The Human Cytomegalovirus Nonstructural Glycoprotein UL148 Reorganizes the Endoplasmic Reticulum

Abstract

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.

HSV Forms an HCMV-like Viral Assembly Center in Neuronal Cells

“…On the other hand, the 510 localization pattern of ER membranes in HSV-infected neuronal cells ( Figure S1) is similar to 511 the common laboratory strains of HCMV-infected fibroblasts, in which ER membranes mostly 512 retain their natural structure (Zhang et al, 2019). This is different from the ER morphology of 513 wild-type HCMV strain TB40/E-infected cells, in which ER membranes are deformed by dilation 514 and ruffling (Zhang et al, 2019). This strain-specific difference is due to the quick loss of a 515 single gene UL148 (which encodes an ER-modification protein in HCMV strain TB40/E) during 516 the passage of the virus in cell cultures (Zhang et al, 2019).…”

“…This is different from the ER morphology of 513 wild-type HCMV strain TB40/E-infected cells, in which ER membranes are deformed by dilation 514 and ruffling (Zhang et al, 2019). This strain-specific difference is due to the quick loss of a 515 single gene UL148 (which encodes an ER-modification protein in HCMV strain TB40/E) during 516 the passage of the virus in cell cultures (Zhang et al, 2019). UL148 has no homolog in HSV, 517 thus the resemblance between ER patterns in HSV-infected cells and HCMV-infected cells is 518 not surprising.…”

“…First, we have 507 observed that Golgi-derived membranes concentrate to the HSV cVAC, similar to the Golgi 508 marker arrangement in HCMV-infected cells (Das et al, 2007, Das andPellett, 2011), 509 suggesting herpesvirus conserved requirement for Golgi function. On the other hand, the 510 localization pattern of ER membranes in HSV-infected neuronal cells ( Figure S1) is similar to 511 the common laboratory strains of HCMV-infected fibroblasts, in which ER membranes mostly 512 retain their natural structure (Zhang et al, 2019). This is different from the ER morphology of 513 wild-type HCMV strain TB40/E-infected cells, in which ER membranes are deformed by dilation 514 and ruffling (Zhang et al, 2019).…”

Endoplasmic Reticulum (ER) Reorganization and Intracellular Retention of CD58 Are Functionally Independent Properties of the Human Cytomegalovirus ER-Resident Glycoprotein UL148

“…UL148 insolubility is not required to prevent the accumulation of highmolecular-weight CD58 glycoforms. We recently observed that UL148 accumulates in a detergent-insoluble form during infection (30). We therefore wished to examine whether any of the CCTA mutations affected UL148 solubility, since this might help us to infer whether the intrinsic insolubility of UL148 is required for retention of CD58.…”

“…Hence, UL148 might cause ER stress by impairing the disposal of misfolded proteins from the ER. Furthermore, UL148 drastically reorganizes the ER, causing the accumulation of unusual electron-dense membranous structures that derive from distended ER cisternae (30). These structures are replete with factors involved in glycoprotein quality control, such as SEL1L, HRD1, and EDEM1, which further suggests that ER proteostasis is altered by UL148.…”