Investigating new roles of the ubiquitin proteasome system in cell death and innate immune signalling

Immune responses are a complex network of interactions between proteins in different cellular processes with multiple layers of regulation. In the present study, we explored the role of some regulators of the ubiquitination and proteasome systems in cell death and innate immune signalling pathways in macrophages. Initial studies focused on a form of regulated cell death termed necroptosis, a type of cell death mediated by the receptor-interacting protein kinases (RIP). RIP kinases are known to interact with E3 ubiquitin ligases Pellino proteins. Pellino 1 has recently been described to target RIP kinases and regulate necroptosis. Firstly, the roles of the E3 ubiquitin ligases Pellino 2 and Pellino 3 were studied. The findings demonstrated that neither of them regulates necroptosis induced by innate immunity triggers. Studies next characterised the role of TLR signalling pathways in the activation of hypoxia-inducible factor 1α (HIF-1α), a critical target of the ubiquitin/proteasome system. Interestingly, these studies revealed that some of the TLRs promote a faster migration form of HIF-1α of approximately 40kDa. The upregulation of the latter was mediated by the TLR adaptor protein TRIF. The role of proteasome and lysosome mediators on processing of full length 110kDa HIF-1α to this smaller form was also assessed. As part of these experimental approaches, an intriguing discovery was made showing that treatment of macrophages with the proteasome inhibitor MG132 induced high levels of the anti-inflammatory cytokine IL10. This effect was dependent on P38 MAPK pathway activation and phosphorylation of the transcription factor CREB. Similar results were seen with proteasome inhibitor Bortezomib which is used clinically in the treatment of multiple myeloma. This effect is interesting considering that IL10 is a growth factor for myeloma cells and some patients treated with Bortezomib develop a refractory response to treatment and progression of disease. Overall, the present research provides novel insights into the roles of some regulators of the ubiquitin and proteasome systems in cell death and inflammatory signalling in macrophages.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

National University of Ireland Maynooth

Year dc:date.issued

2018

Author dc:creator

• Isaza-Correa, Johana M.

Language dc:language

en