Hyperinvasive Meningococci Induce Intra-nuclear Cleavage of the NF-κB Protein p65/RelA by Meningococcal IgA Protease.

International audienceDifferential modulation of NF-κB during meningococcal infection is critical in innate immune response to meningococcal disease. Non-invasive isolates of Neisseria meningitidis provoke a sustained NF-κB activation in epithelial cells. However, the hyperinvasive isolates of the ST-11 clonal complex (ST-11) only induce an early NF-κB activation followed by a sustained activation of JNK and apoptosis. We show that this temporal activation of NF-κB was caused by specific cleavage at the C-terminal region of NF-κB p65/RelA component within the nucleus of infected cells. This cleavage was mediated by the secreted 150 kDa meningococcal ST-11 IgA protease carrying nuclear localisation signals (NLS) in its α-peptide moiety that allowed efficient intra-nuclear transport. In a collection of non-ST-11 healthy carriage isolates lacking NLS in the α-peptide, secreted IgA protease was devoid of intra-nuclear transport. This part of iga polymorphism allows non-invasive isolates lacking NLS, unlike hyperinvasive ST-11 isolates of N. meningitides habouring NLS in their α-peptide, to be carried asymptomatically in the human nasopharynx through selective eradication of their ability to induce apoptosis in infected epithelial cells

ST-11 IgA protease-mediated nuclear cleavage of p65/RelA alters selectively expression of NF-κB responsive genes.

<p>Hec-1-B cells were infected for the indicated periods, After infection of Hec-1-B cells with the indicated strains and periods, mRNA levels of c-FLIP (A), IL-8 (B) and TNF-α (C) were evaluated by real-time PCR. Target mRNA expression was normalized to β-actin mRNA. ***, <i>P</i><0.001<i>; **</i>, <i>P</i><0.01</p

IgA protease of ST-11 isolates promotes sustained activation of JNK and apoptosis of epithelial cells.

<p>(A) Hec-1B cells were infected with the indicated strains. At each time point, samples were lysed and immunoblotted with rabbit polyclonal anti-phospho-JNK antibodies (upper panel). The membranes were subsequently stripped and re-probed with rabbit polyclonal anti-JNK antibodies as protein loading controls. Blots are representative of three separate experiments with similar results. (B) Cells were left uninfected or infected with the indicated strains for 9 h then analysed for apoptosis using annexin V staining and flow cytometry. Histogram bars represent the mean ± SD from three independent experiments. **, <i>P</i> < 0.01, ***, <i>P</i> <0.001.</p

Nuclear cleavage of p65/RelA is carried out by a ST-11 meningococcal secreted serine protease.

<p>(A) For in vivo experiments (left panel), Hec-1B cells were infected for 9h in absence or presence of 1 μg.ml^-1 cycloheximide (CHX), 5μg.ml^-1 chloramphenicol (CMP) or 5 mM PMSF. After incubation cells were harvested, and nuclear fractions were prepared. For <i>in vitro</i> experiments (right panel), nuclear extracts were prepared from LPS-stimulated cells and then incubated with native meningococcal secreted proteins (N-MSP) in absence or presence of 5 mM PMSF, or heat-inactivated MSP (H-MSP) of the ST-11 isolate LNP19995. Samples were resolved by SDS-PAGE and immunoblotted with anti-p65/RelA mAb, anti-IgA protease or anti-NalP sera.Histone H3 expression (lower panel) was used as loading control. Immunoblot is representative of three independent experiments which yielded similar results. (B) Whole lysates of bacteria recovered from (A), were resolved by SDS-PAGE and immunoblotted with anti-IgA protease or anti-NalP sera.Mutant strains 19995<i>Δiga</i> and 19995<i>ΔnalP</i> were used as negative controls. Full length precursors and autocleaved forms are indicated by arrows. * represent a cross reactive bands.</p

Cleavage of p65/RelA correlates with nuclear translocation of IgA protease.

<p>(A) Similarity between amino acid sequences of the hinge region of human IgA1, part of the N-terminal peptide of the human lysosome-associated membrane glycoprotein 1 LAMP1 (Accession N°: AAH06345), synaptobrevin II (Accession N°: AAF15551) targeted by neisseria IgA protease and part of the carboxy terminal peptide of the p65/RelA subunit of NF-κB (Accession N°: CAA80524). The position of amino acid residues are indicated by superscript numbers delimiting each peptide sequence. Specific cleavage sites are indicated in red and the cleavage position is represented by double-headed arrows. (B) Schematic overview of the various domains and sub-domains of neisserial IgA protease. Autocatalyic cleavage sites CS1 and CS2 and their sequences are indicated by double-headed arrows. SS: signal sequence. (C) Nuclear fractions were prepared from Hec-1-B cells infected with LNP19995 or LNP21019 at indicated time points. Samples were resolved in SDS-PAGE and probed with anti-N-terminal p65 mAb or rabbit polyclonal serum specific to IgaP sub-domain or anti-NalP specific serum. Histone H3 was used as loading control.</p

Meningococcal ST-11 isolates promote nuclear cleavage of p65 at late steps of infection.

