Viral mitochondria-localized inhibitor of apoptosis (UL37 exon 1 protein) does not protect human neural precursor cells from human cytomegalovirus-induced cell death

J Gen Virol. 2012 Nov;93(Pt 11):2436-2446. doi: 10.1099/vir.0.044784-0. Epub 2012 Aug 8.

Abstract

Congenital human cytomegalovirus (HCMV) infection can cause severe brain abnormalities. Apoptotic HCMV-infected brain cells have been detected in a congenitally infected infant. In biologically relevant human neural precursor cells (hNPCs), cultured in physiological oxygen tensions, HCMV infection (m.o.i. of 1 or 3) induced cell death within 3 days post-infection (p.i.) and increased thereafter. Surprisingly, its known anti-apoptotic genes, including the potent UL37 exon 1 protein (pUL37x1) or viral mitochondria-localized inhibitor of apoptosis (vMIA), which protects infected human fibroblasts (HFFs) from apoptosis and from caspase-independent, mitochondrial serine protease-mediated cell death, were expressed by 2 days p.i. Consistent with this finding, an HCMV UL37x1 mutant, BADsubstitutionUL37x1 (BADsubUL37x1) induced cell death in hNPCs (m.o.i. = 1) to level which were indistinguishable from parental virus (BADwild-type)-infected hNPCs. Surprisingly, although BADsubUL37x1 is growth defective in permissive HFFs, it produced infectious progeny in hNPCs with similar kinetics and to levels comparable to BADwild-type-infected hNPCs (m.o.i. = 1). While delayed at a lower multiplicity (m.o.i. = 0.3), the BADsubUL37x1 mutant reached similar levels to revertant within 12 days, in contrast to its phenotype in HFFs. The inability of pUL37x1/vMIA to protect hNPCs from HCMV-induced cell death did not result from impaired trafficking as pUL37x1/vMIA trafficked efficiently to mitochondria in transfected hNPCs and in HCMV-infected hNPCs. These results establish that pUL37x1/vMIA, although protective in permissive HFFs, does not protect HCMV-infected hNPCs from cell death under physiologically relevant oxygen tensions. They further suggest that pUL37x1/vMIA is not essential for HCMV growth in hNPCs and has different cell type-specific roles.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Cell Death
  • Cell Line
  • Cytomegalovirus / physiology*
  • Cytopathogenic Effect, Viral
  • Exons
  • Flow Cytometry
  • Gene Expression Regulation, Viral
  • Humans
  • Immediate-Early Proteins / metabolism*
  • Mutation
  • Neural Stem Cells / metabolism*
  • Neural Stem Cells / virology*
  • Oxygen
  • Protein Transport
  • RNA, Viral / genetics
  • RNA, Viral / metabolism

Substances

  • Immediate-Early Proteins
  • RNA, Viral
  • UL37 protein, Human herpesvirus 5
  • Oxygen