The deregulation of kinase cascades drives the development and survival of many human tumours. Kinase-targeted therapeutics therefore offer great promise for ‘personalised’ medicine. However, the beneficial effects of kinase inhibition are often short-lived due to the evolution of drug resistance. Whilst we know that reprogramming of phosphorylation networks underpins drug resistance, the specific role of protein phosphatases in these processes remains largely unexplored. Using a mixture of conventional biochemical approaches and high content microscopy, we have evaluated spatial and temporal components of ERK activation in response to the administration or cessation of the MEK inhibitor AZD6244, in mutant BRAF- and KRAS-driven colorectal cancer (CRC) cell lines and their AZD6244-resistant derivatives. We have also determined the expression patterns of several MAPK phosphatases (MKPs) in these cell models and have correlated a robust induction of DUSP4, DUSP5 and DUSP6 with AZD6244 removal, ERK hyperactivation and nuclear accumulation of ERK in AZD6244-resistant CRC cells. The ablation of DUSP5 expression in these conditions led to enhanced ERK hyperactivation and reduced E-cadherin expression in AZD6244-resistant HCT116 cells which were previously shown to undergo an epithelial-to-mesenchymal transition in response to AZD6244 withdrawal. In AZD6244-resistant HT29 cells, where AZD6244 deprivation leads to cell death, DUSP5 loss had subtle, but inconclusive effects on p-ERK and downstream effectors. This work emphasizes the influential and highly context-dependent role that MKP regulation has in ERK-driven oncogenesis and drug-resistance and has contributed to our current understanding of signal reprogramming events that frequently occur in response to ERK pathway inhibition.
|Date of Award||28 Apr 2021|
|Sponsors||Commonwealth Scholarships Commission|
|Supervisor||Paul Whitley (Supervisor), Andrew Chalmers (Supervisor), Jim Caunt (Supervisor) & Simon Cook (Supervisor)|