An FTLD-associated SQSTM1 variant impacts Nrf2 and NF-κB signalling and is associated with reduced phosphorylation of p62

Elevated oxidative stress has been implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS) and Frontotemporal Lobar Degeneration (FTLD). In response to oxidative stress, the Nrf2 transcription factor activates protective antioxidant genes. A critical regulator of Nrf2 is the inhibitory protein Keapl, which mediates Nrf2 degradation. In response to cellular stress an interaction between Keapl and SQSTM1/p62 (p62), a signalling adaptor protein, allows for increased Nrf2 signalling as it escapes degradation. Mutations in SQSTM1 (encoding p62) are linked with ALS-FTLD. Previously, two ALS-FTLD-associated p62 mutant proteins within the Keapl interacting region (KIR) of p62 were found to be associated with decreased Keapl-p62 binding and Nrf2 activation. Here we report that a non-KIR domain FTLD-associated variant of p62 (p.R110C), affecting a residue close to the N-terminal PB1 oligomerisation domain, also reduces Keapl-p62 binding in cellulo and thereby reduces Nrf2 activity in reporter assays. Further, we observed that expression of p.R110C increased NF-kappa B activation compared with wild type p62. Altered signalling appeared to be linked with reduced phosphorylation of p62 at Serine residues -349 and -403. Our results confirm that ALS-FTLD mutations affecting multiple domains of p62 result in a reduced stress response, suggesting that altered stress signalling may directly contribute to the pathology of some ALS-FTLD cases.