Defective autophagy associated with LC3 puncta in epothilone-resistant cancer cells.
Autophagy is commonly characterized by the redistribution of the microtubule-associated light chain 3 (LC3) protein into cytoplasmic puncta, coinciding with its lipidation, as well as by a decrease in the abundance of autophagic substrates including p62 and ubiquitinylated proteins. Here, we describe a cell line, A549-B480, which, in contrast to its parental A549 line, exhibits massive accumulation of LC3 (or a GFP-LC3 fusion protein) in cytoplasmic puncta. These puncta co-localize with accumulated p62 and ubiquitinylated proteins, yet are not enwrapped by membranes. Indeed, LC3 is not lipidated in A549-B480, even when these cells are cultured in conditions in which A549 cells would develop autophagy. A549-B480 cells have been selected for their resistance against the microtubule-stabilizing agent epothilone B and actually require the continuous presence of epothilone B for their survival. Parental A549 cells treated with epothilone B manifested all signs of bona fide autophagy. In contrast, the autophagic program of A549-B480 was defective, irrespective of the absence or presence of epothilone B, and correlated with the complete absence of Atg7, a protein that is reputed to be essential for autophagy. These results establish novel functional links between microtubules and autophagy, identify a new chemotherapy resistance-associated autophagic defect, and describe the existence of LC3 puncta outside from autophagosomes.
Shen
Shensi
S
INSERM U848, Institut Gustave Roussy and Université Paris Sud-XI, Villejuif, France.
Kepp
Oliver
O
Martins
Isabelle
I
Vitale
Ilio
I
Souquère
Sylvie
S
Castedo
Maria
M
Pierron
Gérard
G
Kroemer
Guido
G
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001343:Autophagy; D000071193:Autophagy-Related Protein 7; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D034261:Epothilones / Q000494:pharmacology*; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D000071456:Sequestosome-1 Protein; D044764:Ubiquitin-Activating Enzymes / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D000970:Antineoplastic Agents; D034261:Epothilones; C477012:MAP1LC3A protein, human; D008869:Microtubule-Associated Proteins; C099718:SQSTM1 protein, human; D000071456:Sequestosome-1 Protein; C509349:ATG7 protein, human; D000071193:Autophagy-Related Protein 7; D044764:Ubiquitin-Activating Enzymes; C093788:epothilone B