title: Beta interferon-mediated activation of signal transducer and activator of transcription protein 1 interferes with Rickettsia conorii replication in human endothelial cells.
abstract: Infection of the endothelial cell lining of blood vessels with Rickettsia conorii, the causative agent of Mediterranean spotted fever, results in endothelial activation. We investigated the effects of R. conorii infection on the status of the Janus kinase (JAK)-signal transducer and activator of transcription protein (STAT) signaling pathway in human microvascular endothelial cells (HMECs), the most relevant host cell type, in light of rickettsial tropism for microvascular endothelium in vivo. R. conorii infection induced phosphorylation of STAT1 on tyrosine 701 and serine 727 at 24, 48, and 72 h postinfection in HMECs. Employing transcription profile analysis and neutralizing antibodies, we further determined that beta interferon (IFN-β) production and secretion are critical for STAT1 activation. Secreted IFN-β further amplified its own expression via a positive-feedback mechanism, while expression of transcription factors interferon regulatory factor 7 (IRF7) and IRF9, implicated in the IFN-β-STAT1 feedback loop, was also induced. Metabolic activity of rickettsiae was essential for the IFN-β-mediated response(s) because tetracycline treatment inhibited R. conorii replication, IFN-β expression, and STAT1 phosphorylation. Inclusion of IFN-β-neutralizing antibody during infection resulted in significantly enhanced R. conorii replication, whereas addition of exogenous IFN-β had the opposite inhibitory effect. Finally, small interfering RNA-mediated knockdown further confirmed a protective role for STAT1 against intracellular R. conorii replication. In concert, these findings implicate an important role for IFN-β-mediated STAT1 activation in innate immune responses of vascular endothelium to R. conorii infection.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA.
authors.forename: Punsiri M
authors.initials: PM
authors.lastname: Colonne
authors.forename: Marina E
authors.initials: ME
authors.lastname: Eremeeva
authors.forename: Sanjeev K
authors.initials: SK
authors.lastname: Sahni
mesh_terms: D000911:Antibodies, Monoclonal; D001808:Blood Vessels / Q000382:microbiology*; D002460:Cell Line; D042783:Endothelial Cells / Q000382:microbiology*; D006801:Humans; D050839:Interferon Regulatory Factor-7 / Q000096:biosynthesis; D050834:Interferon-Stimulated Gene Factor 3, gamma Subunit / Q000096:biosynthesis; D016899:Interferon-beta / Q000096:biosynthesis / Q000276:immunology / Q000378:metabolism*; D053612:Janus Kinases / Q000378:metabolism; D055806:Microvessels / Q000382:microbiology*; D010766:Phosphorylation; D034622:RNA Interference; D034741:RNA, Small Interfering; D020114:Rickettsia conorii / Q000254:growth & development* / Q000378:metabolism*; D050794:STAT1 Transcription Factor / Q000096:biosynthesis / Q000378:metabolism*; D015398:Signal Transduction; D013752:Tetracycline / Q000494:pharmacology
chemical_list: D000911:Antibodies, Monoclonal; D050839:Interferon Regulatory Factor-7; D050834:Interferon-Stimulated Gene Factor 3, gamma Subunit; D034741:RNA, Small Interfering; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D016899:Interferon-beta; D053612:Janus Kinases; D013752:Tetracycline