IKK:Biophysical basis of dynamic regulation

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DESCRIPTION (provided by applicant): IKK is the major signaling hub for inflammatory and innate immune responses. It is an enzyme complex that receives signals from a large number of cellular receptors regulates that activity of the NF-kB family of transcription factors. Misregulation of IKK is associated with many chronic diseases, such as chronic inflammatory pathologies (arthritis, atherosclerosis, etc) and many different types of cancer. Genetic evidence strongly supports IKK's critical and central role in many functions in physiology and pathology, but its potential as a drug target has not been realized. Mechanistic and biophysical studies have been lacking, and we have neither a kinetic understanding of IKK regulation nor structural information. However, what is clear is that IKK mediates signaling specificity by tight dynamic control that is stimulus-specific and induces the expression of specific sets of genes. Recent studies have reported on a tightly coupled activation and inactivation mechanism that can only be described by a multi-state activation-inactivation cycle that involves the function of several enzymes with different functions, such as ubiquitin ligases, kinases, phosphatases, and foldases. Through regulation of these activities, we hypothesize that the IKK cycle is driven in a stimulus- and cell type-specific manner, and that understanding the kinetic relationships will reveal opportunities for rationally targeted pharmacological intervention that discriminate between disease associated misregulation and stimulus-responsive regulation in healthy cells. In this proposal, we will construct a mathematical model of the IKK cycle to explore the dynamic regulation of IKK activity. We will then focus biochemical and biophysical studies on specific control mechanisms. In particular, we test the roles of IKK oligomerization, conformational changes, and upstream kinases in IKK activation and inhibition of IKK. Computational simulations will guide genetic and pharmacological manipulation of IKK dynamics. Finally, we will focus our study on how TNF and IL-1 produce differential dynamic control of IKK; how differential dose response and temporal control determine the efficacy of cytokine traps. PUBLIC HEALTH RELEVANCE: The IkappaB kinase (IKK) complex is large protein kinase that specifically receives signals from cell surface receptors and transmits the signal to downstream effector transcription factor NF-kB. IKK must remain at a low activity state under resting state of the cell and transits into a high activity state upon receiving signals. Any alteration of this tight regulatory mode of IKK results to abnormal cellular outcomes including inflammatory diseases and cancer. The precise mechanism of how IKK-intrinsic and extrinsic cellular mechanisms control IKK activity is poorly understood. This proposal will integrate diverse methodologies that include mathematical modeling, biophysics, biochemistry and genetics to probe IKK regulation.