ctcflos level was determined by PCR and the role of Ctcflos were assessed using antisense oligonucleotides and virus encoding Ctcflos both in vitro and in vivo. The target protein interacted with Ctcflos was identified through RNA pull down assay. Contribution of Ctcflos in glucocorticoid receptor (GR)-mediated Pck1 gene expression was evaluated by chromatin immunoprecipitation, co-immunoprecipitation, in situ proximity ligation assay, and reporter gene analysis. Results A novel lncRNA Ctcflos was identified in the enhancer region of Pck1 gene. Induction of Ctcflos was dependent on the glucocorticoid receptor (GR) in the livers of fasted or dexamethasone-administered mice. Overexpression of Ctcflos by infusion of an adenovirus encoding Ctcflos increased transcript- and protein-level of Pck1, whereas knockdown of Ctcflos using antisense oligonucleotides suppressed. RNA pulldown experiments showed that Ctcflos bound the heterogeneous ribonucleoprotein L (hnRNPL) which interacts with GR. Interestingly, knockdown of hnRNPL upregulated the Pck1 gene. Finally, we found that, in the presence of Ctcflos, the binding between GR and hnRNPL was weakened, whereas the DNA binding of GR was enriched in the Pck1 enhancer region. Conclusions We report the discovery of a novel lncRNA, Ctcflos, that regulates the transcription of Pck1 by modulating GR function. Targeting Ctcflos may provide a new insight into the development of alternative treatments for hyperglycemia by offering specific regulation of hepatic Pck1 gene expression.