Date of Award

12-31-2013

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology/Molecular, Cellular, and Organismal Biology

First Advisor

Alexey Veraksa

Second Advisor

Rick Kesseli

Third Advisor

Linda S. Huang

Abstract

In both insects and mammals, Toll and related receptors are central for the function of the immune system. The core components of the Toll pathway in Drosophila include the ligand Spätzle, the receptor Toll, the intracellular adaptors MyD88 and Tube, and the kinase Pelle. Toll signaling regulates the nuclear accumulation of the NF-κB homologs Dorsal (Dl) and Dif. Inappropriate activation of the Toll pathway often leads to a systemic inflammation phenotype, which is defined as activation of blood cells and elevated expression of innate immunity genes in the absence of infection.

An emerging control mechanism involved in the regulation of the core components of Toll/NF-κB signaling is sumoylation. Another level of control over the Toll/NF-κB pathway is exerted by β-arrestins. Beta arrestins were initially characterized as mediators of G protein coupled receptor (GPCR) desensitization and endocytosis. The Drosophila genome encodes a single ortholog of β-arrestins, Kurtz (Krz), which has been implicated in the regulation of GPCR signaling, as well as Notch, Hedgehog, receptor tyrosine kinase, and Toll pathways.

Previously it was shown that Krz limits the extent of Toll activation during embryogenesis; however the molecular details of this regulation are unknown. Here, I show for the first time that β-arrestin can control Toll signaling and systemic inflammation at the level of sumoylation. I demonstrate that loss of krz results in an upregulation of Toll downstream effectors and that Krz exerts its functions by binding to Ulp1, a SUMO protease. Knockdown of Ulp1 leads to an increase in global sumoylation in vivo and causes Toll hyperactivity phenotypes that are similar to the effects of loss of krz. Mutations in krz and Ulp1 result in nuclear localization of the Toll transcriptional effectors, formation of melanotic masses, and overexpression of Toll target genes, which are the hallmarks of Toll activation. Using Dl as a target for Ulp1-mediated de-sumoylation, I have showed that Krz is required for the optimal SUMO protease activity of Ulp1, and that both proteins are necessary for limiting the Toll pathway activity and preventing an inappropriate inflammatory response.

Comments

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