Biology subjects

Campelo, F.

Publications and source records attributed to Campelo, F..

22 records · Page 2Linked to original sources

bioRxiv2019

SCAP promotes CARTS biogenesis at endoplasmic reticulum-Golgi contact sites

In response to cholesterol deprivation, SCAP escorts SREBP transcription factors from the endoplasmic reticulum (ER) to the Golgi complex for their proteolytic activation, leading to gene expression for cholesterol synthesis and uptake. Here we show that in cholesterol-fed cells ER-localized SCAP interacts through Sac1 phosphoinositide 4-phosphate (PI4P) phosphatase with a VAP/OSBP complex, which mediates counter-transport of ER cholesterol and Golgi PI4P at ER-Golgi contact sites. SCAP knockdown inhibited the turnover of PI4P perhaps due to a cholesterol transport defect and altered the subcellular distribution of the VAP/OSBP complex. As in the case of perturbation of lipid transfer complexes at ER-Golgi contact sites, SCAP knockdown inhibited the biogenesis of the trans-Golgi network-derived transport carriers CARTS, which was reversed by expression of wild-type SCAP but not cholesterol sensing-defective mutants. Altogether, our findings reveal a new role of SCAP under cholesterol-fed conditions in the facilitation of CARTS biogenesis at ER-Golgi contact sites, depending on the ER cholesterol. SummarySCAP is the key regulatory protein in cholesterol metabolism. Wakana et al. describe a new role of SCAP in controlling Golgi PI4P turnover and the biogenesis of the Golgi-derived transport carries CARTS via cholesterol/PI4P exchange machinery at ER-Golgi contact sites.

cell biology↗

bioRxiv2019

Tricalbin-mediated contact sites control ER curvature to maintain plasma membrane integrity

Membrane contact sites (MCS) between the endoplasmic reticulum (ER) and the plasma membrane (PM) play fundamental roles in all eukaryotic cells. ER-PM MCS are particularly abundant in S. cerevisiae, where approximately half of the PM surface is covered by cortical ER (cER). Several proteins, including Ist2, Scs2/22 and Tcb1/2/3 are implicated in cER formation, but the specific roles of these molecules are poorly understood. Here we use cryo-electron tomography to show that ER-PM tethers are key determinants of cER morphology. In particular, Tcb proteins form peaks of extreme curvature on the cER membrane facing the PM. Semi-quantitative modeling and functional assays suggest that Tcb-mediated cER peaks facilitate the transport of lipids from the cER to the PM, necessary to maintain PM integrity under stress conditions. ER peaks were also present at other MCS, implying that membrane curvature enforcement may be a widespread mechanism to expedite lipid transport at MCS.

cell biology↗

bioRxiv2019

TANGO1 regulates membrane tension to mediate procollagen export

The endoplasmic reticulum (ER)-resident transmembrane protein TANGO1 assembles into a ring around COPII subunits at ER exit sites (ERES), and links cytosolic membrane-remodeling machinery, tethers, and ER-Golgi intermediate compartment (ERGIC) membranes to procollagens in the ER lumen (Raote et al., 2018). This arrangement is proposed to create a route for direct transfer of procollagens from ERES to ERGIC membranes via a tunnel. Here, we present a physical model in which TANGO1 forms a linear filament that wraps around COPII lattices at ERES to stabilize the neck of a growing transport intermediate. Importantly, our results show that TANGO1 is able to stabilize ERES-ERGIC opening by regulating ER membrane tension to allow procollagen loading and export from the ER. Altogether, our theoretical approach provides a mechanical framework of TANGO1 as a membrane tension regulator to control procollagen export from the ER.

biophysics↗

bioRxiv2016

Sphingolipid metabolic flow controls phosphoinositide turnover at thetrans Golgi network

Sphingolipids are membrane lipids, which are globally required for eukaryotic life. Sphingolipid composition varies among endomembranes with pre- and post-Golgi compartments being poor and rich in sphingolipids, respectively. Thanks to this different sphingolipid content, pre- and post-Golgi membranes serve different cellular functions. Nevertheless, how subcellular sphingolipid levels are maintained in spite of trafficking and metabolic fluxes is only partially understood. Here we describe a homeostatic control circuit that controls sphingolipid levels at the trans Golgi network. Specifically, we show that sphingomyelin production at the trans Golgi network triggers a signalling reaction leading to PtdIns(4)P dephosphorylation. Since PtdIns(4)P is required for cholesterol, and sphingolipid transport to the trans Golgi network, PtdIns(4)P consumption leads to the interruption of this transport in response to excessive sphingomyelin production. Based on this evidence we envisage a model where this homeostatic circuit maintains the sphingolipid composition of trans Golgi network and thus of post-Golgi compartments constant, against instant fluctuations in the sphingolipid biosynthetic flow.

cell biology↗