Research ArticleBiochemistry

Key determinants of selective binding and activation by the monocyte chemoattractant proteins at the chemokine receptor CCR2

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Science Signaling  23 May 2017:
Vol. 10, Issue 480, eaai8529
DOI: 10.1126/scisignal.aai8529
  • Fig. 1 MCP chemokines display different efficacies and affinities at CCR2.

    (A) Flp-In T-REx 293 cells transiently transfected with plasmids encoding CCR2-RLuc8 and β-arr2–yellow fluorescent protein (YFP) were stimulated with the indicated concentrations of MCP-1, MCP-2, or MCP-3 before being analyzed by BRET to assess the recruitment of β-arr2. Left: Concentration-response data and fitted curves. Right: Relative efficacy, defined as the Emax value relative to that of MCP-1. (B) c-Myc–FLAG–CCR2 Flp-In T-REx 293 cells transiently transfected with plasmid encoding a BRET-based cAMP sensor were treated with 10 μM forskolin in the presence of the indicated concentrations of chemokines. Left: Measurement of the percentage inhibition of forskolin-stimulated cAMP production as a function of chemokine concentration. Right: Potency (pEC50) values. (C) Left: c-Myc–FLAG–CCR2 Flp-In T-REx 293 cells were treated with the indicated concentrations of chemokines for 3 min before the amount of phosphorylated ERK1/2 was measured by AlphaScreen assay. Right: Potency (pEC50) values. (D) Left: Membrane preparations of c-Myc–FLAG–CCR2 Flp-In T-REx 293 cells were incubated with 45 pM 125I–MCP-1 in the presence of the indicated concentrations of chemokines before the extent of binding of 125I–MCP-1 was determined by radioligand-binding assay. Right: Affinities (pIC50) for the three chemokines. (E) Left: c-Myc–FLAG–CCR2 Flp-In T-REx 293 cells were incubated with 100 nM chemokine for the indicated times before the extent of CCR2 internalization was determined by whole-cell anti–c-Myc enzyme-linked immunosorbent assay (ELISA). Right: Cell surface expression of CCR2 60 min after the addition of chemokine as a percentage of the amount of receptor present immediately before chemokine treatment. Data are means ± SEM of three to five experiments, each performed in triplicate. *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001 by one-way analysis of variance (ANOVA) with Dunnett’s multiple-comparison test.

  • Fig. 2 Design and structural validation of MCP-1/MCP-3 chimeras.

    (A) Aligned sequences of MCP-1 and MCP-3 with the three regions that were swapped in the chimeras indicated by boxes. Symbols above the residue labels indicate those previously found to be important in CCR2 binding (*) or activation (^) (27, 28). (B) The structure of MCP-1 (PDB code: 1dok) highlighting the regions swapped in the chimeras. (C) Nomenclature and schematic diagrams of the chimeras with regions from MCP-1 and MCP-3 in blue and red, respectively. (D) Upfield (methyl) region of the 1H NMR spectra of the WT and chimeric chemokines, showing well-dispersed peaks indicative of correct folding. ppm, parts per million.

  • Fig. 3 The N-terminal tail of MCP-1 and MCP-3 is a major determinant of affinity and efficacy.

