Signalling to the microtubule network: Regulation and function of stathmin (STMN) and doublecortin (DCX) phosphorylation
AffiliationBiochemistry and Molecular Biology
MetadataShow full item record
Document TypePhD thesis
Access StatusNo attached file available
© 2014 Dr. Yan Yan Yip
Microtubules are an intricate network of dynamic filaments that undergo substantial reorganisation during cell events such as proliferation, migration and division. These modifications are tightly controlled under various cell conditions by different regulatory proteins. The activities of these regulatory proteins, in turn, are targets of many signalling pathways, some of which are poorly defined. Stathmin (STMN) and doublecortin (DCX) are two key microtubule regulatory proteins. STMN functions as a microtubule destabiliser by sequestering free α/β-tubulin heterodimers. On the other hand, DCX is involved in the stabilisation of the microtubule array via the bundling of microtubule fibres. Both STMN and DCX are prominent phosphoproteins that are regulated via phosphorylation by many kinases depending on cellular contexts. For example, the c-Jun N-terminal kinase (JNK), a member of the mitogen-activated protein kinases (MAPK) family is known to target STMN in stress-stimulated cells. JNK is also responsible for the phosphorylation of residues along the c-terminal of DCX under basal conditions. In addition, deregulation of STMN and DCX activity contributes to aberrant microtubule dynamics which is the hallmark of many pathological conditions. Here, we aim to further delineate the signalling cascades involved in controlling STMN and DCX activity as well as their microtubule structure and dynamics. In chapter three, we elucidated the multi-site STMN phosphorylation under stress conditions. We found that STMN is cooperatively phosphorylated by JNK and protein kinase A (PKA) and is required to maintain the integrity of the microtubule array during hyperosmotic stress, suggesting a role in promoting cell viability. In chapter four, our biochemical characterisation of JNK-mediated phosphorylation of the STMN family proteins, SCG10 and SCLIP, identified critical phosphorylation sites as well as kinase binding domains for these proteins thus paving way for future studies in a cellular model. Finally, we demonstrated that JNK phosphorylation of DCX S28 contributes to the ability of DCX to bind to and regulate microtubule morphology. We also showed DCX S28 is robustly phosphorylated in differentiated SH-SY5Y neuronal cells hence our findings suggests potential contribution of DCX S28 phosphorylation towards cellular processes in the brain. In conclusion, this project revealed intricate signalling mechanisms involved in regulating microtubule dynamics which may have significant roles in physiological and pathological conditions.
Keywordscell signalling; microtubules; stathmin; doublecortin
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