[Show abstract][Hide abstract] ABSTRACT: Liver X receptor (LXR) activation stimulates triglyceride (TG) accumulation in the liver. Several lines of evidence indicate that estradiol-17β (E2) reduces TG levels in the liver; however, the molecular mechanism underlying the E2 effect remains unclear. Here, we show that administration of E2 attenuated sterol regulatory element-binding protein (SREBP)-1 expression and TG accumulation induced by LXR activation in mouse liver. In estrogen receptor alpha (ERα) knockout (KO) and liver-specific ERα KO mice, E2 did not affect SREBP-1 expression or TG levels. Molecular analysis revealed that ERα is recruited to the SREBP-1c promoter through direct binding to LXR and inhibits coactivator recruitment to LXR in an E2-dependent manner. Our findings demonstrate the existence of a novel liver-dependent mechanism controlling TG accumulation through the nonclassical ER/LXR pathway. To confirm that a nonclassical ER/LXR pathway regulates ERα-dependent inhibition of LXR activation, we screened ERα ligands that were able to repress LXR activation without enhancing ERα transcriptional activity, and, as a result, we identified the phytoestrogen, phloretin. In mice, phloretin showed no estrogenic activity; however, it did reduce SREBP-1 expression and TG levels in liver of mice fed a high-fat diet to an extent similar to that of E2. Conclusion: We propose that ER ligands reduce TG levels in the liver by inhibiting LXR activation through a nonclassical pathway. Our results also indicate that the effects of ER on TG accumulation can be distinguished from its estrogenic effects by a specific ER ligand. (Hepatology 2013)
[Show abstract][Hide abstract] ABSTRACT: Ribosome biosynthesis is a major intracellular energy-consuming process. We previously identified a nucleolar factor, nucleomethylin (NML), which regulates intracellular energy consumption by limiting rRNA transcription. Here, we show that, in livers of obese mice, the recruitment of NML to rRNA gene loci is increased to repress rRNA transcription. To clarify the relationship between obesity and rRNA transcription, we generated NML-null (NML-KO) mice. NML-KO mice show elevated rRNA level, reduced ATP concentration, and reduced lipid accumulation in the liver. Furthermore, in high-fat-diet (HFD)-fed NML-KO mice, hepatic rRNA levels are not decreased. Both weight gain and fat accumulation in HFD-fed NML-KO mice are significantly lower than those in HFD-fed wild-type mice. These findings indicate that rRNA transcriptional activation promotes hepatic energy consumption, which alters hepatic lipid metabolism. Namely, hepatic rRNA transcriptional repression by HFD feeding is essential for energy storage.
[Show abstract][Hide abstract] ABSTRACT: The TGF-β superfamily comprises pleiotropic cytokines that regulate SMAD and non-SMAD signaling. TGF-β-SMAD signal transduction is known to be involved in tissue fibrosis, including renal fibrosis. Here, we found that 1,25-dihydroxyvitamin D3-bound [1,25(OH)2D3-bound] vitamin D receptor (VDR) specifically inhibits TGF-β-SMAD signal transduction through direct interaction with SMAD3. In mouse models of tissue fibrosis, 1,25(OH)2D3 treatment prevented renal fibrosis through the suppression of TGF-β-SMAD signal transduction. Based on the structure of the VDR-ligand complex, we generated 2 synthetic ligands. These ligands selectively inhibited TGF-β-SMAD signal transduction without activating VDR-mediated transcription and significantly attenuated renal fibrosis in mice. These results indicate that 1,25(OH)2D3-dependent suppression of TGF-β-SMAD signal transduction is independent of VDR-mediated transcriptional activity. In addition, these ligands did not cause hypercalcemia resulting from stimulation of the transcriptional activity of the VDR. Thus, our study provides a new strategy for generating chemical compounds that specifically inhibit TGF-β-SMAD signal transduction. Since TGF-β-SMAD signal transduction is reportedly involved in several disorders, our results will aid in the development of new drugs that do not cause detectable adverse effects, such as hypercalcemia.
The Journal of clinical investigation 10/2013; 123(11). DOI:10.1172/JCI67804 · 13.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Estrogen receptor alpha (ERα) expression is a risk factor for breast cancer. HDAC inhibitors have been demonstrated to down-regulate ERα expression in ERα-positive breast cancer cell lines, but the molecular mechanisms are poorly understood. Here, we showed that HDAC inhibitors decrease the stability of ERα mRNA, and that knockdown of HDAC3 decreases the stability of ERα mRNA and suppresses estrogen-dependent proliferation of ERα-positive MCF-7 breast cancer cells. In the Oncomine database, expression levels of HDAC3 in ERα-positive tumors are higher than those in ERα-negative tumors, thus suggesting that HDAC3 is necessary for ERα mRNA stability, and is involved in the estrogen-dependent proliferation of ERα-positive tumors.
