Chromatin adaptor Brd4 modulates E2 transcription activity and protein stability

Area of Science:

• Molecular Biology
• Epigenetics
• Virology

Background:

• Brd4 is a chromatin adaptor protein with tandem bromodomains that bind acetylated histones.
• Brd4's role in regulating papillomavirus E2 protein's transcriptional control is not fully understood.
• It remains unclear if Brd4's involvement in transactivation and transrepression is consistent across different E2 proteins.

Purpose of the Study:

• To investigate how Brd4 regulates the function of papillomavirus E2 proteins.
• To determine if Brd4's role in transcriptional regulation is conserved among various E2 proteins.
• To elucidate the molecular mechanisms underlying Brd4-E2 interactions in chromatin.

Main Methods:

• Utilized DNase I footprinting assays with in vitro reconstituted human papillomavirus (HPV) chromatin and nucleosome-free DNA templates.
• Investigated the role of Brd4's bromodomains and E2-interacting region in facilitating E2 binding to chromatin.
• Examined the impact of Brd4 on E2 protein stability and its association with E2 proteins from different HPV types and bovine papillomavirus type 1.

Main Results:

• Brd4 facilitates E2 binding to its target DNA sequences within chromatin, dependent on its bromodomains and E2-binding region.
• Brd4's coactivator and corepressor functions require at least one intact bromodomain.
• Brd4 directly associates with E2 proteins from high-risk (HPV-16, HPV-18), low-risk (HPV-11), and bovine papillomavirus type 1, enhancing their stability against proteasomal degradation.

Conclusions:

• Chromatin adaptors like Brd4 can bridge sequence-specific transcription factors to chromatin, enhancing their DNA binding.
• Brd4 directly interacts with various viral E2 proteins, promoting their stability and influencing their transcriptional activity.
• These findings reveal a conserved mechanism by which Brd4 modulates viral transcription factor function and stability across different papillomaviruses.