Transcriptional activation by hepatocyte nuclear factor-4 in a cell-free system derived from rat liver nuclei

dHNF4 regulates lipid homeostasis and oogenesis in Drosophila melanogaster

The fly genome contains a single ortholog of the evolutionarily conserved transcription factor hepatocyte nuclear factor 4 (HNF4), a broadly and constitutively expressed member of the nuclear receptor superfamily. Like its mammalian orthologs, Drosophila HNF4 (dHNF4) acts as a critical regulator of fatty acid and glucose homeostasis. Because of its role in energy storage and catabolism, the insect fat body controls non-autonomous organs including the ovaries, where lipid metabolism is essential for oogenesis. The present paper used dHNF4 overexpression (OE) in the fat bodies and ovaries to investigate its potential roles in lipid homeostasis and oogenesis. When the developing fat body overexpressed dHNF4, animals exhibited reduced size and failed to pupariate, but no changes in body composition were observed. Conditional OE of dHNF4 in the adult fat body produced a reduction in triacylglycerol content and reduced oogenesis. Ovary-specific dHNF4 OE increased oogenesis and egg-laying, but reduced the number of adult offspring. The phenotypic effects on oogenesis that arise upon dHNF4 OE in the fat body or ovary may be due to its function in controlling lipid utilization.

Kbtbd11 contributes to adipocyte homeostasis through the activation of upstream stimulatory factor 1

The present study aimed to investigate the transcriptional regulation of Kbtbd11 in adipose tissue. To elucidate the physiological role of Kbtbd11 gene expression, adipose Kbtbd11 mRNA expression levels were estimated under various feeding states in wild-type mice. Kbtbd11 expression increased in a time-dependent manner in the adipose tissue in mice fed on chow diet, whereas the promotion of Kbtbd11 mRNA expression by refeeding was attenuated in mice fed on high-fat (HF) diet, suggesting the suppression of Kbtbd11 mRNA expression under HF diets and that changes in mRNA levels were associated with regulation of the transcription activity of Kbtbd11 by some transcription factors. To investigate the transcriptional regulation of Kbtbd11, the fragment upstream of either mouse Kbtbd11 or human KBTBD11 promoter was inserted into a luciferase vector. Luciferase reporter assays revealed that both mouse and human KBTBD11 promoter activity was increased by USF1. Direct USF1 binding to the Ebox in the Kbtbd11 promoter was confirmed by electrophoretic mobility shift and chromatin immunoprecipitation assays. In addition, the adipocyte differentiation marker levels increased instantly in Kbtbd11-overexpressing Usf1 knockdown cells than in Usf1 knockdown cells. These results imply an association of between Kbtbd11 with Usf1 expression and suggest the involvement of Kbtbd11 in a novel adipogenesis pathway.

A novel upstream transcription factor 1 target gene N4bp2l1 that regulates adipogenesis

N4BP2l1, which is highly expressed in oral squamous cell carcinoma, is associated with poor prognosis. However, N4bp2l1's role in adipogenesis remains unknown. We aimed to clarify the expression profile and transcriptional regulation of N4bp2l1 to elucidate the functions underlying the role of N4bp2l1 in adipocyte differentiation. Our results revealed that N4bp2l1 mRNA expression increased in 3T3-L1 cells in a differentiation-dependent manner. To investigate the transcriptional regulation of N4bp2l1, the 2-kb 5′ region upstream of the mouse N4bp2l1 promoter was cloned into a luciferase vector. Luciferase reporter assays indicated that USF1 induces the N4bp2l1 promoter activity. Electrophoretic mobility shift and chromatin immunoprecipitation assays confirmed that USF1 directly binds to the Ebox in the N4bp2l1 promoter. Furthermore, the expressions of adipocyte differentiation markers significantly decreased in N4bp2l1-knockdown cells compared with those in control cells. Our results demonstrated that N4bp2l1 is a novel USF1 target gene that may be involved in adipogenesis regulation.

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N4bp2l1 expression is increased in a differentiation-dependent manner in 3T3-L1.

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N4bp2l1 is a novel USF1 target gene.

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USF1 directly binds to the Ebox in the N4bp2l1 promoter.

