A RasGAP, DAB2IP, regulates lipid droplet homeostasis by serving as GAP toward RAB40C.

William K.K. Wu,Ran Tan,Sidney Yu,Tuanlao Wang,Chunman Li,Xiaomin Luo,Ayano Satoh,Xiaohui Xu

doi:10.18632/oncotarget.19960

Abstract

Lipid droplet (LD) homeostasis involves activities of various RAB small GTPases. Recently, we found RAB40C was one of the RAB proteins regulating LD homeostasis. RAB40C contains a unique SOCS domain that is required for clustering of LDs. However, its precise functional role in LD homeostasis and mechanism of regulation remain largely unknown. In this study, we observed over-accumulation of LDs in cells with RAB40C deleted by Crispr-Cas9 editing. RAB40C appeared to reduce LD accumulation after long term incubation of cells with oleic acid (24 hours). Unexpectedly, we found that Ras GTPase activating protein (GAP), DAB2IP, bound to RAB40C mainly via its GAP domain and could serve as RAB40C GAP. Studies involving overexpression of DAB2IP and its GAP defective mutant and siRNA depletion of DAB2IP all confirmed that DAB2IP negatively regulated the effect of RAB40C on LD homeostasis. These results provide a novel perspective on the regulation of RAB40C and implicate various signalling pathways regulated by DAB2IP, which may play a role in LD homeostasis via RAB40C.

Highlights

Excess neutral lipid molecules, such as triglycerides, sterol esters, and retinyl esters, are stored in lipid droplets (LDs) within hepatocytes and adipocytes [1]
These results provide a novel perspective on the regulation of RAB40C and implicate various signalling pathways regulated by DAB2IP, which may play a role in LD homeostasis via RAB40C
When we serum-starved the cells before incubating with oleic acid of low dose (40 μM), we found that LO2 cells with RAB40C deleted over-accumulated LDs similar to HEK293T knockouts (Figure 1D–1E)

Summary

Introduction

Excess neutral lipid molecules, such as triglycerides, sterol esters, and retinyl esters, are stored in lipid droplets (LDs) within hepatocytes and adipocytes [1]. LDs contain a central core of hydrophobic, neutral lipids covered with a monolayer of phospholipids bound by proteins. The protein components on the LD surface are biologically active and control the synthesis, storage and hydrolysis of the lipid contents and other LD-. Related cellular functions including trafficking of LDs and interactions with other organelles. Proteomic analyses have identified proteins important in intracellular traffic such as small GTPases on LD surfaces [2, 3]. Rab was the best characterized Rab protein functioning on LDs [4,5,6,7,8,9,10,11]. RAB40C was first cloned and characterized from an oligodendrocyte cDNA library [13]

Methods

Results

Conclusion