<p>(A) Meningococcal infection is accompanied by IkBα degradation. Hec-1-B epithelial cells were infected with LNP19995 (ST-11) or LNP21019 (non-ST-11) isolates for the indicated time points or left uninfected. Cytosolic fractions were subjected to immunoblotting analysis for I-κBα. Immunoblotting with anti-GAPDH antibodies was used as a protein loading control. (B) Nuclear translocation of both p65/RelA and p50/NF-κB1 subunits was not altered by meningococcal infection. Hec-1B cells were infected with GFP-expressing LNP19995 or LNP21019 or left non-infected (RPMI). After 9h, cells were fixed with 3.7% PFA, permeabilised and probed with mouse anti-p65/RelA mAb (left panel) or rabbit anti-p50/NF-κB1 (right panel) and Texas red (TR)-conjugated appropriate secondary antibody. Nuclei were stained with DAPI. Fluorescence was analyzed using immuno-fluorescence microscopy. Scale bar (1 μm) is shown. Data are representative of three independent experiments. (C) Nuclear or cytosolic fractions from (A) were analysed by immunoblotting using anti-N-terminal p65/RelA specific mAb (upper panels) or anti-p50/NF-κB1 rabbit polyclonal antibody (lower panels). Shown is a representative blot of three independent experiments. p65/RelA cleavage product p40 is indicated by arrows. (D) The blot of nuclear fractions from (C) was stripped and probed against a goat polyclonal antibody directed against C-terminal region of p65/RelA. The cleavage product p25 is indicated by arrowhead.</p

Integrated analyses of translatome and proteome identify the rules of translation selectivity in RPS14-deficient cells

In ribosomopathies, the Diamond-Blackfan anemia (DBA) or 5q- syndrome, ribosomal protein (RP) genes are affected by mutation or deletion, resulting in bone marrow erythroid hypoplasia. Unbalanced production of ribosomal subunits leading to a limited ribosome cellular content, regulates translation at the expense of the master erythroid transcription factor GATA1. In RPS14-deficient cells mimicking 5q- syndrome erythroid defects, we show that the transcript length, codon bias of the coding sequence (CDS) and 3'UTR structure are the key determinants of translation. In these cells, short transcripts with a structured 3'UTR and high CAI showed a decreased translation efficiency. Quantitative analysis of the whole proteome confirmed that the post-transcriptional changes depended on the transcript characteristics that governed the translation efficiency in conditions of low ribosome availability. In addition, proteins involved in normal erythroid differentiation share most determinants of translation selectivity. Our findings thus indicate that impaired erythroid maturation due to 5q- syndrome may proceed from a translational selectivity at the expense of the erythroid differentiation program and suggest that an interplay between the CDS and UTRs may regulate mRNA translation

IgA protease of ST-11 isolates interacts with and mediates nuclear cleavage of p65/RelA.

<p>(A) Hec-1-B cells were infected with the indicated strains. For each time point, nuclear fractions were prepared and analysed by immunoblotting using anti-p65 mAb. Histone H3 was used as loading control. (B) Localization of IgA protease sub-domains in transfected infected cells. IgaP, Igaα or IgaPα of LNP19995 (upper panel) or LNP21019 (lower panel) were fused to DsRed. Hec-1-B cells were then transfected with either construct or pDsRedN1 plasmid (Empty vector). After 48 hours, cells were washed, fixed with 3.7% PFA and stained with DAPI (blue) before visualisation under the microscope. Scale bar (10 μm) is shown. (C) <i>In vitro</i> activity of purified IgA protease passenger sub-domains against p65. IgaP, Igaα or IgaPα or IgaP^S267V of the strains LNP19995 (upper panel) and LNP21019 (lower panel) were subcloned and purified as C-terminal His₆-tagged proteins. Nuclear extracts (1 μg) from LPS-stimulated Hec-1-B cells were mixed with the indicated concentrations of the purified proteins. The reaction mixtures were incubated at 25°C for 3 hours and then analyzed with antibodies against p65/RelA (N-terminal specific). (D) IgA protease interacts with p65/RelA. Nuclear extracts from LPS-stimulated Hec-1-B cells were mixed with MSP prepared from LNP19995 or 19995<i>Δiga</i> for 6h in presence of 5 mM PMSF. The samples were immunoprecipitated with anti-IgaP specific serum or irrelevant rabbit Ab (left panel) or anti-p65/RelA mAb or irrelevant mAb (right panel) and analyzed by immunoblotting with antibodies against p65/RelA and IgaP, respectively. * indicates antibody heavy chain.</p

Non-ST-11 isolates release α-peptide-lacking IgA protease.

