Deciphering the TANK-dependent signaling pathways through interactomics studies

Understanding of molecular signaling pathways is a prerequisite for drug target design, since signal communication in cells is an interplay network of multiple proteins. While some of them have catalytic or transcriptional functions, some are scaffolds which bind to two or more components in pathways to allow temporal and spatial coordination of signaling cascades. Different modifications of these adaptor proteins such as phosphorylation, ubiquitination, sumoylation, or acetylation may dictate the signaling specificity. In the first part of this thesis, we describe the Lys63-linked polyubiquitination of TANK, a scaffold protein which plays roles in NF-kB- and IRF-activating pathways. In the second part, we report a novel TANK-interacting partner, nucleoporin p62, whose interaction is endogenously detectable in neuronal cell line N2A under the stimulation with soluble CD40 ligand. p62 can bind not only to TANK but also to others of its interacting proteins independently of TANK, although p62 is not a direct substrate for IKK-related kinases, TBK1 and IKKe. A point mutation in p62, Q391P, which is linked to familial infantile bilateral striatal neurodegeneration (IBSN) disease, abolishes solely the association with TANK while impairs all interactions with other binding partners. TANK and p62 are found important for MAPK activation in neuronal cells as ERK phosphorylation is impaired in TANK- or p62-depleted N2A cells whereas p38 phosphorylation is enhanced only upon TANK depletion. Further investigations would be needed to decipher the role of TANK and p62 in the CD40 dependent-ERK activating pathway in order to clarify their implications in cell survival and in IBSN neurodegenerative disease.