CCCTC-binding factor recruitment to the early region of the human papillomavirus 18 genome regulates viral oncogene expression.
Bottom Line: Loss of CTCF binding results in a reduction of a specific alternatively spliced transcript expressed from the early gene region concomitant with an increase in the abundance of unspliced early transcripts.In this study, we show that the essential host cell protein CTCF, which functions in genome-wide chromatin organization and gene regulation, is recruited to the HPV genome and plays an essential role in the regulation of early viral gene expression and transcript processing.These data highlight a novel virus-host interaction important for HPV pathogenicity.
Affiliation: University of St. Andrews, School of Medicine, St. Andrews, Fife, United Kingdom.Show MeSH
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Mentions: The increased cell cycle entry and hyperproliferation observed in the organotypic raft cultures derived from HFK lines maintaining Î”CTCF HPV18 genomes could be due to an increase in the expression of E6 and E7 viral oncoproteins. Detection of these proteins by immunostaining currently is not possible; therefore, raft sections were stained with surrogate markers, p53 as a marker for E6 expression and pRb family member p130 for E7 expression (8, 41). Cells stained positive for p53 in WT HPV18 raft sections were apparent throughout the epithelia as previously reported (42), albeit at a noticeably decreased level compared to that of rafts derived from untransfected HFKs (Fig. 8A). In contrast, p53-positive cells were undetectable in rafts derived from Î”CTCF HPV18 lines (Fig. 8A and B). This observation is consistent with an increase in E6 protein levels in Î”CTCF HPV18 compared to that of the WT, resulting in a decrease in detectable p53 protein. Similarly, immunostaining with p130-specific antibodies revealed significant differences between WT and Î”CTCF HPV18 rafts (Fig. 8C and D). In wild-type HPV18 rafts, p130-positive cells were confined to the upper layers, as previously shown (42) and in contrast to HPV-negative HFK raft sections, where cells stained positive for p130 in the parabasal and lower and upper suprabasal layers. However, immunostaining of p130 in the Î”CTCF HPV18 raft sections revealed an almost complete loss of p130-positive cells in the upper layers, suggesting increased and prolonged expression of E7 protein in the Î”CTCF HPV18 rafts compared to that of the WT.
Affiliation: University of St. Andrews, School of Medicine, St. Andrews, Fife, United Kingdom.