A novel series of IKKβ inhibitors part II: description of a potent and pharmacologically active series of analogs

A novel series of (E)-1-((2-(1-methyl-1H-imidazol-5-yl) quinolin-4-yl) methylene) thiosemicarbazides was discovered as potent inhibitors of IKKβ. In this Letter we document our efforts at further optimization of this series, culminating in 2 with submicromolar potency in a HWB assay and efficacy in a CIA mouse model.     

Natural daucane sesquiterpenes with antiproliferative and proapoptotic activity against human tumor cells

Plants of the genera Ferula and Ferulago are known for their complex content in bioactive secondary metabolites such as coumarins, phenylpropanoids, and sesquiterpenes. We used the ground parts of Ferula communis subsp. communis, Ferula glauca subsp. glauca and Ferulago campestris as natural sources for the isolation of four coumarins (CU-1 to CU-4), two phenylpropanoids (PE-1 and PE-2), one polyacetylene (PA-1) and 16 daucane esters (DE-1 to DE-16). The cytotoxic activity of the isolated compounds was evaluated against a panel of seven human tumor cell lines. Fourteen of the daucane derivatives showed antiproliferative activity at least against one of the human tumor cell lines tested, four compounds (DE-5, DE-8, DE-11, and DE-16) were active against all the tested cell lines. Among them DE-11 was the most cytotoxic compound against HeLa (4.4 ± 0.7 μM), A549 (2.8 ± 1.4 μM), HL-60 (2.6 ± 0.4 μM), K562 (26.5 ± 6.0 μM) RS 4;11 (1.7 ± 0.3 μM) and SEM (2.4 ± 0.1 μM) cell lines, while DE-8 was the most active against Jurkat (3.3 ± 0.8 μM). Preliminary structure-activity relationship suggests that the most active compounds in the daucane series present the trans fusion of the penta- and hepta-atomic cycles, and lipophylic ester groups linked to position 6. Isomeric derivatives such as DE-8 and DE-9 or DE-3, DE-4, and DE-5 exhibited significant differences in their IC(50) supporting that the β orientation for the ester group in the position 2 enhances the cytotoxic activity. Furthermore, the pro-apoptotic effect of the most active compounds evaluated in Jurkat cell line showed that these compounds are able to induce apoptosis in a time and concentration-dependent manner. Our findings suggest the potential role of daucane derivatives as models for the development of proapoptotic compounds.     

Vitamin K does not prevent soft tissue mineralization in a mouse model of pseudoxanthoma elasticum

Pseudoxanthoma elasticum (PXE) is a heritable disease characterized by calcified elastic fibers in cutaneous, ocular and vascular tissues. PXE is caused by mutations in ABCC6, which encodes a protein of the ATP-driven organic anion transporter family. The inability of this transporter to secrete its substrate into the circulation is the likely cause of PXE. Vitamin K plays a role in the regulation of mineralization processes as a co-factor in the carboxylation of calcification inhibitors such as Matrix Gla Protein (MGP). Vitamin K precursor or a conjugated form has been proposed as potential substrate(s) for ABCC6. We investigated whether an enriched diet of vitamin K1 or vitamin K2 (MK4) could stop or slow the disease progression in Abcc6^-/- mice. Abcc6^-/- mice were placed on a diet of either vitamin K1 or MK4 at 5 or 100 mg/kg at prenatal, 3 weeks or 3 months of age. Disease progression was quantified by measuring the calcium content of one side of the mouse muzzle skin and histological staining for calcium of the opposing side. Raising the vitamin K1 or MK4 content of the diet increased the concentration of circulating MK4 in the serum. However, this increase did not significantly affect the MGP carboxylation status or reduce its abnormal abundance, the total calcium content or the pathologic calcification in the whiskers of the 3 treatment groups compared to controls. Our findings showed that raising the dietary intake of vitamin K1 or MK4 was not beneficial in the treatment of PXE and suggested that the availability of vitamin K may not be a limiting factor in this pathology.Key words: pseudoxanthoma elasticum, vitamin K, mineralization, Abcc6, mouse     

First experiences with semi-autonomous robotic harvesting of protein crystals

The demonstration unit of the Universal Micromanipulation Robot (UMR) capable of semi-autonomous protein crystal harvesting has been tested and evaluated by independent users. We report the status and capabilities of the present unit scheduled for deployment in a high-throughput protein crystallization center. We discuss operational aspects as well as novel features such as micro-crystal handling and drip-cryoprotection, and we extrapolate towards the design of a fully autonomous, integrated system capable of reliable crystal harvesting. The positive to enthusiastic feedback from the participants in an evaluation workshop indicates that genuine demand exists and the effort and resources to develop autonomous protein crystal harvesting robotics are justified.     

