AbstractsBiology & Animal Science

The Cbl family of E3 ubiquitin ligases are important negative regulators of multiple receptor and cytoplasmic tyrosine kinases, and participate in a wide variety of cellular processes. Uncoupling of Cbl-mediated negative regulation allows activated receptor tyrosine kinases such as the Met receptor to escape degradation, enhancing their oncogenic potential in vitro and in vivo. Despite the consequences of loss of Cbl-mediated negative regulation for human disease, little is known about the mechanisms regulating Cbl protein levels themselves. In this thesis work, I demonstrate a differential regulation of c-Cbl and Cbl-b downstream of the Met receptor tyrosine kinase. Cbl-b protein levels decrease in response to Met kinase activity, whereas c-Cbl levels remain stable. Cbl-b is partially degraded in a proteasome-dependant manner. This requires Cbl-b ubiquitin ligase activity and a carboxy terminal domain region located between the RING and UBA domains. I conclude that the regulation of c-Cbl and Cbl-b differs downstream of Met, and propose that negative regulation of Cbl-b by a dysregulated Met receptor may contribute to tumourigenesis.