Article

The Critical Role of mRNA Destabilizing Protein Heterogeneous Nuclear Ribonucleoprotein D in 3' Untranslated Region-Mediated Decay of Low-Density Lipoprotein Receptor mRNA in Liver Tissue.

and Department of Medicine, Stanford University, CA (A.B.S., H.L., B.D., M.R.N.).
Arteriosclerosis Thrombosis and Vascular Biology (Impact Factor: 6.34). 10/2013; DOI: 10.1161/ATVBAHA.112.301131
Source: PubMed

ABSTRACT Previous studies showed that low-density lipoprotein receptor (LDLR) mRNA 3' untranslated region (UTR) contains regulatory elements responsible for rapid mRNA turnover in hepatic cells and mediates the mRNA stabilization induced by berberine (BBR). Here, we elucidate the underlying mechanism of BBR's action by characterizing mRNA-binding proteins that modulate LDLR mRNA decay via 3'UTR in liver tissue in vivo.
We generated a transgenic mouse model (Alb-Luc-UTR) that expresses Luc-LDLR3'UTR reporter gene driven by the albumin promoter to study 3'UTR function in mediating LDLR mRNA decay in liver tissue. We show that treating Alb-Luc-UTR mice with BBR led to significant increases in hepatic bioluminescence signals, Luc-UTR mRNA, and LDLR mRNA levels as compared with control mice. These effects were accompanied by specific reductions of mRNA decay-promoting factor heterogeneous nuclear ribonucleoprotein D (hnRNP D) in liver of BBR-treated mice. Knockdown and overexpression studies further demonstrated that hnRNP D p37 isoform plays a major role in promoting hepatic LDLR mRNA degradation. In addition, we examined LDLR mRNA half-life, Luc-UTR reporter activity, and hnRNP D expression levels in cell lines derived from extrahepatic tissues. We demonstrated that strengths of 3'UTR in promoting mRNA degradation correlate with hnRNP D cellular abundances in nonhepatic cell lines, thereby suggesting its involvement in LDLR mRNA degradation beyond liver tissue.
hnRNP D is critically involved in LDLR mRNA degradation in liver tissue in vivo. The inverse relationship of hnRNP D abundance with LDLR mRNA levels after BBR treatment suggests the potential of hnRNP D of being a novel therapeutic target for LDL cholesterol lowering.

0 Bookmarks
 · 
109 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: It is well established that over accumulation of dietary cholesterol in liver inhibits SREBP-mediated LDL receptor (LDLR) gene transcription leading to a reduced hepatic LDLR mRNA level in hypercholesterolemic animals. However, it is unknown whether elevated cholesterol levels could elicit a cellular response to increase LDLR mRNA turnover to further repress LDLR expression in liver tissue. In the current study, we examined the effect of high cholesterol diet on the hepatic expression of LDLR mRNA binding proteins in 3 different animal models and in cultured hepatic cells. Our results demonstrate that high cholesterol feeding specifically elevates the hepatic expression of LDLR mRNA decay promoting factor HNRNPD without affecting expressions of other LDLR mRNA binding proteins in vivo and in vitro. Employing the approach of adenovirus-mediated gene knockdown, we further show that depletion of HNRNPD in liver results in a marked reduction of serum LDL-cholesterol and a substantial increase in liver LDLR expression in hyperlipidemic mice. Additional studies of gene knockdown in Alb-Luc-UTR transgenic mice provide strong evidence supporting the essential role of 3'UTR in HNRNPD-mediated LDLR mRNA degradation in liver tissue. Altogether, this work identifies a novel posttranscriptional regulatory mechanism by which dietary cholesterol inhibits liver LDLR expression via inducing HNRNPD to accelerate LDLR mRNA degradation.
    The Journal of Lipid Research 05/2014; · 4.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Berberine is a plant alkaloid with anti-diabetic action. Activation of AMP-activated protein kinase (AMPK) pathway has been proposed as mechanism for berberine's action. This study aimed to examine whether AMPK activation was necessary for berberine's glucose-lowering effect. We found that in HepG2 hepatocytes and C2C12 myotubes, berberine significantly increased glucose consumption and lactate release in a dose-dependent manner. AMPK and acetyl coenzyme A synthetase (ACC) phosphorylation were stimulated by 20 µmol/L berberine. Nevertheless, berberine was still effective on stimulating glucose utilization and lactate production, when the AMPK activation was blocked by (1) inhibition of AMPK activity by Compound C, (2) suppression of AMPKα expression by siRNA, and (3) blockade of AMPK pathway by adenoviruses containing dominant-negative forms of AMPKα1/α2. To test the effect of berberine on oxygen consumption, extracellular flux analysis was performed in Seahorse XF24 analyzer. The activity of respiratory chain complex I was almost fully blocked in C2C12 myotubes by berberine. Metformin, as a positive control, showed similar effects as berberine. These results suggest that berberine and metformin promote glucose metabolism by stimulating glycolysis, which probably results from inhibition of mitochondrial respiratory chain complex I, independent of AMPK activation.
    PLoS ONE 07/2014; 9(7):e103702. · 3.53 Impact Factor
  • Arteriosclerosis Thrombosis and Vascular Biology 09/2014; 34(9):1791-4. · 5.53 Impact Factor

Full-text

Download
28 Downloads
Available from
Oct 22, 2014