    (A to D) 125I–MCP-1 competition binding, β-arr2 recruitment BRET, and ERK1/2 phosphorylation were assessed for MCP-1 and chimeras in the MCP-1 background (shades of blue) and for MCP-3 and chimeras in the MCP-3 background (shades of red). (A) Membrane preparations of c-Myc–FLAG–CCR2 Flp-In T-REx 293 cells were incubated with 45 pM 125I–MCP-1 in the presence of the indicated concentrations of chemokines before the extent of binding of 125I–MCP-1 was determined by radioligand-binding assay. Top: Competitive displacement data for MCP-1 and chimeras in the MCP-1 background. Bottom: Competitive displacement data for MCP-3 and chimeras in the MCP-3 background. (B) Left: Schematic representations of the WT and chimeric chemokines. As indicated, measurements of the affinity (pKi) of the indicated chemokines for CCR2, as determined by 125I–MCP-1 competition, the potency (pEC50) and efficacy (Emax) of chemokines in the β-arr2 recruitment assay, and the potency (pEC50) and efficacy (Emax) of chemokines in the ERK1/2 phosphorylation assay. (C) Flp-In T-REx 293 cells transiently transfected with plasmids encoding CCR2-RLuc8 and β-arr2–YFP were stimulated with the indicated concentrations of WT or chimeric chemokines before being analyzed by BRET to assess the recruitment of β-arr2. Top: Concentration-response data for MCP-1 and chimeras in the MCP-1 background. Bottom: Concentration-response data for MCP-3 and chimeras in the MCP-3 background. (D) c-Myc–FLAG–CCR2 Flp-In T-REx 293 cells were treated with the indicated concentrations of WT or chimeric chemokines for 3 min before the amount of phosphorylated ERK1/2 was measured by AlphaScreen assay. Top: Concentration-response data for MCP-1 and chimeras in the MCP-1 background. Bottom: Concentration-response data for MCP-3 and chimeras in the MCP-3 background. (E) c-Myc–FLAG–CCR2 Flp-In T-REx 293 cells were incubated with the indicated chemokine (100 nM) for 60 min before the cell surface expression of CCR2 was determined by whole-cell anti–c-Myc ELISA. Expression is presented as a percentage of that of the vehicle control. Data are means ± SEM of three to five experiments, each performed in triplicate. *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001 compared to MCP-1. ^P < 0.05, ^^P < 0.01, ^^^P < 0.001, and ^^^^P < 0.0001 compared to MCP-3. Statistical analysis was by one-way ANOVA with Dunnett’s multiple-comparison test.

  • Fig. 4 Identification of CCR2 residues contributing to MCP-1 and MCP-3 binding and agonism.

    (A to C) 125I–MCP-1 competition binding and ERK1/2 phosphorylation were assessed for MCP-1 and MCP-3 at the WT and mutant CCR2 proteins expressed in Flp-In T-REx 293 cells. (A) Membrane preparations of c-Myc–FLAG–CCR2 Flp-In T-REx 293 cells expressing WT or the indicated mutant receptors were incubated with 45 pM 125I–MCP-1 in the presence of various concentrations of chemokines before the extent of binding of 125I–MCP-1 was determined by radioligand-binding assay. Left: Binding affinity (pKi) of MCP-1 for each WT and mutant receptor (blue). Middle: Binding affinity (pKi) of MCP-3 for each WT and mutant receptor. Right: The differences between the pKi values of MCP-1 and MCP-3 for each WT and mutant receptor (black/gray). ^P < 0.05, compared to the difference observed at the WT receptor;*P < 0.05, compared to zero (that is, indicating difference between chemokines). Analysis was by multiple t test. (B and C) c-Myc–FLAG–CCR2 Flp-In T-REx 293 cells were treated with various concentrations of WT or chimeric chemokines for 3 min before the amount of phosphorylated ERK1/2 was measured by AlphaScreen assay. (B) Left: Potency (pEC50) of MCP-1 for each WT and mutant receptor (blue). Middle: Potency (pEC50) of MCP-3 for each WT and mutant receptor (red). Right: The differences between pEC50 values of MCP-1 and MCP-3 for each WT and mutant receptor (gray/black). *P < 0.05, **P < 0.01 compared to the potency observed at the WT receptor, by one-way ANOVA with Dunnett’s multiple-comparison test. (C) Left: Efficacy (Emax) of MCP-1 for each WT and mutant receptor (blue). Middle: Efficacy (Emax) of MCP-3 for each WT and mutant receptor (red). Right: The ratios between the Emax values of MCP-1 and MCP-3 for each WT and mutant receptor (gray/black). *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001 compared to the values observed at the WT receptor, by one-way ANOVA with Dunnett’s multiple-comparison test. Data are means ± SEM of three to five experiments, each performed in triplicate.

  • Fig. 5 The major subpocket of CCR2 recognizes the N termini of MCP chemokines.

