Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Lackner-Sediki, B.
Effect of R2TP complex and R2TP associated proteins on bile acid metabolism
Humanmedizin; [ Diplomarbeit ] Medizinische Universität Graz; 2021. pp. 48
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- Autor*innen der Med Uni Graz:
- Betreuer*innen:
- Fickert Peter
- Moustafa Tarek
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- Abstract:
- Abstract Background The nuclear hormone receptors (NHRs) LXR and FXR are regulators of numerous metabolic processes and maintain the balance between bile acid (BA) and cholesterol metabolism. The mammalian target of rapamycin (mTORC1), a central regulator of lipid, glucose, and cholesterol metabolism, appears to influence FXR and LXR. Within my thesis, I wanted to contribute to the better understanding of the crosstalk between signaling pathways inside and outside the nucleus. In particular, how mTORC1 regulates the expression of NHRs and related bile acid associated gene expression. Aims Based on the hypothesis that PIKKs and R2TP/PFDL-associated proteins are involved in mTORC1 nuclear receptor communication, the aim of the study is to determine to what extent ZNHIT3, NUFIP, RUVBL1 and TRRAP are involved in mTORC-signaling and to what extent knockdown of these genes affects the function of NHRs. Methods HepG2 cells were treated with NUFIP, RUVBL1, ZNHIT3 and TRRAP siRNAs. Cells were additionally treated with FXR-ligand GW4064 and LXR-ligand GW3965. In another subset, treatment consisted of mTOR inhibitor Torin1. Western blots were performed showing the protein expression levels of FXR, mTOR, and related proteins. Quantitative polymerase chain reaction (qPCR) analyses for LXR and FXR target genes were performed under basal conditions and after stimulation of NHRs by synthetic ligands. Results Knockdown of NUFIP and TRRAP showed a positive effect on mTOR protein expression. FXR protein expression was negatively affected by NUFIP-KD and showed an increase in TRRAP-KD samples. TRRAP-KD, ZNHIT3-KD, NUFIP-KD and RUVBL1-KD decreased mRNA gene expression of LXR and FXR target genes under stimulated conditions. Conclusion FXR was shown to correlate with mTOR expression levels. mTOR is supported by its PIKK family member TRRAP. The R2TP complex and its associated proteins are an important component of translation and are also essential for FXR and LXR. The data obtained point toward a co-regulatory mechanism that impacts genes involved in both cholesterol and bile acid metabolism, mediated in part by FXR and LXR. Based on these important regulatory functions we can speculate that maybe compensatory mechanisms are involved if one or the other nuclear receptor (FXR/LXR) or metabolic pathway (bile acids/cholesterol) is affected.