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Inhibition of 3T3-L1 adipocyte differentiation by N4bp2l1 knockdown.

Transcriptional inhibition by a non-histone protein from low mobility group in homologous and heterologous in vitro systems

An acidic non-histone chromosomal protein of low mobility group (LMG) with pI of 5-5.5 and molecular weight of 160 kDa (named LMG160), has been isolated from rat liver nuclei and its inhibitory effect on transcription of DNA in vitro has been detected in a heterologous prokaryotic in vitro transcription system (T7 RNA polymerase) and also confirmed in the homologous cell-free system of rat liver nuclear extract. The results indicate that in the presence of non-histone protein LMG160, in vitro RNA synthesis represses in the both systems, which can suggest a functional role for this non-histone chromosomal protein.

LXXLL-related motifs in Dax-1 have target specificity for the orphan nuclear receptors Ad4BP/SF-1 and LRH-1

The orphan receptor Ad4BP/SF-1 (NR5A1) is a constitutive activator, and its activity is repressed by another orphan receptor, Dax-1 (NR0B1). In the present study, we investigated the molecular mechanisms underlying this repression by Dax-1. Yeast two-hybrid and transient-transfection assays confirmed the necessity of three LXXLL-related motifs in Dax-1 for interaction with and repression of Ad4BP/SF-1. In vitro pull-down experiments confirmed that Dax-1 interacts with Ad4BP/SF-1 and also with LRH-1 (NR5A2). The target specificity of the LXXLL-related motifs was indicated by the observations that Ad4BP/SF-1, ERalpha (NR3A1), LRH-1, ERR2 (NR3B2), and fly FTZ-F1 (NR5A3) interacted through their ligand binding domains with all the LXXLL-related motifs in Dax-1 whereas HNF4 (NR2A1) and RORalpha (NR1F1) did not. Transcriptional activities of the receptors whose DNA binding domains (DBDs) were replaced by the GAL4 DBD were repressed by Dax-1 to various levels, which correlated with the strength of interaction. Amino acid substitutions revealed that Ad4BP/SF-1 and LRH-1 preferentially interact with L(+1)XXLL-related motifs containing serine, tyrosine, serine, and threonine at positions -2, +2, +3, and +6, respectively. Taken together, our results indicate that the specificities of LXXLL-related motifs in Dax-1 based on their amino acid sequences play an important role in regulation of orphan receptors.

Competitive cofactor recruitment by orphan receptor hepatocyte nuclear factor 4alpha1: modulation by the F domain

For most ligand-dependent nuclear receptors, the status of endogenous ligand modulates the relative affinities for corepressor and coactivator complexes. It is less clear what parameters modulate the switch between corepressor and coactivator for the orphan receptors. Our previous work demonstrated that hepatocyte nuclear factor 4alpha1 (HNF4alpha1, NR2A1) interacts with the p160 coactivator GRIP1 and the cointegrators CBP and p300 in the absence of exogenously added ligand and that removal of the F domain enhances these interactions. Here, we utilized transient-transfection analysis to demonstrate repression of HNF4alpha1 activity by the corepressor silencing mediator of retinoid and thyroid receptors (SMRT) in several cell lines and on several HNF4alpha-responsive promoter elements. Glutathione S-transferase pulldown assays confirmed a direct interaction between HNF4alpha1 and receptor interaction domain 2 of SMRT. Loss of the F domain resulted in marked reduction of the ability of SMRT to interact with HNF4alpha1 in vitro and repress HNF4alpha1 activity in vivo, although the isolated F domain itself failed to interact with SMRT. Surprisingly, loss of both the A/B and F domains restored full repression by SMRT, suggesting involvement of both domains in the SMRT interaction. Finally, we show that when coexpressed along with HNF4alpha1 and GRIP1, CBP, or p300, SMRT can titer out HNF4alpha1-mediated transactivation in a dose-dependent manner and that this competition derives from mutually exclusive binding. Collectively, these results suggest that HNF4alpha can functionally interact with both a coactivator and a corepressor without altering the status of any putative ligand and that the presence of the F domain may play a role in discriminating between the different coregulators.