Epithelial-mesenchymal transition, translocation of Ca2+ signalling complexes and regulation of migration in pancreatic cancer cells

Okeke, Emmanuel
Epithelial-mesenchymal transition, translocation of Ca2+ signalling complexes and regulation of migration in pancreatic cancer cells. PhD thesis, University of Liverpool.

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The high mortality of pancreatic cancer is predominantly caused by tumour metastasis. The formation of metastases is dependent on the co-ordinated processes of epithelial-mesenchymal transition (EMT), cell migration and invasion. The importance of Ca2+ signalling in the formation of metastasis in a number of cancer types has been documented. However, our understanding of the Ca2+ signalling components involved in the metastatic dissemination of pancreatic ductal adenocarcinoma (PDAC, specifically PANC-1) is limited. Inositol 1,4,5-trisphosphate receptors (IP3Rs) and store-operated Ca2+ entry (SOCE) channels are the important Ca2+ signalling mechanisms in this cell type. IP3Rs are Ca2+-releasing channels in the endoplasmic reticulum (ER). After Ca2+ release via IP3Rs, restoring of ER Ca2+ involves SOCE mediated by STIM1, which activates PM Ca2+ channels Orai1 to permit Ca2+ influx. This process of Ca2+ influx takes place in unique structures – ER-PM junctions. The goal of the present study was to determine and characterise the fate of IP3Rs and STIM1-competent ER-PM junctions during EMT and the significance of these Ca2+ signalling mechanisms for PANC-1 cell migration. In the present study, I demonstrated that during EMT, PANC-1 cells undergo a dramatic morphological change from apical-basal polarity to front-rear polarity. In cellular monolayers IP3Rs are juxtaposed to cell-cell contacts and closely co-positioned with markers of the tight and adherens junctions. When individual cells migrate away from their neighbours, IP3Rs and SOCE-competent ER-PM junctions underwent dramatic redistribution from cell-cell contacts to accumulate preferentially at the leading edge of PANC-1 cells, where they are in close apposition with the components of migratory apparatus (e.g. focal adhesions). I further demonstrated that focal adhesions were closely encompassed by IP3Rs, creating potholes in excitable medium in which Ca2+ released through IP3Rs affects the remodelling and turnover of focal adhesions, which in turn is necessary for cell migration. Finally, I demonstrated that the migration of PANC-1 cells was suppressed by inhibition of IP3Rs and SOCE, indicating that these mechanisms are functionally important for migration. Taken together, I successfully demonstrated that Ca2+ signalling complexes concentrate in the leading edge of migrating PANC-1 cells and regulate focal adhesion turnover in order to control cell adhesion dynamics and forward movement of PANC-1 cells.

Item Type: Thesis (PhD)
Additional Information: Date: 2015-01-16 (completed)
Depositing User: Symplectic Admin
Date Deposited: 27 Aug 2015 09:51
Last Modified: 17 Dec 2022 02:07
DOI: 10.17638/02010264
URI: https://livrepository.liverpool.ac.uk/id/eprint/2010264