👤 Kento Yonezawa

Transglutaminase 2 (TG2) is a multifunctional protein that promotes or suppresses tumorigenesis, depending on intracellular location and conformational structure. Acyclic retinoid (ACR) is an orally administered vitamin A derivative that prevents hepatocellular carcinoma (HCC) recurrence by targeting liver cancer stem cells (CSCs). In this study, we examined the subcellular location-dependent effects of ACR on TG2 activity at a structural level and characterized the functional role of TG2 and its downstream molecular mechanism in the selective depletion of liver CSCs. A binding assay with high-performance magnetic nanobeads and structural dynamic analysis with native gel electrophoresis and size-exclusion chromatography-coupled multi-angle light scattering or small-angle X-ray scattering showed that ACR binds directly to TG2, induces oligomer formation of TG2, and inhibits the transamidase activity of cytoplasmic TG2 in HCC cells. The loss-of-function of TG2 suppressed the expression of stemness-related genes, spheroid proliferation and selectively induced cell death in an EpCAM+ liver CSC subpopulation in HCC cells. Proteome analysis revealed that TG2 inhibition suppressed the gene and protein expression of exostosin glycosyltransferase 1 (EXT1) and heparan sulfate biosynthesis in HCC cells. In contrast, high levels of ACR increased intracellular Ca Show less

Nobiletin (NOB), a functional ingredient found in citrus peel, is said to act against diabetes, obesity, and atherosclerosis. It has been reported to activate AMPK pathway, as well as increase SREBP1c, PPARα and PPARγ expression. However, no molecular mechanism has been elucidated to be able to integrate these sporadic findings with some controversies to lead to concrete outcomes. In this study, regulation of HDL biogenesis by NOB was investigated modulating ABCA1 and ABCG1 expression. Regulation of ABCA1/G1 by NOB was investigated in mouse macrophages J774.1. NOB increased mRNA and protein levels of ABCA1/G1, and cell cholesterol release by these factors. It also increased mRNA of PPARγ and LXRα but not PPARα. The increase in ABCA1/G1 mRNA levels by NOB was suppressed by antagonists of PPARγ and LXRα. The increase in PPARγ mRNA levels by NOB was suppressed by an LXRα antagonist, and the increase in LXRα mRNA levels was suppressed by a PPARγ antagonist. NOB increased CD36 mRNA and this was suppressed by an LXRα antagonist. The increase in ABCA1 mRNA by a PPARγ agonist was also suppressed by an LXRα antagonist. NOB did not influence LPL1 mRNA expression levels. NOB stimulated AMPK phosphorylation, and the increase in ABCA1/G1, LXRα and PPARγ mRNA levels and ABCA1/G1 protein levels by NOB was reversed by an AMPK inhibitor. AMPK siRNA suppressed ABCA1 expression. NOB activates AMPK and subsequently LXRα to promote the expression of ABCA1 and ABCG1, and an LXRα - PPARγ loop pathway amplifies these signals. Show less

LXRs, which are nuclear receptors, have 2 isoforms-LXRα and LXRβ. Generally, LXRα is expressed in the liver, kidney, and a limited number of other organs, whereas LXRβ is thought to be expressed ubiquitously. Nevertheless, no clear consensus has been reached on the role of each in kidney lipid metabolism. Many researchers have reported that lipids accumulate in renal tubular epithelial cells during nephrosis. The nephrosis model we used showed the presence of urinary protein 4 days after the induction of illness. Additionally, the model maintained high levels of urinary protein from day 7-14. Lipid accumulation was clearly verified at day 4 and extreme accumulation was observed at day 7. We observed increased expression of LXRα from an early stage of nephrosis. To explore the role of increased LXRα in diseased kidney in vitro, NRK52E, normal kidney tubular epithelial cells, were forced to overexpress LXRα. These cells showed significantly lower lipid accumulation than mock cells did. In contrast, LXRβ knockdown lead to increased lipid accumulation in mock cells, and constancy in overexpressing cells. In normal kidneys, LXRβ is expressed stably to control mainly the intracellular lipids. However, with increasing intracellular lipid accumulation, expression of LXRα and its downstream gene, ABCA1, was upregulated, followed by lipid excretion in an LXRα-dependent manner. This phenomenon strongly suggests the importance of LXRα in lipid metabolism in the diseased kidney. Show less

In a mice study, insulin suppressed apolipoprotein A-V (apoA-V) gene expression in a dose dependent manner. Thus, we investigated the association between apoA-V levels and dyslipidemias in obese children with hyperinsulinemia. The subjects were 17 obese children (15 male, 2 female) aged 11.8 ± 2.4 years. Total cholesterol (TC), high-density lipoprotein cholesterol (HDLC), triglyceride (TG), apoA-V and insulin levels were determined. Obese children with hyperinsulinemia had greater percent overweight, higher TG level, lower HDLC level and lower apoA-V level than those without hyperinsulinemia. In simple regression analysis, apoA-V level correlated negatively with TG (r = -0.613, p = 0.0152) and insulin levels (r = -0.566, p = 0.0279), and positively correlated with HDLC (r = 0.811, p = 0.0002). In stepwise regression analysis, insulin level emerged as the independent determinant of TG level after apoA-V level was taken into account, whereas apoA-V emerged as the independent determinant of HDLC level after adjusting for insulin level. Insulin may be a potent regulator of serum apoA-V level in obesity, and apoA-V level may partly contribute to the development of obesity-associated dyslipidemia. Show less