    (A to C) Full (A) and detailed side views (B) and end-on view (C) (from the extracellular perspective) showing the homology model of CCR2 bound to MCP-1. CCR2 TM helices are colored salmon (TM1), orange (TM2), pale yellow (TM3), pale green (TM4), aquamarine (TM5), light blue (TM6), and violet (TM7); other receptor residues are in gray. Side chain sticks, labeled with single-letter amino acid code and residue number, are shown for several residues discussed in the text in darker shades of the same colors as the helices in which they are located. MCP-1 is in teal with the N terminus in rainbow colors from blue (residue 1) to red (residue 10). In (C), the major (M) and minor (m) subpockets are labeled in red. (D and E) The CXCR4/vMIP-II complex (PDB code: 4rws) is displayed as described for the CCR2/MCP-1 complex in (B) and (C). (F and G) The CCR5/maraviroc complex (PDB code: 4mbs) is displayed as described for the CCR2/MCP-1 complex in (B) and (C). Maraviroc is shown as sticks colored by element (carbon, green; nitrogen, blue; oxygen, red).

  • Table 1 Potency, efficacy, and affinity of the different MCP chemokines at the CCR2 receptor in β-arrestin recruitment, Fsk-stimulated cAMP inhibition, ERK phosphorylation, and radioligand-binding assays.

    β-arr2 recruitment was assessed by BRET in Flp-In T-REx 293 cells transiently transfected with plasmids encoding CCR2-RLuc8 and β-arr2–YFP. Inhibition of cAMP was measured in c-Myc–FLAG–CCR2 Flp-In T-REx 293 cells transiently transfected with a plasmid encoding a BRET-based cAMP sensor. ERK1/2 phosphorylation was measured 3 min after c-Myc–FLAG–CCR2 Flp-In T-REx 293 cells were stimulated with chemokine. 125I–MCP-1 competition binding was measured in membrane preparations of c-Myc–FLAG–CCR2 Flp-In T-REx 293 cells. pEC50 and pKi values are the negative log of EC50 and inhibition constant (Ki) values, respectively, in molar units. Emax values are reported as a percentage of the value for MCP-1. Data are means ± SEM of three or four experiments, each performed in triplicate. *P < 0.05, **P < 0.01, ***P < 0.001 by one-way ANOVA with Dunnett’s multiple-comparison test. Emax is shown relative to that observed with MCP-1.

    β-Arrestin recruitmentcAMP inhibitionERK1/2 phosphorylation125I–MCP-1 binding
    pEC50EmaxpEC50EmaxpEC50EmaxpKi
    MCP-18.32 ± 0.06100 ± 29.10 ± 0.21100 ± 99.16 ± 0.24100 ± 1010.60 ± 0.08
    MCP-27.24 ± 0.26*23 ± 3***7.34 ± 0.14***113 ± 97.58 ± 0.15***119 ± 98.88 ± 0.14***
    MCP-37.33 ± 0.15*56 ± 4**8.47 ± 0.16*109 ± 98.09 ± 0.19***116 ± 109.50 ± 0.12***
  • Table 2 Potency, efficacy, and affinity of the chimeric MCP proteins at CCR2 in β-arrestin recruitment, ERK phosphorylation, and radioligand-binding assays.

    125I–MCP-1 competition binding was measured in membrane preparations of c-Myc–FLAG–CCR2 Flp-In T-REx 293 cells. β-arr2 recruitment was assessed by BRET in Flp-In T-REx 293 cells transiently transfected with plasmids encoding CCR2-RLuc8 and β-arr2–YFP. ERK1/2 phosphorylation was measured 3 to 5 min after c-Myc–FLAG–CCR2 Flp-In T-REx 293 cells were stimulated with chemokine. pEC50 and pKi values are the negative log of EC50 and Ki values, respectively, in molar units. Emax values are relative to the positive control. Data are means ± SEM of three or four experiments, each performed in triplicate. *P < 0.05, **,^^P < 0.01, ***,^^^P < 0.001, compared to MCP-1 or MCP-3, respectively. Statistical analysis was by one-way ANOVA with Dunnett’s multiple-comparison text.

