UL74 of human cytomegalovirus contributes to virus release by promoting secondary envelopment of virions.
The glycoprotein (g) complex gH/gL represents an essential part of the herpesvirus fusion machinery mediating entry of cell-free virions and cell-associated viral spread. In some herpesviruses additional proteins are associated with gH/gL contributing to the cell tropism of the respective virus. Human cytomegalovirus (HCMV) gH/gL forms complexes with either gO (UL74) or proteins of the UL128-131A gene locus. While a contribution of UL128-131A to endothelial cell tropism is known, the role of gO is less clear. We studied the role of gH/gL-associated proteins in HCMV replication in human foreskin fibroblasts (HFF) and human umbilical vein endothelial cells (HUVEC). Deletions of UL74 alone or in combination with mutations of the UL128-131A gene region were introduced into bacterial artificial chromosome vectors derived from the endotheliotropic strain TB40/E. Deletion of UL74 caused a profound defect regarding virus release from infected HFF and HUVEC. Large numbers of capsids accumulated in the cytoplasm of infected HFF but failed to acquire an envelope. Clear cell type differences were observed in the cell-associated spread of the UL74-defective virus. In HFF, focal growth was severely impaired, whereas it was normal in HUVEC. Deletion of UL131A abolished focal growth in endothelial cells. UL74/UL128-131A dual mutants showed severely impaired reconstitution efficiency. Our data suggest that gO plays a critical role in secondary envelopment and release of cell-free virions independent of the cell type but affects cell-associated growth specifically in HFF, whereas UL128-131A contributes to cell-associated spread in HFF and HUVEC.
Jiang
Xiao Jing
XJ
Institut für Medizinische Virologie, Eberhard Karls Universität, Tübingen, Elfriede Aulhorn Strasse 6, D-72076 Tübingen, Germany.
Adler
Barbara
B
Sampaio
Kerstin Laib
KL
Digel
Margarete
M
Jahn
Gerhard
G
Ettischer
Nicole
N
Stierhof
York-Dieter
YD
Scrivano
Laura
L
Koszinowski
Ulrich
U
Mach
Michael
M
Sinzger
Christian
C
D002478:Cells, Cultured; D022202:Chromosomes, Artificial, Bacterial; D003587:Cytomegalovirus / Q000502:physiology*; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008562:Membrane Glycoproteins / Q000502:physiology*; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D016296:Mutagenesis; D016366:Open Reading Frames; D014759:Viral Envelope Proteins / Q000502:physiology*; D014771:Virion / Q000502:physiology*; D014779:Virus Replication
D008562:Membrane Glycoproteins; D014759:Viral Envelope Proteins; C439068:glycoprotein O, cytomegalovirus