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CXCR7 controls competition for recruitment of β-arrestin 2 in cells expressing both CXCR4 and CXCR7.

Coggins NL, Trakimas D, Chang SL, Ehrlich A, Ray P, Luker KE, Linderman JJ, Luker GD - PLoS ONE (2014)

Bottom Line: We then experimentally validated model predictions that co-expression of CXCR4 and CXCR7 on the same cell substantially decreases both the magnitude and duration of CXCL12-regulated recruitment of β-arrestin 2 to CXCR4.These results reveal how competition for β-arrestin 2 controls integrated responses to CXCL12 in cells expressing both CXCR4 and CXCR7.These results advance understanding of normal and pathologic functions of CXCL12, which is critical for developing effective strategies to target these pathways therapeutically.

View Article: PubMed Central - PubMed

Affiliation: Center for Molecular Imaging, Department of Radiology, Department of Microbiology and Immunology, University of Michigan, Ann Arbor, Michigan, United States of America.

ABSTRACT
Chemokine CXCL12 promotes growth and metastasis of more than 20 different human cancers, as well as pathogenesis of other common diseases. CXCL12 binds two different receptors, CXCR4 and CXCR7, both of which recruit and signal through the cytosolic adapter protein β-arrestin 2. Differences in CXCL12-dependent recruitment of β-arrestin 2 in cells expressing one or both receptors remain poorly defined. To quantitatively investigate parameters controlling association of β-arrestin 2 with CXCR4 or CXCR7 in cells co-expressing both receptors, we used a systems biology approach combining real-time, multi-spectral luciferase complementation imaging with computational modeling. Cells expressing only CXCR4 maintain low basal association with β-arrestin 2, and CXCL12 induces a rapid, transient increase in this interaction. In contrast, cells expressing only CXCR7 have higher basal association with β-arrestin 2 and exhibit more gradual, prolonged recruitment of β-arrestin 2 in response to CXCL12. We developed and fit a data-driven computational model for association of either CXCR4 or CXCR7 with β-arrestin 2 in cells expressing only one type of receptor. We then experimentally validated model predictions that co-expression of CXCR4 and CXCR7 on the same cell substantially decreases both the magnitude and duration of CXCL12-regulated recruitment of β-arrestin 2 to CXCR4. Co-expression of both receptors on the same cell only minimally alters recruitment of β-arrestin 2 to CXCR7. In silico experiments also identified β-arrestin 2 as a limiting factor in cells expressing both receptors, establishing that CXCR7 wins the "competition" with CXCR4 for CXCL12 and recruitment of β-arrestin 2. These results reveal how competition for β-arrestin 2 controls integrated responses to CXCL12 in cells expressing both CXCR4 and CXCR7. These results advance understanding of normal and pathologic functions of CXCL12, which is critical for developing effective strategies to target these pathways therapeutically.

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Related in: MedlinePlus

Modeling free β-arrestin 2 and free (unbound to β-arrestin 2) cell surface receptors over time.(A) Model output of the % of initial free β-arrestin 2 through 40 min in CXCR4+, CXCR7+, or CXCR4+-CXCR7+ cells treated with 1000 ng/mL CXCL12-α. (B) Model output of % of initial free (unbound to β-arrestin 2) cell surface receptors through 40 min in cells treated with 1000 ng/mL CXCL12. Legend denotes the specific receptor and cell type on which the receptor is expressed.
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pone-0098328-g004: Modeling free β-arrestin 2 and free (unbound to β-arrestin 2) cell surface receptors over time.(A) Model output of the % of initial free β-arrestin 2 through 40 min in CXCR4+, CXCR7+, or CXCR4+-CXCR7+ cells treated with 1000 ng/mL CXCL12-α. (B) Model output of % of initial free (unbound to β-arrestin 2) cell surface receptors through 40 min in cells treated with 1000 ng/mL CXCL12. Legend denotes the specific receptor and cell type on which the receptor is expressed.

Mentions: Recruitment of β-arrestin 2 to CXCR4+ cells in response to 1000 ng/mL CXCL12 peaks at ≈ 20-22 min and plateaus or decreases through 90 min at all ligand concentrations. We predict an excess of β-arrestin 2 throughout this time (Fig. 4A). In contrast, the number of CXCR4 receptors able to bind β-arrestin 2 decreases to ≈50% of the initial value 40 min after adding CXCL12 (Fig. 4B). Internalized, ligand-bound CXCR4 is degraded, decreasing numbers of cell surface receptors and subsequently reducing the rate of β-arrestin 2 binding. Therefore, β-arrestin 2 recruitment in CXCR4+ cells is limited by the number of cell-surface receptors unbound to β-arrestin 2 and not the amount of β-arrestin 2.


