Oxygen-independent stabilization of hypoxia inducible factor (HIF)-1 during RSV infection.
BACKGROUND
Hypoxia-inducible factor 1 (HIF)-1alpha is a transcription factor that functions as master regulator of mammalian oxygen homeostasis. In addition, recent studies identified a role for HIF-1alpha as transcriptional regulator during inflammation or infection. Based on studies showing that respiratory syncytial virus (RSV) is among the most potent biological stimuli to induce an inflammatory milieu, we hypothesized a role of HIF-1alpha as transcriptional regulator during infections with RSV.


RESULTS
We gained first insight from immunohistocemical studies of RSV-infected human pulmonary epithelia that were stained for HIF-1alpha. These studies revealed that RSV-positive cells also stained for HIF-1alpha, suggesting concomitant HIF-activation during RSV infection. Similarly, Western blot analysis confirmed an approximately 8-fold increase in HIF-1alpha protein 24 h after RSV infection. In contrast, HIF-1alpha activation was abolished utilizing UV-treated RSV. Moreover, HIF-alpha-regulated genes (VEGF, CD73, FN-1, COX-2) were induced with RSV infection of wild-type cells. In contrast, HIF-1alpha dependent gene induction was abolished in pulmonary epithelia following siRNA mediated repression of HIF-1alpha. Measurements of the partial pressure of oxygen in the supernatants of RSV infected epithelia or controls revealed no differences in oxygen content, suggesting that HIF-1alpha activation is not caused by RSV associated hypoxia. Finally, studies of RSV pneumonitis in mice confirmed HIF-alpha-activation in a murine in vivo model.


CONCLUSIONS
Taking together, these studies suggest hypoxia-independent activation of HIF-1alpha during infection with RSV in vitro and in vivo.
Department of Anesthesiology and Intensive Care Medicine, University of Tübingen, Tübingen, Germany.
Helene A
HA
Haeberle
Carin
C
Dürrstein
Peter
P
Rosenberger
Yashoda M
YM
Hosakote
Johannes
J
Kuhlicke
Volkhard A J
VA
Kempf
Roberto P
RP
Garofalo
Holger K
HK
Eltzschig
D000818:Animals; D001784:Blood Gas Analysis; D015153:Blotting, Western; D002460:Cell Line; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D051793:Hypoxia-Inducible Factor 1 / Q000378:metabolism* / Q000502:physiology; D007150:Immunohistochemistry; D051379:Mice; D008807:Mice, Inbred BALB C; D010100:Oxygen / Q000097:blood / Q000378:metabolism*; D034741:RNA, Small Interfering; D018357:Respiratory Syncytial Virus Infections / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D051793:Hypoxia-Inducible Factor 1; D034741:RNA, Small Interfering; D010100:Oxygen