Regulation of Intracellular Signaling by the Inhibitor of Apoptosis (IAP) Proteins.

Abstract

Members of the TNF receptor superfamily, many of which are important for immune and inflammatory responses, have been shown to utilize ubiquitination for signal transduction. Two proteins, cellular inhibitor of apoptosis proteins 1 and 2 (c-IAP1/2), play central roles in the signaling cascades from these receptors through their ubiquitin ligase activity. In certain pathways, c-IAP1/2 actively propagate receptor-mediated signaling through the construction of ubiquitin scaffolds within the receptor signaling complex, while in other situations, c-IAP1/2 constitutively target substrate proteins for ubiquitination and degradation, inhibiting signal transduction. Activation of these signaling pathways is dependent on the degradation of c-IAP1/2, a process that is associated with stimulation of specific members of the TNF receptor superfamily. While the biological properties of c-IAP1/2 are context-dependent, the exact roles and outcomes of c-IAP1/2 activity in these different circumstances are unclear. In the work presented in this dissertation, these diverse roles of c-IAP1/2 in signaling were further explored, characterizing the signaling pathways in which they participate, investigating their regulation, and identifying the downstream consequences of their activity. Using multiple methods to study the function of c-IAP1/2, including activation of TNF receptor superfamily members and treatment with synthetic compounds that target and degrade c-IAP1/2, novel aspects of c-IAP1/2 activity in signaling were characterized. Specifically, the regulation of canonical and non-canonical NF-kappa B activation by c-IAP1/2 was investigated, finding that the consequences of c-IAP1/2 activity were cell type-specific. Furthermore, important regulatory crosstalk between the NF-kappa B signaling pathways was identified in cells that activated both canonical and non-canonical NF-kappa B. Additionally, novel roles for c-IAP1/2 were identified using transcriptome analysis and a technique called Bru-seq, and these roles included the regulation of ribosomal gene expression and protein synthesis. These results may have important clinical implications, since the IAPs are actively being studied as potential therapeutic targets. Collectively, these findings expand our understanding of ubiquitin-dependent signaling and, more specifically, provide crucial insight into the multifaceted functions of c-IAP1 and c-IAP2 in key intracellular signaling pathways.