TFG binds LC3C to regulate ULK1 localization and autophagosome formation (2021)
Figure 4

Figure 4. Inhibition of TFG results in stalled omegasomes and accumulation of abnormal structures.

A) HeLa cells were transfected with specific RNAi oligonucleotides (siTFG) or unrelated oligonucleotides as a negative control (siCTR); after culturing cells in fed (FED) or starvation conditions (STV) for 1h, cells were fixed and labelled with the indicated antibodies. Co-localization analysis was performed by using ImageJ Jacop plugin and mean ± SEM of Mander's coefficients of ULK1, expressed as percentage, is reported (bottom). White arrowheads point at co-localization events between ULK1 and LC3B; white arrows track puncta not co-localizing; N, nucleus. Statistical analyses were performed by two-way ANOVA followed by Tukey's multiple comparison test. *, P<0,05; **, P<0.01; ****, P<0.0001. (n=3 independent experiments, n≥16 fields analysed). Scale bar 5 μm.

B-C) HEK293 cells stably expressing either GFP-ATG13 (B) or GFP-DFCP1 (C) were transiently transfected with specific RNAi oligonucleotides (siTFG) or unrelated oligonucleotides as a negative control (siCTR), together with CFP-LC3B plasmid (visualized in red) and cultured in starved conditions for 40'. Wide-field live-cell imaging of starved cells were taken by cellSens microscope. Representative images of lifespan of both ATG13 (B) and (C) are reported. Images of both ATG13 (B) and DFCP1 (C) forming association with LC3B-II are also shown. The appearance of LC3B on ATG13 (B) (bottom right) and on DFCP1 (bottom right) (C) puncta were quantified and reported. All values are expressed in seconds (sec) as mean ± SEM. Yellow arrowheads point at the DFCP1 and LC3B particles in the first frame from their onset, white arrowheads and white arrows show omegasomes and autophagosomes as indicated. Statistical analyses were performed by unpaired Student's t‐test. *, P<0,05; **, P<0.01.(n=3 independent experiments, n=50 events/condition analysed). Scale bar 1 μm.

D) HeLa cells were transfected as in A). Cells were imaged by TEM. Representative electron micrographs (x26500) are reported. The average number of abnormal structures per cell is shown (bottom graph). N, nucleus; M, mitochondria; ER, endoplasmic reticulum. The average number of abnormal vacuoles per cell was evaluated (upper right). Statistical analysis was performed by unpaired Student's t‐test. ***, P<0,001. A minimum of 50 cells were observed. Cell count was performed (n=3 independent experiments, n≥51 cells analysed). Data are presented as mean ± SEM. Scale bar 500 nm as indicated.

E) HeLa cells stably expressing GFP-ATG13 and CFP-ATG16 were transiently co-transfected with DsRed-Rab7 and TFG siRNA (siTFG). Cells were cultured in starved conditions for 1h. Representative electron micrographs (x3900) and merge of the three fluorophores CLEM are shown. Micrographs at higher magnification (x13500) of a region showing the three fluorophores split and merged is reported. Scale bars: 5 μm upper panels, 1 μm bottom panels.

F) Control (TFG-WT) and patient's (TFG-R106C) fibroblasts were grown in fed or starvation conditions in the presence or absence of CLQ for 1h and then lysed. Protein extracts were analysed by WB to detect ACTIN and LC3B-II as indicated. Densitometry analysis of LC3B-II over ACTIN is shown (right). All data are expressed as the mean ± SEM. Statistical analysis was performed by two-way ANOVA followed by Tukey's multiple comparison test. *, P<0.05; ***, P<0,001. (n=3 independent experiments).

G) Control (TFG-WT) and patient's (TFG-R106C) fibroblasts were grown in fed or starvation conditions for 1h. Cells were fixed, permeabilized, and labelled with anti-ULK (red) antibody. Hoechst was used to stain nuclei. The average of ULK1 puncta number per cell is shown (bottom). All data are expressed as the mean value ± SEM. Statistical analysis was performed by two-way ANOVA followed by Tukey's multiple comparison test. *, P<0.05; ***, P<0,001; ****; P<0,0001. (n=3 independent experiments, n≥14 fields analysed). Scale bar 5 μm.