We then asked whether selective ER export of CNIH-2 is a prerequisite for increasing surface expression of GluAs. GluA1o and CNIH-2 were co-expressed in HeLa cells with either wildtype Sar1 or the H79G mutant and surface expression was quantified using the extracellular epitope tagging approach. As shown in Figure 3B, CNIH-2 increased the surface expression of GluA1o by a factor of 1.7±0.1 (n = 12; p<0.001) in the presence of wildtype Sar1, while this increase was effectively prevented in cells co-expressing Sar1 H79G (1.0±0.04; n = 12; p = 0.732). Surface expression of GluA1o alone was not affected by co-expression of Sar1 H79G (1.01±0.07; n = 9, p = 0.234; data not shown). For reasons of cell toxicity brought about by the Sar1 mutant, data had to be acquired 16 hrs post transfection leading to significantly lower overall expression of GluA1o than observed in previous experiments (Fig. 1). Within the time frame of 16 hrs, we did neither observe changes in cell morphology nor a reduction in GluA1 total protein expression. As the amount of surface protein is not only
