Polarized expression of human P2Y receptors in epithelial cells from kidney, lung, and colon

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Abstract
Eight human G protein-coupled P2Y receptors (P2Y1, P2Y2, P2Y4, P2Y6, P2Y11, P2Y12, P2Y13, and P2Y14) that respond to extracellular nucleotides have been molecularly identified and characterized. P2Y receptors are widely expressed in epithelial cells and play an important role in regulating epithelial cell function. Functional studies assessing the capacity of various nucleotides to promote increases in short-circuit current ( I sc) or Ca2+ mobilization have suggested that some subtypes of P2Y receptors are polarized with respect to their functional activity, although these results often have been contradictory. To investigate the polarized expression of the family of P2Y receptors, we determined the localization of the entire P2Y family after expression in Madin-Darby canine kidney (MDCK) type II cells. Confocal microscopy of polarized monolayers revealed that P2Y1, P2Y11, P2Y12, and P2Y14 receptors reside at the basolateral membrane, P2Y2, P2Y4, and P2Y6 receptors are expressed at the apical membrane, and the P2Y13 receptor is unsorted. Biotinylation studies and I sc measurements in response to the appropriate agonists were consistent with the polarized expression observed in confocal microscopy. Expression of the Gq-coupled P2Y receptors (P2Y1, P2Y2, P2Y4, P2Y6, and P2Y11) in lung and colonic epithelial cells (16HBE14o− and Caco-2 cells, respectively) revealed a targeting profile nearly identical to that observed in MDCK cells, suggesting that polarized targeting of these P2Y receptor subtypes is not a function of the type of epithelial cell in which they are expressed. These experiments highlight the highly polarized expression of P2Y receptors in epithelial cells.

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