SCAP ligands are potent new lipid-lowering drugs.

Upregulation of low-density lipoprotein receptor (LDLr) is a key mechanism to control elevated plasma LDL-cholesterol levels. Here we identify a new class of compounds that directly binds to the sterol regulatory element-binding protein (SREBP) cleavage-activating protein (SCAP). We show that a 14C-labeled, photo-activatable analog specifically labeled both SCAP and a truncated form of SCAP containing the sterol-sensing domain. When administered to hyperlipidemic hamsters, SCAP ligands reduced both LDL cholesterol and triglycerides levels by up to 80% with a three-fold increase in LDLr mRNA in the livers. Using human hepatoma cells, we show that these compounds act through the sterol-responsive element of the LDLr promoter and activate the SCAP/SREBP pathway, leading to increased LDLr expression and activity, even in presence of excess of sterols. These findings have led to the identification of a class of compounds that represent a promising new class of hypolipidemic drugs.     

Replication origins are already licensed in G1 arrested unfertilized sea urchin eggs

Fertilization relieves the oocyte from a cell cycle arrest, inducing progression towards mitotic cycles. While the signalling pathways involved in oocyte to embryo transition have been widely investigated, how they specifically trigger DNA replication is still unclear. We used sea urchin eggs whose oocytes are arrested in G1 to investigate in vivo the molecular mechanisms regulating initiation of replication after fertilization. Unexpectedly, we found that CDC6, Cdt1 and MCM3, components of the pre-replication complexes (pre-RC) which license origins for replication, were already loaded on female chromatin before fertilization. This is the first demonstration of a cell cycle arrest in metazoan in which chromatin is already licensed for replication. In contrast pre-RC assemble on chromatin post-fertilization as in other organisms. These differences in the timing of pre-RC assembly are accompanied by differences in Cdk2 requirement for DNA replication initiation between female and male chromatin post-fertilization. Finally, we demonstrated that a concomitant inhibition of MAP kinase and ATM/ATR pathways releases the block to DNA synthesis. Our findings provide new insight into the mechanisms contributing to the release of G1 arrest and the control of S-phase entry at fertilization.     

Inflammatory monocytes and neutrophils are licensed to kill during memory responses in vivo

Immunological memory is a hallmark of B and T lymphocytes that have undergone a previous encounter with a given antigen. It is assumed that memory cells mediate better protection of the host upon re-infection because of improved effector functions such as antibody production, cytotoxic activity and cytokine secretion. In contrast to cells of the adaptive immune system, innate immune cells are believed to exhibit a comparable functional effector response each time the same pathogen is encountered. Here, using mice infected by the intracellular bacterium Listeria monocytogenes, we show that during a recall bacterial infection, the chemokine CCL3 secreted by memory CD8+ T cells drives drastic modifications of the functional properties of several populations of phagocytes. We found that inflammatory ly6C+ monocytes and neutrophils largely mediated memory CD8+ T cell bacteriocidal activity by producing increased levels of reactive oxygen species (ROS), augmenting the pH of their phagosomes and inducing antimicrobial autophagy. These events allowed an extremely rapid control of bacterial growth in vivo and accounted for protective immunity. Therefore, our results provide evidence that cytotoxic memory CD8+ T cells can license distinct antimicrobial effector mechanisms of innate cells to efficiently clear pathogens.     

sir2 mutants of Kluyveromyces lactis are hypersensitive to DNA-targeting drugs.

A Kluyveromyces lactis mutant, hypersensitive to the DNA-targeting drugs ethidium bromide (EtBr), berenil, and HOE15030, can be complemented by a wild-type gene with homology to SIR2 of Saccharomyces cerevisiae (ScSIR2). The deduced amino acid sequence of the K. lactis Sir2 protein has 53% identity with ScSir2 protein but is 108 residues longer. K. lactis sir2 mutants show decreased mating efficiency, deficiency in sporulation, an increase in recombination at the ribosomal DNA locus, and EtBr-induced death. Some functional equivalence between the Sir2 proteins of K. lactis and S. cerevisiae has been demonstrated by introduction of ScSIR2 into a sir2 mutant of K. lactis. Expression of ScSIR2 on a multicopy plasmid restores resistance to EtBr and complements sporulation deficiency. Similarly, mating efficiency of a sir2 mutant of S. cerevisiae is partially restored by K. lactis SIR2 on a multicopy plasmid. Although these observations suggest that there has been some conservation of Sir2 protein function, a striking difference is that sir2 mutants of S. cerevisiae, unlike their K. lactis counterparts, are not hypersensitive to DNA-targeting drugs.