Abstract
BACKGROUND: p38 mitogen activated protein kinases (p38 MAPKs) respond to stress stimuli and play a role in cell differentiation and apoptosis. Four isoforms of p38 MAPKs have been found; p38-α/β/γ/δ and this project focuses on the role of p38α. There are three pathways leading to p38α activation, the canonical pathway, the ZAP70-mediated pathway and the TAB1-mediated pathway. The latter has been found to occur during myocardial ischaemia. Therefore, if this direct effect of TAB1 on p38α can be controlled and prevented, there might be a potential way to stop or minimise myocardial ischaemic injury. The aim of this project is to investigate the effect of TAB1 on p38α autophosphorylation, as well as assessing competition between this pathway and the canonical cascade of activation. Another signalling pathway, which involves p38α, with a potential role in heart failure, is the amino acid response pathway (AAR). Halofuginone, a compound which activates the AAR pathway, has been implicated in improved cardiac function. Exploring this system by using halofuginone as a tool would provide further insight into whether the activation of this pathway could lead to improvements in several aspects of heart failure, such as hypertrophy, autophagy and inflammation. RESULTS: Using HEK293 cells, co-expression of TAB1 and p38α results in increased phosphorylation of p38α. This phosphorylation is reduced by the p38 inhibitors SB203580 and BIRB796. Mutations in TAB1, preventing p38 binding, diminish TAB1-mediated p38α phosphorylation. Despite spatial overlap in docking domains on p38α, TAB1 does not compete with MKK3b in a mammalian overexpression model. TAB1 and MKK3b induce phosphorylation of p38 independently and this is probably due to their differential in-cell locations, with p38 predominantly localising with MKK3b.p38 appears to be activated in response to halofuginone, and the simultaneous activation of the AAR pathway leads to increased autophagy, changes in the mRNA levels of inflammatory genes, as well as a potential p38-mediated negative feedback mechanism on the AAR pathway. CONCLUSIONS: There is a TAB1-mediated, SB203580-sensitive p38α phosphorylation mechanism which involves direct binding of TAB1 to p38α and induction of p38α autophosphorylation. p38 is activated in response to halofuginone and the associated AAR pathway leads to changes in autophagy and inflammation.
| Date of Award | 2016 |
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| Original language | English |
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| Supervisor | Michael Marber (Supervisor) |