Biology subjects

Malhotra, V.

Publications and source records attributed to Malhotra, V..

24 records · Page 2Linked to original sources

bioRxiv2019

Biallelic TANGO1 mutations cause a novel syndromal disease due to hampered cellular collagen secretion

The transport and Golgi organization 1 (TANGO1) family proteins have been shown to play pivotal roles in the secretory pathway. Full length TANGO1 is a transmembrane protein localised at endoplasmic reticulum exit sites (ERES), where it binds bulky cargo within the ER lumen and recruits membranes from the ER Golgi intermediate compartment (ERGIC) to create an exit route for their export. Tango1 knockout mice display a global collagen secretion defect and perinatal lethality. Here we report the first TANGO1-associated syndrome in humans, which mainly manifests in a collagenopathy. A synonymous substitution that results in exon 8 skipping in most mRNA molecules, ultimately leading to a truncated TANGO1 protein was identified as the disease-causing mutation. The four homozygously affected sons of a consanguineous family display severe dentinogenesis imperfecta, short stature, various skeletal abnormalities, insulin-dependent diabetes mellitus, sensorineural hearing loss, and mild intellectual disability. Functional studies in HeLa and U2OS cells revealed that the corresponding truncated TANGO1 protein is dispersed in the ER and its expression in cells with intact endogenous TANGO1 impairs cellular collagen I secretion.

genetics↗

bioRxiv2019

Reactive oxygen species (ROS) production triggers unconventional secretion of antioxidant enzymes

Nutrient deprivation triggers the release of signal-sequence-lacking Acb1 and the antioxidant superoxide dismutase 1 (SOD1). We now report that secreted SOD1 is functionally active and accompanied by export of other antioxidant enzymes such as thioredoxins, (Trx1 and Trx2) and peroxiredoxin Ahp1, in a Grh1 dependent manner. Our data reveal that starvation leads to production of non-toxic levels of reactive oxygen species (ROS). Treatment of cells with N-acetylcysteine (NAC), which sequesters ROS, prevents antioxidants and Acb1 secretion. Starved cells lacking Grh1 are metabolically active, but defective in their ability to regrow upon return to growth conditions. Treatment with NAC restored the Grh1 dependent effect of starvation on cell growth. In sum, starvation triggers ROS production and cells respond by secreting antioxidants and Acb1, which is an important lipogenic signaling molecule in mammalian cells. We suggest that unconventional secretion of antioxidants and Acb1 like activities maintains cells in a form necessary for growth upon their eventual return from starvation to normal conditions.

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↗

bioRxiv2019

New factors for protein transport identified by a genome-wide CRISPRi screen in mammalian cells

Protein and membrane trafficking pathways are critical for cell and tissue homeostasis. Traditional genetic and biochemical approaches have shed light on basic principles underlying these processes. However, the list of factors required for secretory pathways function remains incomplete, and mechanisms involved in their adaptation poorly understood. Here, we present a powerful strategy based on a pooled genome-wide CRISPRi screen that allowed the identification of new factors involved in protein transport. Two newly identified factors, TTC17 and CCDC157, localized along the secretory pathway and were found to interact with resident proteins of ER-Golgi membranes. In addition, we uncovered that upon TTC17 knockdown, the polarized organization of Golgi cisternae was altered, creating glycosylation defects, and that CCDC157 is an important factor for the fusion of transport carriers to the Golgi complex. In conclusion, our work identified and characterized new actors in the mechanisms of protein transport and secretion, and opens stimulating perspectives for the use of our platform in physiological and pathological contexts.

cell biology↗

bioRxiv2017

A Di-Acidic Motif Targets Cytoplasmic Proteins For Unconventional Protein Secretion

We previously reported that Acb1, a cytoplasmic protein in Saccharomyces cerevisiae that cannot enter the endoplasmic reticulum (ER), was secreted upon nutrient starvation by a Vps4 independent, but ESCRT-I, -II and -III and Grh1 dependent pathway (Curwin et al., 2016). Here, we report that the same conditions result in secretion of another signal sequence lacking protein, superoxide dismutase 1 (SOD1). Similar to Acb1, SOD1 export requires Grh1 and a subset of ESCRT components. Importantly, our analysis reveals the existence of a conserved di-acidic motif (Asp-Glu) in SOD1 and Acb1 that is required for their respective export. This sequence is different from the di-acidic motif (Asp-X-Glu) necessary for export of transmembrane proteins from the ER. We propose that the Asp-Glu sequence acts as a targeting motif for the entry of SOD1 and Acb1, and likely many other proteins, upon nutrient starvation into a common albeit ER-Golgi independent pathway of secretion.

cell biology↗

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↗