The Human Cytomegalovirus Nonstructural Glycoprotein UL148 Reorganizes the Endoplasmic Reticulum

ABSTRACT Human cytomegalovirus (HCMV) encodes an endoplasmic reticulum (ER)-resident glycoprotein, UL148, which activates the unfolded protein response (UPR) but is fully dispensable for viral replication in cultured cells. Hence, its previously ascribed roles in immune evasion and modulation of vir...

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Autores principales:	Hongbo Zhang, Clarissa Read, Christopher C. Nguyen, Mohammed N. A. Siddiquey, Chaowei Shang, Cameron M. Hall, Jens von Einem, Jeremy P. Kamil
Formato:	article
Lenguaje:	EN
Publicado:	American Society for Microbiology 2019
Materias:	cytomegalovirus glycoproteins herpesviruses organelle structure secretory pathway stress adaptation Microbiology QR1-502
Acceso en línea:	https://doaj.org/article/b7fe40a43b0d49eb94d185107616970d
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spelling	oai:doaj.org-article:b7fe40a43b0d49eb94d185107616970d2021-11-15T15:54:47ZThe Human Cytomegalovirus Nonstructural Glycoprotein UL148 Reorganizes the Endoplasmic Reticulum10.1128/mBio.02110-192150-7511https://doaj.org/article/b7fe40a43b0d49eb94d185107616970d2019-12-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.02110-19https://doaj.org/toc/2150-7511ABSTRACT Human cytomegalovirus (HCMV) encodes an endoplasmic reticulum (ER)-resident glycoprotein, UL148, which activates the unfolded protein response (UPR) but is fully dispensable for viral replication in cultured cells. Hence, its previously ascribed roles in immune evasion and modulation of viral cell tropism are hypothesized to cause ER stress. Here, we show that UL148 is necessary and sufficient to drive the formation of prominent ER-derived structures that on average occupy 5% of the infected cell cytoplasm. The structures are sites where UL148 coalesces with cellular proteins involved in ER quality control, such as HRD1 and EDEM1. Electron microscopy revealed that cells infected with wild-type but not UL148-null HCMV show prominent accumulations of densely packed ruffled ER membranes which connect to distended cisternae of smooth and partially rough ER. During ectopic expression of UL148-green fluorescent protein (GFP) fusion protein, punctate signals traffic to accumulate at conspicuous structures. The structures exhibit poor recovery of fluorescence after photobleaching, which suggests that their contents are poorly mobile and do not efficiently exchange with the rest of the ER. Small-molecule blockade of the integrated stress response (ISR) prevents the formation of puncta, leading to a uniform reticular fluorescent signal. Accordingly, ISR inhibition during HCMV infection abolishes the coalescence of UL148 and HRD1 into discrete structures, which argues that UL148 requires the ISR to cause ER reorganization. Given that UL148 stabilizes immature forms of a receptor binding subunit for a viral envelope glycoprotein complex important for HCMV infectivity, our results imply that stress-dependent ER remodeling contributes to viral cell tropism. IMPORTANCE Perturbations to endoplasmic reticulum (ER) morphology occur during infection with various intracellular pathogens and in certain genetic disorders. We identify that a human cytomegalovirus (HCMV) gene product, UL148, profoundly reorganizes the ER during infection and is sufficient to do so when expressed on its own. Our results reveal that UL148-dependent reorganization of the ER is a prominent feature of HCMV-infected cells. Moreover, we find that this example of virally induced organelle remodeling requires the integrated stress response (ISR), a stress adaptation pathway that contributes to a number of disease states. Since ER reorganization accompanies roles of UL148 in modulation of HCMV cell tropism and in evasion of antiviral immune responses, our results may have implications for understanding the mechanisms involved. Furthermore, our findings provide a basis to utilize UL148 as a tool to investigate organelle responses to stress and to identify novel drugs targeting the ISR.Hongbo ZhangClarissa ReadChristopher C. NguyenMohammed N. A. SiddiqueyChaowei ShangCameron M. HallJens von EinemJeremy P. KamilAmerican Society for Microbiologyarticlecytomegalovirusglycoproteinsherpesvirusesorganelle structuresecretory pathwaystress adaptationMicrobiologyQR1-502ENmBio, Vol 10, Iss 6 (2019)
institution	DOAJ
collection	DOAJ
language	EN
topic	cytomegalovirus glycoproteins herpesviruses organelle structure secretory pathway stress adaptation Microbiology QR1-502
