No abstract

The GTPase Rab5 and phosphatidylinositol-3 phosphate [PI(3)P] coordinately regulate endosome trafficking. Rab5 recruits Vps34, the class III phosphoinositide 3-kinase (PI3K), to generate PI(3)P and recruit PI(3)P-binding proteins. Loss of Rab5 and loss of Vps34 have opposite effects on endosome size, suggesting that our understanding of how Rab5 and PI(3)P cooperate is incomplete. Here, we report a novel regulatory loop whereby Caenorhabditis elegans VPS-34 inactivates RAB-5 via recruitment of the TBC-2 Rab GTPase-activating protein. We found that loss of VPS-34 caused a phenotype with large late endosomes, as with loss of TBC-2, and that Rab5 activity (mice have two Rab5 isoforms, Rab5a and Rab5b) is increased in Vps34-knockout mouse embryonic fibroblasts (Vps34 is also known as PIK3C3 in mammals). We found that VPS-34 is required for TBC-2 endosome localization and that the pleckstrin homology (PH) domain of TBC-2 bound PI(3)P. Deletion of the PH domain enhanced TBC-2 localization to endosomes in a VPS-34-dependent manner. Thus, PI(3)P binding of the PH domain might be permissive for another PI(3)P-regulated interaction that recruits TBC-2 to endosomes. Therefore, VPS-34 recruits TBC-2 to endosomes to inactivate RAB-5 to ensure the directionality of endosome maturation.

Succinate is known to act as an inflammatory signal in classically activated macrophages through stabilization of HIF-1α leading to IL-1β production. Relevant to this, hypoxia is known to drive succinate accumulation and release into the extracellular milieu. The metabolic alterations associated with succinate release during inflammation and under hypoxia are poorly understood. Data are presented showing that Mycoplasma arginini infection of VM-M3 cancer cells enhances the Warburg effect associated with succinate production in mitochondria and eventual release into the extracellular milieu. We investigated how succinate production and release was related to the changes of other soluble metabolites, including itaconate and 2-HG. Furthermore, we found that hypoxia alone could induce succinate release from the VM-M3 cells and that this could occur in the absence of glucose-driven lactate production. Our results elucidate metabolic pathways responsible for succinate accumulation and release in cancer cells, thus identifying potential targets involved in both inflammation and hypoxia. This article is part of a Special Issue entitled 20th European Bioenergetics Conference, edited by László Zimányi and László Tretter.

Highlights d PIM1 is highly expressed in suppressive neutrophils during chronic viral infection d PIM1 promotes mitochondrial fitness and cell survival in suppressive neutrophils d PIM kinase inhibition diminishes suppressive neutrophilmediated immunosuppression