Activation of autophagy upon organelle damage.

COLOMBO, M. I.

Carlos Paz (Cordoba)

Workshop; International Workshop Membrane Trafficking: Molecular Mechanisms,; 2005

Autophagy is the major cellular pathway for degradation of long-lived proteins and cytoplasmic organelles. In the last few years, the knowledge of molecular mechanisms responsible for autophagy in response to different stress conditions, such as starvation, has remarkably increased. However, autophagic degradation of damaged organelles is still largely uncharacterised. Here we describe a model of organelle damaging based on inactivation of Golgi apparatus in living cells by crosslinking. We observed that when the Golgi is inactivated, LC3, which localizes on autophagosome membranes after a multi-step post-translational modification process, lost its cytoplasmic distribution and localized on the damaged membranes. Apg12, a preautophagosome protein also changed its distribution showing a punctuate pattern in close proximity to the Golgi, although it did not strictly localize to the Golgi. Similarly, the small GTPase Rab24 was recruited to the injured organelle. Microtubule depolymerization and bafilomycin treatment prevented the targeting of LC3 to the damaged Golgi. Treatment with the alkylating agent N-ethylmaleimide completely abrogated LC3 redistribution. Strikingly, the PI3Kinase inhibitor wortmannin did not affect the localization of LC3 to the altered Golgi, implicating that different signal transduction mechanisms are involved in the autophagy sequestration of a damaged organelle.