262 to 10 and the STAT3 produc tion rate from 0. 211 to 10. The MITF S409A mutation was simulated by setting the MITF S409 phosphoryla tion rate constant to zero. The activation was simulated by elevation of the amount of phosphorylated ERK promotion information and JAK from 10 to 1000. In experiment 17, wild type Inhibitors,Modulators,Libraries MITF, PIAS3 and STAT3 were all transfected and simu lated for 2880 minutes, thereafter simulated for 15 more minutes with and without stimulation. The amount of PIAS3 STAT3 complex was compared. The success criterion used in the sensitivity analysis was that the amount of PIAS3 STAT3 complex should be at least 25% higher with stimulation compared to the case without stimulation. In experiment 18, S409A MITF, PIAS3 and STAT3 were transfected and simulated for 2880 minutes, and thereafter simulated for 15 more minutes with or without stimulation.

The amount of PIAS3 STAT3 complex was compared with Inhibitors,Modulators,Libraries the sti mulated case in experiment 17. The success criterion used in the sensitivity analysis was that the amount of PIAS3 STAT3 complex in the stimulated Inhibitors,Modulators,Libraries case in experi ment 17 should be at least 25% higher than the amount of PIAS3 STAT3 complex in any of the two cases in 18. Experiments 19 to 24 are simulations of the experi ment presented in Figure 3B. Here, the authors have investigated STAT3 transcriptional activity as a response to activation, transfection of PIAS3, and trans fection of various amounts of wild type and S409A mutated MITF in NIH T3T cells. The activation was simulated by elevation of the amounts of phosphorylated ERK and JAK from 10 to 1000.

The transfections of PIAS3, STAT3 and the two different MITF amounts were simulated by elevation of the PIAS3 production rate from 1. 262 to 7, the STAT3 production rate from 0. 262 to 5, and the MITF production rate from 1 to 10 or 50, respectively. The S409A mutation was simulated by setting the MITF phosphorylation rate constant Inhibitors,Modulators,Libraries to zero. The model was run for 2880 minutes to simulate the incubation and then for 360 minutes to simulate the activation. The background luciferase activity of STAT3 was determined by elevation of the STAT3 production rate and running a model simulation for 3240 minutes. The amount of phosphorylated STAT3 in the end was interpreted as an estimate for the lucifer ase activity of STAT3 without activation and without PIAS3 or MITF.

For experiments 19 to 24, the amount of phosphorylated Inhibitors,Modulators,Libraries STAT3 was compared to this background level. In experiment 19, the cells were transfected with STAT3 and activated. The success cri terion used in the sensitivity analysis was the level of phosphorylated STAT3 between that 10 and 20 times the background level. In experiment 20, the cells were transfected with STAT3 and PIAS3 and activated. The success criterion used in the sensitivity analysis was the level of phosphorylated STAT3 between 2. 67 and 5. 33 times the background level.