PI3KC2\u03b1-dependent and VPS34-independent generation of PI3P controls primary cilium-mediated autophagy in response to shear stress

Asma Boukhalfa,Anna Chiara Nascimbeni,Etienne Morel,Emilio Hirsch,Damien Ramel,Muriel Laffargue,Nicolas Dupont,Stephanie Gayral,Patrice Codogno

doi:10.1038/s41467-019-14086-1

Abstract

Cells subjected to stress situations mobilize specific membranes and proteins to initiate autophagy. Phosphatidylinositol-3-phosphate (PI3P), a crucial lipid in membrane dynamics, is known to be essential in this context. In addition to nutriments deprivation, autophagy is also triggered by fluid-flow induced shear stress in epithelial cells, and this specific autophagic response depends on primary cilium (PC) signaling and leads to cell size regulation. Here we report that PI3KC2α, required for ciliogenesis and PC functions, promotes the synthesis of a local pool of PI3P upon shear stress. We show that PI3KC2α depletion in cells subjected to shear stress abolishes ciliogenesis as well as the autophagy and related cell size regulation. We finally show that PI3KC2α and VPS34, the two main enzymes responsible for PI3P synthesis, have different roles during autophagy, depending on the type of cellular stress: while VPS34 is clearly required for starvation-induced autophagy, PI3KC2α participates only in shear stress-dependent autophagy.

Highlights

Cells subjected to stress situations mobilize specific membranes and proteins to initiate autophagy
PI3P is synthesized by PI3KC3/VPS34, PI3KC2α, PI3KC2β, and PI3KC2γ38 and despite significant advances in the field, it is still unclear how, where and why these enzymes contribute to different PI3P pools dedicated to specific cellular processes
We show that primary cilium (PC)-mediated response to mechanical stimulation triggers specific PI3KC2α-dependent PI3P synthesis which participates in autophagic machinery mobilization and in turn in cell volume regulation

Summary

Introduction

Cells subjected to stress situations mobilize specific membranes and proteins to initiate autophagy. While the endosomal system is mostly responsible for sorting, recycling, and degradation of plasma membrane components and external material[9,10], autophagic membranes and their associated machinery are mobilized during stress situations to ensure the degradation of intracellular components by triggering the formation of autophagosomes, which capture cytoplasmic material and subsequently lead it to degradation upon fusion with lysosomes[11,12,13] The formation of these double membrane organelle is initiated by two ATG (autophagy-related) containing complexes: the ULK signaling complex and the PIK3C3 complex I. PI3KC2α is required for the autophagic program associated with mechanical stimulation relayed by the PC, but not essential for nutritional stress response, suggesting that a selective pool of PI3P is generated during shear stress

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Conclusion