Serine 165 phosphorylation of SHARPIN regulates the activation of NF-κB

The adaptor SHARPIN composes, together with the E3 ligases HOIP and HOIL1, the linear ubiquitin chain assembly complex (LUBAC). This enzymatic complex catalyzes and stamps atypical linear ubiquitin chains onto substrates to modify their fate and has been linked to the regulation of the NF-kappa B pathway downstream of most immunoreceptors, inflammation, and cell death. However, how this signaling complex is regulated is not fully understood. Here, we report that a portion of SHARPIN is constitutively phosphorylated on the serine at position 165 in lymphoblastoid cells and can be further induced following T cell receptor stimulation. Analysis of a phosphorylation-resistant mutant of SHARPIN revealed that this mark controls the linear ubiquitination of the NF-kappa B regulator NEMO and allows the optimal activation of NF-kappa B in response to TNF alpha. These results identify an additional layer of regulation of the LUBAC and unveil potential strategies to modulate its action.

Automated summary

The adaptor SHARPIN, together with E3 ligases HOIP and HOIL1, forms the LUBAC complex, which catalyzes the addition of linear ubiquitin chains to substrates. This process is crucial for regulating NF-kappa B signaling downstream of immunoreceptors. Phosphorylation of SHARPIN at serine 165 plays a role in controlling linear ubiquitination of NEMO, affecting NF-kappa B activation in response to TNF alpha. These findings provide insights into the regulation of LUBAC and potential strategies for modulating its activity.