The GTPase ARFRP1 controls the lipidation of chylomicrons in the Golgi of the intestinal epithelium

Abstract

The uptake and processing of dietary lipids by the small intestine is a multistep process that involves several steps including vesicular and protein transport. The GTPase ADP-ribosylation factor-related protein 1 (ARFRP1) controls the ARF-like 1 (ARL1)-mediated Golgi recruitment of GRIP domain proteins which in turn bind several Rab-GTPases. Here, we describe the essential role of ARFRP1 and its interaction with Rab2 in the assembly and lipidation of chylomicrons in the intestinal epithelium. Mice lacking Arfrp1 specifically in the intestine (Arfrp1vil−/−) exhibit an early post-natal growth retardation with reduced plasma triacylglycerol and free fatty acid concentrations. Arfrp1vil−/− enterocytes as well as Arfrp1 mRNA depleted Caco-2 cells absorbed fatty acids normally but secreted chylomicrons with a markedly reduced triacylglycerol content. In addition, the release of apolipoprotein A-I (ApoA-I) was dramatically decreased, and ApoA-I accumulated in the Arfrp1vil−/− epithelium, where it predominantly co-localized with Rab2. The release of chylomicrons from Caco-2 was markedly reduced after the suppression of Rab2, ARL1 and Golgin-245. Thus, the GTPase ARFRP1 and its downstream proteins are required for the lipidation of chylo­microns and the assembly of ApoA-I to these particles in the Golgi of intestinal epithelial cells.

Hepatic trans-Golgi action coordinated by the GTPase ARFRP1 is crucial for lipoprotein lipidation and assembly

“…In a recent study, we showed that chylomicron formation, lipidation as well as apolipoprotein assembly, is dependent on the trans -Golgi and ARFRP1 ( 13 ). ARFRP1 is required for the correct recruitment and action of other GTPases (ARL1 and Rab proteins) that interact with the scaffolding protein golgin-245.…”

“…Diminished lipid droplet fusion and elevated lipolysis were responsible for smaller lipid droplets in brown adipose tissue ( 12 ). Furthermore, in a recent study it was shown that in the intestine ARFRP1 is involved in the formation and lipidation of lipid-carrying chylomicrons ( 13 ). Besides its fundamental role in whole body glucose homeostasis, the liver is further essential for the distribution of lipids in the body via synthesis and secretion of VLDLs.…”

“…Aliquots were used to determine triglyceride concentration in fractions (Serum Triglyceride Determination kit, Sigma, Germany). Proteins in the fractions were concentrated using trichloroacetic acid to be analyzed by Western blotting ( 13 ).…”

“…The activity of microsomal triglyceride transfer protein (MTP) was determined as described in Jaschke et al ( 13 ). Liver tissues were homogenized and 100 g of protein were used for the assay.…”

Multiple activities of Arl1 GTPase in the trans-Golgi network

“…1) (Chang et al, 2015;Cruz-Garcia et al, 2013;Eiseler et al, 2016;Gehart et al, 2012;Hesse et al, 2013;Hsu et al, 2016;Labbaoui et al, 2017;Lieu et al, 2008;Liu et al, 2006;Lock et al, 2005;Marešová and Sychrová, 2010;Marešová et al, 2012;Murray and Stow, 2014;Price et al, 2005;Torres et al, 2014;Yang and Rosenwald, 2016). In mammalian cells, these functions affect a wide range of fundamental cellular processes, including cell polarity (Lock et al, 2005), innate immunity (Bremond et al, 2009;Lieu et al, 2008;Murray and Stow, 2014;Stanley et al, 2012), lipid droplet and chylomicron formation (Hesse et al, 2013;Jaschke et al, 2012), as well as the secretion of insulin (Gehart et al, 2012), chromogranin A (CruzGarcia et al, 2013) and matrix metalloproteinases (MMPs) (Eiseler et al, 2016). In yeast, Arl1 and its effectors are also involved in numerous functions, such as maintenance of cell wall integrity (Liu et al, 2006), ion homeostasis (Marešová and Sychrová, 2010;Munson et al, 2004;Rosenwald et al, 2002), tolerance to stress factors (Jaime et al, 2012;Marešova et al, 2012;Yang and Rosenwald, 2016), regulation of cell proliferation (Benjamin et al, 2011), the unfolded protein response (UPR) (Hsu et al, 2016) and also in the ability of yeast to cause disease (Labbaoui et al, 2017).…”