OGFr is required for OGF's inhibitory action on growth. (A) Northern blot analysis demonstrating the specificity of the OGFr siRNA in KAT-18 cells. Log phase cells were transfected for 24 h with either scrambled siRNA or OGFr siRNA. Quantitative densitometry (percent of OGFr/GAPDH ratio) represent mean ± SEM for 2 blots from independent experiments. Significantly different from non-transfected cultures at p < 0.01 (**). (B) Immunocytochemical detection of OGFr demonstrating the knockdown of receptor protein. Photomicrographs of cultures transfected with OGFr siRNA, scrambled siRNA, or untransfected and stained with OGFr antibodies. Data (mean gray value) represent mean ± SEM for fluorescence measurements of at least 50 cells. Significantly different from non-transfected cells and those transfected with scrambled siRNA at p < 0.001 (***). (C) Growth of KAT-18 cultures transfected with OGFr siRNA or scrambled siRNA for 24 h and treated with either OGF (10-6 M), NTX (10-6 M), or an equivalent volume of sterile water for an additional 48 h; compounds and media were changed daily. Values represent mean ± SE cell counts for 2 aliquots/well and 2 wells/treatment from three experiments. Significantly different at p < 0.001 (***) from cultures that were not transfected as well as cells that were transfected with scrambled siRNA.