# Protease Activated Receptor and Thrombomodulin Signaling by coagulation proteases

> **NIH NIH R01** · OKLAHOMA MEDICAL RESEARCH FOUNDATION · 2024 · $426,250

## Abstract

Project Summary
Thrombomodulin (TM) is an integral membrane receptor on endothelial cells which binds to exosite-
1 of thrombin to switch the specificity of thrombin from a procoagulant to an anticoagulant protease.
The interaction with TM enables thrombin to activate protein C to activated protein C (APC). In
addition to its anticoagulant function, APC binds to endothelial protein C receptor (EPCR) to cleave
protease-activated receptor 1 (PAR1) at Arg46 site to elicit cytoprotective responses in endothelial
cells. The exosite-1-dependent interaction of thrombin with TM on endothelial cells inhibits the
thrombin recognition of PAR1 and procoagulant substrates. TM exerts direct anti-inflammatory
functions through its lectin-like domain by unknown mechanisms. Recent results have indicated an
association between loss of TM expression and uncontrolled cell proliferation and metastasis. Based
on our preliminary data in this application, we hypothesize that the cytoplasmic domain of TM is
linked to the actin cytoskeleton and involved in the regulation of PTEN/AKT/mTOR signaling axis.
TM endows a quiescence phenotype to endothelial cells through modulation of this signaling axis
under basal and stimulated conditions. We demonstrate that interaction of EGF-like domains of TM
with exosite-1 of thrombin and proexosite-1 of prothrombin leads to activation (phosphorylation at
Ser172) of AMPK, thereby TM differentially regulating mTORC1 (inhibition) and mTORC2
(activation) signaling. We hypothesize by this signaling mechanism, TM contributes to regulation of
the vascular tone, maintenance, and stabilization of the barrier permeability function of the
vasculature under steady-state and stimulated conditions. We further demonstrate TM changes the
PAR1 cleavage specificity of thrombin from Arg41 site to Arg46 site, thereby switching the PAR1-
dependent signaling specificity of thrombin from a proinflammatory response to a cytoprotective one.
We have prepared a series of TM receptor constructs, recombinant APC and thrombin derivatives
and TM-null and PAR1-null endothelial cells to investigate the following three Specific Aims: Aim 1
will investigate the mechanism by which TM maintains a quiescence phenotype in endothelial cells.
Aim 2 will investigate the hypothesis that the cytoplasmic domain of TM is linked to the actin
cytoskeleton and involved in regulation of mTOR signaling upon interaction with ligands thrombin
and prothrombin. Aim 3 will investigate mechanisms through which EPCR and TM modulate the
signaling specificity of PAR1 cleavage by coagulation proteases in endothelial cells.

## Key facts

- **NIH application ID:** 10819159
- **Project number:** 5R01HL101917-14
- **Recipient organization:** OKLAHOMA MEDICAL RESEARCH FOUNDATION
- **Principal Investigator:** ALIREZA R. REZAIE
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $426,250
- **Award type:** 5
- **Project period:** 2010-04-01 → 2027-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10819159

## Citation

> US National Institutes of Health, RePORTER application 10819159, Protease Activated Receptor and Thrombomodulin Signaling by coagulation proteases (5R01HL101917-14). Retrieved via AI Analytics 2026-05-26 from https://api.ai-analytics.org/grant/nih/10819159. Licensed CC0.

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