Overexpression of transforming growth factor b induced factor homeobox 1 represses NPC1L1 and lowers markers of intestinal cholesterol absorption Paolo Parini a, b, 1 , Tiffany A. Melhuish c, 1 , David Wotton c , Lilian Larsson a , Osman Ahmed a, d , Mats Eriksson b , Camilla Pramfalk a, e, * a Division of Clinical Chemistry, Department of Laboratory Medicine Sweden b Metabolism Unit, Department of Medicine, Karolinska Institutet, Stockholm, Sweden c Department of Biochemistry and Molecular Genetics and Center for Cell Signaling, University of Virginia, Charlottesville, VA, USA d Department of Biochemistry, Faculty of Medicine, Khartoum University, Khartoum, Sudan e Department of Biosciences and Nutrition, NOVUM, Karolinska Institutet, Stockholm, Sweden article info Article history: Received 26 March 2018 Received in revised form 7 June 2018 Accepted 15 June 2018 Available online 19 June 2018 Keywords: Cholesterol metabolism Lipoproteins Liver Transcription Dyslipidemia abstract Background and aims: Transforming growth factor b induced factor homeobox 1 (TGIF1) is a transcrip- tional repressor that limits the response to transforming growth factor ß signaling and also represses transcription independent of this pathway. Recently, we found higher serum cholesterol levels and more hepatic lipid accumulation in mice lacking Tgif1 , and showed that TGIF1 can repress the expression of Soat2, the gene encoding the cholesterol esterifying enzyme acyl-Coenzyme A:cholesterol acyltransfer- ase 2. Although there is evidence that TGIF1 plays a role in lipid metabolism, its role in this metabolic pathway is not fully characterized. Here we investigate whether overexpression of TGIF1 affects intes- tinal cholesterol absorption. Methods and results: TGIF1 was found to repress human and mouse Niemann-Pick C1 like 1 (Npc1l1) promoter activity in intestinal Caco2 cells. We also found TGIF1 to be able to oppose the induction of the promoter activity by sterol regulatory element binding protein 2 and hepatocyte nuclear factor 1a and 4a. To validate these effects of TGIF1 in vivo, we generated transgenic mice specifically overexpressing TGIF1 in the intestine (Villin-Tgif1). We observed lower intestinal expression levels of Npc1l1 that was associated with lower expression of ATP-binding cassette transporter (Abc) a1, Abcg5, and Abcg8. Villin- Tgif1 mice fed regular chow or a high-fat diet had lower levels of markers of intestinal cholesterol ab- sorption than wild types. Conclusions: We suggest TGIF1 as a new player in intestinal cholesterol metabolism. © 2018 Elsevier B.V. All rights reserved. 1. Introduction Transforming growth factor b induced factor homeobox 1 (TGIF1) was named TG-interacting factor 1 when discovered. TGIF1 is commonly known as a transcriptional repressor which limits the transcriptional output of transforming growth factor b-signaling (TGFb)[1e3]. TGIF1 can be recruited to DNA via interaction with TGFb-activated Smad transcription factors, or can repress tran- scription independent of TGFb. TGIF1 exerts repression of target genes by binding to its cognate binding site or to binding sites for retinoid X receptor a (RXRa)[4,5]. RXRa is a heterodimeric partner of several nuclear receptors (e.g. peroxisome proliferator-activated receptor a and liver X receptor a; LXRa). Hence, TGIF1 may Abbreviations: ABCA1, ATP-binding cassette transporter A1; ACAT2, acyl-Coen- zyme A:cholesterol acyltransferase 2; apo, apolipoprotein; CYP7A1, cholesterol 7a- hydroxylase; HMGCR, 3-hydroxy-3-methylglutaryl-CoA reductase; HNF, hepatocyte nuclear factor; LDL, low density lipoprotein; LXR, liver X receptor; NEFA, nones- terified fatty acid; NPC1L1, Niemann-Pick C1 like 1; PCSK9, proprotein convertase subtilisin/kexin type 9; RXR, retinoid X receptor; SREBP, sterol regulatory element binding protein; TGFb, transforming growth factor b; TGIF1, transforming growth factor b induced factor homeobox 1; TICE, transintestinal cholesterol efflux. * Corresponding author. Division of Clinical Chemistry, Department of Laboratory Medicine, C1-74, Karolinska Institutet at Karolinska University Hospital Huddinge, S-141 86, Stockholm, Sweden. E-mail address: camilla.pramfalk@ki.se (C. Pramfalk). 1 P Parini and TA Melhuish contributed equally to this study. Contents lists available at ScienceDirect Atherosclerosis journal homepage: www.elsevier.com/locate/atherosclerosis https://doi.org/10.1016/j.atherosclerosis.2018.06.867 0021-9150/© 2018 Elsevier B.V. All rights reserved. Atherosclerosis 275 (2018) 246e255