Caspase activity and regulation in Drosophila melanogaster innate immunity

• Author / Creator

  Guntermann, Silvia

• The fine balance struck between life and death is key for the health of all multicellular organisms and therefore the pathways that govern life and death decisions are evolutionarily highly conserved. For example, the human TNF and the Drosophila IMD pathways coordinate signaling elements such as conserved JNK, NF-κB, and caspase modules to drive appropriate responses. Caspases are an evolutionarily conserved family of cysteinyl aspartate proteases with fundamental roles in the opposing processes of cell-survival and cell-death. The caspase Dredd is an essential pro-survival regulator of the IMD mediated immune response. However, the detailed involvement of Dredd in the sequential activation of the IMD cascade, the position of Dredd, and Dredd’s interactions with the IMD pathway were unknown. In addition, the molecular mechanism of Dredd activation and regulation was unclear. In this study I conducted a thorough structural and functional analysis of the mechanism of Dredd activity in IMD signaling. I revealed numerous interactions of Dredd with early activators of the IMD pathway. I showed that the caspase activity inhibitor p35 blocked Dredd activation in a mechanism that is distinct from the general mechanism of p35- dependent caspase inhibition. In addition, Dredd activation appears independent of auto-processing which might be explained by the lack of Dredd linker residues that support auto-processing and may explain Dredd’s sole function in pro- survival responses. In a combination of cell culture and in vivo assays, I demonstrated that Dredd is required for the activation of dJNK signaling upstream of dTAK1 and determined that Dredd additionally functions down- stream of Imd activation. Furthermore, my data uncovered a dual regulation of dIAP2 by RING domain mediated destruction and Dronc mediated N-terminal proteolytic cleavage. In summary, the data indicate a distinct activation mechanism for Dredd and establish dual functions for Dredd in the IMD signaling cascade, where Dredd is required in a proximal signaling complex for the early transduction of a phospho-relay to Rel and dJNK as well as for the subsequent activation of Rel. The data also uncover a novel role for Dronc in immune signaling. Combined the findings underline the importance and complexity of non-apoptotic roles of caspases.

• Subjects / Keywords

  • Innate immunity
  • Caspase

• Graduation date

  Spring 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R37S7J153

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.