PURPOSE: RSV infects airway epithelial cells causing exacerbations in asthmatics, bronchiolitis in infants, and pneumonia in immunocompromised hosts. A link between childhood RSV infection and subsequent inflammation and asthma has been demonstrated, but the mechanism is unknown. p53 is a cellular protein that induces cell cycle arrest in response to other forms of stress, and its levels are negatively regulated by other proteins, including MDM2 and PKR. RSV induces cell survival to permit viral replication and later triggers production of type I interferon, which can increase p53. We hypothesize that RSV initially decreases p53 to permit cell survival and cell replication followed later by a type I interferon mediated increase in p53 and cell death.
METHODS: A549 and primary airway epithelial cells were exposed to RSV for 0-72 hours. Phospho-mdm2, p53, p21, STAT-1, STAT-2, IRF-1, and PKR protein were detected using Western-blots.
RESULTS: RSV increased phospho-mdm2 after 3-6 hours of exposure. PKR increased at 6-16 hours. The amount of p53 decreased 6-48 hours after RSV infection. The decrease in p53 resulted in a decrease in p21, a downstream protein modulated by p53. The levels of STAT-1, STAT-2, and IRF-1 (type I interferon mediated proteins) increased from 16-48 hours after RSV. The level of p53 recovered and was again seen at 48-72 hours after infection.
CONCLUSION: RSV increases the activity of phospho-mdm2 and PKR, decreasing p53. This decrease permits cell survival and viral replication and lasts until 48-72 hours when p53 increases due to activation of type I interferon.
CLINICAL IMPLICATIONS: These observations suggest that p53 and interferon-mediated proteins might be important targets for therapy in RSV infection.VA Merit Review grant; NIH: HL073967-01, HL077431-01 and RR00059 from the General Clinical Research Centers Program, NCRR, NIH.
DISCLOSURE: Dayna Groskreutz Basel, None.