PtdIns(3)P-bound UVRAG coordinates Golgi–ER retrograde and Atg9 transport by differential interactions with the ER tether and the beclin 1 complex

Abstract

ER-Golgi membrane transport and autophagy are intersecting trafficking pathways that are tightly regulated and crucial for homeostasis, development and diseases. Here, we identify UVRAG, a Beclin1-binding autophagic factor, as a PI(3)P-binding protein that depends on PI(3)P for its ER localization. We further show that UVRAG interacts with RINT-1, and acts as an integral component of the RINT-1-containing ER tethering complex, which couples phosphoinositide metabolism to COPI-vesicle tethering. Displacement or knockdown of UVRAG profoundly disrupted COPI cargo transfer to the ER and Golgi integrity. Intriguingly, autophagy caused the dissociation of UVRAG from the ER tether, which in turn worked in concert with the Bif-1-Beclin-PI(3)KC3 complex to mobilize Atg9 translocation for autophagosome formation. These findings identify a regulatory mechanism that coordinates Golgi-ER retrograde and autophagy-related vesicular trafficking events through physical and functional interactions between UVRAG, phosphoinositide, and their regulatory factors, thereby ensuring spatiotemporal fidelity of membrane trafficking and maintenance of organelle homeostasis.

Rint1 inactivation triggers genomic instability, ER stress and autophagy inhibition in the brain

“…Several studies demonstrated that RINT1 is involved in ER-Golgi trafficking in vitro. 16,17,[19][20][21] Lin et al 19 associated the observed mitotic defects with Golgi dispersion and centrosome amplification. We demonstrated that centrosome amplification in MEFs is not correlated with mitotic defects and in NSC is not detected at all.…”

“…Studies reported that ER stress led to autophagy [30][31][32] and that RINT1 was associated with autophagy. 21 Therefore, we decided to monitor autophagy in Rint1-deficient cortices. We found that Rint1-deficient neurons exhibited autophagosome accumulation as indicated by the accumulation of LC3B punctate in cortical neurons and the increased conversion of the unconjugated LC3B-I to the phosphatidylethanolamine-conjugated form LC3B-II in E15.5 and E17.5 cortices (Figures 6a and b).…”

“…RINT1 was shown to interact with UVRAG, a protein essential for Atg9-vesicle formation, but this interaction only occurs in the absence of autophagy induction. 21 Interestingly, RINT1 interaction partner BNIP1 was reported to be involved in mitochondrial autophagy. 65 Sec22B was shown to regulate clearance of autophagosomes indirectly by assuring the anterograde transport of lysosomal proteases from ER via Golgi to lysosomes.…”

“…13 RINT1 was identified as a Rad50-interacting protein involved in G2/M checkpoint 14 and was shown to be involved in telomerase independent maintenance of telomeres via the interaction with p130. 15 The importance of RINT1 in Golgi-ER trafficking and thus in homeostasis of Cisand Trans-Golgi was demonstrated in vitro [16][17][18][19][20][21] where in vivo studies were limited by the early embryonic lethality (E5.5) associated with Rint1 inactivation. 19 Rint1 was proposed to be a tumor suppressor gene since its heterozygous mutation predisposed to tumor, 19 but it was also reported to act like an oncogene in glioblastomas.…”

Differential regulatory functions of three classes of phosphatidylinositol and phosphoinositide 3-kinases in autophagy

“…155 Interestingly, UVRAG, as a PtdIns3P-binding effector per se, shuttles between ER and autophagic membranes, coordinating different membrane trafficking events, and maintaining organelle homeostasis under various conditions. 156 In a PtdIns3P-dependent manner, UVRAG is bound to the ER tethering protein complex RINT1-ZW10-NBAS, involved in Golgi-to-ER transport; however, when autophagy is induced, UVRAG is dissociated from the ER and is bound to the SH3GLB1/Bif-1-BECN1-PIK3C3 complex. 156 UVRAG is necessary for vesicle tethering and fusion in the endocytic system.…”