FIGURE 1.

Differences in ligand-independent internalization of wild type and tail-swap mutant CXCR4 and CXCR7 receptors. HEK293 cells were transiently transfected with constructs for HA-tagged receptors as indicated. A–H, surface receptors were pulse labeled with anti-HA antibody applied to live HEK293 cells at 4 °C. Confocal images show the subcellular localization of the labeled receptors after the anti-HA pulse (A–D) or after a 30-min ligand-free interval at 37 °C (E–H). I, quantitative analysis of receptor internalization by ELISA. Surface receptor levels after different ligand-free intervals are given as percentage of the surface receptor level immediately after pulse labeling (starting value). Data represent mean ± S.E. calculated from 4 independent experiments with 4 repeats each. Two-way ANOVA comparing wild type receptor and tail-swap mutant. Scale bar = 10 μm in A–H.