Snq2-yEGFP is another macro-ER-phagy cargo and its co-overexpression with DsRed-Snc1-PEM has a synergistic effect.
A-C. Overexpressed Snq2-GFP accumulates in the ER and induces UPR in ypt1-1 mutant cells. Snq2-yEGFP was overexpressed in WT and ypt1-1 mutant cells and the following effects were analyzed as described for Fig 1A–1C, respectively: increase in the level of Snq2-yEGFP protein (A), accumulation of Snq2-yEGFP in aberrant ER structures (B), and induction of the UPR response (C, GFP-Snc1-PEM is shown for comparison). B. The ER marker Sec61 was tagged with mCherry at its C-terminus in WT and ypt1-1 mutant cells. Shown from left to right: DIC, GFP, mCherry, Merge, % cells with intracellular Snq2 and % cells in which Snq2 co-localized with Sec61. D-F. Synergistic effect of co-overexpression of Snq2-GFP with DsRed-Snc1-PEM in atg11∆ mutant cells. WT (left) and atg11∆ mutant cells (right) were transformed with plasmids for overexpression of Snq2, Snc1-PEM or both Snq2 and Snc1-PEM. D. Immunoblot analysis and quantification. Shown from top to bottom: Snq2-yEGFP (using anti-GFP antibodies), Ds-Red-Snc1-PEM (using anti-Snc1 antibodies), G6PDH (loading control), and a bar graph showing fold increase of Snq2-yEGFP (green) and Ds-Red-Snc1-PEM (red) in atg11∆ mutant cells over WT. E. Accumulation of macro-ER-phagy cargos in aberrant intracellular structures using live-cells microscopy. Shown from left to right: DIC, GFP, DsRed and Merge. Shown from top to bottom: Snq2, Snc1-PEM, Snq2+Snc1-PEM, and % cells with co-localization (relevant only for co-overexpression) (% cells with ER-phagy cargo accumulation in aberrant intracellular structures is shown in S5A Fig). F. Fluorescence level of intracellular structures (ratio over PM) in atg11∆ mutant cells. The bar graph shows Snq2-yEGFP (green) and Ds-Red-Snc1-PEM (red) fluorescence (20 cells were analyzed for each strain). When co-overexpressed in atg11∆ mutant cells, the fluorescence level of either protein accumulating in aberrant structures is ~5 fold higher than when overexpressed individually. +/- and error bars represent STDEV. Results in this figure represent at least two independent experiments.