The subcellular localisation, tissue expression, substrate specificity and binding partners of stress-activated protein kinase-3

Naomi Wynne Court

Research output: ThesisDoctoral Thesis

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Abstract

[Truncated abstract] Cells need to be able to detect changes in their surrounding environment and transduce these signals into the appropriate cellular compartments. One of the major ways that the cell achieves this signal transduction is through the process of phosphorylation. Protein kinases are the enzymes responsible for catalysing this transfer of phosphate groups from ATP to amino acid residues of their specific substrates. A subfamily of serine/threonine kinases known as the Mitogen-Activated Protein Kinases (MAPKs) is essential in a diverse range of cell processes including growth, metabolism, differentiation and death. The first identified MAPKs, the Extracellular Signal-Regulated Kinases (ERKs), were found to be activated in response to mitogenic stimuli such as growth factors. However, since the discovery of the ERKs, other pathways leading to the activation of related kinases have been recognised. These kinases are preferentially activated in response to stress, and are thus termed “Stress-Activated Protein Kinases” or SAPKs. They consist of the c-Jun N-terminal kinase isoforms 1, 2 and 3 (also called SAPK1γ, SAPK1α and SAPKβ respectively) and the p38 MAPKs, p38α, p38β, p38γ and p38δ (also called SAPK2a, SAPK2b, SAPK3 and SAPK4 respectively). A major challenge in this field has been to identify the substrates and functions of the SAPKs. This has been partly achieved by the development of inhibitors for the JNK MAPKs and SAPK2a/b. However, no inhibitors currently exist that specifically inhibit SAPK3 and SAPK4. Therefore, elucidating the function of these SAPKs has proved more difficult. Recent studies suggest that SAPK3 may play a unique role in the cell compared to other members of the p38 MAPK family. For example, several signalling proteins appear to specifically activate SAPK3 in certain circumstances while not activating other members of the p38 MAPK family. In addition, SAPK3 contains a unique sequence motif that allows it to bind to specialised domains known as PDZ domains. The interaction of SAPK3 with proteins containing these domains may regulate its subcellular localisation and interactions with other proteins in the cell. This project was undertaken to expand the knowledge on the expression, localisation, substrate specificity and binding partners of SAPK3. In Chapter 3 of this thesis, a SAPK3 monoclonal antibody was evaluated for its ability to specifically recognise endogenous SAPK3 protein. SAPK3 was found to be expressed in immortalised cell lines and primary cultures of neonatal rat myocytes, and to be colocalised with the mitochondria of these cells. This co-localisation remained unaltered in response to treatment with the nuclear export inhibitor Leptomycin B, and with exposure to osmotic shock, suggesting that SAPK3 substrates may be localised at the mitochondria
Original languageEnglish
QualificationDoctor of Philosophy
Publication statusUnpublished - 2004

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