# Biased agonsim of CXCL12 stimulation of the atypical and classical receptors, ACKR3 and CXCR4

> **NIH NIH F32** · UNIVERSITY OF CALIFORNIA, SAN DIEGO · 2020 · $67,446

## Abstract

Project Abstract
CXCL12 stimulation of the chemokine receptors CXCR4 and ACKR3 drives cellular migration during
development, immune system mobility, and inflammatory responses. The trio plays a major role in cancers
where they promote metastasis and tumor proliferation. Thus, both receptors are promising targets for
therapeutics, with ongoing clinical trials of compounds targeting CXCR4 and ACKR3 ligands in development.
Despite the common agonist, CXCR4 and ACKR3 have decidedly different responses. While CXCR4 signals
through both G proteins and β-arrestins like other classical G protein-coupled receptors (GPCRs), ACKR3 only
couples with arrestins. . CXCR4 and ACKR3 are structurally alike and bind CXCL12 in a similar manner, yet
the receptors appear to activate by different mechanisms. CXCR4 is extremely sensitive to changes to the
chemokine interaction, with single-point mutations leading the high-affinity agonist to act as an antagonist.
Conversely, ACKR3 is promiscuous, with nearly all ligands tested acting as agonists. How these differences
translate into the biased signaling is an open question. I propose to investigate the how the CXCL12 signal is
interpreted by these receptors by resolving how the ligand affects the receptor conformation and the secondary
interactions with kinases and β-arrestins. The central hypothesis of this proposal is that these interactions will
be different for the classical and atypical receptors and the results of the presented experiments will provide
insights into receptor-level biased signaling. This hypothesis will be pursued by three specific aims. Aim 1:
Identify the structural rearrangements of ACKR3 induced by CXCL12 binding by determining the high
resolution crystal structure of the complex. The resulting structure will reveal the specific interactions through
an atypical receptor that are induced by CXCL12 binding and structural basis of activation. Aim 2: Determine
how CXCL12-activated ACKR3 is phosphorylated and interacts with β-arrestin. This aim will determine what
kinases phosphorylate the ACKR3, where those phosphates are incorporated and how the pattern of
modification alters β-arrestin interactions and signaling. Aim 3: Determine how β-arrestin interacts with
CXCL12-stimulated CXCR4 by imaging the complex with electron microscopy and ultimately resolving the
structure of the CXCL12:CXCR4:β-arrestin complex. Together, these studies will present an unparalleled view
into how receptor-mediated biased agonism is manifested by classical and atypical GPCRs. Determining how
these receptors respond the natural stimulus will ultimately facilitate future drug development.

## Key facts

- **NIH application ID:** 9992448
- **Project number:** 1F32GM137505-01
- **Recipient organization:** UNIVERSITY OF CALIFORNIA, SAN DIEGO
- **Principal Investigator:** Christopher T Schafer
- **Activity code:** F32 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $67,446
- **Award type:** 1
- **Project period:** 2020-03-16 → 2023-03-15

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9992448

## Citation

> US National Institutes of Health, RePORTER application 9992448, Biased agonsim of CXCL12 stimulation of the atypical and classical receptors, ACKR3 and CXCR4 (1F32GM137505-01). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9992448. Licensed CC0.

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