Ubiquitination is one of the major post-translational modifications that control multiple cellular pathways, and at its centre sits the E3 ubiquitin ligases family. This group of proteins recruit target substrates and facilitate the transfer of ubiquitin onto said targets to be degraded via the proteasome. Since they control the abundance of proteins, E3 ubiquitin ligases are involved in numerous signalling pathways and the deregulation of the substrates and/or the E3 ubiquitin ligases are often involved in multiple diseases such as cancer.
In our study, we aim to systematically identify and target novel E3 ubiquitin ligases in cancer to assess their potential for drug development. We performed a bioinformatics screen for all known E3 ubiquitin ligases using the DepMap database to filter out the genes that are essential for cancer cells to survive. We then performed an arrayed CRISPR Cas9 screen to validate the essentiality of the top hits from our bioinformatics screen, before moving on to a targeted protein degradation platform using the dTAG system.
From our preliminary CRISPR data we have observed a number of E3 ubiquitin ligases that show promising effects in slowing down the growth of multiple cancer types. We are now moving on towards a targeted protein degradation approach using the dTAG system to further validate the essentiality of our targets. The dTAG system is a better tool than the CRISPR Cas9 system, since it better mimics the effects of a drug on cancer cells as it temporarily depletes the target protein rather than permanently. It also serves as a feasible tool to test the effect of the degradation of a protein in the lab before the lengthy process of developing a PROTAC for the target protein.
E3 ubiquitin ligases have always been regarded as undruggable proteins; the emergence of the PROTAC technology could enable us to target and degrade E3 ligases. Our study aims to answer two big questions, can we find E3 ubiquitin ligases that are essential for cancer cells’ survival? and do E3 ligases make viable targets that are worth developing a PROTAC for?