An investigation into the physiological role of annexin A11
The calcium-dependent phospholipid-binding protein annexin A11 was discovered over 25 years ago, however little is known about its function. This thesis supports a role for annexin A11 in the cell cycle and suggests an association with the microtubule network. Recent studies have implicated annexin A11 in the autoimmune disease sarcoidosis, which is further investigated in this study. A single nucleotide polymorphism within annexin A11 (R230C) was identified as a highly associated susceptibility locus for sarcoidosis. Over-expression of annexin A11WT and annexin A11R230C showed no difference in their distribution. Stimulation with ionomycin, which induces a rise in intracellular calcium, resulted in the translocation of both variants to the plasma membrane and nuclear envelope with approximately the same time course. The calcium-dependent translocation of annexin A11 is therefore unaffected by the R230C mutation. In this one aspect there appears to be no difference between the two variants, however much still remains to be investigated such as the potential extracellular roles of these variants and their function in immune cells. Much of the work in this thesis has focused on elucidating the function of wild type annexin A11, particularly during the cell cycle. During mitosis the distribution of annexin A11 is highly dynamic and localises to the mitotic spindle at metaphase and anaphase, as well as the midbody at cytokinesis. The use of methanol fixation highlighted the co-localisation of annexin A11 with the microtubule network throughout mitosis, as well as at interphase. Furthermore annexin A11 was shown to concentrate at the centrosome, again during both mitosis and interphase. Several centrosomal proteins also localise to the midbody and are key regulators of mitotic progression, supporting a similar role for annexin A11. Furthermore the centrosomal localisation of annexin A11 may serve as an ideal docking site from which it can be easily targeted throughout the cell. This study highlights the novel localisation of annexin A11 to the centrosome and the microtubule network. Furthermore these findings contribute to a growing picture for the role of annexin A11 in the cell cycle, particularly with regards to its use of the microtubule network – a feature which may also have a role in interphase cells.