A Western blotting analysis on the level of LC3B protein in HeLa cells transfected with plex-MCS (CTRL) or plex-HA-SOX6 expression plasmid. α-tubulin protein was used as the internal control. △ was used to indicate the non-specific band. B The RT-qPCR (SYBR Green) analysis on the levels of SOX6 mRNA in HeLa, CaSki, and SiHa cells. β-Actin (ACTB) mRNA was used as the internal control. C Western blotting analysis on the levels of endogenous SOX6 in HeLa, CaSki, and SiHa cells. D Western blotting analysis on the level of LC3B protein in CaSki cells transfected with plex-MCS (CTRL) or plex-HA-SOX6 expression plasmid. E Representative confocal microscopy images and F relative number of GFP-LC3B puncta in HeLa cells co-transfected with GFP-LC3 and plex-MCS (CTRL), plex-HA-SOX6 or plex-HA-SOX6ΔHMG expression plasmids. G Western blotting analysis on the level of LC3B protein in HeLa-HA-SOX6-tet and HeLa-HA-SOX6ΔHMG-tet cells treated with or without Dox (4 μg/mL) for 48 h, respectively. H Representative confocal microscopy images and I relative number of GFP-LC3B puncta in HeLa-HA-SOX6-tet and HeLa-HA-SOX6ΔHMG-tet cells transfected with GFP-LC3 expression plasmid and treated with or without Dox (4 μg/mL) for 48 h, respectively. J Transmission electron microscopy analysis and K relative amount of autophagic structures (indicated by red arrow) in HeLa-HA-SOX6-tet and HeLa-HA-SOX6ΔHMG-tet cells treated with or without Dox (4 μg/mL) for 48 h. L Representative confocal microscopy images, M relative amount of GFP-puncta, and N relative amount of autophagosomes (GFP-positive, RFP-positive) and autolysosomes (GFP-negative, RFP-positive) in HeLa-HA-SOX6-tet and HeLa-HA-SOX6ΔHMG-tet cells transfected with mRFP-GFP-LC3 adenovirus reporter and treated with or without Dox (4 μg/mL) treatment for 48 h, respectively. O Western blotting analysis on the level of p62/SQSTM1 protein in HeLa cells and P in CaSki cells transfected with plex-MCS (CTRL) or plex-HA-SOX6 expression plasmid. Q The direct sequencing results on the PCR product of SOX6 gene from two HeLa-SOX6KO clones. The red arrow head indicates the location of the indel (insertion–deletion) mutation in each allele. R Western blotting analysis on the levels of p62/SQSTM1 in two HeLa-SOX6KO clones compared with the control HeLa cell (lenti-V2). Data are mean ± SEM of three independent experiments or at least 50 cells scored (**P < 0.01, ***P < 0.001, one-way ANOVA and post hoc Tukey tests).