Sphingosylphosphorylcholine activates an amiloride-insensitive Na+-H+-exchange mechanism in GH4C1 cells

Role of Sphingosylphosphorylcholine in Tumor and Tumor Microenvironment

Sphingosylphosphorylcholine (SPC) is a unique type of lysosphingolipid found in some diseases, and has been studied in cardiovascular, neurological, and inflammatory phenomena. In particular, SPC’s studies on cancer have been conducted mainly in terms of effects on cancer cells, and relatively little consideration has been given to aspects of tumor microenvironment. This review summarizes the effects of SPC on cancer and tumor microenvironment, and presents the results and prospects of modulators that regulate the various actions of SPC.

PKC mediates GnRH activation of a Na+/H+ exchanger in goldfish somatotropes

Previous results suggest that gonadotropin-releasing hormone (GnRH) stimulation of somatotropin secretion in goldfish involves activation of Na(+)/H(+) exchange (NHE). We tested the hypothesis that GnRH alkalinizes intracellular pH (pH(i)) via protein kinase C (PKC) activation of NHE. Two types of alkalinization responses were observed in identified goldfish somatotropes preloaded with the pH-sensitive dye BCECF; the rate of pH(i) changes went from a neutral or slightly negative slope to either a positive or a less negative slope relative to control. Two GnRHs, the PKC-activating TPA, and dioctanoyl glycerol each caused an alkalinization in 70-90% of somatotropes. The PKC inhibitors, Bis II and Gö6976, the NHE inhibitor amiloride, or Na(+)-free solution attenuated TPA and GnRHs actions, suggesting that PKC mediates GnRH activation of NHE. Since amiloride and Na(+)-free solution caused acidification in somatotropes at rest, regulation of basal pH(i) in these cells likely involves Na(+) flux through amiloride-sensitive NHE.

Epidermal growth factor and sphingosine-1-phosphate stimulate Na+/H+ exchanger activity in the human placental syncytiotrophoblast

The Na+/H+ exchanger (NHE) has a key role in intracellular pH ([pH]i) regulation of the syncytiotrophoblast in the human placenta and may have a role in the life cycle of this cell. In other cells the NHE (actually a family of up to 9 isoforms) is regulated by a variety of factors, but its regulation in the syncytiotrophoblast has not been studied. Here, we tested the hypotheses that EGF and sphingosine-1-phosphate (S1P), both of which affect trophoblast apoptosis and, in other cell types, NHE activity, stimulate syncytiotrophoblast NHE activity. Villous fragments from term human placentas were loaded with the pH-sensitive dye, BCECF. NHE activity was measured by following the recovery of syncytiotrophoblast [pH]i following an imposed acid load, in the presence and absence of EGF, S1P, and specific inhibitors of NHE activity. Both EGF and S1P caused a dose-dependent upregulation of NHE activity in the syncytiotrophoblast. These effects were blocked by amiloride 500 microM (a nonspecific NHE blocker) and HOE694 100 microM (NHE blocker with NHE1 and 2 isoform selectivity). Effects of EGF were also reduced by the NHE3 selective blocker S3226 (used at 1 microM). These data provide the first evidence that both EGF and S1P stimulate NHE activity in the syncytiotrophoblast; they appear to do so predominantly by activating the NHE1 isoform.

Dimethylsphingosine increases cytosolic calcium and intracellular pH in human T lymphocytes

N,N-Dimethyl-D-erythro-sphingosine (DMS) is the N-methyl derivative of sphingosine; both are activators of sphingosine-dependent protein kinases. The aim of this work was to study the effect of DMS on cytosolic calcium and intracellular pH (pHi) in human T lymphocytes. The variations of calcium and pH were determined by fluorescence digital imaging using Fura-2-AM and BCECF-AM, respectively. DMS increased both pHi and Ca(2+)-cytoslic in human T lymphocytes. These effects were dose-dependent. This drug induced a fast increase in pHi and a release of calcium from different intracellular calcium pools than thapsigargin. DMS also induced a Ca(2+)-influx different from the store-operated calcium channels, since drug effect was not modified by 30 microM SKF 96365. The influx of calcium induced by DMS was completely blocked by preincubation in the presence of nickel, or lanthanum, while the increase in pHi was no affected. However, the presence of cadmium reduced but does not block Ca(2+)-influx. The inhibition of G-protein by 100 ng/mL pertussis toxin, and the inhibition of tyrosine kinases by genistein significantly reduced the cytosolic calcium increase induced by DMS by an inhibition of both, release of calcium from intracellular pools and influx from extracellular medium. The inhibition of pools emptiness by these drugs was related with the inhibition that they induce in the DMS cytosolic alcalinization. In summary, DMS increases pHi and as consequence releases calcium from intracellular pools, and it increases calcium-influx through a channel different from store-operated channel (SOC). Both cytosolic calcium and pHi increase are modulated by G-proteins and tyrosine kinases.