title: Rickettsia conorii infection stimulates the expression of ISG15 and ISG15 protease UBP43 in human microvascular endothelial cells.
abstract: Rickettsia conorii, an obligate intracellular bacterium and the causative agent of Mediterranean spotted fever, preferentially infects microvascular endothelial cells of the mammalian hosts leading to onset of innate immune responses, characterized by the activation of intracellular signaling mechanisms, release of pro-inflammatory cytokines and chemokines, and killing of intracellular rickettsiae. Our recent studies have shown that interferon (IFN)-β, a cytokine traditionally considered to be involved in antiviral immunity, plays an important role in the autocrine/paracrine regulation of host defense mechanisms and control of R. conorii growth in the host endothelial cells. Here, we show that R. conorii infection induces the expression of ISG15 (an interferon-stimulated gene coding a protein of 17kD) and UBP43 (an ISG15-specific protease) at the levels of mRNA and protein and report the evidence of ISGylation of as yet unidentified target proteins in cultured human microvascular endothelium. Infection-induced expression of ISG15 and UBP43 requires intracellular replication of rickettsiae and production of IFN-β, because treatment with tetracycline and presence of an antibody capable of neutralizing IFN-β activity resulted in near complete attenuation of both responses. Inhibition of R. conorii-induced ISG15 by RNA interference results in significant increase in the extent of rickettsial replication, whereas UBP43 knockdown yields a reciprocal inhibitory effect. In tandem, these results demonstrate the stimulation of interferon-β-mediated innate immune mechanisms capable of perturbing the growth and replication of pathogenic rickettsiae and provide first evidence for ISG15-mediated post-translational modification of host cellular proteins during infection with an intracellular bacterium.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA.
authors.forename: Punsiri M
authors.initials: PM
authors.lastname: Colonne
authors.forename: Abha
authors.initials: A
authors.lastname: Sahni
authors.forename: Sanjeev K
authors.initials: SK
authors.lastname: Sahni
mesh_terms: D019898:Autocrine Communication; D001907:Boutonneuse Fever / Q000201:enzymology*; D002478:Cells, Cultured; D016207:Cytokines / Q000096:biosynthesis* / Q000235:genetics; D010450:Endopeptidases / Q000096:biosynthesis* / Q000235:genetics; D004730:Endothelium, Vascular / Q000187:drug effects / Q000201:enzymology*; D055785:Gene Knockdown Techniques; D006801:Humans; D016899:Interferon-beta / Q000494:pharmacology; D055806:Microvessels / Q000187:drug effects / Q000201:enzymology; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D020114:Rickettsia conorii; D043222:Ubiquitin Thiolesterase; D014452:Ubiquitins / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D016207:Cytokines; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D014452:Ubiquitins; C074034:ISG15 protein, human; D016899:Interferon-beta; D010450:Endopeptidases; C485560:USP18 protein, human; D043222:Ubiquitin Thiolesterase
references.citation: J Clin Microbiol. 2003 Dec;41(12):5466-72
references.pmid: 14662926
references.citation: Nat Med. 2004 Dec;10(12):1374-8
references.pmid: 15531891
references.citation: Acta Gastroenterol Belg. 2011 Mar;74(1):91-2
references.pmid: 21563660
references.citation: Front Biosci. 2003 Jan 01;8:e197-201
references.pmid: 12456377
references.citation: Trends Parasitol. 2010 Apr;26(4):205-12
references.pmid: 20207197
references.citation: Infect Dis Clin North Am. 2008 Sep;22(3):515-30, ix
references.pmid: 18755388
references.citation: Thromb Haemost. 2009 Dec;102(6):1071-9
references.pmid: 19967137
references.citation: J Infect Dis. 2008 Aug 15;198(4):576-85
references.pmid: 18582199
references.citation: Thromb Res. 2007;119(5):531-49
references.pmid: 16875715
references.citation: Ann N Y Acad Sci. 1990;590:168-86
references.pmid: 2116101
references.citation: J Immunol. 2008 Nov 1;181(9):6467-72
references.pmid: 18941237
references.citation: Proc Natl Acad Sci U S A. 2008 Mar 11;105(10):3974-9
references.pmid: 18305167
references.citation: EMBO J. 2006 Jun 7;25(11):2358-67
references.pmid: 16710296
references.citation: Proc Natl Acad Sci U S A. 1996 Jan 9;93(1):211-5
references.pmid: 8552607
references.citation: Biochim Biophys Acta. 2010 May;1802(5):485-96
references.pmid: 20153823
references.citation: Infect Immun. 2011 Sep;79(9):3733-43
references.pmid: 21690236
references.citation: J Med Microbiol. 2009 Apr;58(Pt 4):521-525
references.pmid: 19273650
references.citation: J Immunol. 2005 Jul 15;175(2):847-54
references.pmid: 16002682
references.citation: J Biol Chem. 2002 Apr 26;277(17):14703-11
references.pmid: 11854279
references.citation: Clin Microbiol Infect. 2009 Dec;15 Suppl 2:303-4
references.pmid: 19438651
references.citation: Curr Top Microbiol Immunol. 2007;316:337-57
references.pmid: 17969455
references.citation: Biochem Biophys Res Commun. 2003 Aug 1;307(3):431-4
references.pmid: 12893238
references.citation: Proc Natl Acad Sci U S A. 2006 Jan 31;103(5):1440-5
references.pmid: 16434471
references.citation: Cell. 2010 Oct 15;143(2):187-90
references.pmid: 20946978
references.citation: Infect Agents Dis. 1996 Jun;5(3):127-43
references.pmid: 8805076
references.citation: Proc Natl Acad Sci U S A. 2010 Feb 2;107(5):2253-8
references.pmid: 20133869
references.citation: Microb Pathog. 2004 Jun;36(6):293-301
references.pmid: 15120155