Respiratory syncytial virus infection alters surfactant protein A expression in human pulmonary epithelial cells by reducing translation efficiency.
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.
Bruce
Shirley R
SR
Dept. of Pediatrics, Univ. of Texas-Houston Medical School, 6431 Fannin, Houston, TX 77030, USA.
Atkins
Constance L
CL
Colasurdo
Giuseppe N
GN
Alcorn
Joseph L
JL
D015152:Blotting, Northern; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D007371:Interferon-gamma / Q000494:pharmacology; D008168:Lung / Q000166:cytology / Q000378:metabolism*; D011132:Polyribosomes / Q000378:metabolism; D014176:Protein Biosynthesis; D037662:Pulmonary Surfactant-Associated Protein A / Q000235:genetics / Q000378:metabolism*; D020871:RNA Stability; D012333:RNA, Messenger / Q000096:biosynthesis*; D018357:Respiratory Syncytial Virus Infections / Q000235:genetics / Q000378:metabolism* / Q000821:virology; D018113:Respiratory Syncytial Virus, Human / Q000472:pathogenicity; D054875:Ubiquitination
D037662:Pulmonary Surfactant-Associated Protein A; D012333:RNA, Messenger; D007371:Interferon-gamma