Characterization of a Novel Golgi Apparatus-Localized Latency Determinant Encoded by Human Cytomegalovirus

Abstract

Human cytomegalovirus (HCMV) exists indefinitely in infected individuals by a yet poorly characterized latent infection in hematopoietic cells. We previously demonstrated a requirement for the putative UL138 open reading frame (ORF) in promoting a latent infection in CD34؉ hematopoietic progenitor cells (HPCs) infected in vitro. In our present study, we have identified two coterminal transcripts of 2.7 and 3.6 kb and a 21-kilodalton (kDa) protein (pUL138) that are derived from the UL138 locus with early-late gene kinetics during productive infection. The UL138 transcripts and protein are detected in both fibroblasts and HPCs. A recombinant virus, FIX-UL138 STOP , that synthesizes the UL138 transcripts but not the protein exhibited a partial loss-of-latency phenotype in HPCs, similar to the phenotype observed for the UL138-null recombinant virus. This finding suggests that the UL138 protein is required for latency, but it does not exclude the possibility that the UL138 transcripts or other ORFs also contribute to latency. The mechanisms by which pUL138 contributes to latency remain unknown. While the 86-and 72-kDa immediate-early proteins were not detected in HPCs infected with HCMV in vitro, pUL138 did not function directly to suppress expression from the major immediate-early promoter in reporter assays. Interestingly, pUL138 localizes to the Golgi apparatus in infected cells but is not incorporated into virus particles. The localization of pUL138 to the Golgi apparatus suggests that pUL138 contributes to HCMV latency by a novel mechanism. pUL138 is the first HCMV protein demonstrated to promote an infection with the hallmarks of latency in CD34 ؉ HPCs.

Analysis of latent viral gene expression in natural and experimental latency models of human cytomegalovirus and its correlation with histone modifications at a latent promoter

“…These changes did not appear to be due to any overt decreases in viral genome copy number during differentiation ( Fig. 2c), as reported by Petrucelli et al (2009). A caveat of this analysis was the detection of weak but detectable UL138 RNA expression just prior to LPS maturation (Fig.…”

“…However, increasing evidence suggests the presence of a limited but distinct viral transcription profile in latently infected cells (Cheung et al, 2006;Goodrum et al, 2002;Kondo et al, 1996), although most are not latency-specific: the cytomegalovirus latency transcripts (CLTs) (Kondo et al, 1996;Lunetta & Wiedeman, 2000;White et al, 2000) LUNA (latent undefined nuclear antigen; UL81-82as) (Bego et al, 2005) and UL138 (Petrucelli et al, 2009) are all detected during lytic infection, and the viral homologue of interleukin-10 (IL-10) expressed during HCMV latent infection (LAcmv-IL10) is an alternately spliced form of the lytic viral IL-10 (cmvIL-10) encoded from the UL111A locus (Jenkins et al, 2004;Kotenko et al, 2000).…”

Reconstruction of the complete human cytomegalovirus genome in a BAC reveals RL13 to be a potent inhibitor of replication

“…[21][22][23], a regulator of latency (gene UL138; refs. 24,25), and several other uncharacterized functions. Therefore, the U L /b′ region is likely to contribute to virulence via several pathways.…”

Viral Interleukin-10 Expressed by Human Cytomegalovirus during the Latent Phase of Infection Modulates Latently Infected Myeloid Cell Differentiation

“…Following terminal cell differentiation of these cells into myeloid dendritic cells (DCs) and macrophages, latent virus has the ability to reactivate, resulting in the production of new, infectious virions and often severe disease in immunocompromised individuals (11,14,28,37,49,50,59,63). Only a subset of viral genes are transcriptionally active during latency (2,8,12,13,17,23,34,47), including HCMV UL111A, a gene that encodes homologs of the potent immunomodulatory cytokine human interleukin-10 (hIL-10). UL111A is transcriptionally active during both productive and latent phases of infection and encodes several viral IL-10 proteins (17,(24)(25)(26)46) which exert a diverse range of immunomodulatory functions, including inhibition of cytokine synthesis and major histocompatibility complex (MHC) expression by myeloid cells, stimulation of B cells, and suppression of DC maturation and cytotrophoblast function (5-7, 9, 16, 18, 36, 51, 52, 61).…”