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.
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.
Wu
J
J
Signal Pharmaceuticals, Inc., San Diego, California 92121, USA. jwu@signalpharm.com
O'Neill
J
J
Barbosa
M S
MS
D001483:Base Sequence; D003587:Cytomegalovirus / Q000235:genetics* / Q000378:metabolism*; D017931:DNA Primers / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D017781:Genes, Immediate-Early; D015751:Genes, pol; D005909:Glioblastoma / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics* / Q000378:metabolism*; D008562:Membrane Glycoproteins; D011401:Promoter Regions, Genetic; D012091:Repetitive Sequences, Nucleic Acid; D016329:Sp1 Transcription Factor / Q000235:genetics* / Q000378:metabolism*; D015534:Trans-Activators; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured; D014759:Viral Envelope Proteins; D014764:Viral Proteins
D017931:DNA Primers; D004268:DNA-Binding Proteins; C069186:IE2 protein, Cytomegalovirus; D017874:Immediate-Early Proteins; D008562:Membrane Glycoproteins; D016329:Sp1 Transcription Factor; D015534:Trans-Activators; C077406:UL115 protein, Human herpesvirus 5; D014759:Viral Envelope Proteins; D014764:Viral Proteins; C071440:glycoprotein H, Cytomegalovirus; C499358:glycoprotein H, Human cytomegalovirus; C439068:glycoprotein O, cytomegalovirus