FIGURE 1.

PP2A regulates GABA_B receptor expression. (A) Phosphorylation/dephosphorylation of GABA_B2(S783) affects expression of GABA_B receptors. Neurons were transfected either with wild type HA-tagged GABA_B2, a HA-tagged GABA_B2 mutant with inactivated S783 phosphorylation site 783 (S783A) or with a mutation mimicking phosphorylation of this site (S783D) along with wild type GABA_B1. Expression of HA-tagged GABA_B receptors was determined after 2 days by staining with antibodies directed against the HA-tag. Left: Representative images of total GABA_B receptor expression (scale bar: 10 μm). Right: Quantification of GABA_B2 staining. Expression levels were normalized to the control (wild type HA-GABA_B2). The data represent the mean ± SD of 87–144 neurons from three independent. Brown–Forsythe and Welch ANOVA with Games Howell’s multiple comparison test (****p < 0.0001). (B–E) Overexpression of the catalytic subunit of PP2A (PP2A-C) downregulates total and cell surface expression of GABA_B receptors in neurons. Neurons were transfected with EGFP and either PP2A-C or an inactive mutant of PP2A-C (L199P). Cell surface and total endogenous GABA_B1 (B,C) and endogenous GABA_B2 (D,E) was determined after 2 days via staining with GABA_B1 and GABA_B2 antibodies. Left: Representative images (scale bar: 5 μm). Right: Quantification of GABA_B receptor staining. Signals were normalized to the control (only transfected with EGFP). The data represent the mean ± SD of 87–144 neurons from three independent. Brown–Forsythe and Welch ANOVA with Games Howell’s multiple comparison test (ns, p > 0.05, *p < 0.05, ****p < 0.0001).