Implication of Sphingosine-1-Phosphate Receptor 2 (S1PR2) in Differentiation and Dedifferentiation of Epithelial Renal Cells

Abstract

Epithelial cell differentiation is a process that involves the mesenchymal-epithelial transition (MET) and includes cell cycle arrest, cell-cell junction maturation in addition to changes in cell migration capacity. The epithelial-mesenchymal transition (EMT) is a dynamic process by which fully differentiated epithelial cells can acquire a mesenchymal phenotype. During EMT, cell adhesion and apical-basal polarity are lost, and the cytoskeleton is reorganized. Previous results from our laboratory showed that in Madin-Darby canine kidney cells (MDCK) under different culture conditions can achieve different stages of differentiation resembling MET. Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid, produced by the phosphorylation of sphingosine by sphingosine kinases (SKs), which is involved in different processes such as proliferation, cell growth, differentiation, and migration. S1P can act both intracellularly as a second messenger or extracellularly as a ligand of 5 different G protein-coupled receptors (S1PR1-5). In the present work, we evaluated the importance of S1P acting on S1PR2 in the modulation of MET and EMT. We found that there are differences in the action of S1PR2 in MDCK cells that depends on the differentiation stage. S1PR2 positively modulates the passage from polarized to differentiated cells through MET. Inhibition of S1PR2 blocks adherens junction establishment, as well as apical and basal polarity. On the other hand, once cells have acquired the differentiated phenotype, S1PR2 induces the dedifferentiation of epithelial cells through EMT. Inhibition of S1PR2 triggers changes in EMT markers, such as rearrangements of the actin cytoskeleton, expression of vimentin, and nuclear translocation of beta-catenin, as well as Slug. The expression levels of S1PR2 in the different stages of differentiation of MDCK cells did not show significant differences. Instead, immunofluorescence studies showed that during cell differentiation, S1PR2 was progressively enriched at the plasma membrane. These results suggest that the location of S1PR2 depends on the stage of cell differentiation, and this determines its role. These findings highlight the great versatility of S1P on the control of physiological and pathophysiological processes.