Glycosylphosphatidylinositols (GPIs) are ubiquitous in eukaryotes and serve to anchor a variety of proteins to the exoplasmic leaflet of cellular membranes. GPIs are synthesized in the endoplasmic reticulum (ER), in excess of the amount needed for protein modification. The fate of the excess GPIs is unknown, but they may be retained in the ER, transported to other membranes, and/or metabolized. In relation to this problem, we were interested in determining whether GPIs were transported to the plasma membrane and whether, like GPI-anchored proteins, their presence was confined to the apical plasma membrane domain in polarized epithelial cells. Polarized Madin-Darby canine kidney epithelial cell monolayers were incubated with [H]mannose or [H]ethanolamine to label GPIs and then infected with enveloped viruses. We used influenza virus (flu) and vesicular stomatitis virus (VSV) for these experiments as these viruses are assembled at the cell surface and acquire their envelope lipids from the plasma membrane. Furthermore, flu and VSV bud specifically from the apical and basolateral plasma membrane domains, respectively. Flu and VSV were isolated from the apical and basolateral media, respectively, and subjected to lipid analysis. Radiolabeled GPIs were found in both viruses. Moreover, the membrane concentration of GPIs (i.e. GPI radioactivity normalized to membrane mass) in the two viruses was essentially the same. These observations suggest that (i) non-protein-linked GPIs are located at the plasma membrane; (ii) since GPIs are synthesized in the ER, they must be transported from the ER to the plasma membrane; and (iii) transport of non-protein-linked GPIs is not influenced by the sorting processes that target GPI-anchored proteins exclusively to the apical plasma membrane.

CiteULike

Complore

Connotea

Del.icio.us

Digg

Reddit

Technorati

This article has been cited by other articles:

				S. Pang, P. Urquhart, and N. M. Hooper N-Glycans, not the GPI anchor, mediate the apical targeting of a naturally glycosylated, GPI-anchored protein in polarised epithelial cells J. Cell Sci., October 1, 2004; 117(21): 5079 - 5086. [Abstract] [Full Text] [PDF]

				E. Vassella, P. Butikofer, M. Engstler, J. Jelk, and I. Roditi Procyclin Null Mutants of Trypanosoma brucei Express Free Glycosylphosphatidylinositols on Their Surface Mol. Biol. Cell, April 1, 2003; 14(4): 1308 - 1318. [Abstract] [Full Text] [PDF]

				N. A. Baumann, J. Vidugiriene, C. E. Machamer, and A. K. Menon Cell Surface Display and Intracellular Trafficking of Free Glycosylphosphatidylinositols in Mammalian Cells J. Biol. Chem., March 15, 2000; 275(10): 7378 - 7389. [Abstract] [Full Text] [PDF]

				J. H. Benting, A. G. Rietveld, and K. Simons N-Glycans Mediate the Apical Sorting of a GPI-anchored, Raft-associated Protein in Madin-Darby Canine Kidney Cells J. Cell Biol., July 26, 1999; 146(2): 313 - 320. [Abstract] [Full Text] [PDF]

				J. E. Ralton and M. J. McConville Delineation of Three Pathways of Glycosylphosphatidylinositol Biosynthesis in Leishmania mexicana. PRECURSORS FROM DIFFERENT PATHWAYS ARE ASSEMBLED ON DISTINCT POOLS OF PHOSPHATIDYLINOSITOL AND UNDERGO FATTY ACID REMODELING J. Biol. Chem., February 13, 1998; 273(7): 4245 - 4257. [Abstract] [Full Text] [PDF]

				A. Maisner, G. Zimmer, M. K. Liszewski, D. M. Lublin, J. P. Atkinson, and G. Herrler Membrane Cofactor Protein (CD46) Is a Basolateral Protein That Is Not Endocytosed. IMPORTANCE OF THE TETRAPEPTIDE FTSL AT THE CARBOXYL TERMINUS J. Biol. Chem., August 15, 1997; 272(33): 20793 - 20799. [Abstract] [Full Text] [PDF]

				N. Singh, L.-N. Liang, M. L. Tykocinski, and A. M. Tartakoff A Novel Class of Cell Surface Glycolipids of Mammalian Cells. FREE GLYCOSYL PHOSPHATIDYLINOSITOLS J. Biol. Chem., May 31, 1996; 271(22): 12879 - 12884. [Abstract] [Full Text] [PDF]

				L. Abrami, M. Fivaz, T. Kobayashi, T. Kinoshita, R. G. Parton, and F. G. van der Goot Cross-talk between Caveolae and Glycosylphosphatidylinositol-rich Domains J. Biol. Chem., August 10, 2001; 276(33): 30729 - 30736. [Abstract] [Full Text] [PDF]