Nicotinic acid has, like the Roman God Janus, two faces. One is the vitamin. The other is the broad-spectrum lipid drug. The Canadian pathologist Rudolf Altschul discovered 50 years ago that nicotinic acid in gram doses lowered plasma levels of cholesterol. From the point of view of treatment of the dyslipidaemias that are risk factors for clinical atherosclerosis nicotinic acid is a miracle drug. It lowers the levels of all atherogenic lipoproteins--VLDL and LDL with subclasses as well as Lp(a)--and in addition it raises more than any other drug the levels of the protective HDL lipoproteins. Trials have shown that treatment with nicotinic acid reduces progression of atherosclerosis, and clinical events and mortality from coronary heart disease. The new combination treatment with statin-lowering LDL and nicotinic acid-raising HDL is reviewed. A basic effect of nicotinic acid is the inhibition of fat-mobilizing lipolysis in adipose tissue leading to a lowering of plasma free fatty acids, which has many metabolic implications which are reviewed. The very recent discovery of a nicotinic acid receptor and the finding that the drug stimulates the expression of the ABCA 1 membrane cholesterol transporter have paved the way for exciting and promising new 50 years in the history of nicotinic acid.

SUMMARY Current models of HIV-1 morphogenesis hold that newly synthesized viral Gag polyproteins traffic to and assemble at the cell membrane into spherical protein shells. The resulting late-budding structure is thought to be released by the cellular ESCRT machinery severing the membrane tether connecting it to the producer cell. Using electron tomography and scanning transmission electron microscopy, we find that virions have a morphology and composition distinct from late-budding sites. Gag is arranged as a continuous but incomplete sphere in the released virion. In contrast, late-budding sites lacking functional ESCRT exhibited a nearly closed Gag sphere. The results lead us to propose that budding is initiated by Gag assembly, but is completed in an ESCRT-dependent manner before the Gag sphere is complete. This suggests that ESCRT functions early in HIV-1 release—akin to its role in vesicle formation—and is not restricted to severing the thin membrane tether.

Structural studies have provided detailed insights into different functional states of the ribosome and its interaction with factors involved in nascent peptide folding, processing, and targeting. However, how the translational machinery is organized spatially in native cellular environments is not yet well understood. Here we have mapped individual ribosomes in electron tomograms of intact human cells by template matching and determined the average structure of the ribosome in situ. Characteristic features of active ribosomes in the cellular environment were assigned to the tRNA channel, elongation factors, and additional densities near the peptide tunnel. Importantly, the relative spatial configuration of neighboring ribosomes in the cell is clearly nonrandom. The preferred configurations are specific for active polysomes and were largely abrogated in puromycin-treated control cells. The distinct neighbor orientations found in situ resemble configurations of bacterial polysomes in vitro, indicating a conserved supramolecular organization with implications for nascent polypeptide folding.

The class III phosphatidylinositol 3-kinase complex I (PI3KC3-C1) that functions in early autophagy consists of the lipid kinase VPS34, the scaffolding protein VPS15, the tumor suppressor BECN1, and the autophagy-specific subunit ATG14. The structure of the ATG14-containing PI3KC3-C1 was determined by single-particle EM, revealing a V-shaped architecture. All of the ordered domains of VPS34, VPS15, and BECN1 were mapped by MBP tagging. The dynamics of the complex were defined using hydrogen–deuterium exchange, revealing a novel 20-residue ordered region C-terminal to the VPS34 C2 domain. VPS15 organizes the complex and serves as a bridge between VPS34 and the ATG14:BECN1 subcomplex. Dynamic transitions occur in which the lipid kinase domain is ejected from the complex and VPS15 pivots at the base of the V. The N-terminus of BECN1, the target for signaling inputs, resides near the pivot point. These observations provide a framework for understanding the allosteric regulation of lipid kinase activity.DOI: http://dx.doi.org/10.7554/eLife.05115.001

