This is consistent with the experimental finding that loss of KSR1 expression attenuated ERK signaling and abolished the capability of oncogenic Ras to induce skin cancer in KSR2/2 mice. Moreover, our simulation suggested that double knockout of KSR and MP1 significantly reduced the strength and duration of ERK activation with the peak being reduced by 8-fold. Experimental and computational studies have shown that, due to its scaffolding activities, KSR enhances the efficiency of ERK activation without altering the fundamental system outputs, i.e. the incoming signals are amplified or attenuated in different biological contexts and at different KSR concentrations. Underlying this fundamental consistency is a complex interplay AG-013736 VEGFR/PDGFR inhibitor between conventional pathway and pathways mediated by scaffolds. Based on models of the MAPK cascade with generic scaffold proteins, shown in Figure 2 and 3, KSR at cell membranes releases activated signaling molecules and competes with the conventional unscaffolded pathway for inactive signaling molecules. The former PLX4032 action enhances and the latter action reduces the capability of the conventional pathway for ERK activation. If the former action outweighs the latter, then KSR is expected to enhance ERK activation not only by its own signaling but also by synergistically increasing the signaling of the conventional unscaffolded pathway. The contribution of the conventional pathway with and without KSR and the KSR-mediated pathway with and without the conventional route of ERK activation were compared. The results show that the level of ERK activation arising from signaling via the conventional pathway in the presence of KSR is significantly increased with respect to that without KSR whereas the level of ERK activation arising from signaling via the KSRmediated pathway in the presence of the conventional one is slightly decreased when compared to that without the conventional pathway. Consistently, Figure 8C shows the synergistic effect of the conventional and KSR-mediated pathways on ERK activation. Therefore, our simulation study suggested that the signal-enhancing action of KSR on the conventional pathway significantly outweighs its signal-reducing action on the conventional module, leading to a significantly stronger combined signaling from the two membrane modules than the simple sum of each individual component. This synergistic effect may enable sizable ERK activation at moderate or suboptimal levels of KSR in many cells. Distinct signaling dynamics of the membrane and late endosome components in response to varying EGF levels Since under various physiological conditions, concentrations of growth factors are more likely to change and present in a gradient instead of being constant, we set out to examine whether there exists any significant perturbations in the signaling dynamics of the membrane and late endosomal components in response to varying EGF levels.