Ouabain Induces Transcript Changes and Activation of RhoA/ROCK Signaling in Cultured Epithelial Cells (MDCK).

Ouabain, an organic compound with the ability to strengthen the contraction of the heart muscle, was originally derived from plants. It has been observed that certain mammalian species, including humans, naturally produce ouabain, leading to its classification as a new type of hormone. When ouabain binds to Na+/K+-ATPase, it elicits various physiological effects, although these effects are not well characterized. Previous studies have demonstrated that ouabain, within the concentration range found naturally in the body (10 nmol/L), affects the polarity of epithelial cells and their intercellular contacts, such as tight junctions, adherens junctions, and gap junctional communication. This is achieved by activating signaling pathways involving cSrc and Erk1/2. To further investigate the effects of ouabain within the hormonally relevant concentration range (10 nmol/L), mRNA-seq, a high-throughput sequencing technique, was employed to identify differentially expressed transcripts. The discovery that the transcript encoding MYO9A was among the genes affected prompted an exploration of whether RhoA and its downstream effector ROCK were involved in the signaling pathways through which ouabain influences cell-to-cell contacts in epithelial cells. Supporting this hypothesis, this study reveals the following: (1) Ouabain increases the activation of RhoA. (2) Treatment with inhibitors of RhoA activation (Y27) and ROCK (C3) eliminates the enhancing effect of ouabain on the tight junction seal and intercellular communication via gap junctions. These findings further support the notion that ouabain acts as a hormone to emphasize the epithelial phenotype.

Analysis of NTPDase2 in the cell membrane using fluorescence recovery after photobleaching (FRAP).

NTPDase2, a member of the CD39/NTPDase family, is an ecto-nucleotidase anchored to the plasma membrane by two transmembrane domains, with a catalytic site facing the extracellular space and preferentially hydrolyzing nucleoside triphosphates. While NTPDase2 is expressed in many cell types, its unique functionality, mobility and dynamics at the cell membrane remain unexplored. We therefore constructed a recombinant NTPDase2 linked to the yellow fluorescent protein (EYFP) to investigate its dynamics by confocal microscopy. The present study shows that the expression of EYFP-NTPDase2 in different cell lines does not affect its proliferation, migration and adhesion to extracellular matrices (ECM). Moreover, in human embryonic kidney cells 293 (HEK293) grown on collagen type I and fibronectin, EYFP-NTPDase2 fluorescence is greater in free plasma membrane regions than in cell-cell contacts, in comparison with cells grown on other substrates. Differences in the time required for fluorescence recovery after photobleaching (FRAP) in free membrane regions and cell-cell contacts indicate that the mobility of EYFP-NTPDase2 depends on the matrix to which the cells are attached. © 2018 International Society for Advancement of Cytometry.