The metabolism of chylomicron remnants and VLDL was studied in healthy controls and normo-(NTG) and hypertriglyceridemic (HTG) patients with coronary artery disease after intake of an oral fat load. Specific determination of apo B-48 and B-100 enabled separation of the respective contribution of the two lipoprotein species. The postprandial plasma levels of small (Sf 20-60) and large (Sf 60-400) chylomicron remnants increased in controls and NTG patients. In contrast, only large chylomicron remnants increased in the HTG patients. An increase of large VLDL was seen in response to the oral fat load in all groups, whereas small VLDL were either unchanged in the controls and the NTG patients, or decreased in the HTG patient group. The whole plasma concentration of C apolipoproteins was essentially uninfluenced by the oral fat load, whereas the content in large triglyceride-rich lipoproteins paralleled the apo B elevations in controls and NTG patients. An even more prominent increase of apo B in large triglyceriderich lipoproteins in the HTG group was not accompanied by an increase of C apolipoproteins. These findings indicate that chylomicrons compete with VLDL for removal of triglycerides by lipoprotein lipase and that the postprandial metabolism of triglyceride-rich lipoproteins is severely defective in hypertriglyceridemia. (J. Clin. Invest. 1993.91:748-758.) Key words: chylomicron remnants * very low density lipoprotein -apolipoprotein B-48 * apolipoprotein B-100 * apolipoprotein C-I1

The ESCRTs catalyze reverse-topology scission from the inner face of membrane necks in HIV budding, multivesicular endosome biogenesis, cytokinesis, and other pathways. We encapsulated ESCRT-III subunits Snf7, Vps24, and Vps2, and the AAA+ ATPase Vps4 such that membrane nanotubes reflecting the correct topology of scission could be pulled from giant vesicles. Upon ATP release by photo-uncaging, this system was capable of generating forces within the nanotubes in a manner dependent upon Vps4 catalytic activity and Vps4 coupling to the ESCRT-III proteins. Imaging of scission revealed Snf7 and Vps4 puncta within nanotubes whose presence followed ATP release, correlated with force generation and nanotube constriction, and preceded scission. These observations directly verify long-standing predictions that ATP-hydrolyzing assemblies of ESCRT-III and Vps4 sever membranes.

Thirty-one consecutive unselected hyperlipidaemic patients were treated daily with 4 g of nicotinic acid for 6 weeks. The concentrations in serum of lipoprotein Lp(a), and the major lipoprotein classes, were determined before and after the treatment. Nicotinic acid significantly reduced the serum levels of Lp(a) in the whole patient group. Linear regression analysis showed a strong negative relationship between the percentage reduction of Lp(a) and the serum triglyceride level before treatment (r = -0.78), which implied that for patients with a serum triglyceride concentration above 7.5 mmol l-1 there was a rise of Lp(a). The average individual percentage decrease of the concentration of Lp(a) was calculated after the exclusion of four patients who had serum triglyceride levels above 10 mmol l-1. The decrease was 38% with a 95% confidence interval of 28-47%. The absolute decrease of Lp(a) was correlated with the pretreatment levels of Lp(a) (r = 0.91). Within the whole group of patients there was a linear relationship between the percentage decrease of Lp(a) and that of LDL cholesterol (r = 0.88). This latter strong relationship might be due to an inhibition of the synthesis of the protein common to the two lipoproteins, apolipoprotein B.

The structure of immature and mature HIV-1 particles has been analyzed in detail by cryo electron microscopy, while no such studies have been reported for cellular HIV-1 budding sites. Here, we established a system for studying HIV-1 virus-like particle assembly and release by cryo electron tomography of intact human cells. The lattice of the structural Gag protein in budding sites was indistinguishable from that of the released immature virion, suggesting that its organization is determined at the assembly site without major subsequent rearrangements. Besides the immature lattice, a previously not described Gag lattice was detected in some budding sites and released particles; this lattice was found at high frequencies in a subset of infected T-cells. It displays the same hexagonal symmetry and spacing in the MA-CA layer as the immature lattice, but lacks density corresponding to NC-RNA-p6. Buds and released particles carrying this lattice consistently lacked the viral ribonucleoprotein complex, suggesting that they correspond to aberrant products due to premature proteolytic activation. We hypothesize that cellular and/or viral factors normally control the onset of proteolytic maturation during assembly and release, and that this control has been lost in a subset of infected T-cells leading to formation of aberrant particles.