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J. Virol., 01 1998, 236-244, Vol 72, No. 1
J Wu, J O'Neill and MS Barbosa
Human cytomegalovirus (HCMV) gene expression is highly cell and tissue
specific. Cell factor-mediated regulatory interactions are involved in
regulating the restricted expression of the HCMV major immediate-early (IE)
gene (J. F. Baskar, P. P. Smith, G. Nilaver, R. A. Jupp, S. Hoffmann, N. J.
Peffer, D. J. Tenney, A. M. Colberg-Poley, P. Ghazal, and J. A. Nelson,
70:3207-3213, 1996). To gain an understanding of HCMV early gene
activation, we studied the effect of each of the three major IE proteins,
IE72, IE86, and IE55, on the HCMV DNA polymerase gene (pol; UL54) promoter.
In transient-expression assays, the IE86 protein alone was able to
transactivate the pol promoter, but IE72 and IE55 were not, in permissive
U373MG cells. However, we were unable to detect IE86-mediated
transactivation in nonpermissive HeLa or C33-A cells. Using electrophoretic
mobility shift assays (EMSAs), we found that expression of the IE86 protein
in U373MG cells resulted in specific binding of a DNA complex to an
inverted-repeat element, IR1, of the pol promoter. Antibody supershifting
and EMSA-Western blotting experiments further showed that IE86 and the
cellular transcription factor Sp1 were components of the IR1 DNA-binding
complex. Furthermore, we found that binding of DNA by Sp1 was dramatically
increased in the presence of IE86. Interestingly, this IE86-induced
DNA-binding activity of Sp1 was inhibited by a repressor activity presented
in HeLa cells. In summary, our study suggests that a viral regulatory
protein can modulate the DNA binding activity of a cellular transcription
factor, resulting in cell- specific transactivation of viral genes.
Copyright © 1998, American Society for Microbiology
Transcription factor Sp1 mediates cell-specific trans-activation of the human cytomegalovirus DNA polymerase gene promoter by immediate-early protein IE86 in glioblastoma U373MG cells
Signal Pharmaceuticals, Inc., San Diego, California 92121, USA. jwu@signalpharm.com
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