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Published on: October 24, 2016
Disturbed function of TBL1X has a differential effect on T3-regulated gene expression in two human liver cell models
Yalan Hu1,2, Lorraine Soares De Oliveira3,4, Kim Falize1
1Endocrine Laboratory, Department of Laboratory Medicine, University of Amsterdam, Amsterdam, the Netherlands.
Background:
Mutations in TBL1X, part of the NCOR1/SMRT corepressor complex, were identified in patients with hereditary X-linked central congenital hypothyroidism and associated hearing loss. The role of TBL1X in thyroid hormone (TH) action, however, is incompletely understood. The aim of the present study was to investigate the role of TBL1X on T3-regulated gene expression in two human liver cell models.
Methods:
A human hepatoma cell line (HepG2) wherein TBL1X was downregulated using siRNAs, and human-induced pluripotent stem cell-derived hepatocytes (iHeps) generated from individuals with a TBL1X N365Y mutation. Both cell types were treated with increasing concentrations of T3. The expression of T3-regulated genes was measured by qPCR.
Results:
KLF9, CPT1A, and PCK1 mRNA expression were higher upon T3 stimulation in the HepG2 cells with decreased TBL1X expression compared to controls, while DIO1 mRNA expression was lower. Hemizygous TBL1X N365Y iHeps exhibited decreased expression of CPT1A, G6PC1, PCK1, FBP1, and ELOVL2 compared to cells with the heterozygous TBL1X N365Y allele, but KLF9 and HMGCS2 expression was unaltered.
Conclusion:
Downregulation of TBL1X in HepG2 cells and the TBL1X N365Y variant in iHeps have differential effects on T3-regulated gene expression. This suggests that TBL1X may play a gene context role in TH action.
Insights
TBL1X mutations are linked to hypothyroidism and hearing loss. This study shows TBL1X impacts thyroid hormone gene regulation differently depending on the cell type and specific mutation.
Area of Science:
- Endocrinology
- Molecular Biology
- Genetics
Background:
- Mutations in TBL1X, a component of the NCOR1/SMRT corepressor complex, are associated with X-linked central congenital hypothyroidism and hearing loss.
- The precise function of TBL1X in thyroid hormone (TH) action remains unclear.
- This research investigates TBL1X's role in regulating gene expression influenced by triiodothyronine (T3).
Purpose of the Study:
- To elucidate the role of TBL1X in T3-regulated gene expression.
- To compare the effects of TBL1X downregulation and a specific mutation (N365Y) on TH target genes in human liver cells.
Main Methods:
- Utilized a human hepatoma cell line (HepG2) with TBL1X downregulated via siRNA.
- Employed human-induced pluripotent stem cell-derived hepatocytes (iHeps) from individuals with a TBL1X N365Y mutation.
- Measured T3-regulated gene expression using quantitative PCR (qPCR) after T3 stimulation.
Main Results:
- In HepG2 cells, TBL1X downregulation led to increased KLF9, CPT1A, and PCK1 mRNA and decreased DIO1 mRNA expression following T3 stimulation.
- Hemizygous TBL1X N365Y iHeps showed reduced expression of CPT1A, G6PC1, PCK1, FBP1, and ELOVL2 compared to heterozygous cells.
- KLF9 and HMGCS2 expression remained unchanged in TBL1X N365Y iHeps.
Conclusions:
- TBL1X downregulation and the N365Y variant exhibit distinct effects on T3-regulated gene expression in different cellular contexts.
- These findings suggest TBL1X plays a context-dependent role in thyroid hormone action.
