Budding yeast (Saccharomyces cerevisiae) responds to iron deprivation both by Aft1-Aft2-dependent transcriptional activation of genes involved in cellular iron uptake and by Cth1-Cth2-specific degradation of certain mRNAs coding for iron-dependent biosynthetic components. Here, we provide evidence for a novel principle of iron-responsive gene expression. This regulatory mechanism is based on the modulation of transcription through the iron-dependent variation of levels of regulatory metabolites. As an example, the LEU1 gene of branched-chain amino acid biosynthesis is downregulated under iron-limiting conditions through depletion of the metabolic intermediate ␣-isopropylmalate, which functions as a key transcriptional coactivator of the Leu3 transcription factor. Synthesis of ␣-isopropylmalate involves the iron-sulfur protein Ilv3, which is inactivated under iron deficiency. As another example, decreased mRNA levels of the cytochrome c-encoding CYC1 gene under iron-limiting conditions involve heme-dependent transcriptional regulation via the Hap1 transcription factor. Synthesis of the iron-containing heme is directly correlated with iron availability. Thus, the ironresponsive expression of genes that are downregulated under iron-limiting conditions is conferred by two independent regulatory mechanisms: transcriptional regulation through iron-responsive metabolites and posttranscriptional mRNA degradation. Only the combination of the two processes provides a quantitative description of the response to iron deprivation in yeast.

BackgroundFeline immunodeficiency virus (FIV) is a global pathogen of Felidae species and a model system for Human immunodeficiency virus (HIV)-induced AIDS. In felids such as the domestic cat (Felis catus), APOBEC3 (A3) genes encode for single-domain A3Z2s, A3Z3 and double-domain A3Z2Z3 anti-viral cytidine deaminases. The feline A3Z2Z3 is expressed following read-through transcription and alternative splicing, introducing a previously untranslated exon in frame, encoding a domain insertion called linker. Only A3Z3 and A3Z2Z3 inhibit Vif-deficient FIV. Feline A3s also are restriction factors for HIV and Simian immunodeficiency viruses (SIV). Surprisingly, HIV-2/SIV Vifs can counteract feline A3Z2Z3.ResultsTo identify residues in feline A3s that Vifs need for interaction and degradation, chimeric human–feline A3s were tested. Here we describe the molecular direct interaction of feline A3s with Vif proteins from cat FIV and present the first structural A3 model locating these interaction regions. In the Z3 domain we have identified residues involved in binding of FIV Vif, and their mutation blocked Vif-induced A3Z3 degradation. We further identified additional essential residues for FIV Vif interaction in the A3Z2 domain, allowing the generation of FIV Vif resistant A3Z2Z3. Mutated feline A3s also showed resistance to the Vif of a lion-specific FIV, indicating an evolutionary conserved Vif–A3 binding. Comparative modelling of feline A3Z2Z3 suggests that the residues interacting with FIV Vif have, unlike Vif-interacting residues in human A3s, a unique location at the domain interface of Z2 and Z3 and that the linker forms a homeobox-like domain protruding of the Z2Z3 core. HIV-2/SIV Vifs efficiently degrade feline A3Z2Z3 by possible targeting the linker stretch connecting both Z-domains.ConclusionsHere we identified in feline A3s residues important for binding of FIV Vif and a unique protein domain insertion (linker). To understand Vif evolution, a structural model of the feline A3 was developed. Our results show that HIV Vif binds human A3s differently than FIV Vif feline A3s. The linker insertion is suggested to form a homeo-box domain, which is unique to A3s of cats and related species, and not found in human and mouse A3s. Together, these findings indicate a specific and different A3 evolution in cats and human.Electronic supplementary materialThe online version of this article (doi:10.1186/s12977-016-0274-9) contains supplementary material, which is available to authorized users.

APOBEC4 (A4) is a member of the AID/APOBEC family of cytidine deaminases. In this study we found a high mRNA expression of A4 in human testis. In contrast, there were only low levels of A4 mRNA detectable in 293T, HeLa, Jurkat or A3.01 cells. Ectopic expression of A4 in HeLa cells resulted in mostly cytoplasmic localization of the protein. To test whether A4 has antiviral activity similar to that of proteins of the APOBEC3 (A3) subfamily, A4 was co-expressed in 293T cells with wild type HIV-1 and HIV-1 luciferase reporter viruses. We found that A4 did not inhibit the replication of HIV-1 but instead enhanced the production of HIV-1 in a dose-dependent manner and seemed to act on the viral LTR. A4 did not show detectable cytidine deamination activity in vitro and weakly interacted with single-stranded DNA. The presence of A4 in virus producer cells enhanced HIV-1 replication by transiently transfected A4 or stably expressed A4 in HIV-susceptible cells. APOBEC4 was capable of similarly enhancing transcription from a broad spectrum of promoters, regardless of whether they were viral or mammalian. We hypothesize that A4 may have a natural role in modulating host promoters or endogenous LTR promoters.

Nucleophosmin (NPM1, also known as B23, numatrin or NO38) is a pentameric RNA-binding protein with RNA and protein chaperon functions. NPM1 has increasingly emerged as a potential cellular factor that directly associates with viral proteins; however, the significance of these interactions in each case is still not clear. In this study, we have investigated the physical interaction of NPM1 with both human immunodeficiency virus type 1 (HIV-1) Rev and Herpes Simplex virus type 1 (HSV-1) US11, two functionally homologous proteins. Both viral proteins show, in mechanistically different modes, high affinity for a binding site on the N-terminal oligomerization domain of NPM1. Rev, additionally, exhibits low-affinity for the central histone-binding domain of NPM1. We also showed that the proapoptotic cyclic peptide CIGB-300 specifically binds to NPM1 oligomerization domain and blocks its association with Rev and US11. Moreover, HIV-1 virus production was significantly reduced in the cells treated with CIGB-300. Results of this study suggest that targeting NPM1 may represent a useful approach for antiviral intervention.

