Niemann-Pick C1-Like 1: A Key Player in Intestinal Cholesterol Absorption

Niemann-Pick C1-Like 1 (NPC1-L1), as its name indicates, was identified in 2000 as a homolog of NPC1. Its major physiological function was clarified by a research group in Shöring’s laboratory who had long been searching for a target of ezetimibe, a cholesterol-lowering drug. They published a paper on 2004 in Science, reporting a reduction of intestinal cholesterol absorption and a lack of effects of ezetimibe in NPC1-L1 knockout mice. With subsequent studies that confirmed their findings, it is now clear that NPC1-L1 is a key player in one of the major pathways of intestinal cholesterol absorption and that it is the target of ezetimibe. This review summarizes what has been shown up to now about the structure and function of NPC1-L1. This review also refers to ABCG5/G8, a member of ABC family transporters, which co-localizes with NPC1-L1 on the intestinal epithelial cells and appears to work in a closely related manner

Hyperuricemia as a Risk Factor for Cardiovascular Diseases

Serum uric acid level above 7 mg/dl is defined as hyperuricemia, which gives rise to the monosodium urate (MSU), causing gout and urolithiasis. Hyperuricemia is an independent risk factor as well as a marker for hypertension, heart failure, atherosclerosis, atrial fibrillation, and chronic kidney disease. MSU crystals, soluble uric acid (UA), or oxidative stress derived from xanthine oxidoreductase (XOR) might be plausible explanations for the association of cardio-renovascular diseases with hyperuricemia. In macrophages, MSU activates the Nod-like receptor family, pyrin　domain containing 3(NLRP3) inflammasome, and proteolytic processing mediated by caspase-1 with enhanced interleukin (IL)-1β and IL-18 secretion. Soluble UA accumulates intracellularly through UA transporters (UAT) in vascular and atrial myocytes, causing endothelial dysfunction ad atrial electrical remodeling. XOR generates reactive oxygen species (ROS) that lead to cardiovascular diseases. Since it remains unclear whether asymptomatic hyperuricemia could be a risk factor for cardiovascular and kidney diseases, European and American guidelines do not recommend pharmacological treatment for asymptomatic patients with cardio-renovascular diseases. The Japanese guideline, on the contrary, recommends pharmacological treatment for hyperuricemia with CKD to protect renal function, and it attaches importance of the cardio-renal interaction for the treatment of asymptomatic hyperuricemia patients with hypertension and heart failure

Inhibitory effects of local anesthetics on the proteasome and their biological actions

Local anesthetics (LAs) inhibit endoplasmic reticulum-associated protein degradation, however the mechanisms remain elusive. Here, we show that the clinically used LAs pilsicainide and lidocaine bind directly to the 20S proteasome and inhibit its activity. Molecular dynamic calculation indicated that these LAs were bound to the β5 subunit of the 20S proteasome, and not to the other active subunits, β1 and β2. Consistently, pilsicainide inhibited only chymotrypsin-like activity, whereas it did not inhibit the caspase-like and trypsin-like activities. In addition, we confirmed that the aromatic ring of these LAs was critical for inhibiting the proteasome. These LAs stabilized p53 and suppressed proliferation of p53-positive but not of p53-negative cancer cells

Characterization of the novel mutant A78T-HERG from a long QT syndrome type 2 patient: Instability of the mutant protein and stabilization by heat shock factor 1

Background:The human ether-a-go-go-related gene (HERG) encodes the α-subunit of rapidly activating delayed-rectifier potassium channels. Mutations in this gene cause long QT syndrome type 2 (LQT2). In most cases, mutations reduce the stability of the channel protein, which can be restored by heat shock (HS). Methods: We identified the novel mutant A78T-HERG in a patient with LQT2. The purpose of the current study was to characterize this mutant protein and test whether HS and heat shock factors (HSFs) could stabilize the mutant protein. A78T-HERG and wild-type HERG (WT-HERG) were expressed in HEK293 cells and analyzed by immunoblotting, immunoprecipitation, immunofluorescence, and whole-cell patch clamping. Results: When expressed in HEK293 cells, WT-HERG gave rise to immature and mature forms of the protein at 135 and 155 kDa, respectively. A78T-HERG gave rise only to the immature form, which was heavily ubiquitinated. The proteasome inhibitor MG132 increased the expression of immature A78T-HERG and increased both the immature and mature forms of WT-HERG. WT-HERG, but not A78T-HERG, was expressed on the plasma membrane. In whole-cell patch clamping experiments, depolarizing pulses evoked E4031-sensitive HERG channel currents in cells transfected with WT-HERG, but not in cells transfected with A78T-HERG. The A78V mutant, but not A78G mutant, remained in the immature form similarly to A78T. Maturation of the A78T-HERG protein was facilitated by HS, expression of HSF-1, or exposure to geranyl geranyl acetone. Conclusions: A78T-HERG was characterized by protein instability and reduced expression on the plasma membrane. The stability of the mutant was partially restored by HSF-1, indicating that HSF-1 is a target for the treatment for LQT2 caused by the A78T mutation in HERG