Roza Berhanu Lemma

• Fan, Qiong; Nørgaard, Rikke Christine; Grytten, Ivar; Ness, Cecilie; Lucas, Christin; Vekterud, Kristin; Södling, Helen; Matthews, Jason; Lemma, Roza Berhanu; Gabrielsen, Odd Stokke; Bindesbøll, Christian; Ulven, Stine Marie; Nebb, Hilde Irene; Grønning-Wang, Line Mariann & Sæther, Thomas (2020). LXRα Regulates ChREBPα Transactivity in a Target Gene-Specific Manner through an Agonist-Modulated LBD-LID Interaction. Cells.  ISSN 2073-4409.  9(5), s 1- 26 . doi: 10.3390/cells9051214 Full text in Research Archive. Show summary

  The cholesterol-sensing nuclear receptor liver X receptor (LXR) and the glucose-sensing transcription factor carbohydrate responsive element-binding protein (ChREBP) are central players in regulating glucose and lipid metabolism in the liver. More knowledge of their mechanistic interplay is needed to understand their role in pathological conditions like fatty liver disease and insulin resistance. In the current study, LXR and ChREBP co-occupancy was examined by analyzing ChIP-seq datasets from mice livers. LXR and ChREBP interaction was determined by Co-immunoprecipitation (CoIP) and their transactivity was assessed by real-time quantitative polymerase chain reaction (qPCR) of target genes and gene reporter assays. Chromatin binding capacity was determined by ChIP-qPCR assays. Our data show that LXRα and ChREBPα interact physically and show a high co-occupancy at regulatory regions in the mouse genome. LXRα co-activates ChREBPα and regulates ChREBP-specific target genes in vitro and in vivo. This co-activation is dependent on functional recognition elements for ChREBP but not for LXR, indicating that ChREBPα recruits LXRα to chromatin in trans. The two factors interact via their key activation domains; the low glucose inhibitory domain (LID) of ChREBPα and the ligand-binding domain (LBD) of LXRα. While unliganded LXRα co-activates ChREBPα, ligand-bound LXRα surprisingly represses ChREBPα activity on ChREBP-specific target genes. Mechanistically, this is due to a destabilized LXRα:ChREBPα interaction, leading to reduced ChREBP-binding to chromatin and restricted activation of glycolytic and lipogenic target genes. This ligand-driven molecular switch highlights an unappreciated role of LXRα in responding to nutritional cues that was overlooked due to LXR lipogenesis-promoting function.

• Fan, Qiong; Nørgaard, Rikke Christine; Grytten, Ivar; Ness, Cecilie Maria; Lucas, Christin; Vekterud, Kristin; Soedling, Helen; Matthews, Jason; Lemma, Roza Berhanu; Gabrielsen, Odd Stokke; Bindesbøll, Christian; Ulven, Stine Marie; Nebb, Hilde Irene; Grønning-Wang, Line Mariann & Sæther, Thomas (2019). Open the LID: LXRα regulates ChREBPα transactivity in a target gene-specific manner through an agonist-modulated LBD-LID interaction. BioRxiv.  ISSN 0362-4331. . doi: 10.1101/2019.12.20.869974 Show summary

  The cholesterol-sensing nuclear receptor liver X receptor (LXR) and the glucose-sensing transcription factor carbohydrate responsive element-binding protein (ChREBP) are central players in regulating glucose and lipid metabolism in liver. We have previously shown that LXR regulates ChREBP transcription and activity; however, the underlying mechanisms are unclear. In the current study, we demonstrate that LXRα and ChREBPα interact physically, and show a high co-occupancy at regulatory regions in the mouse genome. LXRα co-activates ChREBPα, and regulates ChREBP-specific target genes in vitro and in vivo. This co-activation is dependent on functional recognition elements for ChREBP, but not for LXR, indicating that ChREBPα recruits LXRα to chromatin in trans. The two factors interact via their key activation domains; ChREBPα’s low glucose inhibitory domain (LID) and the ligand-binding domain (LBD) of LXRα. While unliganded LXRα co-activates ChREBPα, ligand-bound LXRα surprisingly represses ChREBPα activity on ChREBP-specific target genes. Mechanistically, this is due to a destabilized LXRα:ChREBPα interaction, leading to reduced ChREBP-binding to chromatin and restricted activation of glycolytic and lipogenic target genes. This ligand-driven molecular switch highlights an unappreciated role of LXRα that was overlooked due to LXR lipogenesis-promoting function.

