Tollip regulates proinflammatory responses to interleukin-1 and lipopolysaccharide

Activation of interleukin-1 (IL-1) receptor (IL-1R), Toll-like receptor 2 (TLR2), and TLR4 triggers NF-kappaB and mitogen-activated protein kinase (MAPK)-dependent signaling, thereby initiating immune responses. Tollip has been implicated as a negative regulator of NF-kappaB signaling triggered by these receptors in in vitro studies. Here, deficient mice were used to determine the physiological contribution of Tollip to immunity. NF-kappaB, as well as MAPK, signaling appeared normal in Tollip-deficient cells stimulated with IL-1beta or the TLR4 ligand lipopolysaccharide (LPS). Similarly, IL-1beta- and TLR-driven activation of dendritic cells and lymphocytes was indistinguishable from wild-type cells. In contrast, the production of the proinflammatory cytokines, IL-6 and tumor necrosis factor alpha was significantly reduced after IL-1beta and LPS treatment at low doses but not at lethal doses of LPS. Tollip therefore controls the magnitude of inflammatory cytokine production in response to IL-1beta and LPS.     

Life with a single isoform of Akt: mice lacking Akt2 and Akt3 are viable but display impaired glucose homeostasis and growth deficiencies

To address the issues of isoform redundancy and isoform specificity of the Akt family of protein kinases in vivo, we generated mice deficient in both Akt2 and Akt3. In these mice, only the Akt1 isoform remains to perform essential Akt functions, such as glucose homeostasis, proliferation, differentiation, and early development. Surprisingly, we found that Akt2(-/-) Akt3(-/-) and even Akt1(+/-) Akt2(-/-) Akt3(-/-) mice developed normally and survived with minimal dysfunctions, despite a dramatic reduction of total Akt levels in all tissues. A single functional allele of Akt1 appears to be sufficient for successful embryonic development and postnatal survival. This is in sharp contrast to the previously described lethal phenotypes of Akt1(-/-) Akt2(-/-) mice and Akt1(-/-) Akt3(-/-) mice. However, Akt2(-/-) Akt3(-/-) mice were glucose and insulin intolerant and exhibited an approximately 25% reduction in body weight compared to wild-type mice. In addition, we found substantial reductions in relative size and weight of the brain and testis in Akt2(-/-) Akt3(-/-) mice, demonstrating an in vivo role for both Akt2 and Akt3 in the determination of whole animal size and individual organ sizes.     

Autophagy controls IL-1beta secretion by targeting pro-IL-1beta for degradation

Autophagy is a key regulator of cellular homeostasis that can be activated by pathogen-associated molecules and recently has been shown to influence IL-1β secretion by macrophages. However, the mechanisms behind this are unclear. Here, we describe a novel role for autophagy in regulating the production of IL-1β in antigen-presenting cells. After treatment of macrophages with Toll-like receptor ligands, pro-IL-1β was specifically sequestered into autophagosomes, whereas further activation of autophagy with rapamycin induced the degradation of pro-IL-1β and blocked secretion of the mature cytokine. Inhibition of autophagy promoted the processing and secretion of IL-1β by antigen-presenting cells in an NLRP3- and TRIF-dependent manner. This effect was reduced by inhibition of reactive oxygen species but was independent of NOX2. Induction of autophagy in mice in vivo with rapamycin reduced serum levels of IL-1β in response to challenge with LPS. These data demonstrate that autophagy controls the production of IL-1β through at least two separate mechanisms: by targeting pro-IL-1β for lysosomal degradation and by regulating activation of the NLRP3 inflammasome.     

From inflammasomes to fevers, crystals and hypertension: how basic research explains inflammatory diseases

Pattern-recognition receptors, such as Toll-like receptors and NOD-like receptors (NLRs), are able through the recognition of pathogen-associated molecular patterns and danger-associated molecular patterns to sense microbe-dependent and microbe-independent danger and thereby initiate innate immune responses. In some autoinflammatory conditions, abnormalities in NLR signaling pathways are involved in pathogenesis, as exemplified by NOD2 mutations associated with Crohn's disease. Some other NLRs are components of the inflammasome, a caspase-1- and prointerleukin-1beta-activating complex. Clinical and experimental studies are beginning to reveal the central role of the inflammasome in innate immunity. Here, we focus on monogenic hereditary inflammatory diseases, such as Muckle-Wells syndrome, which are associated with mutations in proteins that modulate the activity of the inflammasome, and on some multifactorial disorders, such as Type 2 diabetes and hypertension.     

The membrane attack complex of complement: lipid insertion of tubular and nontubular polymerized C9

The membrane-restricted photoactivatable carbene generator 3-(trifluoromethyl)-3-(m-[125I]-iodophenyl)diazirine [Brunner, J., & Semenza, G. (1981) Biochemistry 20, 7174-7182] was used to label the subunits of the membrane attack complex of complement (C5b-9). C5b-9 complexes either were assembled from serum on erythrocyte membranes or were reconstituted from purified components on liposomes. After irradiation, most of the probe is bound to C9 independent of the membrane system used, indicating that the wall of the transmembrane channel is predominantly composed of C9. No difference was observed whether polymerized C9 was in the tubular or nontubular form [Podack, E. R., & Tschopp, J. (1983) J. Biol. Chem. 257, 15204-15212], showing that tubule closure is not essential for successful lipid insertion. The same label distribution between the two forms of polymerized C9 was obtained by analyzing zinc-polymerized C9 in the absence of C5b-8. Since the photoreactive probe reacted with at least two distinct polypeptide segments within C9, lipid interaction does not occur via a single segment of hydrophobic amino acids.     

PIDD orchestrates translesion DNA synthesis in response to UV irradiation

PIDD has been implicated in survival and apoptotic pathways in response to DNA damage, and a role for PIDD was recently identified in non-homologous end-joining (NHEJ) repair induced by γ-irradiation. Here, we present an interaction of PIDD with PCNA, first identified in a proteomics screen. PCNA has essential functions in DNA replication and repair following UV irradiation. Translesion synthesis (TLS) is a process that prevents UV irradiation-induced replication blockage and is characterized by PCNA monoubiquitination and interaction with the TLS polymerase eta (polη). Both of these processes are inhibited by p21. We report that PIDD modulates p21-PCNA dissociation, and promotes PCNA monoubiquitination and interaction with polη in response to UV irradiation. Furthermore, PIDD deficiency leads to a defect in TLS that is associated, both in vitro and in vivo, with cellular sensitization to UV-induced apoptosis. Thus, PIDD performs key functions upon UV irradiation, including TLS, NHEJ, NF-κB activation and cell death.