Article

Myeloid-specific tristetraprolin deficiency in mice results in extreme lipopolysaccharide sensitivity in an otherwise minimal phenotype.

Laboratory of Signal Transduction, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA.
The Journal of Immunology (Impact Factor: 5.36). 04/2012; 188(10):5150-9. DOI: 10.4049/jimmunol.1103700
Source: PubMed

ABSTRACT Tristetraprolin (TTP) is a mRNA-destabilizing protein that binds to AU-rich elements in labile transcripts, such as the mRNA encoding TNF, and promotes their deadenylation and degradation. TTP-deficient (knockout [KO]) mice exhibit an early-onset, severe inflammatory phenotype, with cachexia, erosive arthritis, left-sided cardiac valvulitis, myeloid hyperplasia, and autoimmunity, which can be prevented by injections of anti-TNF Abs, or interbreeding with TNF receptor-deficient mice. To determine whether the excess TNF that causes the TTP KO phenotype is produced by myeloid cells, we performed myeloid-specific disruption of Zfp36, the gene encoding TTP. We documented the lack of TTP expression in LPS-stimulated bone marrow-derived macrophages from the mice, whereas fibroblasts expressed TTP mRNA and protein normally in response to serum. The mice exhibited a minimal phenotype, characterized by slight slowing of weight gain late in the first year of life, compared with the early-onset, severe weight loss and inflammation seen in the TTP KO mice. Instead, the myeloid-specific TTP KO mice were highly and abnormally susceptible to a low-dose LPS challenge, with rapid development of typical endotoxemia signs and extensive organ damage, and elevations of serum TNF levels to 110-fold greater than control. We conclude that myeloid-specific TTP deficiency does not phenocopy complete TTP deficiency in C57BL/6 mice under normal laboratory conditions, implying contributions from other cell types to the complete phenotype. However, myeloid cell TTP plays a critical role in protecting mice against LPS-induced septic shock, primarily through its posttranscriptional regulation of TNF mRNA stability.

Full-text

Available from: Deborah J Stumpo, Jun 15, 2015
0 Followers
 · 
60 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: TTP is an anti-inflammatory protein that acts by binding to AREs in its target mRNAs, such as Tnf mRNA, and promoting their deadenylation and decay. TNF released from inflammatory cells can then stimulate gene expression in tissue cells, such as fibroblasts. To determine whether TTP could affect the decay of TNF-induced transcripts in fibroblasts, we exposed primary embryonic fibroblasts and stable fibroblast cell lines, derived from WT and TTP KO mice, to TNF. The decay rates of transcripts encoded by several early-response genes, including Cxcl1, Cxcl2, Ier3, Ptgs2, and Lif, were significantly slowed in TTP-deficient fibroblasts after TNF stimulation. These changes were associated with TTP-dependent increases in CXCL1, CXCL2, and IER3 protein levels. The TTP-susceptible transcripts contained multiple, conserved, closely spaced, potential TTP binding sites in their 3'-UTRs. WT TTP, but not a nonbinding TTP zinc finger mutant, bound to RNA probes that were based on the mRNA sequences of Cxcl1, Cxcl2, Ptgs2, and Lif. TTP-promoted decay of transcripts encoding chemokines and other proinflammatory mediators is thus a critical post-transcriptional regulatory mechanism in the response of secondary cells, such as fibroblasts, to TNF released from primary immune cells. © Society for Leukocyte Biology.
    Journal of Leukocyte Biology 02/2015; 97(4). DOI:10.1189/jlb.3A0214-106R · 4.30 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Inorganic arsenic species are potent environmental toxins and causes of numerous health problems. Most studies have assumed that arsenic-induced changes in mRNA levels result from effects on gene transcription. To evaluate the prevalence of changes in mRNA stability in response to sodium arsenite in human fibroblasts. We used microarray analyses to determine changes in steady state mRNA levels, and mRNA decay rates, following 24 h exposure to non-cytotoxic concentrations of sodium arsenite, and confirmed some of these changes using real-time RT-PCR. In arsenite-exposed cells, there were 186 significantly increased probe set-identified transcripts, while 167 significantly decreased. When decay rates were analyzed after actinomycin D, only 4992 (9.1%) of probe set-identified transcripts decayed by more than 25% after 4 h. Of these, 70 were among the 353 whose steady state levels were altered by arsenite, and of these, only 4 exhibited significantly different decay rates between arsenite and control treatment. Real-time RT-PCR confirmed a major, significant arsenite-induced stabilization of the mRNA encoding δ aminolevulinate synthase 1 (ALAS1), the rate limiting enzyme in heme biosynthesis. This change presumably accounted for at least part of the 2.7-fold increase in steady state ALAS1 mRNA levels seen after arsenite treatment. This could reflect decreases in cellular heme caused by the massive induction by arsenite of heme oxygenase mRNA (HMOX1) (68 fold increase), the rate-limiting enzyme in heme catabolism. We conclude that arsenite modification of mRNA stability is relatively uncommon, but in some instances can result in significant changes in gene expression.
    Environmental Health Perspectives 11/2014; DOI:10.1289/ehp.1408626 · 7.03 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Zinc finger protein 36, C3H type-like 1 (ZFP36L1) is one of several Zinc Finger Protein 36 (Zfp36) family members, which bind AU rich elements within 3' untranslated regions (UTRs) to negatively regulate the post-transcriptional expression of targeted mRNAs. The prototypical member of the family, Tristetraprolin (TTP or ZFP36), has been well-studied in the context of inflammation and plays an important role in repressing pro-inflammatory transcripts such as TNF-α. Much less is known about the other family members, and none have been studied in the context of infection. Using macrophage cell lines and primary alveolar macrophages we demonstrated that, like ZFP36, ZFP36L1 is prominently induced by infection. To test our hypothesis that macrophage production of ZFP36L1 is necessary for regulation of the inflammatory response of the lung during pneumonia, we generated mice with a myeloid-specific deficiency of ZFP36L1. Surprisingly, we found that myeloid deficiency of ZFP36L1 did not result in alteration of lung cytokine production after infection, altered clearance of bacteria, or increased inflammatory lung injury. Although alveolar macrophages are critical components of the innate defense against respiratory pathogens, we concluded that myeloid ZFP36L1 is not essential for appropriate responses to bacteria in the lungs. Based on studies conducted with myeloid-deficient ZFP36 mice, our data indicate that, of the Zfp36 family, ZFP36 is the predominant negative regulator of cytokine expression in macrophages. In conclusion, these results imply that myeloid ZFP36 may fully compensate for loss of ZFP36L1 or that Zfp36l1-dependent mRNA expression does not play an integral role in the host defense against bacterial pneumonia.
    PLoS ONE 10/2014; 9(10):e109072. DOI:10.1371/journal.pone.0109072 · 3.53 Impact Factor