Figure 3.

KDEL proteins modulate the ability of the KDEL receptor to induce the phenotype of ARF1 inactivation, as assessed by Golgi redistribution to the ER. (A) Increasing receptor expression increases Golgi redistribution to the ER. HeLa cells were transiently transfected with increasing amounts of a plasmid encoding the KDEL receptor, and then assessed for Golgi-specific glycosylation of Tac-E19 (Upper). Direct immunoblotting of whole-cell lysates with an anti-myc antibody reveals increasing level of receptor expression (Lower). (B) The co-overexpression of lysozyme-KDEL and the KDEL receptor enhances the ability of the receptor to induce Golgi redistribution to the ER. HeLa cells were transiently transfected with either nothing or a plasmid encoding lysozyme-KDEL and increasing amounts of a plasmid encoding the KDEL receptor, and then assessed for Golgi-specific glycosylation of Tac-E19. The ratio of endo H-resistant to endo H-sensitive Tac-E19 is quantified for three separate experiments, and the bar graph represents the mean with standard error. There is a significant difference (P < 10⁻⁴) in the effect of co-overexpressing the KDEL receptor with its KDEL ligand (KDEL) versus overexpressing the receptor alone (None), by the two-way factorial ANOVA and contrast test. (C) The co-overexpression of lysozyme-AARL and the KDEL receptor does not enhance the ability of the receptor to induce Golgi redistribution to the ER. HeLa cells were transiently transfected with either nothing or a plasmid encoding lysozyme-AARL and increasing amounts of a plasmid encoding the KDEL receptor, and then assessed for Golgi-specific glycosylation of Tac-E19. The results of three separate experiments are quantified, and their mean with standard error are represented by a bar graph. There is no significant difference (P = 0.96) in comparing the effects of overexpressing the KDEL receptor with a control ligand (AARL) versus overexpressing the receptor alone (None), by the two-way factorial ANOVA and contrast test.