PARP-1 deficiency blocks IL-5 expression through calpain-dependent degradation of STAT-6 in a murine asthma model

BACKGROUND

We recently showed that poly(ADP-ribose)polymerase-1 (PARP-1) may play a role in allergen (ovalbumin)-induced airway eosinophilia, potentially through a specific effect on IL-5 production. We also reported that while IL-5 replenishment promotes reversal of eosinophilia in lungs of PARP-1(-/-) mice, IL-4 or Immunoglobulin E replenishment do not, suggesting a potentially significant regulatory relationship between PARP-1 and IL-5.

OBJECTIVE

To explore the mechanism by which PARP-1 regulates IL-5 production and to determine how PARP-1 inhibition blocks allergen-induced eosinophilia.

METHODS

This study was conducted using a murine model of allergic airway inflammation and primary splenocytes.

RESULTS

PARP-1 knockout-associated reduction in IL-5 upon allergen exposure occurs at the mRNA level. Such an effect appears to take place after IL-4 receptor activation as PARP-1 inhibition exerted no effect on JAK1/JAK3 activation. Signal transducer and activator of transcription-6 (STAT-6) protein was severely downregulated in spleens of PARP-1(-/-) mice without any effect on mRNA levels, suggesting an effect on protein integrity rather than gene transcription. Interestingly, the degradation of STAT-6 in PARP-1(-/-) mice required allergen stimulation. Additionally, PARP-1 enzymatic activity appears to be required for STAT-6 integrity. The downregulation of STAT-6 coincided with mRNA and protein reduction of GATA-binding protein-3 and occupancy of its binding site on the IL-5 gene promoter. IL-4 was sufficient to induce STAT-6 downregulation in both PARP-1(-/-) mice and isolated splenocytes. Such degradation may be mediated by calpain, but not by proteasomes.

CONCLUSION

These results demonstrate a novel function of PARP-1 in regulating IL-5 expression during allergen-induced inflammation and explain the underlying mechanism by which PARP-1 inhibition results in IL-5 reduction.

Two dimensional non equilibrium pH gel electrophoresis mapping of cytosolic protein changes caused by dietary protein depletion in mouse liver

Two-dimensional non-equilibrium pH gel electrophoresis (2D-NEPHGE) analysis was used to evaluate the effects of dietary protein depletion on the protein composition of mouse liver cytosol. Analysing the cytosol from both normal and protein depleted liver, the position in gels of more than three hundred protein spots was determined. After 5 days of protein depletion, about 20% of the spots either increased or decreased more than 2 fold. Five spots of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were recognised by specific antibodies. The glutathione S-transferase (GSTs) subunits Ybl, Yc and Yf were identified by the simultaneous analysis of both glutathione-binding cytosolic proteins and the corresponding standards. As estimated by internal optical density (IOD) of spots, the changes caused by protein depletion in GAPDH and GST subunit contents were similar to those obtained by other methods. By means of mass spectrometric analysis of tryptic peptides generated from spots and/or comparison of two-dimensional gel electrophoretic patterns, carbonic anhydrase III (CAIII), Cu, Zn superoxide dismutase (CuZnSOD) and a cytochrome P450 cytosolic protein (cyt P450) were identified. These three proteins, as well as GSTs, are related with intracellular detoxification and free radical scavenging systems. Their contents were regulated by dietary protein restriction in a manner indicative of diminished liver defence against oxidising agents.