Molecular mechanisms and physiological roles of Atg5/Atg7-independent alternative autophagy

Abstract

ATG5 and ATG7 are considered to be essential molecules for the induction of autophagy. However, we found that cells lacking ATG5 or ATG7 can still form autophagosomes/ autolysosomes and perform autophagic protein degradation when subjected to certain types of stress. Although the lipidation of LC3 is accepted as a good indicator of autophagy, this did not occur during ATG5/ATG7-independent alternative autophagy. Unlike conventional autophagy, autophagosomes appeared to be generated in a Rab9-dependent manner by the fusion of the phagophores with vesicles derived from the trans-Golgi and late endosomes. Therefore, mammalian autophagy can occur via at least two different pathways; the ATG5/ATG7-dependent conventional pathway and an ATG5/ATG7-independent alternative pathway.