p47 licenses activation of the immune deficiency pathway in the tick <i>Ixodes scapularis</i>

Abstract

The E3 ubiquitin ligase X-linked inhibitor of apoptosis (XIAP) acts as a molecular rheostat for the immune deficiency (IMD) pathway of the tick <i>Ixodes scapularis</i> How XIAP activates the IMD pathway in response to microbial infection remains ill defined. Here, we identified the XIAP enzymatic substrate p47 as a positive regulator of the <i>I. scapularis</i> IMD network. XIAP polyubiquitylates p47 in a lysine 63-dependent manner and interacts with the p47 ubiquitin-like (UBX) module. p47 also binds to Kenny (IKKγ/NEMO), the regulatory subunit of the inhibitor of nuclear factor (NF)- κB kinase complex. Replacement of the amino acid lysine to arginine within the p47 linker region completely abrogated molecular interactions with Kenny. Furthermore, mitigation of <i>p47</i> transcription levels through RNA interference in <i>I. scapularis</i> limited Kenny accumulation, reduced phosphorylation of IKKβ (IRD5), and impaired cleavage of the NF-κB molecule Relish. Accordingly, disruption of <i>p47</i> expression increased microbial colonization by the Lyme disease spirochete <i>Borrelia burgdorferi</i> and the rickettsial agent <i>Anaplasma phagocytophilum</i> Collectively, we highlight the importance of ticks for the elucidation of paradigms in arthropod immunology. Manipulating immune signaling cascades within <i>I. scapularis</i> may lead to innovative approaches to reducing the burden of tick-borne diseases.