Biology subjects

Parashuraman, S.

Publications and source records attributed to Parashuraman, S..

5 recordsLinked to original sources

bioRxiv2025

Mechanical Cues Regulate Cargo Sorting and Export at the Golgi

The secretory pathway is a sophisticated endomembrane machinery designed to transport and deliver proteins and lipids to intracellular organelles and the extracellular space. While the molecular components of the secretory pathway are well understood, less is known about their regulation, especially by mechanical cues. Here, we report that substrate stiffness stimulates conventional secretion. We have unravelled a molecular pathway that links a mechanical cue through Src and FAK kinases to promote the trafficking of secretory proteins out of the Golgi apparatus and prevent their post-Golgi lysosomal degradation. Phosphoproteomic analysis revealed the Golgi-specific Brefeldin A resistance factor 1 (GBF1) as a key downstream mechano-responsive regulator, whose phosphorylation state orchestrates post-Golgi cargo sorting, directing proteins either toward secretion or to lysosomes. Finally, we identified AMPK as a stiffness-dependent upstream regulator of GBF1 phosphorylation. Together, our data reveal a molecular regulatory loop in which matrix stiffness positively regulates cellular secretion via the Src-FAK-AMPK-GBF1 axis, which can have relevant medical implications in conditions like cancer and fibrosis and their treatment.

cell biology↗

bioRxiv2022

Prioritization of driver genes in cancer-associated copy number alterations identifies B4GALT5 as a glycooncogene

Cancer is a disease resulting from aberrant communication between cells of a multicellular organism. The glycan coat that surrounds the cells is an important player in cellular communication. While altered cell surface glycans are known biomarkers for cancer, glycan biosynthesis itself has not been considered a potential oncogenic pathway. So, to understand the oncogenic potential of the glycan biosynthetic pathways we have analyzed the copy number alterations (CNA) of genes encoding for glycosylation regulators (glycogenes) in cancer genome datasets and identify novel glyco-oncogenes and glyco-tumor suppressor genes (TSGs). CNA of oncogenes and TSGs is an important cancer-associated genetic alteration that associates with worst prognosis. Nevertheless, identity of the driver genes in the copy number altered segments of the genome remains obscure in most cases. We developed a prioritization pipeline based on bioinformatic and experimental criteria to identify putative driver genes. In addition to correctly identifying several well-established oncogenes/TSGs, this pipeline discerns several novel oncogenes and TSGs, some of which are glycogenes. Further, among glyco-oncogenes there is an enrichment for glycosphingolipid biosynthetic pathway and trans-Golgi associated lysosomal sorting machinery and among glyco-TSGs there is an enrichment for early N-glycan biosynthetic enzymes. As a proof-of-principle we show that one of the identified glycooncogene B4GALT5, encoding a key enzyme in the glycosphingolipid pathway exhibits oncogenic property of promoting increased growth of hepatocellular carcinoma cells. Thus, this study identifies glycosylation pathways with oncoregulatory properties and opens up a new group of enzymes as potential therapeutic targets for cancer.

cancer biology↗

bioRxiv2020

Regulated compartmentalization of enzymes in Golgi by GRASP55 controls cellular glycosphingolipid profile and function

Glycans are important regulators of cell and organismal physiology. This requires that the glycan biosynthesis be controlled to achieve specific cellular glycan profiles. Glycans are assembled in the Golgi apparatus on secretory cargoes that traverse it. The mechanisms by which the Golgi apparatus ensures cell- and cargo-specific glycosylation remain obscure. We investigated how the Golgi apparatus regulates glycosylation by studying biosynthesis of glycosphingolipids, glycosylated lipids with critical roles in signalling and differentiation. We identified the Golgi matrix protein GRASP55 as a controller of sphingolipid glycosylation by regulating the compartmentalized localization of key sphingolipid biosynthetic enzymes in the Golgi. GRASP55 controls the localization of the enzymes by binding to them and regulating their entry into peri-Golgi vesicles. Impairing GRASP55-enzyme interaction decompartmentalizes these enzymes, changes the substrate flux across competing glycosylation pathways that results in alteration of the cellular glycosphingolipid profile. This GRASP55 regulated pathway of enzyme compartmentalization allows cells to make cell density-dependent adaptations in glycosphingolipid biosynthesis to suit cell growth needs. Thus, the Golgi apparatus controls the cellular glycan (glycosphingolipid) profile by governing competition between biosynthetic reactions through regulated changes in enzyme compartmentalization.

cell biology↗

bioRxiv2019

Retrograde Transport of Golgi Enzymes by GOLPH3 Across Maturing Cisternae Regulates Glycan Assembly on Sphingolipids and CellGrowth

Glycans are ubiquitous sugar polymers with major biological functions that are assembled by glyco-enzymes onto cargo molecules during their transport through the Golgi complex. How the Golgi determines glycan assembly is poorly understood. By relying on the Golgi cisternal maturation model and using the glyco-enzyme adaptor and oncoprotein GOLPH3 as a molecular tool, we define the first example of how the Golgi controls glycosylation and associated cell functions. GOLPH3, acting as a component of the cisternal maturation mechanism, selectively binds and recycles a subset of glyco-enzymes of the glycosphingolipid synthetic pathway, hinders their escape to the lysosomes and hence increases their levels through a novel lysosomal degradation-regulated mechanism. This enhances the production of specific growth-inducing glycosphingolipids and reprograms the glycosphingolipid pathway to potentiate mitogenic signaling and cell proliferation. These findings unravel unforeseen organizing principles of Golgi-dependent glycosylation and delineate a paradigm for glycan assembly by the Golgi transport mechanisms. Moreover, they indicate a new role of cisternal maturation as a regulator of glycosylation, and outline a novel mechanism of action for GOLPH3-induced proliferation.

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↗