Background: SHARPIN (Src homology 3 and multiple ankyrin repeat domains protein (SHANK)-associated RH domain-interacting protein) as part of the linear ubiquitin chain assembly complex (LUBAC) catalyses the addition of linear (Met1-linked) ubiquitin chains to substrates. As part of this complex SHARPIN acts as a multi-functional modulator of immune and inflammatory responses through regulation of NfkB activation. In addition, SHARPIN can act as a negative regulator of integrin function. Despite platelets being anucleate cells several studies have determined potential roles for both ubiquitination and NfkB in regulating platelet function, however little is known about either linear ubiquitination and/or SHARPIN in platelets.

Aims: To determine the role of SHARPIN in platelet linear ubiquitination and platelet function.

Methods: Platelet functional responses (integrin activation, P-selectin expression, ATP secretion and in vitro thrombus formation) and platelet ubiquitination were determined in platelets from mice homozygous for SHARPIN^cpdm allele (cpdm/cpdm), which lack SHARPIN expression.

Results: We confirmed that SHARPIN was expressed in platelets from wild-type mice but not mice homozygous for SHARPIN^cpdm allele (cpdm/cpdm) and that this correlated with a reduction in linear ubiquitination. Platelet function in response to thrombin was unaffected. In contrast, CRP-XL- and U46619- mediated platelet responses were significantly reduced and thrombus formation under flow on a collagen-coated surface was impaired. Despite the reported role for NfkB in regulating platelet function we were unable to recapitulate the cpdm/cpdm phenotype by inhibiting IκBα phosphorylation.

Conclusions: The absence of SHARPIN in platelets from cpdm/cpdm mice results in impaired linear ubiquitination, functional responses to CRP and U46619 and thrombus formation, indicating an important role for SHARPIN in platelet functional responses.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/important-role-for-sharpin-in-supporting-platelet-linear-ubiquitination-and-thrombus-formation/