Differential redistribution of Ca2+-handling proteins during polarisation of MDCK cells: Effects on Ca2+ signalling

The spatial organisation of the Ca2+ signal in microdomains enables the regulation of various processes in specific regions of the cell and is essential for the versatility of cell responses to various stimuli. Ca2+ signals can be independently regulated in the cytoplasm and in the nucleoplasm. Increases in the concentration of Ca2+ in the nucleus can have specific effects different from those due to increases of Ca2+ in the cytoplasm. We investigated the influence of cell polarity on the subcellular distribution of molecules responsible for intracellular Ca2+ homeostasis (Ca2+ release channels, Ca2+ pumps and Ca2+ binding proteins) and its influence on the intracellular Ca2+ signal in MDCK cells with respect to its cytoplasmic or nucleoplasmic localisation. The intracellular Ca2+ store was largely reorganised during cell polarisation, with a differential redistribution of IP3R, Ca2+-binding proteins and SERCA between the nuclear envelope and the periphery of the cell. This was accompanied by morphological changes in cell shape, which condense the cytoplasm around the nucleus, and in the shape of the nucleus, resulting in invaginations of the nuclear envelope. This facilitates Ca2+ exchanges between the cytoplasm and the nucleoplasm, and preserves the ability to generate nucleoplasmic Ca2+ transients in agonist-stimulated polarised MDCK cells.