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Genome-wide siRNA screen identifies SMCX, EP400, and Brd4 as E2-dependent regulators of human papillomavirus oncogene
Jennifer A Smith1, Elizabeth A White, Mathew E Sowa
1Department of Pathology, Harvard Medical School, Boston, MA 02115, USA.
Abstract:
An essential step in the pathogenesis of human papillomavirus (HPV)-associated cancers is the dysregulated expression of the viral oncogenes. The papillomavirus E2 protein can silence the long control region (LCR) promoter that controls viral E6 and E7 oncogene expression. The mechanisms by which E2 represses oncogene expression and the cellular factors through which E2 mediates this silencing are largely unknown. We conducted an unbiased, genome-wide siRNA screen and series of secondary screens that identified 96 cellular genes that contribute to the repression of the HPV LCR. In addition to confirming a role for the E2-binding bromodomain protein Brd4 in E2-mediated silencing, we identified a number of genes that have not previously been implicated in E2 repression, including the demethylase JARID1C/SMCX as well as EP400, a component of the NuA4/TIP60 histone acetyltransferase complex. Each of these genes contributes independently and additively to E2-mediated silencing, indicating that E2 functions through several distinct cellular complexes to repress E6 and E7 expression.
Insights
Human papillomavirus (HPV) oncogene expression is silenced by the E2 protein, which works with newly identified cellular factors. This research reveals novel mechanisms for controlling HPV oncogenes, crucial for understanding HPV-associated cancers.
Area of Science:
- Molecular Biology
- Virology
- Cancer Pathogenesis
Background:
- Dysregulated expression of human papillomavirus (HPV) oncogenes is critical for HPV-associated cancer development.
- The HPV E2 protein can repress the long control region (LCR) promoter, thereby silencing viral E6 and E7 oncogene expression.
- The precise mechanisms and cellular factors involved in E2-mediated repression remain largely uncharacterized.
Purpose of the Study:
- To identify cellular genes and complexes that mediate the repression of the HPV LCR by the E2 protein.
- To elucidate the molecular mechanisms underlying E2-mediated silencing of viral oncogenes.
Main Methods:
- An unbiased, genome-wide small interfering RNA (siRNA) screen was employed to identify host factors involved in HPV LCR repression.
- Secondary screens were performed to validate and further investigate the identified genes.
- The role of specific identified genes, such as Brd4, JARID1C/SMCX, and EP400, in E2-mediated silencing was assessed.
Main Results:
- A screen identified 96 cellular genes contributing to the repression of the HPV LCR.
- The study confirmed the involvement of Brd4, an E2-binding bromodomain protein, in E2-mediated silencing.
- Novel factors, including the demethylase JARID1C/SMCX and EP400 (a component of the NuA4/TIP60 complex), were implicated in E2 repression.
- These identified genes act independently and additively to contribute to E2-mediated silencing.
Conclusions:
- The HPV E2 protein utilizes multiple distinct cellular complexes to achieve the repression of viral E6 and E7 oncogenes.
- The findings uncover novel cellular pathways and factors involved in controlling HPV oncogene expression, offering potential therapeutic targets for HPV-associated cancers.
