# Discoveries at the Crossroads of Integrin and Inflammatory Signaling in Platelets

> **NIH NIH R01** · UNIVERSITY OF CALIFORNIA, SAN DIEGO · 2020 · $387,500

## Abstract

PROJECT SUMMARY
Platelet studies have had a profound impact on our understanding of adhesion receptor function
as exemplified by the adhesion and signaling roles of integrin αIIbβ3 in hemostasis and
thrombosis. Less is known about whether and how αIIbβ3 signaling regulates platelets in their
roles as sentinels and effectors of immunity and inflammation. In this regard, we have discovered
that αIIbβ3 interacts through its αIIb cytoplasmic tail with SHARPIN, an obligate component of the
linear ubiquitin chain assembly complex (LUBAC). This complex is the only known enzyme
responsible for M1 linear ubiquitination of key proteins involved in immune and inflammatory
signaling through the NF-κB pathway in leukocytes. Platelets express many proteins of the
canonical NF-κB pathway. Therefore, we will now employ complementary approaches, including
studies of peripheral blood platelets, megakaryocytes and platelets derived from human induced
pluripotent stem cells, and gene-targeted mice to test the following central hypothesis: Through
dynamic and mutually exclusive interactions with αIIbβ3 and LUBAC, SHARPIN regulates platelet
function in inflammation and immunity as well as in hemostasis and thrombosis. Aim 1 will employ
biochemical and advanced imaging techniques to test whether physical and functional linkages
exist between αIIbβ3, LUBAC and the NF-κB pathway in human and mouse platelets. Attention
will be focused on whether SHARPIN functions to maintain αIIbβ3 in a low-affinity state in resting
platelets, but dissociates from αIIb and assembles the LUBAC complex to facilitate αIIbβ3 and
NF-κB activation in response to platelet agonists generated during hemostasis and inflammation.
Aim 2 will introduce genetic modifications into human megakaryocytes and platelets derived from
induced pluripotent stem cells to model the effects of SHARPIN knockdown or knockout on αIIbβ3
and LUBAC functions in the appropriate primary cells. Using this system, optogenetic techniques
new to the platelet field will be used to determine the functional consequences of conditional
SHARPIN interactions with αIIbβ3 or with its two LUBAC protein partners. Aim 3 will address
whether SHARPIN is required for αIIbβ3 and platelet functions in response to inflammatory stimuli
and vascular injury in vivo. To accomplish this, platelet-specific SHARPIN knockout mice will be
generated using the Pf4-Cre system and studied in several mouse models of platelet-dependent
inflammation, hemostasis and thrombosis. Altogether, these studies will provide new insights into
the role of SHARPIN in platelet pathobiology, with mechanistic and potential therapeutic
implications beyond hemostasis and for platelets in inflammation and immunity.

## Key facts

- **NIH application ID:** 9940750
- **Project number:** 5R01HL056595-23
- **Recipient organization:** UNIVERSITY OF CALIFORNIA, SAN DIEGO
- **Principal Investigator:** SANFORD J SHATTIL
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $387,500
- **Award type:** 5
- **Project period:** 1996-07-01 → 2021-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9940750

## Citation

> US National Institutes of Health, RePORTER application 9940750, Discoveries at the Crossroads of Integrin and Inflammatory Signaling in Platelets (5R01HL056595-23). Retrieved via AI Analytics 2026-06-23 from https://api.ai-analytics.org/grant/nih/9940750. Licensed CC0.

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