Inducible STAT1 expression in stably transfected MEF cell lines. WT, STAT1-/- (S1-/-) and STAT1-/- cells reconstituted with inducible STAT1 (S2RS #8) were treated with rapalog at the dose indicated for 24 h (A) or treated with 100 nM rapalog for the times indicated (B). To analyze STAT1 protein stability, cells were treated with 100 nM rapalog for 12 h, washed three times with PBS and further incubated without inducer. STAT1 protein expression was determined with WB analysis and loading was controlled via probing for ERK protein (A-C). Cells were treated as in A and B, stimulated with 100 U/ml IFNγ for 15 min or left untreated, lysed and 15 μg total cell extract subjected to EMSA analysis using hSIE oligonucleotides as probes (D). Similar results were obtained with other reconstituted clones.