Respiratory syncytial virus infection alters surfactant protein A expression in human pulmonary epithelial cells by reducing translation efficiency.

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.

• Authors: Shirley R Bruce, Constance L Atkins, Giuseppe N Colasurdo, Joseph L Alcorn
• Journal: American journal of physiology. Lung cellular and molecular physiology (Am J Physiol Lung Cell Mol Physiol) Vol. 297 Issue 4 Pg. L559-67 (Oct 2009) ISSN: 1522-1504 [Electronic] United States
• PMID: 19525387 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)

Chemical References

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

Topics

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