Clinical isolates of the modern Mycobacterium tuberculosis lineage 4 evade host defense in human macrophages through eluding IL-1\u3b2-induced autophagy article

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), has infected over 1.7 billion people worldwide and causes 1.4 million deaths annually. Recently, genome sequence analysis has allowed the reconstruction of Mycobacterium tuberculosis complex (MTBC) evolution, with the identification of seven phylogeographic lineages: four referred to as evolutionarily "ancient", and three "modern". The MTBC strains belonging to "modern" lineages appear to show enhanced virulence that may have warranted improved transmission in humans over ancient lineages through molecular mechanisms that remain to be fully characterized. To evaluate the impact of MTBC genetic diversity on the innate immune response, we analyzed intracellular bacterial replication, inflammatory cytokine levels, and autophagy response in human primary macrophages infected with MTBC clinical isolates belonging to the ancient lineages 1 and 5, and the modern lineage 4. We show that, when compared to ancient lineage 1 and 5, MTBC strains belonging to modern lineage 4 show a higher rate of replication, associated to a significant production of proinflammatory cytokines (IL-1\u3b2, IL-6, and TNF-\u3b1) and induction of a functional autophagy process. Interestingly, we found that the increased autophagic flux observed in macrophages infected with modern MTBC is due to an autocrine activity of the proinflammatory cytokine IL-1\u3b2, since autophagosome maturation is blocked by an interleukin-1 receptor antagonist. Unexpectedly, IL-1\u3b2-induced autophagy is not disadvantageous for the survival of modern Mtb strains, which reside within Rab5-positive phagosomal vesicles and avoid autophagosome engulfment. Altogether, these results suggest that autophagy triggered by inflammatory cytokines is compatible with a high rate of intracellular bacilli replication and may therefore contribute to the increased pathogenicity of the modern MTBC lineages

Control of Drosophila endocycles by E2F and CRL4(CDT2)

Endocycles are variant cell cycles comprised of DNA synthesis (S)- and gap (G)-phases but lacking mitosis1,2. Such cycles facilitate post-mitotic growth in many invertebrate and plant cells, and are so ubiquitous that they may account for up to half the world’s biomass3,4. DNA replication in endocycling Drosophila cells is triggered by cyclin E/cyclin dependent kinase 2 (CYCE/CDK2), but this kinase must be inactivated during each G-phase to allow the assembly of pre-Replication Complexes (preRCs) for the next S-phase5,6. How CYCE/CDK2 is periodically silenced to allow re-replication has not been established. Here, using genetic tests in parallel with computational modelling, we show that the endocycles of Drosophila are driven by a molecular oscillator in which the E2F1 transcription factor promotes CycE expression and S-phase initiation, S-phase then activates the CRL4CDT2 ubiquitin ligase, and this in turn mediates the destruction of E2F1 (ref. 7). We propose that it is the transient loss of E2F1 during S phases that creates the window of low Cdk activity required for preRC formation. In support of this model overexpressed E2F1 accelerated endocycling, whereas a stabilized variant of E2F1 blocked endocycling by deregulating target genes, including CycE, as well as Cdk1 and mitotic cyclins. Moreover, we find that altering cell growth by changing nutrition or target of rapamycin (TOR) signalling impacts E2F1 translation, thereby making endocycle progression growth-dependent. Many of the regulatory interactions essential to this novel cell cycle oscillator are conserved in animals and plants1,2,8, indicating that elements of this mechanism act in most growth-dependent cell cycles