Full-length, glycosylated NSP4 is localized to plasma membrane caveolae by a novel raft isolation technique

J Virol. 2007 Jun;81(11):5472-83. doi: 10.1128/JVI.01862-06. Epub 2007 Mar 21.

Abstract

Rotavirus NSP4, initially characterized as an endoplasmic reticulum intracellular receptor, is a multifunctional viral enterotoxin that induces diarrhea in murine pups. There have been recent reports of the secretion of a cleaved NSP4 fragment (residues 112 to 175) and of the association of NSP4 with LC3-positive autophagosomes, raft membranes, and microtubules. To determine if NSP4 traffics to a specific subset of rafts at the plasma membrane, we isolated caveolae from plasma membrane-enriched material that yielded caveola membranes free of endoplasmic reticulum and nonraft plasma membrane markers. Analyses of the newly isolated caveolae from rotavirus-infected MDCK cells revealed full-length, high-mannose glycosylated NSP4. The lack of Golgi network-specific processing of the caveolar NSP4 glycans supports studies showing that NSP4 bypasses the Golgi apparatus. Confocal imaging showed the colocalization of NSP4 with caveolin-1 early and late in infection, elucidating the temporal and spatial NSP4-caveolin-1 association during infection. These data were extended with fluorescent resonance energy transfer analyses that confirmed the NSP4 and caveolin-1 interaction in that the specific fluorescently tagged antibodies were within 10 nm of each other during infection. Cells transfected with NSP4 showed patterns of staining and colocalization with caveolin-1 similar to those of infected cells. This study presents an endoplasmic reticulum contaminant-free caveola isolation protocol; describes the presence of full-length, endoglycosidase H-sensitive NSP4 in plasma membrane caveolae; provides confirmation of the NSP4-caveolin interaction in the presence and absence of other viral proteins; and provides a final plasma membrane destination for Golgi network-bypassing NSP4 transport.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Caveolae / metabolism*
  • Caveolae / ultrastructure
  • Caveolae / virology
  • Cell Line
  • Dogs
  • Glycoproteins / isolation & purification
  • Glycoproteins / metabolism*
  • Glycosylation
  • HT29 Cells
  • Humans
  • Membrane Microdomains / metabolism*
  • Membrane Microdomains / virology
  • Octoxynol
  • Rotavirus / metabolism
  • Toxins, Biological / isolation & purification
  • Toxins, Biological / metabolism*
  • Viral Nonstructural Proteins / isolation & purification
  • Viral Nonstructural Proteins / metabolism*

Substances

  • Glycoproteins
  • NS28 protein, rotavirus
  • Toxins, Biological
  • Viral Nonstructural Proteins
  • Octoxynol