AbstractOncogenic activation of the Ras-ERK pathway is frequently observed in human cancers. Dual-specificity MAP kinase phosphatases (DUSPs or MKPs) are important negative regulators of this pathway and could therefore play an important role in modulating the oncogenic potential of signalling. DUSP5 and DUSP6/MKP-3 are ERK-specific MKPs, which are classical negative feedback regulators of pathway activity, but are differentially localised, with DUSP5 found in the nucleus and DUSP6/MKP-3 in the cytoplasm. However, to date their potential roles in modulating the oncogenic potential of the Ras-ERK pathway is unclear. This project aimed to use a range of biochemical and genetic techniques in order to determine whether these enzymes play functional roles in modulating the spatiotemporal regulation of ERK signalling and, in particular, to use murine cancer models to explore the effects of MKP deletion on the initiation and/or progression of mutant Ras-induced tumours.
Here we show that DUSP5 is an essential regulator of nuclear ERK activity and gene expression in response to acute Ras/ERK pathway activation and this work provides a mechanistic underpinning for our observation that DUSP5 has a tumour suppressor function in the murine model of DMBA/TPA-induced skin carcinogenesis. We also show that the endogenous expression of mutant KRasG12D in murine fibroblasts induces the expression of both DUSP5 and DUSP6/MKP-3, suggesting these proteins are involved in the negative feedback response, which constrains ERK activity following constitutive pathway activation. Finally, using mouse models of KRasG12D-driven pancreatic cancer, we demonstrate that the deletion of either DUSP5 or DUSP6/MKP-3 accelerates the initiation of acinar-to-ductal metaplasia (ADM) and pancreatic intra-epithelial neoplasia (PanINs). However, with respect to the development of invasive pancreatic ductal adenocarcinoma (PDAC), loss of DUSP6/MKP-3 seems a more potent driver. Our data confirm that these MKPs do play an important role in modulating the initiation and development of Ras-induced tumours in this clinically relevant murine cancer model. The variable penetrance of the pancreatic phenotypes observed following the loss of either DUSP5 or DUSP6/MKP-3 could reflect either the differing ability of these MKPs to regulate the strength of ERK activity or differential effects on the nuclear and cytoplasmic fractions of ERK respectively.
|Date of Award
|Stephen Keyse (Supervisor)