Molecular basis of transcription factor regulation by ubiquitin specific proteases

The ubiquitin signal virtually controls all cellular functions including transcription. In this project we will study the molecular basis of how ubiquitination and particularly deubiquitination control gene expression by modifying a transcription factor. The largest family of deubiquitinating enzymes encoded in the human genome are ubiquitin specific proteases (USPs). We will investigate the impact of recently discovered mono-ubiquitination events on the structure and interactions of transcription factor ELK-1. In response to mitogens ELK-1 promotes cell growth, differentiation, and survival. Interestingly, ELK-1's activity is inhibited by mono-ubiquitination of its DNA binding ETS domain. In turn, ELK-1 ubiquitination can be reversed by the deubiquitinating enzyme USP17 to regulate cell cycle progression and proliferation, but no structural information is currently available for USP17 and how specificity is achieved is unknown. We will use structural biology tools to investigate the effect of mono-ubiquitination on the conformation of ELK-1 and probe its interaction with DNA using biochemical and biophysical methods. In a second line of investigation we will characterize the interaction of ELK-1 with the deubiquitinating enzyme USP17 and other USPs in order to better understand the mechanism of ELK-1's regulation by ubiquitination and how USPs specifically recognize ubiquitinated substrate proteins. Together, this will shed light onto the mechanism by which ubiquitination of a transcription factor influences its structure and interactions and how it can be reversed by the action of deubiquitinating enzymes to control gene expression.