Effect of mOSM-RFP on mOSM-induced nuclear translocation of STAT3, STAT3-mediated gene induction. (A) MEFΔSTAT3 stably transfected with STAT3-eGFP were stimulated with 5 ng/ml mOSM for 20 min in the presence of 5% of 10-fold concentrated supernatant containing mOSM-RFP or supernatant from mock transfected cells (mock SN) as indicated. Cells were fixed and analyzed by confocal microscopy. Scale bars represent 10 μm. (B) MEF were stimulated for 45 min with varying amounts of mOSM in the presence of mOSM-RFP as indicated. Induction of mSOCS3 mRNA was quantified by qrt-PCR. mHPRT mRNA served as an internal standard.