Glioblastoma is the most common malignant primary brain tumor. To date, clinically relevant biomarkers are restricted to isocitrate dehydrogenase (IDH) gene 1 or 2 mutations and O6-methylguanine DNA methyltransferase (MGMT) promoter methylation. Long non-coding RNAs (lncRNAs) have been shown to contribute to glioblastoma pathogenesis and could potentially serve as novel biomarkers. The clinical significance of HOXA Transcript Antisense RNA, Myeloid-Specific 1 (HOTAIRM1) was determined by analyzing HOTAIRM1 in multiple glioblastoma gene expression data sets for associations with prognosis, as well as, IDH mutation and MGMT promoter methylation status. Finally, the role of HOTAIRM1 in glioblastoma biology and radiotherapy resistance was characterized in vitro and in vivo. We identified HOTAIRM1 as a candidate lncRNA whose up-regulation is significantly associated with shorter survival of glioblastoma patients, independent from IDH mutation and MGMT promoter methylation. Glioblastoma cell line models uniformly showed reduced cell viability, decreased invasive growth and diminished colony formation capacity upon HOTAIRM1 down-regulation. Integrated proteogenomic analyses revealed impaired mitochondrial function and determination of reactive oxygen species (ROS) levels confirmed increased ROS levels upon HOTAIRM1 knock-down. HOTAIRM1 knock-down decreased expression of transglutaminase 2 (TGM2), a candidate protein implicated in mitochondrial function, and knock-down of TGM2 mimicked the phenotype of HOTAIRM1 down-regulation in glioblastoma cells. Moreover, HOTAIRM1 modulates radiosensitivity of glioblastoma cells both in vitro and in vivo. Our data support a role for HOTAIRM1 as a driver of biological aggressiveness, radioresistance and poor outcome in glioblastoma. Targeting HOTAIRM1 may be a promising new therapeutic approach.

Foamy viruses (FV) are retroviruses that are widely distributed in primate and non-primate animal species. We tested here FV with capsids of simian and non-simian origin for sensitivity to interferon-β (IFN-β). Our data show significant inhibition of FV by IFN-β early in infection of human HOS and THP-1 but not of HEK293T cells. The post-entry restriction of FV was not mediated by the interferon-induced MxB protein that was recently identified as a capsid-interacting restriction factor targeting Human immunodeficiency virus (HIV) before integration. Neither the ectopic expression of MxA or MxB in HEK293T cells nor the lack of MxB expression in CRISPR/CAS MxB THP-1 knockout cells impacted the infection of the tested FV. IFN-β treated THP-1 and THP-1 KO MxB cells showed the same extend of restriction to FV. Together, the data demonstrate that IFN-β inhibits FV early in infection and that MxB is not a restriction factor of FV.

Histone deacetylase (HDAC) inhibitors such as suberoylanilide hydroxamic acid (SAHA) are not commonly used in clinical practice for treatment of B‐cell lymphomas, although a subset of patients with refractory or relapsed B‐cell lymphoma achieved partial or complete remissions. Therefore, the purpose of this study was to identify molecular features that predict the response of B‐cell lymphomas to SAHA treatment. We designed an integrative approach combining drug efficacy testing with exome and captured target analysis (DETECT). In this study, we tested SAHA sensitivity in 26 B‐cell lymphoma cell lines and determined SAHA‐interacting proteins in SAHA resistant and sensitive cell lines employing a SAHA capture compound (CC) and mass spectrometry (CCMS). In addition, we performed exome mutation analysis. Candidate validation was done by expression analysis and knock‐out experiments. An integrated network analysis revealed that the Src tyrosine kinase Gardner‐Rasheed feline sarcoma viral (v‐fgr) oncogene homolog (FGR) is associated with SAHA resistance. FGR was specifically captured by the SAHA‐CC in resistant cells. In line with this observation, we found that FGR expression was significantly higher in SAHA resistant cell lines. As functional proof, CRISPR/Cas9 mediated FGR knock‐out in resistant cells increased SAHA sensitivity. In silico analysis of B‐cell lymphoma samples (n = 1200) showed a wide range of FGR expression indicating that FGR expression might help to stratify patients, which clinically benefit from SAHA therapy. In conclusion, our comprehensive analysis of SAHA‐interacting proteins highlights FGR as a factor involved in SAHA resistance in B‐cell lymphoma.

Successful replication of Human immunodeficiency virus (HIV)-1 depends on the expression of various cellular host factors, such as the interleukin-2 inducible T-cell kinase (ITK), a member of the protein family of TEC-tyrosine kinases. ITK is selectively expressed in T-cells and coordinates signaling pathways downstream of the T-cell receptor and chemokine receptors, including PLC-1 activation, Ca2+-release, transcription factor mobilization, and actin rearrangements. The exact role of ITK during HIV-1 infection is still unknown. We analyzed the function of ITK during HIV-1 replication and showed that attachment, fusion of virions with the cell membrane and entry into Jurkat T-cells was inhibited when ITK was knocked down. In contrast, reverse transcription and provirus expression were not affected by ITK deficiency. Inhibited ITK expression did not affect the CXCR4 receptor on the cell surface, whereas CD4 and LFA-1 integrin levels were slightly enhanced in ITK knockdown cells and heparan sulfate (HS) expression was completely abolished in ITK depleted T-cells. However, neither HS expression nor other attachment factors could explain the impaired HIV-1 binding to ITK-deficient cells, which suggests that a more complex cellular process is influenced by ITK or that not yet discovered molecules contribute to restriction of HIV-1 binding and entry.