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Journal of Virology, April 2004, p. 3953-3964, Vol. 78, No. 8
0022-538X/04/$08.00+0     DOI: 10.1128/JVI.78.8.3953-3964.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

NFI-Ski Interactions Mediate Transforming Growth Factor ß Modulation of Human Papillomavirus Type 16 Early Gene Expression

Amy Baldwin, Lucia Pirisi, and Kim E. Creek*

Department of Pathology and Microbiology, University of South Carolina School of Medicine, Columbia, South Carolina 29208

Received 27 August 2003/ Accepted 17 December 2003

Human papillomaviruses (HPVs) are present in virtually all cervical cancers. An important step in the development of malignant disease, including cervical cancer, involves a loss of sensitivity to transforming growth factor ß (TGF-ß). HPV type 16 (HPV16) early gene expression, including that of the E6 and E7 oncoprotein genes, is under the control of the upstream regulatory region (URR), and E6 and E7 expression in HPV16-immortalized human epithelial cells is inhibited at the transcriptional level by TGF-ß. While the URR contains a myriad of transcription factor binding sites, including seven binding sites for nuclear factor I (NFI), the specific sequences within the URR or the transcription factors responsible for TGF-ß modulation of the URR remain unknown. To identify potential transcription factors and binding sites involved in TGF-ß modulation of the URR, we performed DNase I footprint analysis on the HPV16 URR using nuclear extracts from TGF-ß-sensitive HPV16-immortalized human keratinocytes (HKc/HPV16) treated with and without TGF-ß. Differentially protected regions were found to be located around NFI binding sites. Electrophoretic mobility shift assays, using the NFI binding sites as probes, showed decreased binding upon TGF-ß treatment. This decrease in binding was not due to reduced NFI protein or NFI mRNA levels. Mutational analysis of individual and multiple NFI binding sites in the URR defined their role in TGF-ß sensitivity of the promoter. Overexpression of the NFI family members in HKc/HPV16 decreased the ability of TGF-ß to inhibit the URR. Since the oncoprotein Ski has been shown to interact with and increase the transcriptional activity of NFI and since cellular Ski levels are decreased by TGF-ß treatment, we explored the possibility that Ski may provide a link between TGF-ß signaling and NFI activity. Anti-NFI antibodies coimmunoprecipitated endogenous Ski in nuclear extracts from HKc/HPV16, confirming that NFI and Ski interact in these cells. Ski levels dramatically decreased upon TGF-ß treatment of HKc/HPV16, and overexpression of Ski eliminated the ability of TGF-ß to inhibit the URR. Based on these studies, we propose that TGF-ß inhibition of HPV16 early gene expression is mediated by a decrease in Ski levels, which in turn dramatically reduces NFI activity.

* Corresponding author. Mailing address: Department of Pathology and Microbiology, University of South Carolina School of Medicine, 6439 Garners Ferry Rd., Columbia, SC 29208. Phone: (803) 733-3153. Fax: (803) 733-1515. E-mail: creek{at}med.sc.edu.

Journal of Virology, April 2004, p. 3953-3964, Vol. 78, No. 8
0022-538X/04/$08.00+0     DOI: 10.1128/JVI.78.8.3953-3964.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Favre-Bonvin, A., Reynaud, C., Kretz-Remy, C., Jalinot, P. (2005). Human Papillomavirus Type 18 E6 Protein Binds the Cellular PDZ Protein TIP-2/GIPC, Which Is Involved in Transforming Growth Factor {beta} Signaling and Triggers Its Degradation by the Proteasome. J. Virol. 79: 4229-4237 [Abstract] [Full Text]  


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