    β-Arrestin recruitmentERK1/2 phosphorylation125I–MCP-1 binding
    pEC50EmaxpEC50EmaxpKi
    MCP-18.00 ± 0.130.100 ± 0.006^^^7.87 ± 0.3237.8 ± 3.410.67 ± 0.18^^
    MCP1-3117.30 ± 0.210.067 ± 0.006*6.84 ± 0.1740.3 ± 3.29.90 ± 0.18
    MCP1-1318.32 ± 0.130.11 2 ± 0.006^^^7.64 ± 0.2643.7 ± 3.710.53 ± 0.17^^
    MCP1-1138.12 ± 0.130.111 ± 0.006^^^7.58 ± 0.4646.7 ± 6.810.68 ± 0.16^^
    MCP1-1338.45 ± 0.270.103 ± 0.009^^7.86 ± 0.4236.4 ± 5.010.84 ± 0.16^^
    MCP1-3337.82 ± 0.580.034 ± 0.009***6.95 ± 0.2924.0 ± 3.110.02 ± 0.17
    MCP-37.63 ± 0.170.060 ± 0.004**7.21 ± 0.3134.3 ± 4.09.50 ± 0.19**
    MCP3-1338.24 ± 0.110.0135 ± 0.005^^^8.12 ± 0.3325.9 ± 2.310.36 ± 0.14
    MCP3-3137.17 ± 0.220.051 ± 0.006***7.43 ± 0.2733.1 ± 3.07.45 ± 0.23***,^^
    MCP3-3317.65 ± 0.220.056 ± 0.006**7.66 ± 0.3621.7 ± 2.3*8.77 ± 0.33***
    MCP3-3117.13 ± 0.390.050 ± 0.010***7.87 ± 0.1440.0 ± 1.67.32 ± 0.32***,^^
    MCP3-1117.61 ± 0.200.134 ± 0.010^^^7.99 ± 0.3621.3 ± 2.4*9.80 ± 0.17
  • Table 3 Characterization of CCR2 mutants.

    Cell surface expression (receptor abundance) was measured by anti–c-Myc ELISA in c-Myc–FLAG–CCR2 Flp-In T-REx 293 cells, and data are expressed as a percentage of the abundance of the WT receptor. The affinities (pKi) of MCP-1 and MCP-3 for WT and mutant CCR2 proteins were measured by 125I–MCP-1 competition binding assays with cell membrane preparations. The potency (pEC50) and efficacy (Emax) values of MCP-1 and MCP-3 for WT and mutant CCR2 proteins in ERK1/2 phosphorylation assays were measured 3 min after c-Myc–FLAG–CCR2 Flp-In T-REx 293 cells were stimulated with chemokine. pEC50 and pKi values are the negative log of EC50 and Ki values, respectively, in molar units. Emax values are relative to the positive control. Data are means ± SEM of three or four experiments, each performed in triplicate. For radioligand binding, ^P < 0.05 as compared to MCP-1 for each mutant. Analysis was by multiple t test. For ERK1/2 phosphorylation, *P < 0.05, **P < 0.01, ***P < 0.001 as compared to WT CCR2. Analysis was by one-way ANOVA with Dunnett’s multiple-comparison test.

    MutationLocation#Cell surface expressionpKipERK1/2
    pEC50
    pERK1/2
    Emax (% FBS)
    MCP-1MCP-3MCP-1MCP-3MCP-1MCP-3
    WT100 ± 310.82 ± 0.189.64 ± 0.19^8.01 ± 0.237.30 ± 0.2338.9 ± 335.5 ± 4.5
    K34ATM1 (1.28)119 ± 1210.42 ± 0.279.70 ± 0.428.41 ± 0.247.70 ± 0.2355.5 ± 2.5***45.0 ± 2.8
    Y120FTM3 (3.32)118 ± 1311.15 ± 0.189.65 ± 0.26^7.92 ± 0.327.58 ± 0.3325.4 ± 2**16.6 ± 1.6***
    V187/V189AECL2108 ± 611.36 ± 0.299.85 ± 0.32^7.99 ± 0.267.28 ± 0.2330.5 ± 230.8 ± 2.3
    N199A/T203ATM5 (5.35/5.39)116 ± 711.42 ± 0.2910.17 ± 0.477.66 ± 0.237.35 ± 0.3332.8 ± 220.2 ± 2.3**
    R206ATM5 (5.42)112 ± 710.29 ± 0.2210.12 ± 0.338.25 ± 0.317.81 ± 0.3411.0 ± 0.8***14.8 ± 2.5***
    Y259FTM6 (6.51)99 ± 610.44 ± 0.2310.20 ± 0.148.78 ± 0.36*8.57 ± 0.26**31.9 ± 1.739.3 ± 1.7
    I263A/N266ATM6 (6.55/6.58)107 ± 810.79 ± 0.248.99 ± 0.17^9.46 ± 0.39**8.22 ± 0.3824.7 ± 2***36.9 ± 3.4
    E270A/F272ATM6/ECL399 ± 1311.68 ± 0.3910.06 ± 0.31^7.36 ± 0.207.36 ± 0.2022.3 ± 1.3***22.1 ± 1.5**
    D284ATM7 (7.32)104 ± 510.91 ± 0.169.52 ± 0.25^8.83 ± 0.40**7.80 ± 0.1834.9 ± 239.1 ± 1.9
    E291ATM7 (7.39)107 ± 910.26 ± 0.249.03 ± 0.22^7.66 ± 0.407.09 ± 0.4827.9 ± 3*12.1 ± 2.2***

