Abstract
SHANK-associated RH domain interactor (SHARPIN) inhibits integrins through interaction with the integrin α-subunit. In addition, SHARPIN enhances nuclear factor-kappaB (NF-κB) activity as a component of the linear ubiquitin chain assembly complex (LUBAC). However, it is currently unclear how regulation of these seemingly different roles is coordinated. Here, we show that SHARPIN binds integrin and LUBAC in a mutually exclusive manner. We map the integrin binding site on SHARPIN to the ubiquitin-like (UBL) domain, the same domain implicated in SHARPIN interaction with LUBAC component RNF31 (ring finger protein 31), and identify two SHARPIN residues (V267, L276) required for both integrin and RNF31 regulation. Accordingly, the integrin α-tail is capable of competing with RNF31 for SHARPIN binding in vitro. Importantly, the full SHARPIN RNF31-binding site contains residues (F263A/I272A) that are dispensable for SHARPIN-integrin interaction. Importantly, disrupting SHARPIN interaction with integrin or RNF31 abolishes SHARPIN-mediated regulation of integrin or NF-κB activity, respectively. Altogether these data suggest that the roles of SHARPIN in inhibiting integrin activity and supporting linear ubiquitination are (molecularly) distinct.
Highlights
Similar to the catalytic subunit of linear ubiquitin chain assembly complex (LUBAC) (RNF31; ring finger protein 31, known as HOIL-1-Interacting Protein (HOIP)) [6], bind the conserved central ubiquitin-like domain (UBL) of SHARPIN
SHARPIN has three conserved functional domains; the N-terminal pleckstrin homology (PH) superfold that mediates homomultimerization [10,11], the central UBL domain and the C-terminal NPL4 zinc finger domain (NZF) that is required for LUBAC function [6]
Integrins and RNF31 both interact with the UBL domain of SHARPIN
Summary
Similar to the catalytic subunit of LUBAC (RNF31; ring finger protein 31, known as HOIL-1-Interacting Protein (HOIP)) [6], bind the conserved central ubiquitin-like domain (UBL) of SHARPIN. RNF31 and integrin bind to SHARPIN in a mutually exclusive manner, suggesting that the roles of SHARPIN in inhibiting integrin activity and supporting linear ubiquitination are molecularly distinct.
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