CXCR7 controls competition for recruitment of β-arrestin 2 in cells expressing both CXCR4 and CXCR7.

Coggins NL, Trakimas D, Chang SL, Ehrlich A, Ray P, Luker KE, Linderman JJ, Luker GD - PLoS ONE (2014)

Modeling free β-arrestin 2 and free (unbound to β-arrestin 2) cell surface receptors over time.(A) Model output of the % of initial free β-arrestin 2 through 40 min in CXCR4+, CXCR7+, or CXCR4+-CXCR7+ cells treated with 1000 ng/mL CXCL12-α. (B) Model output of % of initial free (unbound to β-arrestin 2) cell surface receptors through 40 min in cells treated with 1000 ng/mL CXCL12. Legend denotes the specific receptor and cell type on which the receptor is expressed.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4045718&req=5

pone-0098328-g004: Modeling free β-arrestin 2 and free (unbound to β-arrestin 2) cell surface receptors over time.(A) Model output of the % of initial free β-arrestin 2 through 40 min in CXCR4+, CXCR7+, or CXCR4+-CXCR7+ cells treated with 1000 ng/mL CXCL12-α. (B) Model output of % of initial free (unbound to β-arrestin 2) cell surface receptors through 40 min in cells treated with 1000 ng/mL CXCL12. Legend denotes the specific receptor and cell type on which the receptor is expressed.
Mentions: Recruitment of β-arrestin 2 to CXCR4+ cells in response to 1000 ng/mL CXCL12 peaks at ≈ 20-22 min and plateaus or decreases through 90 min at all ligand concentrations. We predict an excess of β-arrestin 2 throughout this time (Fig. 4A). In contrast, the number of CXCR4 receptors able to bind β-arrestin 2 decreases to ≈50% of the initial value 40 min after adding CXCL12 (Fig. 4B). Internalized, ligand-bound CXCR4 is degraded, decreasing numbers of cell surface receptors and subsequently reducing the rate of β-arrestin 2 binding. Therefore, β-arrestin 2 recruitment in CXCR4+ cells is limited by the number of cell-surface receptors unbound to β-arrestin 2 and not the amount of β-arrestin 2.

Bottom Line: We then experimentally validated model predictions that co-expression of CXCR4 and CXCR7 on the same cell substantially decreases both the magnitude and duration of CXCL12-regulated recruitment of β-arrestin 2 to CXCR4.These results reveal how competition for β-arrestin 2 controls integrated responses to CXCL12 in cells expressing both CXCR4 and CXCR7.These results advance understanding of normal and pathologic functions of CXCL12, which is critical for developing effective strategies to target these pathways therapeutically.

View Article: PubMed Central - PubMed

Affiliation: Center for Molecular Imaging, Department of Radiology, Department of Microbiology and Immunology, University of Michigan, Ann Arbor, Michigan, United States of America.

ABSTRACT
Chemokine CXCL12 promotes growth and metastasis of more than 20 different human cancers, as well as pathogenesis of other common diseases. CXCL12 binds two different receptors, CXCR4 and CXCR7, both of which recruit and signal through the cytosolic adapter protein β-arrestin 2. Differences in CXCL12-dependent recruitment of β-arrestin 2 in cells expressing one or both receptors remain poorly defined. To quantitatively investigate parameters controlling association of β-arrestin 2 with CXCR4 or CXCR7 in cells co-expressing both receptors, we used a systems biology approach combining real-time, multi-spectral luciferase complementation imaging with computational modeling. Cells expressing only CXCR4 maintain low basal association with β-arrestin 2, and CXCL12 induces a rapid, transient increase in this interaction. In contrast, cells expressing only CXCR7 have higher basal association with β-arrestin 2 and exhibit more gradual, prolonged recruitment of β-arrestin 2 in response to CXCL12. We developed and fit a data-driven computational model for association of either CXCR4 or CXCR7 with β-arrestin 2 in cells expressing only one type of receptor. We then experimentally validated model predictions that co-expression of CXCR4 and CXCR7 on the same cell substantially decreases both the magnitude and duration of CXCL12-regulated recruitment of β-arrestin 2 to CXCR4. Co-expression of both receptors on the same cell only minimally alters recruitment of β-arrestin 2 to CXCR7. In silico experiments also identified β-arrestin 2 as a limiting factor in cells expressing both receptors, establishing that CXCR7 wins the "competition" with CXCR4 for CXCL12 and recruitment of β-arrestin 2. These results reveal how competition for β-arrestin 2 controls integrated responses to CXCL12 in cells expressing both CXCR4 and CXCR7. These results advance understanding of normal and pathologic functions of CXCL12, which is critical for developing effective strategies to target these pathways therapeutically.

Show MeSH
Related in: MedlinePlus