The Warburg Micro Syndrome‐associated Rab3GAP‐Rab18 module promotes autolysosome maturation through the Vps34 Complex I

Abstract

Warburg micro syndrome (WMS) is a hereditary autosomal neuromuscular disorder in humans caused by mutations in Rab18, Rab3GAP1, or Rab3GAP2 genes. Rab3GAP1/2 forms a heterodimeric complex, which acts as a guanosine nucleotide exchange factor and activates Rab18. Although the genetic causes of WMS are known, it is still unclear whether loss of the Rab3GAP‐Rab18 module affects neuronal or muscle cell physiology or both, and how. In this work, we characterize a Rab3GAP2 mutant Drosophila line to establish a novel animal model for WMS. Similarly to symptoms of WMS, loss of Rab3GAP2 leads to highly decreased motility in Drosophila that becomes more serious with age. We demonstrate that these mutant flies are defective for autophagic degradation in multiple tissues including fat cells and muscles. Loss of Rab3GAP‐Rab18 module members leads to perturbed autolysosome morphology due to destabilization of Rab7‐positive autophagosomal and late endosomal compartments and perturbation of lysosomal biosynthetic transport. Importantly, overexpression of UVRAG or loss of Atg14, two alternative subunits of the Vps34/PI3K (vacuole protein sorting 34/phosphatidylinositol 3‐kinase) complexes in fat cells, mimics the autophagic phenotype of Rab3GAP‐Rab18 module loss. We find that GTP‐bound Rab18 binds to Atg6/Beclin1, a permanent subunit of Vps34 complexes. Finally, we show that Rab3GAP2 and Rab18 are present on autophagosomal and autolysosomal membranes and colocalize with Vps34 Complex I subunits. Our data suggest that the Rab3GAP‐Rab18 module regulates autolysosomal maturation through its interaction with the Vps34 Complex I, and perturbed autophagy due to loss of the Rab3GAP‐Rab18 module may contribute to the development of WMS.

Interactions of Lipid Droplets with the Intracellular Transport Machinery

“…A recent study suggests the molecular mechanism by which Rab18 could regulate macroautophagy. Takats and coworkers [112] used a Drosophila model system which provided evidence that Vps34 Complex I, which is an important protein complex involved in maturation of autophagosomes to lysosomes, and is an effector of Rab18. In this study, they reported a GTP-dependent interaction between Rab18 and the Atg6 component of the complex.…”

Current Knowledge of Endolysosomal and Autophagy Defects in Hereditary Spastic Paraplegia

“…Finally, it has been suggested that Rab3GAP2, whose loss of function causes SPG69 [ 13 , 176 ], is involved in autophagy at different levels: autophagosome formation and autophagosome–autolysosome maturation [ 67 , 68 ]. Rab3GAP2 is the noncatalytic subunit of the heterodimeric Rab3GAP complex, which has been proposed to regulate Rab18 activity and autolysosome maturation.…”

“…Rab3GAP2 is the noncatalytic subunit of the heterodimeric Rab3GAP complex, which has been proposed to regulate Rab18 activity and autolysosome maturation. Indeed, autophagy defects are observed in a Rab3GAP2-deficient Drosophila model [ 68 ]. In contrast, another study has also suggested a role of Rab3GAP in autophagy but earlier in the pathway since it was shown that, in human primary fibroblasts, depletion in Rab3GAP2 led to an impaired lipidation of ATG8 family members necessary for autophagosome formation and the autophagy pathway [ 67 ].…”

RAB39B's role in membrane traffic, autophagy, and associated neuropathology

“…Prominent among these is Rab1/Ypt1 (Davis & Ferro‐Novick, 2015; J. Wang et al, 2013; Zoppino, Militello, Slavin, Alvarez, & Colombo, 2010), its GEF; the transport protein particle complex (Stanga et al, 2019), and its GAP TBC1D14 (Lamb, Longatti, & Tooze, 2016; Longatti et al, 2012). Many other Rabs, including Rab2 (Ding et al, 2019), RAB3GAPs (Spang et al, 2014), Rab5 (Zhou et al, 2019), Rab6 (Ayala, Kim, & Neufeld, 2018), Rab7a (Heo et al, 2018; Kuchitsu & Fukuda, 2018; Tan & Tang, 2019), Rab10 (Li et al, 2016), Rab11 (Puri et al, 2018), Rab18 (Feldmann et al, 2017; Nian et al, 2019; Takáts et al, 2020), and Rab33B (Morgan, Cutrona, & Simpson, 2019) have also been shown to participate in different steps and contexts of autophagy (Ao, Zou, & Wu, 2014; Chua, Gan, & Tang, 2011; Lamb et al, 2016).…”

“…Rab2 (Ding et al, 2019), RAB3GAPs (Spang et al, 2014), Rab5 (Zhou et al, 2019), Rab6 (Ayala, Kim, & Neufeld, 2018), Rab7a (Heo et al, 2018;Kuchitsu & Fukuda, 2018;Tan & Tang, 2019), Rab10 (Li et al, 2016), Rab11 (Puri et al, 2018), Rab18 (Feldmann et al, 2017;Nian et al, 2019;Takáts et al, 2020), and Rab33B (Morgan, Cutrona, & Simpson, 2019) have also been shown to participate in different steps and contexts of autophagy (Ao, Zou, & Wu, 2014;Chua, Gan, & Tang, 2011;.…”