Abstract
Individual signaling pathways operate in the context of the broader signaling network. Thus, the response of a cell to signals from the environment is affected by the state of the signaling network, such as the clinically relevant example of whether some components in the network are inhibited. The cytokine tumor necrosis factor-α (TNF-α) promotes opposing cellular behaviors under different conditions; the outcome is influenced by the state of the network. For example, in the mouse intestinal epithelium, inhibition of the mitogen-activated protein kinase (MAPK) kinase MEK alters the timing of TNF-α-induced apoptosis. We investigated whether MAPK signaling directly influences TNF-α-induced apoptosis or whether network-level effects secondary to inhibition of the MAPK pathway alter the cellular response. We found that inhibitors of the MAPK kinase kinase Raf, MEK, or extracellular signal-regulated kinase (ERK) exerted distinct effects on the timing and magnitude of TNF-α-induced apoptosis in the mouse intestine. Furthermore, even different MEK inhibitors exerted distinct effects; one, CH5126766, potentiated TNF-α-induced apoptosis, and the others reduced cell death. Computational modeling and experimental perturbation identified the kinase Akt as the primary signaling node that enhanced apoptosis in the context of TNF-α signaling in the presence of CH5126766. Our work emphasizes the importance of integrated network signaling in specifying cellular behavior in response to experimental or therapeutic manipulation. More broadly, this study highlighted the importance of considering the network-level effects of pathway inhibitors and showed the distinct effects of inhibitors that share the same target.