Project number 23

The Ubiquitin Pathway as a new frontier in liver cancer therapy

Deubiquitinating enzymes (DUBs) reverse the ubiquitination process, providing a tool for manipulating protein homeostasis. DUBs have recently emerged as promising targets for the development of first-in-class innovative anti-cancer medicines with high therapeutic impact. During our preliminary studies, we have found that upregulation of the deubiquitinase USP21 is observed in up to 50% of hepatocarcinomas (HCCs) and associated with poorer patient survival. Further expression analysis of USP21 transcripts in HCC has revealed overexpression of a single USP21 isoform (USP21-c), suggesting that this cancer-specific isoform may play a crucial role in HCC development. In fact, USP21-c overexpression triggers cell transformation, while USP21 suppression inhibits cancer cell growth. We will further explore the tumorigenic properties of USP21-c by generating rAAV-based USP21-c mouse liver models. Using high-throughput proteomics for ubiquitinated proteins, we plan to assess alterations in the ubiquitination pattern by USP21-c overexpression during different stages of liver cancer development. Next we will identify potential USP21-c specific substrates by combining the global proteomics approach with lysis-free protein complex methods such as Virotrap and BioID. We will also explore the therapeutic potential of inhibiting USP21-c both in vitro and in vivo using rAAV-based delivery of CRISPR-Cas9 reagents or locked nucleic acid antisense oligonucleotides (LNAs). We will elucidate how these strategies affect the ubiquitination pattern and growth of HCC cells in vivo. The studies proposed here will be translated into novel precision medicine approaches for HCC patients characterized by aberrant USP21 expression. All proteomics approaches including the protein complex studies will be performed under the supervision of Sven Eyckerman, while all the biological validation in model systems will be guided by Anna Sablina.

Keywords
ubiquitination, deubiquitinase, liver cancer, proteomics, drug development

Supervisors
Anna Sablina, VIB Lab for Mechanism of Cell Transformation, KU Leuven, Leuven
Sven Eyckerman,VIB Medical Biotechnology Center, UGent, Gent