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Rab18 is not necessary for lipid droplet biogenesis or turnover in human mammary carcinoma cells

ABSTRACT: Rab GTPases recruit peripheral membrane proteins and can define organelle identity. Rab18 localizes to the ER but also to the surfaces of lipid droplets (LDs), where it has been implicated in effector protein recruitment and in defining LD identity. Here, we studied Rab18 localization and function in SUM159 cells. Rab18 localized to the ER and to LD membranes upon LD induction, with the latter depending on the Rab18 activation state. In cells lacking Rab18, LDs were modestly reduced in size and numbers, but we found little evidence for Rab18 function in LD formation, LD turnover upon cell starvation, or the targeting of several proteins to LDs. We conclude that Rab18 is not a general, necessary component of the protein machinery involved in LD biogenesis or turnover, but instead likely plays a specialized role in specific cell types

INSTRUMENT(S): Q Exactive

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Breast, Cell Culture

DISEASE(S): Breast Cancer

SUBMITTER: Zon Weng Lai

LAB HEAD: Tobias Walther

PROVIDER: PXD009683 | Pride | 2018-06-06

REPOSITORIES: Pride

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			Action	DRS
	20170908_CJ_LDproteomeLK1.raw	Raw
	20170908_CJ_LDproteomeLK2.raw	Raw
	20170908_CJ_LDproteomeLK3.raw	Raw
	20170908_CJ_LDproteomeLK4.raw	Raw
	20170908_CJ_LDproteomeLK5.raw	Raw

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RAB18 impacts autophagy via lipid droplet-derived lipid transfer and is rescued by ATG9A

Project description:Autophagy is a lysosomal degradation pathway that mediates protein and organelle turnover and maintains cellular homeostasis. Autophagosomes transport cargo to lysosomes and their formation is dependent on an appropriate lipid supply. Here, we show that the knockout of the RAB GTPase RAB18 interferes with lipid droplet (LD) metabolism, resulting in an impaired fatty acid mobilization. The reduced LD-derived lipid availability influences autophagy and provokes adaptive modifications of the autophagy network, which include increased ATG2B expression and ATG12-ATG5 conjugate formation as well as enhanced ATG2B and ATG9A phosphorylation. Phosphorylation of ATG9A directs this transmembrane protein to the site of autophagosome formation and this particular modification is sufficient to rescue autophagic activity under basal conditions in the absence of RAB18. However, it is incapable of enabling an increased autophagy under inductive conditions. Thus, we illustrate the role of RAB18 in connecting LDs and autophagy, further emphasize the importance of LD-derived lipids for the degradative pathway, and characterize an ATG9A phosphorylation-dependent autophagy rescue mechanism as an adaptive response that maintains autophagy under conditions of reduced LD-derived lipid availability.

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A fluorescent perilipin 2 knock-in mouse model reveals a high abundance of lipid droplets in the developing and adult brain

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