Identifying Novel Interaction Between CDK8 Kinase Module and The Deubiquitinating Enzyme Ubiquitin Specific Protease 7 (USP7)

Ubiquitin Specific Protease 7 (USP7) is a deubiquitinating enzyme that regulates and interacts with various cellular substrates, playing regulatory roles in various pathways such as DNA damage repair and epigenetics. This thesis explores the role of USP7 in regulating components of gene expression regulators. The gene expression of target genes is fine-tuned by the transcriptional co-activator, the Mediator complex. Our group has determined that Cyclin Dependent Kinase 8 (CDK8) and Mediator Complex Subunit 12 (MED12), components of the kinase module in the Mediator complex, contain consensus sequences for binding to the N-terminus of USP7. Using various co-immunoprecipitation, pulldowns, tissue culture, and western blotting related techniques, our findings show that USP7, using the DWGF motif at its N-terminus, interacts with and stabilizes protein levels of MED12 and CDK8. This provides insights onto the cellular role of USP7 in gene expression, giving such novel interactions therapeutic potential for diseases such as cancer.