    #Ballesteros and Weinstein numbering of TM residues is shown in parentheses (33).

    Supplementary Materials

    • www.sciencesignaling.org/cgi/content/full/10/480/eaai8529/DC1

      Fig. S1. Neither MCP-2 nor MCP-3 is a biased agonist at CCR2 relative to MCP-1.

      Fig. S2. NMR spectra of chemokine chimeras.

      Fig. S3. MCP3-111 displays biased agonism relative to MCP-3.

      Fig. S4. Homology model of CCR2 bound to MCP-1, showing the positions of the mutated residues.

      Fig. S5. 125I–MCP-1 competition binding and ERK1/2 phosphorylation concentration response curves for CCR2 mutants.

      Fig. S6. Graphical comparisons of chemokine binding and ERK1/2 phosphorylation parameters across the set of CCR2 mutants.

      Fig. S7. The amino acid sequences of MCP-1 (P8A), WT MCP-3, and the chimeric chemokines.

      Table S1. Biased agonism parameters for MCP chemokines at CCR2.

      Table S2. MCP3-111 displays biased agonism at CCR2 compared to MCP-3.

      Table S3. Expected and observed molecular masses of WT and chimeric chemokines.

    • Supplementary Materials for:

      Key determinants of selective binding and activation by the monocyte chemoattractant proteins at the chemokine receptor CCR2

      Zil E. Huma, Julie Sanchez, Herman D. Lim, Jessica L. Bridgford, Cheng Huang, Bradyn J. Parker, Jiann G. Pazhamalil, Benjamin T. Porebski, Kevin D. G. Pfleger, J. Robert Lane, Meritxell Canals,* Martin J. Stone*

      *Corresponding author. Email: martin.stone{at}monash.edu (M.J.S.); meri.canals{at}monash.edu (M.C.)

      This PDF file includes:

      • Fig. S1. Neither MCP-2 nor MCP-3 is a biased agonist at CCR2 relative to MCP-1.
      • Fig. S2. NMR spectra of chemokine chimeras.
      • Fig. S3. MCP3-111 displays biased agonism relative to MCP-3.
      • Fig. S4. Homology model of CCR2 bound to MCP-1, showing the positions of the mutated residues.
      • Fig. S5. 125I–MCP-1 competition binding and ERK1/2 phosphorylation concentration response curves for CCR2 mutants.
      • Fig. S6. Graphical comparisons of chemokine binding and ERK1/2 phosphorylation parameters across the set of CCR2 mutants.
      • Fig. S7. The amino acid sequences of MCP-1 (P8A), WT MCP-3, and the chimeric chemokines.
      • Table S1. Biased agonism parameters for MCP chemokines at CCR2.
      • Table S2. MCP3-111 displays biased agonism at CCR2 compared to MCP-3.
      • Table S3. Expected and observed molecular masses of WT and chimeric chemokines.

      [Download PDF]

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      Format: Adobe Acrobat PDF

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      Citation: Z. E. Huma, J. Sanchez, H. D. Lim, J. L. Bridgford, C. Huang, B. J. Parker, J. G. Pazhamalil, B. T. Porebski, K. D. G. Pfleger, J. R. Lane, M. Canals, M. J. Stone, Key determinants of selective binding and activation by the monocyte chemoattractant proteins at the chemokine receptor CCR2. Sci. Signal. 10, eaai8529 (2017).

      © 2017 American Association for the Advancement of Science

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