Robots, pipelines, polyproteins: enabling multiprotein expression in prokaryotic and eukaryotic cells

Multiprotein complexes catalyze vital biological functions in the cell. A paramount objective of the SPINE2 project was to address the structural molecular biology of these multiprotein complexes, by enlisting and developing enabling technologies for their study. An emerging key prerequisite for studying complex biological specimens is their recombinant overproduction. Novel reagents and streamlined protocols for rapidly assembling co-expression constructs for this purpose have been designed and validated. The high-throughput pipeline implemented at IGBMC Strasbourg and the ACEMBL platform at the EMBL Grenoble utilize recombinant overexpression systems for heterologous expression of proteins and their complexes. Extension of the ACEMBL platform technology to include eukaryotic hosts such as insect and mammalian cells has been achieved. Efficient production of large multicomponent protein complexes for structural studies using the baculovirus/insect cell system can be hampered by a stoichiometric imbalance of the subunits produced. A polyprotein strategy has been developed to overcome this bottleneck and has been successfully implemented in our MultiBac baculovirus expression system for producing multiprotein complexes.     

A genetic screen identifies BRCA2 and PALB2 as key regulators of G2 checkpoint maintenance

To identify key connections between DNA-damage repair and checkpoint pathways, we performed RNA interference screens for regulators of the ionizing radiation-induced G2 checkpoint, and we identified the breast cancer gene BRCA2. The checkpoint was also abrogated following depletion of PALB2, an interaction partner of BRCA2. BRCA2 and PALB2 depletion led to premature checkpoint abrogation and earlier activation of the AURORA A-PLK1 checkpoint-recovery pathway. These results indicate that the breast cancer tumour suppressors and homologous recombination repair proteins BRCA2 and PALB2 are main regulators of G2 checkpoint maintenance following DNA-damage.     

Expression and in vivo rescue of human ABCC6 disease-causing mutants in mouse liver

Loss-of-function mutations in ABCC6 can cause chronic or acute forms of dystrophic mineralization described in disease models such as pseudoxanthoma elasticum (OMIM 26480) in human and dystrophic cardiac calcification in mice. The ABCC6 protein is a large membrane-embedded organic anion transporter primarily found in the plasma membrane of hepatocytes. We have established a complex experimental strategy to determine the structural and functional consequences of disease-causing mutations in the human ABCC6. The major aim of our study was to identify mutants with preserved transport activity but failure in intracellular targeting. Five missense mutations were investigated: R1138Q, V1298F, R1314W, G1321S and R1339C. Using in vitro assays, we have identified two variants; R1138Q and R1314W that retained significant transport activity. All mutants were transiently expressed in vivo, in mouse liver via hydrodynamic tail vein injections. The inactive V1298F was the only mutant that showed normal cellular localization in liver hepatocytes while the other mutants showed mostly intracellular accumulation indicating abnormal trafficking. As both R1138Q and R1314W displayed endoplasmic reticulum localization, we tested whether 4-phenylbutyrate (4-PBA), a drug approved for clinical use, could restore their intracellular trafficking to the plasma membrane in MDCKII and mouse liver. The cellular localization of R1314W was significantly improved by 4-PBA treatment, thus potentially rescuing its physiological function. Our work demonstrates the feasibility of the in vivo rescue of cellular maturation of some ABCC6 mutants in physiological conditions very similar to the biology of the fully differentiated human liver and could have future human therapeutic application.     

De novo designed proteins from a library of artificial sequences function in Escherichia coli and enable cell growth

A central challenge of synthetic biology is to enable the growth of living systems using parts that are not derived from nature, but designed and synthesized in the laboratory. As an initial step toward achieving this goal, we probed the ability of a collection of >10(6) de novo designed proteins to provide biological functions necessary to sustain cell growth. Our collection of proteins was drawn from a combinatorial library of 102-residue sequences, designed by binary patterning of polar and nonpolar residues to fold into stable 4-helix bundles. We probed the capacity of proteins from this library to function in vivo by testing their abilities to rescue 27 different knockout strains of Escherichia coli, each deleted for a conditionally essential gene. Four different strains--ΔserB, ΔgltA, ΔilvA, and Δfes--were rescued by specific sequences from our library. Further experiments demonstrated that a strain simultaneously deleted for all four genes was rescued by co-expression of four novel sequences. Thus, cells deleted for ～0.1% of the E. coli genome (and ～1% of the genes required for growth under nutrient-poor conditions) can be sustained by sequences designed de novo.     

Sorting nexin 17 facilitates LRP recycling in the early endosome

The low-density lipoprotein (LDL) receptor-related protein (LRP) is a multiligand endocytic receptor and a member of the LDL receptor family. Here we show that sorting nexin 17 (Snx 17) is part of the cellular sorting machinery that regulates cell surface levels of LRP by promoting its recycling. While the phox (PX) domain of Snx 17 interacts with phosphatidylinositol-3-phosphate for membrane association, the FERM domain and the carboxyl-terminal region participate in LRP binding. Immunoelectron microscopy shows that the membrane-bound fraction of Snx 17 is localized to the limiting membrane and recycling tubules of early endosomes. The NPxY motif, proximal to the plasma membrane in the LRP cytoplasmic tail, is identified as the Snx 17-binding motif. Functional mutation of this motif did not interfere with LRP endocytosis, but decreased LRP recycling from endosomes, resulting in increased lysosomal degradation. Similar effects are found after knockdown of endogenous Snx 17 expression by short interfering RNA. We conclude that Snx 17 binds to a motif in the LRP tail distinct from the endocytosis signals and promotes LRP sorting to the recycling pathway in the early endosomes.