Regulation of the deubiquitinase CYLD in innate immune signalling

Thesis

Innate immune receptors are vital for protection against invading pathogens and the downstream signalling events of these are controlled by ubiquitination. Classically, ubiquitin was described to serve as a degradative signal. However, of the eight possible types of ubiquitin linkages, most have been assigned non-degradative roles and instead serve scaffolding functions for recruitment and activation of proteins. M1- and K63- chains are two such linkages and have crucial roles in mediating immune signalling events, with the balance between their deposition onto receptor components, and removal, determining the magnitude and duration of the signalling.

Linear ubiquitin chain assembly complex (LUBAC) is the only E3 known to generate M1-chains and is essential for productive signalling. It is regulated by its two associated deubiquitinating enzymes (DUBs), CYLD and OTULIN, which associate with the catalytic subunit, HOIP. However, the mechanism through which CYLD interacts with LUBAC is unclear. As such, this study aimed to characterise how CYLD is specifically recruited to the LUBAC complex and subsequently determine the factors that are mediating its activation.

In this thesis, I describe the identification of SPATA2 as a factor linking CYLD with LUBAC, thereby facilitating regulation of innate immune signalling by CYLD. In the second part of the thesis I investigate the regulation of CYLD’s catalytic activity by phosphorylation. My studies reveal a novel phosphorylation site (S568) on CYLD which regulates CYLD activity and its ability to restrict innate immune signalling.

In summary, this study identified a novel binding partner of CYLD and characterised the phosphorylation-mediated activation of its DUB activity. This provides an explanation as to how CYLD is recruited to signalling complexes in a LUBACdependent manner, as well as novel mechanistic insight into how innate immune signalling events may be fine-tuned by regulation of CYLD.

Authors: Leske, D

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford