Figure 9. Phosphorylation is required for sst₃ down-regulation.

HEK293 cells stably expressing the wild-type or mutant sst₃ receptors were treated with 1μM somatostatin for 0, 2, 4, 6, or 24 hours. Cells were lysed and immunoblotted with the phosphorylation-independent anti-HA antibodies. Blots were stripped and reprobed with the antitransferrin receptor antibody to confirm equal loading of the gel (TfR, transferrin receptor). Receptor monomers were quantified and expressed as percentage of untreated cells. Data correspond to the mean ± SEM from 5 independent experiments. Results were analyzed by two-way ANOVA followed by the Bonferroni post hoc test (*, P < .05). The positions of molecular mass markers are indicated on the left (in kDa).