• Rodriguez- Castañeda, Fernando; Lemma, Roza Berhanu; Cuervo Torre, Ignacio; Bengtsen, Mads; Moen, Lisa Marie; Ledsaak, Marit; Eskeland, Ragnhild & Gabrielsen, Odd Stokke (2018). The SUMO protease SENP1 and the chromatin remodeller CHD3 interact and jointly affect chromatin accessibility and gene expression. Journal of Biological Chemistry.  ISSN 0021-9258.  293(40), s 15439- 15454 . doi: 10.1074/jbc.RA118.002844 Full text in Research Archive. Show summary

  The small ubiquitin-like modifier (SUMO) post-translationally modifies lysine residues of transcription factors and co-regulators and thereby contributes to an important layer of control of the activities of these transcriptional regulators. Likewise, deSUMOylation of these factors by the sentrin-specific proteases (SENPs) also plays a role in gene regulation, but whether SENPs functionally interact with other regulatory factors that control gene expression is unclear. In the present work, we focused on SENP1, specifically, on its role in activation of gene expression investigated through analysis of the SENP1 interactome, which revealed that SENP1 physically interacts with the chromatin remodeler chromodomain helicase DNA-binding protein 3 (CHD3). Using several additional methods, including GST pull-down and co-immunoprecipitation assays, we validated and mapped this interaction, and using CRISPR-Cas9–generated CHD3- and SENP1-KO cells (in the haploid HAP1 cell line), we investigated whether these two proteins are functionally linked in regulating chromatin remodeling and gene expression. Genome-wide ATAC-Seq analysis of the CHD3- and SENP1-KO cells revealed a large degree of overlap in differential chromatin openness between these two mutant cell lines. Moreover, motif analysis and comparison with ChIP-Seq profiles in K562 cells pointed to an association of CHD3 and SENP1 with CCCTC-binding factor (CTCF) and SUMOylated chromatin–associated factors. Lastly, genome-wide RNA-Seq also indicated that these two proteins co-regulate the expression of several genes. We propose that the functional link between chromatin remodeling by CHD3 and deSUMOylation by SENP1 uncovered here provides another level of control of gene expression.

• Fuglerud, Bettina Maria; Lemma, Roza Berhanu; Wanichawan, Pimthanya; Sundaram, Arvind; Eskeland, Ragnhild & Gabrielsen, Odd Stokke (2017). A c-Myb mutant causes deregulated differentiation due to impaired histone binding and abrogated pioneer factor function. Nucleic Acids Research (NAR).  ISSN 0305-1048.  45(13), s 7681- 7696 . doi: 10.1093/nar/gkx364 Full text in Research Archive.

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• Fan, Qiong; Nørgaard, Rikke Christine; Grytten, Ivar; Ness, Cecilie Maria; Lucas, Christin; Vekterud, Kristin; Södling, Helen; Matthews, Jason; Lemma, Roza Berhanu; Gabrielsen, Odd Stokke; Bindesbøll, Christian; Ulven, Stine Marie; Nebb, Hilde Irene; Grønning-Wang, Line Mariann & Sæther, Thomas (2019). LXRα interacts with the glucose-sensing transcription factor ChREBPα to regulate its transcriptional activity.. Show summary

  The cholesterol-sensing nuclear receptor Liver X Receptor (LXR) and the glucose-sensing transcription factor carbohydrate responsive element-binding protein (ChREBP) are central players in the regulation of glucose and lipid metabolism. LXR does this job in part by regulating the expression of ChREBP. We have previously shown that LXR also regulates ChREBP activity. To get a better understanding of mechanisms at play, we asked if LXR and ChREBP interact physically. Interestingly, LXRα binds to ChREBPα, but not the shorter isoform ChREBPβ. Co-immunoprecipitation (CoIP) of different LXR and ChRBEP domains shows that it is ChREBPα’s low glucose inhibitory domain (LID), which is lacking in ChREBPβ, that interacts with the ligand-binding domain (LBD) of LXRα. In line with this, we see a surprisingly high co-occupancy of LXR and ChREBP on regulatory regions in the mouse genome when re-analysing two independently published chromatin immunoprecipitation-sequencing (ChIP-seq) datasets. Moreover, Functional studies show that LXRα is able to co-activate together with ChREBPα, but not ChREBPβ, and increase ChREBP-specific target gene expression in vitro and in vivo. Unexpectedly however, ligand-engaged LXR exhibits a repressive effect on the expression of the same genes in primary mouse hepatocytes, in contrast to what we observe with target genes that are common to LXR and ChREBP. Performing CoIP and ChIP on selected target genes, we demonstrate mechanistically that the repressive effect most likely is due to a weakened ChREBPα:LXRα interaction and reduced binding of ChREBP to chromatin. Altogether, the novel transcriptional complex comprising ChREBPα and LXRα adds to the intricate integration of nutrient signals in glucose and lipid metabolism.

• Fan, Qiong; Nørgaard, Rikke Christine; Grytten, Ivar; Ulven, Stine Marie; Lucas, Christin; Bindesbøll, Christian; Lemma, Roza Berhanu; Gabrielsen, Odd Stokke; Grønning-Wang, Line Mariann; Nebb, Hilde Irene & Sæther, Thomas (2018). LXRα interacts with the glucose-sensing transcription factor ChREBPα and increases its transcriptional activity.

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