Vps21 Directs the PI3K-PI(3)P-Atg21-Atg16 Module to Phagophores via Vps8 for Autophagy

Abstract

Phosphatidylinositol 3-phosphate (PI(3)P) serves important functions in endocytosis, phagocytosis, and autophagy. PI(3)P is generated by Vps34 of the class III phosphatidylinositol 3-kinase (PI3K) complex. The Vps34-PI3K complex can be divided into Vps34-PI3K class II (containing Vps38, endosomal) and Vps34-PI3K class I (containing Atg14, autophagosomal). Most PI(3)Ps are associated with endosomal membranes. In yeast, the endosomal localization of Vps34 and PI(3)P is tightly regulated by Vps21-module proteins. At yeast phagophore assembly site (PAS) or mammalian omegasomes, PI(3)P binds to WD-repeat protein interacting with phosphoinositide (WIPI) proteins to further recruit two conjugation systems, Atg5-Atg12·Atg16 and Atg8-PE (LC3-II), to initiate autophagy. However, the spatiotemporal regulation of PI(3)P during autophagy remains obscure. Therefore, in this study, we determined the effect of Vps21 on localization and interactions of Vps8, Vps34, Atg21, Atg8, and Atg16 upon autophagy induction. The results showed that Vps21 was required for successive colocalizations and interactions of Vps8-Vps34 and Vps34-Atg21 on endosomes, and Atg21-Atg8/Atg16 on the PAS. In addition to disrupted localization of the PI3K complex II subunits Vps34 and Vps38 on endosomes, the localization of the PI3K complex I subunits Vps34 and Atg14, as well as Atg21, was partly disrupted from the PAS in vps21∆ cells. The impaired PI3K-PI(3)P-Atg21-Atg16 axis in vps21∆ cells might delay autophagy, which is consistent with the delay of early autophagy when Atg21 was absent. This study provides the first insight into the upstream sequential regulation of the PI3K-PI(3)P-Atg21-Atg16 module by Vps21 in autophagy.

Bifidobacterium infantis-Mediated Herpes Simplex Virus-TK/Ganciclovir Treatment Inhibits Cancer Metastasis in Mouse Model

“…ATG16 plays a key role in autophagy and forms the Atg5-Atg12-Atg16 complex [72]. Autophagy inhibition strongly promotes metastasis to the lung in breast cancer models [73].…”

Phagophore closure, autophagosome maturation and autophagosome fusion during macroautophagy in the yeast Saccharomyces cerevisiae

“…2). How Vps21 mediates this regulation is unclear, but the recent finding showing that this Rab GTPase might be involved in recruiting the autophagy-specific PtdIns3K complex onto autophagosomal membranes [38], may provide a mechanistic clue since several ESCRT complex subunits bind to PtdIns3P [24]. It is also unknown whether the Atg17-Snf7 interaction is at the extremities of the phagophore, where autophagosomes are supposed to close.…”