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Characterization of a novel Golgi apparatus-localized latency determinant encoded by human cytomegalovirus

Alex Petrucelli1, Michael Rak, Lora Grainger

  • 1Department of Immunobiology, University of Arizona, Tucson, Arizona 85721, USA.

Journal of Virology
|March 20, 2009
PubMed

Insights

Human cytomegalovirus (HCMV) latency in hematopoietic cells requires the UL138 protein. This protein, detected in fibroblasts and progenitor cells, localizes to the Golgi apparatus, suggesting a novel latency mechanism.

Area of Science:

  • Virology
  • Immunology
  • Cell Biology

Background:

  • Human cytomegalovirus (HCMV) establishes lifelong latent infections, primarily in hematopoietic cells.
  • The precise mechanisms governing HCMV latency, particularly in hematopoietic progenitor cells (HPCs), remain incompletely understood.
  • Previous research indicated a role for the UL138 open reading frame (ORF) in HCMV latency.

Purpose of the Study:

  • To investigate the role of the UL138 locus and its protein product (pUL138) in HCMV latency.
  • To characterize the expression kinetics and cellular localization of pUL138 during productive infection.
  • To elucidate the contribution of pUL138 to the maintenance of HCMV latency in CD34(+) HPCs.

Main Methods:

  • Generation of recombinant HCMV viruses, including a UL138-null and a protein-synthesis-deficient mutant (FIX-UL138(STOP)).
  • Analysis of UL138 transcript and protein expression in infected fibroblasts and CD34(+) HPCs.
  • Assessment of viral latency phenotypes in HPCs using recombinant viruses.
  • Cellular localization studies of pUL138 using immunofluorescence microscopy.
  • Reporter assays to evaluate the impact of pUL138 on the major immediate-early promoter.

Main Results:

  • Two coterminal transcripts (2.7 and 3.6 kb) and a 21-kDa protein (pUL138) were identified from the UL138 locus with early-late gene kinetics.
  • Both UL138 transcripts and pUL138 were detected in fibroblasts and HPCs during productive infection.
  • Recombinant viruses lacking pUL138 (UL138-null or FIX-UL138(STOP)) exhibited a partial loss-of-latency phenotype in HPCs.
  • pUL138 was found to localize to the Golgi apparatus in infected cells and was not incorporated into virions.
  • pUL138 did not directly suppress the major immediate-early promoter activity.

Conclusions:

  • The pUL138 protein is essential for establishing and/or maintaining HCMV latency in CD34(+) HPCs.
  • While UL138 transcripts may contribute, the protein itself appears critical for HCMV latency.
  • The Golgi localization of pUL138 suggests a novel mechanism contributing to HCMV latency.
  • pUL138 is the first identified HCMV protein directly promoting latency with characteristic features in CD34(+) HPCs.

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