<p>(A) Subcellular localisation of IgA protease in infected cells. Hec-1B cells were infected with GFP-expressing LNP19995 or LNP21019 (green) or left uninfected. After 12 h of infection, cells were fixed with 4% PFA, permeabilised and stained with anti-IgaP polyclonal serum and Texas Red (TR)-conjugated anti-rabbit IgG (red). Nuclei were stained with DAPI. Fluorescence was analyzed using immunofluorescence microscopy. Data are representative of three independent experiments. (B) Analysis of ST-11 and non-ST-11 isolates by PCR using primers specific to α-peptide sub-domain. PCR products were amplified from genomic DNA of strains indicated above the gel, using the couple of primers alphaFwNhe / alphaRevSma. PCR products were separated by electrophoresis in 1% agarose gels and stained with ethidium bromide. PCR amplification generated amplicons of ~ 1500 bp in all ST-11 isolates, while amplicon sizes ranged between 687 and 770 bp in non-ST-11 isolates. Molecular sizes (kb) are indicated in the left side. (C) Upper panel. Non scaled schematic representation of the passenger subdomains of meningococcal IgA protease from isolates LNP19995 (ST-11) and LNP21019 (non-ST-11). The positions of autocatalytic processing sites and their sequences (PPSP) are indicated. Arrows indicate positions of NLSs in α-peptide of the ST-11 isolate. Lower panel. Five hundred nanograms of the C-terminal His₆-tagged passenger domain of the strains LNP19995 (IgaPα₁₉₉₉₅) or LNP21019 (IgaPα₂₁₀₁₉) were mixed with 5 or 10 μg of MSPs. After 3 h, the reaction mixtures were analyzed with immunoblot using anti-His tag mAb. The different cleavage products are indicated by arrows. Mw indicates the molecular weight. (D) IgA protease of ST-11 isolates restores the capacity of non-ST-11 isolates in cleaving nuclear p65. Each of the 19995<i>Δiga</i> and 21019<i>Δiga</i> were complemented with the heterologous <i>iga</i> allele of the WT strain LNP21019 and LNP19995, respectively. Hec-1-B cells were infected for 12 h with the parental WT strains, the isogenic <i>iga</i> knock-out mutant strains or the heterologous complemented strains. Nuclear fractions prepared from infected cells, were resolved by SDS-PAGE and were probed with anti-p65 mAb (N-terminal specific) or polyclonal serum anti-IgaP. LPS-treated cells were used as positive control for nuclear translocation of NF-κB. Immunoblot with anti histone H3 was used as loading control.</p

p53 activation during ribosome biogenesis regulates normal erythroid differentiation

International audienceThe role of ribosome biogenesis in erythroid development is supported by the recognition of erythroid defects in ribosomopathies in both Diamond-Blackfan anemia and 5q- syndrome. Whether ribosome biogenesis exerts a regulatory function on normal erythroid development is still unknown. In the present study, a detailed characterization of ribosome biogenesis dynamics during human and murine erythropoiesis shows that ribosome biogenesis is abruptly interrupted by the drop of rDNA transcription and the collapse of ribosomal protein neo-synthesis. Its premature arrest by RNA polI inhibitor, CX-5461 targets the proliferation of immature erythroblasts. We also show that p53 is activated spontaneously or in response to CX-5461 concomitantly to ribosome biogenesis arrest, and drives a transcriptional program in which genes involved in cell cycle arrest, negative regulation of apoptosis and DNA damage response were upregulated. RNA polI transcriptional stress results in nucleolar disruption and activation of ATR-CHK1-p53 pathway. Our results imply that the timing of ribosome biogenesis extinction and p53 activation are crucial for erythroid development. In ribosomopathies in which ribosome availability is altered by unbalanced production of ribosomal proteins, the threshold of ribosome biogenesis down-regulation could be prematurely reached and together with pathological p53 activation prevents a normal expansion of erythroid progenitors