Differential roles for the interferon-inducible IFI16 and AIM2 innate immune sensors for cytosolic DNA in cellular senescence of human fibroblasts

The IFN-inducible IFI16 and AIM2 proteins act as innate immune sensors for cytosolic double-stranded DNA (dsDNA). On sensing dsDNA, the IFI16 protein induces the expression of IFN-β whereas the AIM2 protein forms an inflammasome, which promotes the secretion of IL-1β. Given that the knockdown of IFI16 expression in human diploid fibroblasts (HDF) delays the onset of cellular senescence, we investigated the potential roles for the IFI16 and AIM2 proteins in cellular senescence. We found that increased IFI16 protein levels in old (vs. young) HDFs were associated with the induction of IFN-β. In contrast, increased levels of the AIM2 protein in the senescent (vs. old) HDFs were associated with increased production of IL-1β. The knockdown of type I IFN-α receptor subunit, which reduced the basal levels of the IFI16 but not of the AIM2, protein delayed the onset of cellular senescence. Accordingly, increased constitutive levels of IFI16 and AIM2 proteins in ataxia telangiectasia mutated (ATM) HDFs were associated with the activation of the IFN signaling and increased levels of IL-1β. The IFN-β treatment of the young HDFs, which induced the expression of IFI16 and AIM2 proteins, activated a DNA damage response and also increased basal levels of IL-1β. Interestingly, the knockdown of AIM2 expression in HDFs increased the basal levels of IFI16 protein and activated the IFN signaling. In contrast, the knockdown of the IFI16 expression in HDFs decreased the basal and dsDNA-induced activation of the IFN signaling. Collectively, our observations show differential roles for the IFI16 and AIM2 proteins in cellular senescence and associated secretory phenotype.     

Rab11 is required for tubulogenesis of Malpighian tubules in Drosophila melanogaster

Intracellular vesicular trafficking is one of the important tools in maintaining polarity, adhesion, and shape of epithelial cells. Rab11, a subfamily of the Ypt/Rab gene family of ubiquitously expressed GTPases and a molecular marker of recycling endosomes, transports different components of plasma membrane. Here, we report that Rab11 affects tubulogenesis of Malpighian tubules (MTs). MTs are simple polarized epithelial tubular structures, considered as functional analogue of human kidney. Rab11 has pleiotropic effects on MTs development as down‐regulation of Rab11 in principal cells (PCs) of MTs from embryonic stages of development results in reduced endoreplication, clustering of cells, disorganized cytoskeleton, and disruption of polarity leading to shortening of MTs in third instar larvae. Rab11 is also required for proper localization of different transporters in PCs, essential for physiological activity of MTs. Collectively, our data suggest that Rab11 plays a key role in the process of tubulogenesis of MTs in Drosophila.     

Design,synthesis, and biological evaluation of a small molecule oral agonist of the glucagon-like-peptide-1 receptor

An absolute or relative deficiency of pancreatic β-cells mass and functionality is a crucial pathological feature common to type 1 diabetes mellitus and type 2 diabetes mellitus. Glucagon-like-peptide-1 receptor (GLP1R) agonists have been the focus of considerable research attention for their ability to protect β-cell mass and augment insulin secretion with no risk of hypoglycemia. Presently commercially available GLP1R agonists are peptides that limit their use due to cost, stability, and mode of administration. To address this drawback, strategically designed distinct sets of small molecules were docked on GLP1R ectodomain and compared with previously known small molecule GLP1R agonists. One of the small molecule PK2 (6-((1-(4-nitrobenzyl)-1H-1,2,3-triazol-4-yl)methyl)-6H-indolo[2,3-b]quinoxaline) displays stable binding with GLP1R ectodomain and induces GLP1R internalization and increasing cAMP levels. PK2 also increases insulin secretion in the INS-1 cells. The oral administration of PK2 protects against diabetes induced by multiple low-dose streptozotocin administration by lowering high blood glucose levels. Similar to GLP1R peptidic agonists, treatment of PK2 induces β-cell replication and attenuate β-cell apoptosis in STZ-treated mice. Mechanistically, this protection was associated with decreased thioredoxin-interacting protein expression, a potent inducer of diabetic β-cell apoptosis and dysfunction. Together, this report describes a small molecule, PK2, as an orally active nonpeptidic GLP1R agonist that has efficacy to preserve or restore functional β-cell mass.     

