Respiratory Syncytial Virus Infection Alters Surfactant Protein A Expression in Human Pulmonary Epithelial Cells by Reducing Translation Efficiency

Am J Physiol Lung Cell Mol Physiol. 2009 Oct;297(4):L559-67. doi: 10.1152/ajplung.90507.2008. Epub 2009 Jun 12.

Abstract

Infection of neonatal lung by respiratory syncytial virus (RSV) is a common cause of respiratory dysfunction. Lung alveolar type II and bronchiolar epithelial (Clara) cells secrete surfactant protein A (SP-A), a collectin that is an important component of the pulmonary innate immune system. SP-A binds to the virus, targeting the infectious agent for clearance by host defense mechanisms. We have previously shown that while the steady-state level of SP-A mRNA increases approximately threefold after RSV infection, steady-state levels of cellular and secreted SP-A protein decrease 40-60% in human type II cells in primary culture, suggesting a mechanism where the virus alters components of the innate immune response in infected cells. In these studies, we find that changes in SP-A mRNA and protein levels in RSV-infected NCI-H441 cells (a bronchiolar epithelial cell line) recapitulate the results in SP-A expression observed in primary lung cells. While SP-A protein is normally ubiquitinated, there is no change in the level of SP-A protein ubiquitination or proteasome activity during RSV infection, suggesting that the reduced levels of SP-A protein are not due to degradation by activated proteasomes. SP-A mRNA is appropriately processed and exported from the nucleus to the cytoplasm during RSV infection. As evidenced by polysome analysis of SP-A mRNA and pulse-chase analysis of newly synthesized SP-A protein, we find a decrease in translational efficiency that is specific for SP-A mRNA. Therefore, the decrease in SP-A protein levels observed after RSV infection of pulmonary bronchiolar epithelial cells results from a mechanism that affects SP-A mRNA translation efficiency.

Publication types

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

MeSH terms

  • Blotting, Northern
  • Cell Nucleus / metabolism
  • Cells, Cultured
  • Epithelial Cells / metabolism*
  • Humans
  • Immunoblotting
  • Immunoprecipitation
  • Interferon-gamma / pharmacology
  • Lung / cytology
  • Lung / metabolism*
  • Polyribosomes / metabolism
  • Protein Biosynthesis*
  • Pulmonary Surfactant-Associated Protein A / genetics
  • Pulmonary Surfactant-Associated Protein A / metabolism*
  • RNA Stability
  • RNA, Messenger / biosynthesis*
  • Respiratory Syncytial Virus Infections / genetics
  • Respiratory Syncytial Virus Infections / metabolism*
  • Respiratory Syncytial Virus Infections / virology
  • Respiratory Syncytial Virus, Human / pathogenicity
  • Ubiquitination

Substances

  • Pulmonary Surfactant-Associated Protein A
  • RNA, Messenger
  • Interferon-gamma