The ciliopathies are a group of disorders caused by structural or functional defects in cilia and their anchoring structures, the basal bodies. Despite significant advances in identifying ciliopathy genes, the basic causative disease mechanisms are poorly understood. Recent studies have highlighted the cilium as an important sensor, leading to a host of paracrine signaling defects in ciliopathy patients and model organisms. Towards understanding the mechanism of signal transduction from the cilium, we and others have uncovered evidence that intimate a direct relationship between ciliary function and the proteasome. First, a significant fraction of the proteasome localizes to the pericentriolar region; second, several basal body proteins mutated in ciliopathies interact directly with regulatory subunits of the proteasome;finally, our recent data indicate that defects in proteasome-mediated degradation of signaling molecules such as Gli3, ?-catenin, NICD and I-?B probably underlies observed signaling defects in numerous ciliary mutants. My goal is to explore the relationship between the primary cilium and the proteasome. My hypotheses are grounded on the above facts and the following two observations: a) the proteasome is known to alter its composition under certain conditions, such as cellular stress;and b) the ciliary proteome database contains several regulatory subunits of the proteasome. Therefore, I propose to ask a) whether ciliary signaling induces compositional changes of proteasome;and b) whether mutations in ciliary components of the proteasome contribute causal and/or modifying alleles to patients with ciliopathies. To answer these questions, I will 1) investigate the composition of the proteasome upon suppression of three ciliopathy proteins (BBS4, a basal body protein;IFT88, an anterograde IFT protein;and IFT139, a retrograde IFT protein);2) test the physiological relevance of the compositional changes by overexpressing or suppressing candidate subunits of proteasome in a series of established reporter cell lines and zebrafish models suppressed for the same set of genes;and ask whether such manipulations improve or deteriorate the previously established knock-down;3) sequence the coding regions of all apparent ciliary components of the ubiquitin-proteasome system (UPS) in a diverse ciliopathy cohort, followed by functional evaluation of appropriate changes. These studies will contribute to the better mechanistic understanding of the relationship between ciliary function and signal transduction and will inform the genetic architecture of ciliopathies. Moreover, the potential link between proteasomal function and ciliary signaling represents a significant shift in our understanding of this organelle and opens a host of new therapeutic possibilities.
A major challenge in medical genetics is that mutations at a causal disease gene cannot fully explain the typical clinical variability seen in patients;this in turns hampers both prognosis and clinical management. To address this problem, the goal of our study is to explore the functional and genetic interaction between compositional change of proteasome and known ciliopathy genes and to better understand the biological factors and mechanisms that underscore clinical variability. Our study will improve our understanding of ciliary- mediated signaling and expand our knowledge of the genetic architecture of ciliopathies, with potentially profound impact on the design of therapeutic paradigms.
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