Distinct regulation of autophagic activity by Atg14L and Rubicon associated with Beclin 1–phosphatidylinositol-3-kinase complex

Abstract

Beclin 1, a mammalian autophagy protein that is implicated in development, tumor suppression, neurodegeneration and cell death, exists in complex with Vps34, the class III phosphatidylinositol 3-kinase (PI-3K) that mediates multiple vesicle trafficking pathways including endocytosis and autophagy. However, the precise role of the Beclin 1-Vps34 complex in autophagy regulation remains to be elucidated. Combining mouse genetics and biochemistry, we uncover a large in vivo Beclin 1 complex containing the known proteins Vps34, p150/Vps15 and UVRAG, as well as novel proteins Atg14L (yeast Atg14-like) and Rubicon (RUN domain and cysteine-rich domain containing, Beclin 1-interacting protein). Characterization of these novel proteins reveals that Atg14L enhances Vps34 lipid kinase activity and up-regulates autophagy, whereas Rubicon reduces Vps34 activity and down-regulates autophagy. We show that Beclin 1 and Atg14L synergistically promote formation of double-membraned organelles that are associated with Atg5 and Atg12, whereas forced expression of Rubicon results in aberrant late endosomal/lysosomal structures and impaired autophagosome maturation. We hypothesize that by forming distinct protein complexes, Beclin 1 and its binding proteins orchestrate the precise function of the class III PI-3K in regulating autophagy at multiple steps.

Autophagy-active beclin-1 correlates with favourable clinical outcome in non-Hodgkin lymphomas

“…Depending on the partners involved in the protein macro-aggregate, beclin-1 can regulate autophagy, endosome formation or apoptosis. 10,33,34 In this study, we considered the role of beclin-1 as an autophagy regulator, because this process has been shown to have a crucial role in lymphatic tissue homeostasis. 6,7,27 On formation of the autophagosome, the microtubule-associated protein LC3 (isoform I) is modified to generate the truncated and lipidated isoform LC3-II, that is eventually inserted into the autophagosome membrane.…”

“…8 Through its interaction with class III phosphatidyl-inositol-3-phosphate kinase (PI3kIII/ Vps34), beclin-1 (also known as atg6/Vps30) regulates autophagy. 9,10 Autophagy is a lysosomaldependent pathway for macromolecular and organelle degradation that has a pivotal role in cell homeostasis. 11 Autophagy begins with the entrapment of the substrate (protein aggregates, aged and oxidized membranes or organelles) by a multilayered membrane originated in the proximity of the endoplasmic reticulum and trans Golgi network.…”

A current perspective of autophagosome biogenesis

“…In yeast, the autophagy-specific PI3K complex is composed of four proteins: Vps34 (catalytic unit), Vps15, Atg6/Vps30, and Atg14 [31]. In mammals, Beclin 1 [32,33] and Atg14L/Barkor [34][35][36][37] are identified as the orthologues of Atg6/Vps30 and Atg14, respectively. It is thought that the production of PI3P is initiated by the dot-like accumulation of the Atg14/Atg14L-containing PI3K complex at the PAS (in yeast) or on the endoplasmic reticulum (ER) (in mammals; discussed below).…”

Autophagy Modulation As a Potential Therapeutic Target for Liver Diseases

“…Atg9 is postulated to contribute to delivery of membranes required in autophagosome formation. [10][11][12][13][14][15][16][17][18] The core machinery of autophagy comprises of four steps. These are: a) Induction: the process of autophagosome formation starts with the dissociation of mTOR complex 1 (mTORC1) from ULK1 complex.…”