BECN1 is involved in the initiation of mitophagy: It facilitates PARK2 translocation to mitochondria

The autophagy protein BECN1/Beclin 1 is known to play a central role in autophagosome formation and maturation. The results presented here demonstrate that BECN1 interacts with the Parkinson disease-related protein PARK2. This interaction does not require PARK2 translocation to mitochondria and occurs mostly in cytosol. However, our results suggest that BECN1 is involved in PARK2 translocation to mitochondria because loss of BECN1 inhibits CCCP- or PINK1 overexpression-induced PARK2 translocation. Our results also demonstrate that the observed PARK2-BECN1 interaction is functionally important. Measurements of the level of MFN2 (mitofusin 2), a PARK2 substrate, demonstrate that depletion of BECN1 prevents PARK2 translocation-induced MFN2 ubiquitination and loss. BECN1 depletion also rescues the MFN2 loss-induced suppression of mitochondrial fusion. In sum, our results demonstrate that BECN1 interacts with PARK2 and regulates PARK2 translocation to mitochondria as well as PARK2-induced mitophagy prior to autophagosome formation.     

Interferon action: nucleolar and nucleoplasmic localization of the interferon-inducible 72-kD protein that is encoded by the Ifi 204 gene from the gene 200 cluster

The interferons are cytokines with antiviral, cell growth regulatory, and immunomodulatory activities. These activities are mediated by the proteins induced by the interferons. Earlier we described a gene cluster (the 200 cluster) consisting of at least six adjacent, interferon-activatable genes located next to the erythroid alpha-spectrin locus on murine chromosome 1. The genes of the cluster arose by repeated gene duplication and they specify proteins with pronounced sequence similarity. We have now raised polyclonal antibodies against a segment from one of these proteins (the 204 protein of 72 kD). Using these, we established that the 204 protein is a phosphoprotein whose level in cells from various murine lines can be increased up to 75-fold upon treatment with alpha interferon. Experiments involving fractionation of cell lysates and indirect immunofluorescence microscopy of control and interferon-treated cells revealed that the 204 protein is nucleolar and nucleoplasmic. This conclusion was confirmed by co-localization with B23, a known nucleolar protein. The 204 protein is the first interferon-induced protein found to be located in the nucleoli, the subcellular organelles of ribosomal RNA production and ribosome assembly. It remains to be seen whether the 204 protein affects any of these processes. Studies on 204 protein function should be facilitated by the availability of complete cDNA clones and the finding of cell lines in which the expression of this protein is impaired.     

Factors affecting the synthesis and distribution ofβ-lactamase inMycobacterium smegmatis SN2 cultures

A high level of extracellular -lactamase activity was detected in cultures ofMycobacterium smegmatis SN2. The extracellular distribution of the enzyme varied with growth conditions such as additional carbon source and pH of the medium. Addition of chloramphenicol tothe culture inhibited the increase in the extracellular -lactamase activity. Cell wall damage or autolysis may be responsible for the extracellular -lactamase activity.     

Studies on the role of the 2''-5''-oligoadenylate synthetase-RNase L pathway in beta interferon-mediated inhibition of encephalomyocarditis virus replication.

Interferons inhibit the replication of vesicular stomatitis virus (VSV), but not of encephalomyocarditis virus (EMCV), in mouse JLSV-11 cells. We report the isolation of clonal derivatives from this cell line in which the replication of both viruses is impaired by interferons. These clones were selected from the parental line by virtue of their rescue by interferon treatment from the cytopathic effects of EMCV infection. In one such clone, RK8, the replication of VSV and EMCV and the production of resident murine leukemia virus were inhibited by interferon. On the other hand, in clone RK6, which was isolated without any selection, the replication of VSV, but not of EMCV, was impaired by interferons. The levels of 2'-5'-oligoadenylate synthetase mRNA and enzyme activity were similarly elevated upon interferon treatment in the two clones. However, the level of RNase L, as determined by binding and cross-linking of a radiolabeled 2'-5'-oligoadenylate derivative, was much lower in RK6 cells than in RK8 cells. In accord with this observation, the introduction of 2'-5'-oligoadenylates into cells inhibited protein synthesis much less strongly in RK6 cells than in RK8 cells. These results are consistent with the notion that the 2'-5'-oligoadenylate-dependent RNase L may be a mediator of the inhibition of EMCV replication by interferons.