Figure 4.

Calpain inhibition blocks degradation of STAT-6 in PARP-1^−/− splenocytes upon IL-4 stimulation. Splenocytes isolated from WT or PARP-1^−/− mice were treated with IL-4 in the absence or presence of 20 µM of the proteasome inhibitor MG132 or the calpain inhibitor ALLN. Cells were collected 12 h after treatment and subjected to protein extraction. Proteins were then subjected to immunoblot analysis with antibodies to STAT-6 or actin. (B) The immunoblot results in A were quantified and expressed as STAT-6 relative (over actin). *Difference from the control that received neither IL-4 nor protease inhibitors; #, Difference from IL-4-treated cells without protease inhibitors, p< 0.01. (C) Lysates from control cells that were treated with MG132 or left untreated were subjected to immunoblot analysis with antibodies to ubiquitin.