Imaging pIgR in MDCK and rat parotid cell lines

Polymeric immunoglobulin receptor (pIgR) is the main transport mechanism for moving immunoglobulin A across the epithelial barrier and into saliva or onto any epithelial surface. In salivary glands there are two rates at which pIgR can transport IgA across salivary cells- the unstimulated and the nerve-stimulated rate. In studies of polarised MDCK cells the movement of pIgR across the cell (from basolateral to apical membranes) was regulated by the phosphorylation of cytoplasmic residues. Objective: to image the same GFP linked pIgR molecule transfected into MDCK and a rat parotid cell line. Method: the cloned sequence for rat pIgR (gift of Dr G. Banting, Univ of Bristol) was inserted into a GFP vector and stably transfected in type 1 MDCK cells and a rat parotid cell line. Cells were grown in petri dishes with a coverslip base and imaging of the expressed pIgR-GFP molecule was achieved by confocal microscopy. Cultures of cells were stimulated by Forskolin (1 uM) – a protein kinase C activator or H89 (1 uM)- a protein kinase C inhibitor for up to 4 hours and images were taken every hour. Results: in MDCK cells the pIgR-GFP readily localised in or near the membrane of the cells, stimulation with Forskolin caused the fluorescence to relocate to the cytoplasm and H89 caused the release of fluorescence from the cells. In the rat parotid cell line Forskolin or H89 reduced the cytoplasmic fluorescence. Conclusion: Using the same transcript pIgR localises to different compartments of the cell depending on the cell type and therefore suggests that studies of pIgR movement and control in MDCK cells may not be relevant to studies of pIgR in salivary cells.