Abstract A41: The ASK1/IKK signaling axis mediates crosstalk between inflammation and apoptosis

Abstract

Abstract Inflammation plays a well-established role in the promotion of tumorigenesis. The inflammatory response is mediated in large part by the inhibitor of kappa b (IKK) and nuclear factor κB (NfκB) signaling pathway. This signaling pathway can promote inflammation induced-tumorigenesis and inhibit apoptosis through protection against reactive oxygen species (ROS). The action of ROS is in part controlled by the apoptosis signal regulating kinase 1 (ASK1). ASK1 activation can initiate pro-apoptotic signaling cascades through mitogen activated protein kinases (MAPKs) Jun N-terminal Kinase (JNK) and p38. Improper regulation of ASK1 has been implicated in a wide array of diseases, including cancer. NfκB promotes tumor growth through activation of pro-growth and survival genes and decreases apoptosis through impairing JNK activation. This work has identified an unexpected, direct, non-genetic method of cell death inhibition by an upstream regulator of NfκB, IKK. We have found that IKK can phosphorylate ASK1 Ser967, which leads to the recruitment of 14–3–3 proteins, decreased ASK1 kinase activity and ASK1-mediated apoptosis. To further elucidate the relationship between ASK1 and IKK, the interaction interface was identified and the consequences on ASK1-mediated signaling were studied. IKK and ASK1 were shown to interact in cells by immunoprecipitation of both overexpressed and endogenous proteins. Furthermore, the direct interaction between these kinases was confirmed through time resolved – fluorescence resonance energy transfer (TR-FRET). The ASK1/IKK interaction interface was dissected through iterative deletional mutagenesis and protein complementation assays. ASK1 activity was assessed by measuring H2O2 induced apoptosis, neurite outgrowth of ASK1-inducible cells, and phosphorylation of ASK1 Ser967 and downstream targets under several IKK states. IKK prevented stress-induced dephosphorylation of ASK1 and inhibited ASK1 mediated apoptosis. These data suggest the existence of an IKK/ASK1 signaling node that negatively regulates apoptosis in response to pro-survival conditions. Characterization of this interaction could lead to development of targeted agents for ASK1 and IKK related diseases. Citation Information: Cancer Prev Res 2011;4(10 Suppl):A41.