Signaling pathway involved in the inhibitory effect of FTY720P on the Na+/K+ ATPase in HepG2 cells

Abstract

The Na + /K + ATPase modulates the activity of many transporters in the liver, and maintains the ionic constancy of the intracellular milieu, preserving thus normal functioning of hepatocytes. Previous work showed that FTY720P, a sphingosine one phosphate receptor agonist used in the treatment of multiple sclerosis, exerts in HepG2 cells, an inhibitory effect on the activity of the ATPase, mediated via PGE2. This study is an attempt to identify the signaling molecules involved downstream of the prostaglandin. The activity of the ATPase was assayed by measuring the amount of inorganic phosphate liberated in presence and absence of ouabain, a specific inhibitor of the enzyme. The effect of FTY720P and PGE2 disappeared completely in presence of PF-04418948, a blocker of EP2 receptors, RpcAMP, an inhibitor of PKA, PD98059, an inhibitor of ERK, as well as in presence of PTIO, a nitric oxide synthase inhibitor, but was mimicked by butaprost, an EP2 agonist, dbcAMP, a cell permeable cAMP analogue, and SNAP1,a nitric oxide generator. PGE2 and dbcAMP increased the expression of phosphorylated ERK but not total ERK. This increase did not appear however in presence of PTIO, indicating that PKA is upstream of NO. It was concluded that FTY 720P induces PGE2 release which activates NOS leading to NO production and ERK activation. ERK then inhibits directly or indirectly the Na + /K + ATPase.

The epinephrine-induced PGE2 reduces Na+/K+ ATPase activity in Caco-2 cells via PKC, NF-κB and NO

“…In many previous works, we showed that PGE2 modulates the activity of the Na + /K + ATPase via nitric oxide (NO) [5,6]. In this work also, epinephrine and PGE2 did not exert their effect in presence of PTIO (Fig 4A and 4B), a scavenger of NO.…”

FTY720P Upregulates the Na+/K+ ATPase in HepG2 Cells by Activating S1PR3 and Inducing PGE2 Release

“…If FTY720P has a similar activity profile to that of S1P, then we would expect it to exert a dual and opposite time dependent effect on the ATPase leading to time dependent alterations in liver activities. We demonstrated previously in Caco-2 cells [11] and in HepG2 cells [12,13], a significant FTY720P-induced inhibition of the Na + /K + ATPase at 15min whether at two hours FTY720P exerts in HepG2 cells, like S1P, a stimulatory effect is a question that we aim to address in this work. This work is thus a follow up and a continuation of the previous one and is undertaken to complete the time course study.…”

Fluoride Exposure Induces Inhibition of Sodium-and Potassium-Activated Adenosine Triphosphatase (Na+, K+-ATPase) Enzyme Activity: Molecular Mechanisms and Implications for Public Health

“…Consistent with this, the U.S. National Research Council (NRC) reported that the conclusions from available studies is that sufficient F − exposure appears to bring about increases in blood glucose or impaired glucose tolerance in some individuals and the increase the severity of some types of diabetes [150]. Again, it has been shown that mechanistic pathway by which hyperglycaemia inhibits NKA activity is via activation of PKC and phospholipase A2 (PLA2), resulting in the liberation of arachidonic acid (AA) and increased the production of prostaglandin E2 (PGE2), which are known inhibitors of NKA activity [406,421,422]. Importantly, several in vitro human tissue models have consistently demonstrated that F − in micromolar concentrations of 1–10 µM significantly increases the synthesis of cAMP, AA, PGE2 and PLA2 in a dose dependent manner [249,423,424].…”