scholarly journals The Role of Glycans in Apical Sorting of Proteins in Polarized Epithelial Cells

Glycosylation ◽  
10.5772/48214 ◽  
2012 ◽  
Author(s):  
Kristian Prydz ◽  
Gro Live ◽  
Heidi Tveit
Keyword(s):  
Epithelial Cells ◽  
Polarized Epithelial Cells ◽  
Apical Sorting

N-glycans as apical targeting signals in polarized epithelial cells.

2005 ◽  
Vol 72 ◽  
pp. 39-45 ◽  
Author(s):  
Paula Urquhart ◽  
Susan Pang ◽  
Nigel M. Hooper
Keyword(s):  
Epithelial Cells ◽  
Kidney Cells ◽  
Apical Surface ◽  
Madin Darby Canine Kidney ◽  
Targeting Signals ◽  
Polarized Epithelial Cells ◽  
Apical Sorting ◽  
Darby Canine Kidney ◽  
Canine Kidney

MDCK (Madin-Darby canine kidney) cells represent a good model of polarized epithelium to investigate the signals involved in the apical targeting of proteins. As reported previously, GPI (glycosylphosphatidylinositol) anchors mediate the apical sorting of proteins in polarized epithelial cells through their interaction with lipid rafts. However, using a naturally N-glycosylated and GPI-anchored protein, we found that the GPI anchor does not influence the targeting of the protein. It is, in fact, the N-glycans that signal the protein to the apical surface. In the present review, the role of N-glycans and GPI anchors as apical signals is discussed along with the putative mechanisms involved.

scholarly journals The MAL Protein, an Integral Component of Specialized Membranes, in Normal Cells and Cancer

Cells ◽  
2021 ◽  
Vol 10 (5) ◽  
pp. 1065
Author(s):  
Armando Rubio-Ramos ◽  
Leticia Labat-de-Hoz ◽  
Isabel Correas ◽  
Miguel A. Alonso
Keyword(s):  
Epithelial Cells ◽  
Large Body ◽  
Original Description ◽  
Cell Types ◽  
Future Research ◽  
Transmembrane Segments ◽  
Epsilon Toxin ◽  
Proteolipid Proteins ◽  
Polarized Epithelial Cells

The MAL gene encodes a 17-kDa protein containing four putative transmembrane segments whose expression is restricted to human T cells, polarized epithelial cells and myelin-forming cells. The MAL protein has two unusual biochemical features. First, it has lipid-like properties that qualify it as a member of the group of proteolipid proteins. Second, it partitions selectively into detergent-insoluble membranes, which are known to be enriched in condensed cell membranes, consistent with MAL being distributed in highly ordered membranes in the cell. Since its original description more than thirty years ago, a large body of evidence has accumulated supporting a role of MAL in specialized membranes in all the cell types in which it is expressed. Here, we review the structure, expression and biochemical characteristics of MAL, and discuss the association of MAL with raft membranes and the function of MAL in polarized epithelial cells, T lymphocytes, and myelin-forming cells. The evidence that MAL is a putative receptor of the epsilon toxin of Clostridium perfringens, the expression of MAL in lymphomas, the hypermethylation of the MAL gene and subsequent loss of MAL expression in carcinomas are also presented. We propose a model of MAL as the organizer of specialized condensed membranes to make them functional, discuss the role of MAL as a tumor suppressor in carcinomas, consider its potential use as a cancer biomarker, and summarize the directions for future research.

scholarly journals Human Respiratory Syncytial Virus Glycoproteins Are Not Required for Apical Targeting and Release from Polarized Epithelial Cells

2008 ◽  
Vol 82 (17) ◽  
pp. 8664-8672 ◽  
Author(s):  
Melissa Batonick ◽  
Antonius G. P. Oomens ◽  
Gail W. Wertz
Keyword(s):  
Respiratory Syncytial Virus ◽  
Epithelial Cells ◽  
Apical Membrane ◽  
Human Respiratory Syncytial Virus ◽  
Viral Gene ◽  
Recombinant Viruses ◽  
Intracellular Targeting ◽  
Polarized Epithelial Cells ◽  
Syncytial Virus ◽  
Apical Sorting

ABSTRACT Human respiratory syncytial virus (HRSV) is released from the apical membrane of polarized epithelial cells. However, little is known about the processes of assembly and release of HRSV and which viral gene products are involved in the directional maturation of the virus. Based on previous studies showing that the fusion (F) glycoprotein contained an intrinsic apical sorting signal and that N- and O-linked glycans can act as apical targeting signals, we investigated whether the glycoproteins of HRSV were involved in its directional targeting and release. We generated recombinant viruses with each of the three glycoprotein genes deleted individually or in groups. Each deleted gene was replaced with a reporter gene to maintain wild-type levels of gene expression. The effects of deleting the glycoprotein genes on apical maturation and on targeting of individual proteins in polarized epithelial cells were examined by using biological, biochemical, and microscopic assays. The results of these studies showed that the HRSV glycoproteins are not required for apical maturation or release of the virus. Further, deletion of one or more of the glycoprotein genes did not affect the intracellular targeting of the remaining viral glycoproteins or the nucleocapsid protein to the apical membrane.

scholarly journals Calcium levels in the Golgi complex regulate clustering and apical sorting of GPI-APs in polarized epithelial cells

2021 ◽  
Vol 118 (33) ◽  
pp. e2014709118
Author(s):  
Stéphanie Lebreton ◽  
Simona Paladino ◽  
Dandan Liu ◽  
Maria Nitti ◽  
Julia von Blume ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Epithelial Cells ◽  
Golgi Complex ◽  
Calcium Binding ◽  
Calcium Concentration ◽  
Apical Surface ◽  
Vital Functions ◽  
Molecular Machinery ◽  
Polarized Epithelial Cells ◽  
Apical Sorting

Glycosylphosphatidylinositol-anchored proteins (GPI-APs) are lipid-associated luminal secretory cargoes selectively sorted to the apical surface of the epithelia where they reside and play diverse vital functions. Cholesterol-dependent clustering of GPI-APs in the Golgi is the key step driving their apical sorting and their further plasma membrane organization and activity; however, the specific machinery involved in this Golgi event is still poorly understood. In this study, we show that the formation of GPI-AP homoclusters (made of single GPI-AP species) in the Golgi relies directly on the levels of calcium within cisternae. We further demonstrate that the TGN calcium/manganese pump, SPCA1, which regulates the calcium concentration within the Golgi, and Cab45, a calcium-binding luminal Golgi resident protein, are essential for the formation of GPI-AP homoclusters in the Golgi and for their subsequent apical sorting. Down-regulation of SPCA1 or Cab45 in polarized epithelial cells impairs the oligomerization of GPI-APs in the Golgi complex and leads to their missorting to the basolateral surface. Overall, our data reveal an unexpected role for calcium in the mechanism of GPI-AP apical sorting in polarized epithelial cells and identify the molecular machinery involved in the clustering of GPI-APs in the Golgi.

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