Rotavirus Disrupts Calcium Homeostasis by NSP4 Viroporin Activity

ABSTRACT Many viruses alter intracellular calcium homeostasis. The rotavirus nonstructural protein 4 (NSP4), an endoplasmic reticulum (ER) transmembrane glycoprotein, increases intracellular levels of cytoplasmic Ca2+ ([Ca2+]cyto) through a phospholipase C-independent pathway, which is required for...

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Autores principales:	Joseph M. Hyser, Matthew R. Collinson-Pautz, Budi Utama, Mary K. Estes
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Lenguaje:	EN
Publicado:	American Society for Microbiology 2010
Materias:	Microbiology QR1-502
Acceso en línea:	https://doaj.org/article/cebda0418e3644eb916811af7e0bb554
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spelling	oai:doaj.org-article:cebda0418e3644eb916811af7e0bb5542021-11-15T15:38:17ZRotavirus Disrupts Calcium Homeostasis by NSP4 Viroporin Activity10.1128/mBio.00265-102150-7511https://doaj.org/article/cebda0418e3644eb916811af7e0bb5542010-12-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.00265-10https://doaj.org/toc/2150-7511ABSTRACT Many viruses alter intracellular calcium homeostasis. The rotavirus nonstructural protein 4 (NSP4), an endoplasmic reticulum (ER) transmembrane glycoprotein, increases intracellular levels of cytoplasmic Ca2+ ([Ca2+]cyto) through a phospholipase C-independent pathway, which is required for virus replication and morphogenesis. However, the NSP4 domain and mechanism that increases [Ca2+]cyto are unknown. We identified an NSP4 domain (amino acids [aa] 47 to 90) that inserts into membranes and has structural characteristics of viroporins, a class of small hydrophobic viral proteins that disrupt membrane integrity and ion homeostasis to facilitate virus entry, assembly, or release. Mutational analysis showed that NSP4 viroporin activity was mediated by an amphipathic α-helical domain downstream of a conserved lysine cluster. The lysine cluster directed integral membrane insertion of the viroporin domain and was critical for viroporin activity. In epithelial cells, expression of wild-type NSP4 increased the levels of free cytoplasmic Ca2+ by 3.7-fold, but NSP4 viroporin mutants maintained low levels of [Ca2+]cyto, were retained in the ER, and failed to form cytoplasmic vesicular structures, called puncta, which surround viral replication and assembly sites in rotavirus-infected cells. When [Ca2+]cyto was increased pharmacologically with thapsigargin, viroporin mutants formed puncta, showing that elevation of calcium levels and puncta formation are distinct functions of NSP4 and indicating that NSP4 directly or indirectly responds to elevated cytoplasmic calcium levels. NSP4 viroporin activity establishes the mechanism for NSP4-mediated elevation of [Ca2+]cyto, a critical event that regulates rotavirus replication and virion assembly. IMPORTANCE Rotavirus is the leading cause of viral gastroenteritis in children and young animals. Rotavirus infection and expression of nonstructural protein 4 (NSP4) alone dramatically increase cytosolic calcium, which is essential for replication and assembly of infectious virions. This work identifies the intracellular mechanism by which NSP4 disrupts calcium homeostasis by showing that NSP4 is a viroporin, a class of virus-encoded transmembrane pores. Mutational analyses identified residues critical for viroporin activity. Viroporin mutants did not elevate the levels of cytoplasmic calcium in mammalian cells and were maintained in the endoplasmic reticulum rather than forming punctate vesicular structures that are critical for virus replication and morphogenesis. Pharmacological elevation of cytoplasmic calcium levels rescued puncta formation in viroporin mutants, demonstrating that elevation of calcium levels and puncta formation are distinct NSP4 functions. While viroporins typically function in virus entry or release, elevation of calcium levels by NSP4 viroporin activity may serve as a regulatory function to facilitate virus replication and assembly.Joseph M. HyserMatthew R. Collinson-PautzBudi UtamaMary K. EstesAmerican Society for MicrobiologyarticleMicrobiologyQR1-502ENmBio, Vol 1, Iss 5 (2010)
