PCSK9 is a natural inhibitor of LDL receptor (LDLR) that binds the extracellular domain of LDLR and triggers its intracellular degradation. PCSK9 and LDLR are coordinately regulated at the transcriptional level by sterols through their promoter-imbedded sterol response elements (SRE) and co-induced by statins. Identification of regulatory networks modulating PCSK9 transcription is important for developing selective repressors of PCSK9 to improve statin efficacy by prolonging the up-regulation of LDLR. Interestingly, the plant-derived hypocholesterolemic compound berberine (BBR) up-regulates LDLR expression while down-regulating PCSK9. In our investigations to define mechanisms underlying the transcriptional suppression of PCSK9 by BBR in HepG2 cells, we have identified a highly conserved hepatocyte nuclear factor 1 (HNF1) binding site residing 28 bp upstream from SRE as a critical sequence motif for PCSK9 transcription and its regulation by BBR. Mutation of the HNF1 site reduced PCSK9 promoter activity >90%. A battery of functional assays identified HNF1α as the predominant trans-activator for PCSK9 gene working through this sequence motif. We further provide evidence suggesting that HNF1 site works cooperatively with SRE as HNF1 mutation significantly attenuated the activity of nuclear SREBP2 to transactivate PCSK9 promoter. Finally, we show that a coordinate modest reduction of HNF1α and nuclear SREBP2 by BBR led to a strong suppression of PCSK9 transcription through these two critical regulatory sequences. This is the first described example of SREBP pairing with HNF1 to control an important regulatory pathway in cholesterol homeostasis. This work also provides a mechanism for how BBR suppresses PCSK9 transcription.

Aryl hydrocarbon receptor (AhR) activation by 2,3,7,8-tetrachlorodibenzio-p-dioxin (TCDD) leads to immune suppression associated with the induction of regulatory T cells (T reg ) expressing the transcription factor Foxp3. The immunological mechanisms of suppression are not well understood however dendritic cells (DC) are considered a key target for AhR-mediated immune suppression. Here we show that activation of AhR by TCDD induces DC indoleamine-2,3-dioxygenase 1 (IDO1) and indoleamine 2,3-dioxygenase-like protein (IDO2). Induction of IDO1 and IDO2 was also found in lung and spleen associated with an increase of the T reg marker Foxp3 in spleen of TCDD-treated C57BL/6 mice, which is suppressed by inhibition of IDO. These data indicate that AhR-activation is an important signaling pathway for IDO expression and suggest a critical role of IDO in the mechanism leading to the generation of T reg that mediates the immune suppression through activation of AhR.

This article is available online at http://www.jlr.org effect of statins in dyslipidemic hamsters. J. Lipid Res . 2010. 51: 1486-1495. Supplementary key words LDL receptor • rosuvastatin • berberineThe number of LDL receptors (LDLR) expressed on the surface of hepatocytes is a primary determinant for plasma LDL-cholesterol (LDL-C) levels ( 1 ). Hepatic LDLR mediates the uptake of LDL particles from the circulation and delivers the receptor-bound LDL to the endosomal system for degradation while the LDLR returns to the cell surface. Statins are competitive inhibitors of HMG-CoA reductase, the rate-limiting enzyme in the cellular cholesterol biosynthetic pathway. The inhibition of cholesterol de novo synthesis leads to increased numbers of cell surface LDLR by activation of LDLR gene transcription. Thus, statins are the most widely prescribed drugs to treat hypercholesterolemia and combined hyperlipidemia.Contrary to human studies in which statins effectively lower plasma total cholesterol (TC) and LDL-C, in animal studies, the LDL reducing effects of statins exhibit great species differences. Statins reduce plasma TC and LDL-C as the major drug action in rabbits, miniature pigs, dogs, monkeys, and guinea pigs ( 2-4 ) but not in rodents such as rats and hamsters ( 5-7 ). In rats and hamsters fed either a Abstract We investigated the role of proprotein convertase subtilisin/kexin type 9 (PCSK9) in the resistance of dyslipidemic hamsters to statin-induced LDL-cholesterol (LDL-C) reduction and the molecular mechanism by which statins modulated PCSK9 gene expression in vivo. We utilized the fructose diet-induced dyslipidemic hamsters as an in vivo model and rosuvastatin to examine its effects on liver PCSK9 and LDL receptor (LDLR) expression and serum lipid levels. We showed that rosuvastatin induced PCSK9 mRNA to a greater extent than LDLR mRNA in the hamster liver. The net result was that hepatic LDLR protein level was reduced. This correlated closely with an increase in serum LDL-C with statin treatment. More importantly, we demonstrated that in addition to an increase in sterol response element binding protein 2 (SREBP2) expression, rosuvastatin treatment increased the liver expression of hepatocyte nuclear factor 1 ␣ (HNF1 ␣ ), the newly identifi ed key transactivator for PCSK9 gene expression. Our study suggests that the inducing effect of rosuvastatin on HNF1 ␣ is likely a underlying mechanism accounting for the higher induction of PCSK9 than LDLR because of the utilization of two transactivators (HNF1 ␣ and SREBP2) in PCSK9 transcription versus one (SREBP2) in LDLR transcription. Thus, the net balance is in favor of PCSK9-induced degradation of LDLR in the hamster liver, abrogating the effect of rosuvastatin on LDL-C lowering. Press, January 4, 2010 DOI 10.1194 Abbreviations: BBR, berberine; HNF1, hepatocyte nuclear factor 1; LDL-C, LDL-cholesterol; LDLR, LDL receptor; PCSK9, proprotein convertase subtilisin/kexin type 9; SREBP, sterol response element binding protein; TC , total cholesterol; TG, triglyceri...

Metal-semiconductor heterostructures are promising visible light photocatalysts for many chemical reactions. Here, we use high-resolution superlocalization imaging to reveal the nature and photocatalytic properties of the surface reactive sites on single Au-CdS hybrid nanocatalysts. We experimentally reveal two distinct, incident energy-dependent charge separation mechanisms that result in completely opposite photogenerated reactive sites (e(-) and h(+)) and divergent energy flows on the hybrid nanocatalysts. We find that plasmon-induced hot electrons in Au are injected into the conduction band of the CdS semiconductor nanorod. The specifically designed Au-tipped CdS heterostructures with a unique geometry (two Au nanoparticles at both ends of each CdS nanorod) provide more convincing high-resolution single-turnover mapping results and clearly prove the two charge separation mechanisms. Engineering the direction of energy flow at the nanoscale can provide an efficient way to overcome important challenges in photocatalysis, such as controlling catalytic activity and selectivity. These results bear enormous potential impact on the development of better visible light photocatalysts for solar-to-chemical energy conversion.