Cytoprotective role of autophagy against BH3 mimetic gossypol in ATG5 knockout cells generated by CRISPR-Cas9 endonuclease

• We employed CRISPR/Cas9 genome editing to establish ATG5 knockout cell lines.
• The inhibitory effect of gossypol on cell proliferation was weaker on ATG5 knockout cells than that on WT cells.
• Gossypol induced ATG5- and LC3-independent autophagy in ATG5 knockout cells.
• Gossypol blocked the later stages of the autophagy process in WT cells.
• ATG5-independent autophagy may underlie the chemoresistant phenotype of cancer cells.

Previously, we demonstrated the association between autophagy and gossypol-induced growth inhibition of mutant BRAF melanoma cells. Here, we investigate the role of autophagy in ATG5 knockout cell lines generated by the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas-mediated genome editing. The MTT assay revealed that the inhibitory effect of gossypol was weaker on ATG5 knockout cells than that on the wild type (WT) cells. The conversion of non-autophagic LC3-I to autophagic LC3-II and RT-PCR confirmed the functional gene knockout. However, Cyto-ID autophagy assay revealed that gossypol induced ATG5- and LC3-independent autophagy in ATG5 knockout cells. Moreover, gossypol acts as an autophagy inducer in ATG5 knockout cells while blocking the later stages of the autophagy process in WT cells, which was determined by measuring autophagic flux after co-treatment of gossypol with chloroquine (late-stage autophagy inhibitor). On the other hand, inhibition of autophagy with 3-MA or Beclin-1 siRNA caused a partial increase in the sensitivity to gossypol in ATG5 knockout cells, but not in the WT cells. Together, our findings suggest that the resistance to gossypol in ATG5 knockout cells is associated with increased cytoprotective autophagy, independent of ATG5.