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Infect. Immun., Jul 1997, 2786-2791, Vol 65, No. 7
LA Sporn, SK Sahni, NB Lerner, VJ Marder, DJ Silverman, LC Turpin and AL Schwab
Rickettsia rickettsii, the etiologic agent of Rocky Mountain spotted fever,
is an obligate intracellular bacterial organism that infects primarily the
vascular endothelial cells (EC). A component of the EC response to
infection is transcriptional activation, which may contribute to the
thrombotic and inflammatory consequences of disease. In this study, we
explore R. rickettsii-induced activation of the nuclear factor-kappaB/Rel
(NF-kappaB) family of transcription factors involved in early
transcriptional responses to injurious stimuli. Two NF-kappaB species were
activated by infection and reacted with a double- stranded oligonucleotide
probe corresponding to the kappaB binding domain of the murine kappa
light-chain gene enhancer. Gel supershift analysis demonstrated the
reactivity of these complexes with antibodies against p65 and p50, and the
induced species were tentatively identified as p50-p50 homodimers and
p50-p65 heterodimers. Semiquantitative reverse transcription-PCR analysis
revealed dramatic increases in the steady-state levels of mRNA coding for
the inhibitory subunit of NF-kappaB (IkappaB alpha), transcription of which
is enhanced by the binding of NF-kappaB within the IkappaB alpha promoter
region. NF-kappaB activation was first detected 1.5 h following infection
and was biphasic, with an early peak of activation at approximately 3 h, a
return to baseline levels at 14 h, and even higher levels of activation at
24 h. It is likely that NF-kappaB activation requires cellular uptake of R.
rickettsii, since treatment of EC with cytochalasin B during infection to
block entry inhibited activation by only 70% at 3 h. R. rickettsii-induced
activation of NF-kappaB may be an important controlling factor in the
transcriptional responses of EC to infection with this obligate
intracellular organism.
Copyright © 1997, American Society for Microbiology
Rickettsia rickettsii infection of cultured human endothelial cells induces NF-kappaB activation
Department of Medicine, University of Rochester School of Medicine & Dentistry, New York 14642, USA.
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