Data of Sphingosine kinase and sphingosine-1-phosphate regulate epithelial cell architecture by the modulation of de novo sphingolipid synthesis

Sphingolipids regulate several aspects of cell behavior and it has been demonstrated that cells adjust their sphingolipid metabolism in response to metabolic needs. Particularly, sphingosine-1-phosphate (S1P), a final product of sphingolipid metabolism, is a potent bioactive lipid involved in the regulation of various cellular processes, including cell proliferation, cell migration, actin cytoskeletal reorganization and cell adhesion. In previous work in rat renal papillae, we showed that sphingosine kinase (SK) expression and S1P levels are developmentally regulated and control de novo sphingolipid synthesis. The aim of the present study was to evaluate the participation of SK/S1P pathway in the triggering of cell differentiation by external hypertonicity. We found that hypertonicity evoked a sharp decrease in SK expression, thus activating the de novo sphingolipid synthesis pathway. Furthermore, the inhibition of SK activity evoked a relaxation of cell-cell adherens junction (AJ) with accumulation of the AJ complex (E-cadherin/β-catenin/α-catenin) in the Golgi complex, preventing the acquisition of the differentiated cell phenotype. This phenotype alteration was a consequence of a sphingolipid misbalance with an increase in ceramide levels. Moreover, we found that SNAI1 and SNAI2 were located in the cell nucleus with impairment of cell differentiation induced by SK inhibition, a fact that is considered a biochemical marker of epithelial to mesenchymal transition. So, we suggest that the expression and activity of SK1, but not SK2, act as a control system, allowing epithelial cells to synchronize the various branches of sphingolipid metabolism for an adequate cell differentiation program.

鞘脂类调节细胞行为的多个方面，已有研究表明，细胞会根据代谢需求调整其鞘脂类代谢。特别是，鞘氨醇-1-磷酸（S1P），作为鞘脂类代谢的终产物，是一种具有强大生物活性的脂质，参与调节多种细胞过程，包括细胞增殖、细胞迁移、肌动蛋白细胞骨架重组和细胞粘附。在先前对大鼠肾乳头的研究中，我们展示了鞘氨醇激酶（SK）的表达和S1P水平受发育调控，并控制鞘脂类的新生合成。本研究旨在评估SK/S1P通路在由外部高渗性诱导的细胞分化触发中的作用。我们发现，高渗性诱导SK表达的急剧下降，从而激活了鞘脂类新生合成途径。此外，SK活性的抑制引发了细胞间粘附复合物（AJ）的松弛，AJ复合物（E-钙粘蛋白/β-连环蛋白/α-连环蛋白）在高尔基体的积累，防止了分化细胞表型的获得。这种表型改变是鞘脂类失衡的结果，表现为鞘氨醇水平的增加。此外，我们观察到SNAI1和SNAI2定位于细胞核中，SK抑制诱导的细胞分化受损，这一事实被认为是上皮到间质转化的生化标志。因此，我们提出，SK1的表达和活性，而非SK2，作为调控系统，允许上皮细胞同步鞘脂类代谢的各个分支，以实现适当的细胞分化程序。