Biochemical and Biophysical Research Communications 02/2013; 432(2). DOI:10.1016/j.bbrc.2013.02.007 · 2.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In the adult hippocampus dentate gyrus (DG), newly born neurons are functionally integrated into existing circuits and play important roles in hippocampus-dependent memory. However, it remains unclear how neural plasticity regulates the integration pattern of new neurons into preexisting circuits. Because dendritic spines are major postsynaptic sites for excitatory inputs, spines of new neurons were visualized by retrovirus-mediated labeling to evaluate integration. Long-term potentiation (LTP) was induced at 12, 16, or 21 days postinfection (dpi), at which time new neurons have no, few, or many spines, respectively. The spine expression patterns were investigated at one or two weeks after LTP induction. Induction at 12 dpi increased later spinogenesis, although the new neurons at 12 dpi didn't respond to the stimulus for LTP induction. Induction at 21 dpi transiently mediated spine enlargement. Surprisingly, LTP induction at 16 dpi reduced the spine density of new neurons. All LTP-mediated changes specifically appeared within the LTP-induced layer. Therefore, neural plasticity differentially regulates the integration of new neurons into the activated circuit, dependent on their developmental stage. Consequently, new neurons at different developmental stages may play distinct roles in processing the acquired information by modulating the connectivity of activated circuits via their integration.
PLoS ONE 09/2012; 7(9):e45270. DOI:10.1371/journal.pone.0045270 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: During permanent memory formation, recall of acquired place memories initially depends on the hippocampus and eventually become hippocampus-independent with time. It has been suggested that the quality of original place memories also transforms from a precise form to a less precise form with similar time course. The question arises of whether the quality of original place memories is determined by brain regions on which the memory depends.
To directly test this idea, we introduced a new procedure: a non-associative place recognition memory test in mice. Combined with genetic and pharmacological approaches, our analyses revealed that place memory is precisely maintained for 28 days, although the recall of place memory shifts from hippocampus-dependent to hippocampus-independent with time. Moreover, the inactivation of the hippocampal function does not inhibit the precision of remote place memory.
These results indicate that the quality of place memories is not determined by brain regions on which the memory depends.
[Show abstract][Hide abstract] ABSTRACT: Protein ubiquitination is a post-translational protein modification that regulates many biological conditions. Trip12 is a HECT-type E3 ubiquitin ligase that ubiquitinates ARF and APP-BP1. However, the significance of Trip12 in vivo is largely unknown. Here we show that the ubiquitin ligase activity of Trip12 is indispensable for mouse embryogenesis. A homozygous mutation in Trip12 (Trip12(mt/mt)) that disrupts the ubiquitin ligase activity resulted in embryonic lethality in the middle stage of development. Trip12(mt/mt) embryos exhibited growth arrest and increased expression of the negative cell cycle regulator p16. In contrast, Trip12(mt/mt) ES cells were viable. They had decreased proliferation, but maintained both the undifferentiated state and the ability to differentiate. Trip12(mt/mt) ES cells had increased levels of the BAF57 protein (a component of the SWI/SNF chromatin remodeling complex) and altered gene expression patterns. These data suggest that Trip12 is involved in global gene expression and plays an important role in mouse development.
PLoS ONE 10/2011; 6(10):e25871. DOI:10.1371/journal.pone.0025871 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Clinical evidence suggests that antiestrogens inhibit the development of androgen-insensitive prostate cancer. Here, we show that the estrogen receptor β (ERβ) mediates inhibition by the antiestrogen ICI 182,780 (ICI) and its enhancement by estrogen. ERβ associated with gene promoters through the tumor-suppressing transcription factor KLF5 (Krüppel-like zinc finger transcription factor 5). ICI treatment increased the recruitment of the transcription coactivator CBP [CREB (adenosine 3',5'-monophosphate response element-binding protein)-binding protein] to the promoter of FOXO1 through ERβ and KLF5, which enhanced the transcription of FOXO1. The increase in FOXO1 abundance led to anoikis in prostate cancer cells, thereby suppressing tumor growth. In contrast, estrogen induced the formation of complexes containing ERβ, KLF5, and the ubiquitin ligase WWP1 (WW domain containing E3 ubiquitin protein ligase 1), resulting in the ubiquitination and degradation of KLF5. The combined presence of KLF5 and ERβ positively correlated with longer cancer-specific survival in prostate cancer patients. Our results demonstrate that estrogens and antiestrogens affect prostate tumor growth through ERβ-mediated regulation of KLF5.
