The PDZ ligand motif affects receptor endocytosis and recycling.

<p>A. Receptor expressing cells were surface biotinylated; after treatment with SST-28 for the times indicated, cells were treated with glutathione to remove biotin from remaining cell surface receptors. Internalized, biotinylated receptors were purified (ABC) and quantified by Western blotting as before. PM, plasma membrane sample, no agonist treatment, no stripping. B. Quantification of the data shown in A. The signal obtained in the PM control sample was set as the 100% value for each receptor variant. **, ***: significantly different from wt at this time point; p<0.01, p<0.001, respectively. Data are derived from three to five independent experiments for each time point. C. Recycling was analyzed by surface biotinylation of receptor expressing cells, followed by internalization in the presence of agonist (15 min, 1 µM SST28) and stripping with glutathione. Recycled receptors were then stripped again at the time points indicated. To avoid lysosomal degradation as observed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0088529#pone-0088529-g001" target="_blank">Fig.1</a>, cells were treated with the lysosomal inhibitor leupeptin (100 µM; starting 24 h before the experiment). Intracellular, biotinylated receptors were then purified and analyzed by Western blotting as before. D. Quantitation of the data obtained in C shows that the SSTR5ΔCT receptor recycles faster than the wt receptor. *, **: significantly different from wt at this time point; p<0.05, p<0.01, respectively (t-test); n = 3 for each time point.