Transglutaminase 2 is involved in autophagosome maturation.
Autophagy is a highly conserved cellular process responsible for the degradation of long-lived proteins and organelles. Autophagy occurs at low levels under normal conditions, but it is enhanced in response to stress, e.g. nutrient deprivation, hypoxia, mitochondrial dysfunction and infection. "Tissue" transglutaminase (TG2) accumulates, both in vivo and in vitro, to high levels in cells under stressful conditions. Therefore, in this study, we investigated whether TG2 could also play a role in the autophagic process. To this end, we used TG2 knockout mice and cell lines in which the enzyme was either absent or overexpressed. The ablation of TG2 protein both in vivo and in vitro, resulted in an evident accumulation of microtubule-associated protein 1 light chain 3 cleaved isoform II (LC3 II) on pre-autophagic vesicles, suggesting a marked induction of autophagy. By contrast, the formation of the acidic vesicular organelles in the same cells was very limited, indicating an impairment of the final maturation of autophagolysosomes. In fact, the treatment of TG2 proficient cells with NH4Cl, to inhibit lysosomal activity, led to a marked accumulation of LC3 II and damaged mitochondria similar to what we observed in TG2-deficient cells. These data indicate a role for TG2-mediated post-translational modifications of proteins in the maturation of autophagosomes accompanied by the accumulation of many damaged mitochondria.
D'Eletto
Manuela
M
Department of Biology, University of Rome Tor Vergata, Rome, Italy.
Farrace
Maria Grazia
MG
Falasca
Laura
L
Reali
Valentina
V
Oliverio
Serafina
S
Melino
Gennaro
G
Griffin
Martin
M
Fimia
Gian Maria
GM
Piacentini
Mauro
M
D000818:Animals; D001343:Autophagy / Q000187:drug effects; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004622:Embryo, Mammalian / Q000166:cytology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000648:ultrastructure; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D019204:GTP-Binding Proteins / Q000172:deficiency / Q000378:metabolism*; D055786:Gene Knockout Techniques; D006801:Humans; D008247:Lysosomes / Q000187:drug effects / Q000648:ultrastructure; D008561:Membrane Fusion / Q000187:drug effects; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D009206:Myocardium / Q000166:cytology / Q000648:ultrastructure; D010588:Phagosomes / Q000201:enzymology*; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D022142:Secretory Vesicles / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D013194:Staining and Labeling; D011503:Transglutaminases / Q000172:deficiency / Q000378:metabolism*
D003432:Cross-Linking Reagents; C480860:Map1lc3b protein, mouse; D008869:Microtubule-Associated Proteins; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D019204:GTP-Binding Proteins