Date: Wednesday, 21 July 2021

Venue: Cheung Kung Hai Lecture Theatre 1, G/F, William M.W. Mong Block, Faculty of Medicine Building, 21 Sassoon Road, Pokfulam, Hong Kong

Time: 5:00 p.m. - 6:00 p.m.

5:00 p.m.

Speaker: Dr. Peng ZHOU (Post-doctoral Fellow)
Primary Supervisor: Dr. Alan Siu Lun WONG
Presentation Title: A Three-Way Combinatorial CRISPR Screen for Analyzing Interactions among Druggable Targets
Abstract: We present a CRISPR-based multi-gene knockout screening system and toolkits for extensible assembly of barcoded high-order combinatorial guide RNA libraries en masse. We apply this system for systematically identifying three-way synergistic therapeutic target combinations and successfully validate triple-combination regimens for suppression of cancer cell growth. This system overcomes the practical challenges of experimenting on a large number of high-order genetic and drug combinations and can be applied to uncover the rare synergistic interactions between druggable targets.

5:30 p.m. 

Speaker: Dr. Si XIE (Post-doctoral Fellow)
Primary Supervisor: Dr. Chengmin QIAN
Presentation Title: The stable DNMT1/USP7/PCNA/PAF15-Ub2 complex facilitates the first-wave of DNA methylation maintenance
Abstract: DNMT1 interacts with multiple nuclear factors including PCNA, UHRF1 and ubiquitinated histone H3 for faithful DNA methylation maintenance during replication. We provide structural and biochemical evidence that dual mono-ubiquitinated PAF15 (PAF15-Ub2) interacts with DNMT1 and stimulates its enzymatic activity. We demonstrated that PAF15-Ub2 level is dependent on chromatin-bound PCNA throughout S phase, and stable DNMT1/PCNA/PAF15-Ub2 complex travels along with replication machinery to establish the first wave of DNA methylation recovery. Depletion of PAF15 results in a delayed DNA methylation recovery in newly replicated DNA. Lastly, we showed the physical interaction of DNMT1 with USP7 inhibits USP7 deubiquitinase activity but enhances DNMT1 enzymatic activity. DNMT1 association with PAF15-Ub2 limits deubiquitination of PAF15-Ub2 by USP7. Therefore, the stable DNMT1/USP7/PCNA/PAF15-Ub2 complex ensures PAF15-Ub2 mediated DNA methylation recovery along with the progression of replication forks. Collectively, our study supports that multi-layered regulatory mechanisms orchestrate to ensure faithful DNA methylation inheritance during replication.

ALL ARE WELCOME

Should you have any enquiries, please feel free to contact Miss River Wong at 3917 9216.