• The role of MAPK signalling pathways in leukemic cell death

      Williams, John; Ireland, Elyse; Cordingley, Michelle (University of Chester, 18/09/2018)
      Mitogen-activated protein kinase (MAPK) signalling pathways are important signalling pathways involved in mediating various cellular processes including both cell survival and cell death. The c-Jun N-terminal kinase (JNK) pathway, the p38 pathway and the extracellular signal-regulated kinase (ERK1/2) pathway are three well-studied conventional MAPK signalling pathways. Previous research has shown these MAPK signalling pathways play an important role in the development and progression of leukaemia and in the response of leukemic cells to therapy. Whilst it appears to be well established that the constitutive activation of ERK mediates leukemic cell survival, the roles of the JNK and p38 signalling pathways in leukemogenesis, in particular the role in acute myeloid leukaemia (AML), are less well understood. This thesis investigates the role of the JNK, p38 and ERK signalling pathways in leukemic death. MAPK signalling pathways were targeted in the U937 monocytic cell line using small molecule MAPK inhibitors in combination with various cell stressors: UV light, chemotherapeutic agents (doxorubicin and vincristine) and heat treatment. The effects on cell death were examined using plate-based assays, flow cytometry and fluorescence microscopy. Preliminary investigations were also performed in peripheral blood mononuclear cells (PBMCs) from healthy individuals to allow a comparison to non-leukemic cells. Results show inhibition of ERK signalling in U937 cells induced cell death and ERK signalling had little effect on UV-induced and heat treatment-induced cell death. JNK signalling and p38 signalling provided protection against UVinduced cell death in both U937 cells and in PBMCs from healthy individuals. JNK and p38 signalling mediated cell survival in response to heat treatment to a certain extent. JNK signalling was required for the induction of cell death induced by doxorubicin whereas p38 signalling provided a level of protection against doxorubicin-induced cell death. U937 cells were found to be more sensitive to vincristine treatment than PBMCs from healthy individuals and the activation of JNK and p38 signalling was essential for vincristine-induced cell death in U937 cells. Taken together, the results presented in this thesis demonstrate that the roles of the JNK, p38 and ERK signalling pathways in leukemic cell death are stimuli-specific. This highlights the importance of understanding the involvement of particular pathways in the response to specific chemotherapeutic agents, in order to provide effective leukaemia therapy. Therapeutic inhibition of MAPK signalling pathways to increase the sensitivity of leukemic cells to chemotherapy could be beneficial when MAPKs are involved in providing protection against chemotherapy-induced cell death. For chemotherapies which require MAPK activation for cell death, failure to activate MAPKs may provide a mechanism for chemoresistance. Therapeutic methods to enhance activation of the pathways provide a possible approach to increase the susceptibility of leukemic cells to death.