FIGURE 5.

ERK or βTRCP and STAT1 serine 7272 is required for STAT1 degradation. A,βTRCP silencing reduces STAT1 degradation following oxidative stress. MEF cells were transfected with βTRCP siRNA or control luciferase siRNA and exposed to H₂O₂ at the indicated times. Western blotting was carried out with the indicated antibodies anti-STAT1α antibody (C-24) (ST1) or anti-βTRCP (βTRCP). Similar results were observed in three independent experiments. GAPDH, glyceraldehyde-3-phosphate dehydrogenase. B, ERK or βTRCP silencing results in STAT1 protein up-regulation. MEF cells were transfected with either βTRCP- (TP), ERK1- (E1), ERK2- (E2), or luciferase (Lu) (control)-specific siRNA oligonucleotides and exposed to H₂O₂ (200 μm). Western blotting was performed with the indicated antibodies. Similar results were observed in three independent experiments. C, exogenous expression of βTRCP reduces phospho-STAT1 serine 727 following oxidative stress. Wild-type MEF cells were transfected with HA-tagged βTRCP and exposed to H₂O₂ (200 μm) for 4 h alone or in the presence of the proteasome inhibitor lactacystin (LC). Western blotting was performed with the indicated antibodies, anti-phosphoserine STAT1 (pST1) or anti-HA (HA). Similar results were observed in three independent experiments.