Kinetics of β-arrestin 2 recruitment to CXCR4 or CXCR7.

<p>(A and B) MDA-MB-231 breast cancer cells expressing CXCR4-CBRN/β-arrestin 2-CBC (A) or CXCR7-CBRN/β-arrestin 2-CBC (B) were treated with increasing concentrations of CXCL12-α (ng/mL) as denoted in the legend. Data were collected as photon flux units. Photon flux values for each time point then were normalized to values obtained for control cells not incubated with CXCL12 at each time point through 40 min and at 90 min. Data are expressed as mean values ± SEM for fold change relative to control (n = 4 per point). (C and D) Experimental data were used to tune parameters for a computational model describing numbers of receptors per cell bound to β-arrestin 2. Model outputs for CXCR4 (C) and CXCR7 (D) were plotted as fold change relative to cells not treated with CXCL12. (E, F) Internalization of cell surface CXCR4 (E) or CXCR7 (F) following 40 min or 30 min, respectively, of incubation with CXCL12 was measured by flow cytometry. Values for 0 ng/ml CXCL12 describe internalization of CXCR4 or CXCR7 in the absence of ligand. Experimental data for CXCR7 were replotted based on previously published results <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098328#pone.0098328-Luker1" target="_blank">[12]</a>. Model fits also are shown.