institution	DOAJ
collection	DOAJ
language	EN
topic	Microbiology QR1-502
spellingShingle	Microbiology QR1-502 Joseph M. Hyser Matthew R. Collinson-Pautz Budi Utama Mary K. Estes Rotavirus Disrupts Calcium Homeostasis by NSP4 Viroporin Activity
description	ABSTRACT Many viruses alter intracellular calcium homeostasis. The rotavirus nonstructural protein 4 (NSP4), an endoplasmic reticulum (ER) transmembrane glycoprotein, increases intracellular levels of cytoplasmic Ca2+ ([Ca2+]cyto) through a phospholipase C-independent pathway, which is required for virus replication and morphogenesis. However, the NSP4 domain and mechanism that increases [Ca2+]cyto are unknown. We identified an NSP4 domain (amino acids [aa] 47 to 90) that inserts into membranes and has structural characteristics of viroporins, a class of small hydrophobic viral proteins that disrupt membrane integrity and ion homeostasis to facilitate virus entry, assembly, or release. Mutational analysis showed that NSP4 viroporin activity was mediated by an amphipathic α-helical domain downstream of a conserved lysine cluster. The lysine cluster directed integral membrane insertion of the viroporin domain and was critical for viroporin activity. In epithelial cells, expression of wild-type NSP4 increased the levels of free cytoplasmic Ca2+ by 3.7-fold, but NSP4 viroporin mutants maintained low levels of [Ca2+]cyto, were retained in the ER, and failed to form cytoplasmic vesicular structures, called puncta, which surround viral replication and assembly sites in rotavirus-infected cells. When [Ca2+]cyto was increased pharmacologically with thapsigargin, viroporin mutants formed puncta, showing that elevation of calcium levels and puncta formation are distinct functions of NSP4 and indicating that NSP4 directly or indirectly responds to elevated cytoplasmic calcium levels. NSP4 viroporin activity establishes the mechanism for NSP4-mediated elevation of [Ca2+]cyto, a critical event that regulates rotavirus replication and virion assembly. IMPORTANCE Rotavirus is the leading cause of viral gastroenteritis in children and young animals. Rotavirus infection and expression of nonstructural protein 4 (NSP4) alone dramatically increase cytosolic calcium, which is essential for replication and assembly of infectious virions. This work identifies the intracellular mechanism by which NSP4 disrupts calcium homeostasis by showing that NSP4 is a viroporin, a class of virus-encoded transmembrane pores. Mutational analyses identified residues critical for viroporin activity. Viroporin mutants did not elevate the levels of cytoplasmic calcium in mammalian cells and were maintained in the endoplasmic reticulum rather than forming punctate vesicular structures that are critical for virus replication and morphogenesis. Pharmacological elevation of cytoplasmic calcium levels rescued puncta formation in viroporin mutants, demonstrating that elevation of calcium levels and puncta formation are distinct NSP4 functions. While viroporins typically function in virus entry or release, elevation of calcium levels by NSP4 viroporin activity may serve as a regulatory function to facilitate virus replication and assembly.
format	article
author	Joseph M. Hyser Matthew R. Collinson-Pautz Budi Utama Mary K. Estes
author_facet	Joseph M. Hyser Matthew R. Collinson-Pautz Budi Utama Mary K. Estes
author_sort	Joseph M. Hyser
title	Rotavirus Disrupts Calcium Homeostasis by NSP4 Viroporin Activity
title_short	Rotavirus Disrupts Calcium Homeostasis by NSP4 Viroporin Activity
title_full	Rotavirus Disrupts Calcium Homeostasis by NSP4 Viroporin Activity
title_fullStr	Rotavirus Disrupts Calcium Homeostasis by NSP4 Viroporin Activity
title_full_unstemmed	Rotavirus Disrupts Calcium Homeostasis by NSP4 Viroporin Activity
title_sort	rotavirus disrupts calcium homeostasis by nsp4 viroporin activity
publisher	American Society for Microbiology
publishDate	2010
url	https://doaj.org/article/cebda0418e3644eb916811af7e0bb554
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Rotavirus Disrupts Calcium Homeostasis by NSP4 Viroporin Activity

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