[Show abstract][Hide abstract] ABSTRACT: In response to a shortage of intracellular energy, mammalian cells reduce energy consumption and induce cell cycle arrest, both of which contribute to cell survival. Here we report that a novel nucleolar pathway involving the energy-dependent nucleolar silencing complex (eNoSC) and Myb-binding protein 1a (MYBBP1A) is implicated in these processes. Namely, in response to glucose starvation, eNoSC suppresses rRNA transcription, which results in a reduction in nucleolar RNA content. As a consequence, MYBBP1A, which is anchored to the nucleolus via RNA, translocates from the nucleolus to the nucleoplasm. The translocated MYBBP1A induces acetylation and accumulation of p53 by enhancing the interaction between p300 and p53, which eventually leads to the cell cycle arrest (or apoptosis). Taken together, our results indicate that the nucleolus works as a sensor that transduces the intracellular energy status into the cell cycle machinery.
[Show abstract][Hide abstract] ABSTRACT: A number of external and internal insults disrupt nucleolar structure, and the resulting nucleolar stress stabilizes and activates p53. We show here that nucleolar disruption induces acetylation and accumulation of p53 without phosphorylation. We identified three nucleolar proteins, MYBBP1A, RPL5, and RPL11, involved in p53 acetylation and accumulation. MYBBP1A was tethered to the nucleolus through nucleolar RNA. When rRNA transcription was suppressed by nucleolar stress, MYBBP1A translocated to the nucleoplasm and facilitated p53-p300 interaction to enhance p53 acetylation. We also found that RPL5 and RPL11 were required for rRNA export from the nucleolus. Depletion of RPL5 or RPL11 blocked rRNA export and counteracted reduction of nucleolar RNA levels caused by inhibition of rRNA transcription. As a result, RPL5 or RPL11 depletion inhibited MYBBP1A translocation and p53 activation. Our observations indicated that a dynamic equilibrium between RNA generation and export regulated nucleolar RNA content. Perturbation of this balance by nucleolar stress altered the nucleolar RNA content and modulated p53 activity.
The EMBO Journal 02/2011; 30(6):1054-66. DOI:10.1038/emboj.2011.23 · 10.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Neurogenesis occurs in the adult hippocampus of various animal species. A substantial fraction of newly generated neurons die before they mature, and the survival rate of new neurons are regulated in an experience-dependent manner. Previous study showed that high-frequency stimulation (HFS) of perforant path fibers to the hippocampal dentate gyrus (DG) induces the long-term potentiation (LTP) in the DG, and enhances the survival of newly generated neurons in the DG. In this study, we addressed whether a time period exists during which the survival of new neurons is maximally sensitive to the HFS. We found that the enhancement of cell survival by HFS was exclusively restricted to the specific narrow period during immature stages of new neurons (7-10 days after birth). Furthermore, the pharmacological blockade of LTP induction suppressed the enhancement of cell survival by the HFS. These results suggest that the LTP induction within a narrow critical period of immature stages enhances the survival of newly generated neurons in rat DG.
[Show abstract][Hide abstract] ABSTRACT: A recent study has revealed that fear memory may be vulnerable following retrieval, and is then reconsolidated in a protein synthesis-dependent manner. However, little is known about the molecular mechanisms of these processes. Activin betaA, a member of the TGF-beta superfamily, is increased in activated neuronal circuits and regulates dendritic spine morphology. To clarify the role of activin in the synaptic plasticity of the adult brain, we examined the effect of inhibiting or enhancing activin function on hippocampal long-term potentiation (LTP). We found that follistatin, a specific inhibitor of activin, blocked the maintenance of late LTP (L-LTP) in the hippocampus. In contrast, administration of activin facilitated the maintenance of early LTP (E-LTP). We generated forebrain-specific activin- or follistatin-transgenic mice in which transgene expression is under the control of the Tet-OFF system. Maintenance of hippocampal L-LTP was blocked in the follistatin-transgenic mice. In the contextual fear-conditioning test, we found that follistatin blocked the formation of long-term memory (LTM) without affecting short-term memory (STM). Furthermore, consolidated memory was selectively weakened by the expression of follistatin during retrieval, but not during the maintenance phase. On the other hand, the maintenance of memory was also influenced by activin overexpression during the retrieval phase. Thus, the level of activin in the brain during the retrieval phase plays a key role in the maintenance of long-term memory.