spellingShingle	cytomegalovirus glycoproteins herpesviruses organelle structure secretory pathway stress adaptation Microbiology QR1-502 Hongbo Zhang Clarissa Read Christopher C. Nguyen Mohammed N. A. Siddiquey Chaowei Shang Cameron M. Hall Jens von Einem Jeremy P. Kamil The Human Cytomegalovirus Nonstructural Glycoprotein UL148 Reorganizes the Endoplasmic Reticulum
description	ABSTRACT Human cytomegalovirus (HCMV) encodes an endoplasmic reticulum (ER)-resident glycoprotein, UL148, which activates the unfolded protein response (UPR) but is fully dispensable for viral replication in cultured cells. Hence, its previously ascribed roles in immune evasion and modulation of viral cell tropism are hypothesized to cause ER stress. Here, we show that UL148 is necessary and sufficient to drive the formation of prominent ER-derived structures that on average occupy 5% of the infected cell cytoplasm. The structures are sites where UL148 coalesces with cellular proteins involved in ER quality control, such as HRD1 and EDEM1. Electron microscopy revealed that cells infected with wild-type but not UL148-null HCMV show prominent accumulations of densely packed ruffled ER membranes which connect to distended cisternae of smooth and partially rough ER. During ectopic expression of UL148-green fluorescent protein (GFP) fusion protein, punctate signals traffic to accumulate at conspicuous structures. The structures exhibit poor recovery of fluorescence after photobleaching, which suggests that their contents are poorly mobile and do not efficiently exchange with the rest of the ER. Small-molecule blockade of the integrated stress response (ISR) prevents the formation of puncta, leading to a uniform reticular fluorescent signal. Accordingly, ISR inhibition during HCMV infection abolishes the coalescence of UL148 and HRD1 into discrete structures, which argues that UL148 requires the ISR to cause ER reorganization. Given that UL148 stabilizes immature forms of a receptor binding subunit for a viral envelope glycoprotein complex important for HCMV infectivity, our results imply that stress-dependent ER remodeling contributes to viral cell tropism. IMPORTANCE Perturbations to endoplasmic reticulum (ER) morphology occur during infection with various intracellular pathogens and in certain genetic disorders. We identify that a human cytomegalovirus (HCMV) gene product, UL148, profoundly reorganizes the ER during infection and is sufficient to do so when expressed on its own. Our results reveal that UL148-dependent reorganization of the ER is a prominent feature of HCMV-infected cells. Moreover, we find that this example of virally induced organelle remodeling requires the integrated stress response (ISR), a stress adaptation pathway that contributes to a number of disease states. Since ER reorganization accompanies roles of UL148 in modulation of HCMV cell tropism and in evasion of antiviral immune responses, our results may have implications for understanding the mechanisms involved. Furthermore, our findings provide a basis to utilize UL148 as a tool to investigate organelle responses to stress and to identify novel drugs targeting the ISR.
format	article
author	Hongbo Zhang Clarissa Read Christopher C. Nguyen Mohammed N. A. Siddiquey Chaowei Shang Cameron M. Hall Jens von Einem Jeremy P. Kamil
author_facet	Hongbo Zhang Clarissa Read Christopher C. Nguyen Mohammed N. A. Siddiquey Chaowei Shang Cameron M. Hall Jens von Einem Jeremy P. Kamil
author_sort	Hongbo Zhang
title	The Human Cytomegalovirus Nonstructural Glycoprotein UL148 Reorganizes the Endoplasmic Reticulum
title_short	The Human Cytomegalovirus Nonstructural Glycoprotein UL148 Reorganizes the Endoplasmic Reticulum
title_full	The Human Cytomegalovirus Nonstructural Glycoprotein UL148 Reorganizes the Endoplasmic Reticulum
title_fullStr	The Human Cytomegalovirus Nonstructural Glycoprotein UL148 Reorganizes the Endoplasmic Reticulum
title_full_unstemmed	The Human Cytomegalovirus Nonstructural Glycoprotein UL148 Reorganizes the Endoplasmic Reticulum
title_sort	human cytomegalovirus nonstructural glycoprotein ul148 reorganizes the endoplasmic reticulum
publisher	American Society for Microbiology
publishDate	2019
url	https://doaj.org/article/b7fe40a43b0d49eb94d185107616970d
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The Human Cytomegalovirus Nonstructural Glycoprotein UL148 Reorganizes the Endoplasmic Reticulum

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