Ezrin/radixin/moesin are required for the purinergic P2X7 receptor (P2X7R)-dependent processing of the amyloid precursor protein.

The amyloid precursor protein (APP) can be cleaved by α-secretases in neural cells to produce the soluble APP ectodomain (sAPPα), which is neuroprotective. We have shown previously that activation of the purinergic P2X7 receptor (P2X7R) triggers sAPPα shedding from neural cells. Here, we demonstrate that the activation of ezrin, radixin, and moesin (ERM) proteins is required for the P2X7R-dependent proteolytic processing of APP leading to sAPPα release. Indeed, the down-regulation of ERM by siRNA blocked the P2X7R-dependent shedding of sAPPα. We also show that P2X7R stimulation triggered the phosphorylation of ERM. Thus, ezrin translocates to the plasma membrane to interact with P2X7R. Using specific pharmacological inhibitors, we established the order in which several enzymes trigger the P2X7R-dependent release of sAPPα. Thus, a Rho kinase and the MAPK modules ERK1/2 and JNK act upstream of ERM, whereas a PI3K activity is triggered downstream. For the first time, this work identifies ERM as major partners in the regulated non-amyloidogenic processing of APP.

3-(R)-[3-(2-methoxyphenylthio-2-(S)-methylpropyl]amino-3,4-dihydro-2H-1,5-benzoxathiepine bromhydrate (F 15845) prevents ischemia-induced heart remodeling by reduction of the intracellular Na+ overload.

The present study investigates whether 3-(R)-[3-(2-methoxyphenylthio-2-(S)-methylpropyl]amino-3,4-dihydro-2H-1,5-benzoxathiepine bromhydrate (F 15845), a new, persistent sodium current blocker, can reduce the ischemic Na(+) accumulation and exert short- and long-term cardioprotection after myocardial infarction. First, F 15845 concentration-dependently reduced veratrine-induced diastolic contracture (IC(50) = 0.14 microM) in isolated atria. Second, F 15845 from 1 microM preserved viability in 54.2 +/- 12.5% of isolated cardiomyocytes exposed to lysophosphatidylcholine. Third, the effect of F 15845 on intracellular Na(+) of isolated hearts from control and diabetic db/db mice was monitored using (23)Na-nuclear magnetic resonance spectroscopy. F 15845 (0.3 microM) significantly counteracted [Na(+)](i) increase during no-flow ischemia in control mouse hearts. In diabetic db/db mouse hearts, the reduction in [Na(+)](i) was delayed relative to control. However, it was more marked and maintained upon reperfusion. The cardioprotective properties after myocardial infarction associated with short- (24-h) and long-term (14-day) reperfusion were measured in anesthetized rats. After 24-h reperfusion, F 15845 (5 mg/kg) significantly reduced infarct size (32.4 +/- 1.7% with vehicle and 24.2 +/- 3.4% with F 15845; P < 0.05) and decrease of troponin I levels (524 +/- 93 microg/l with vehicle versus 271 +/- 63 microg/l with F 15845; P < 0.05). It is important that F 15845 limits the long-term expansion of infarct size (35.2 +/- 2.6%, n = 19 versus 46.7 +/- 1.6%, n = 27 in the vehicle group; P < 0.001). Overall, F 15845 attenuates [Na(+)](i) and prevents (or reverses) contractile and biochemical dysfunction in ischemic and remodeling heart. F 15845 constitutes a new generation of cardioprotective agent.

ERM proteins mediate the effects of Na+/H+ exchanger (NHE1) activation in cardiac myocytes.

AIMS: Ezrin, radixin, and moesin (ERM) proteins have been implicated in regulating signalling molecules. The aim of the present study was to investigate the activity and subcellular distribution of ERM proteins in cardiac myocytes from both Wistar and diabetic Goto-Kakizaki (GK) rats, and the role of these proteins in mediating the downstream effects of the cardiac sarcolemmal Na+/H+ exchanger (NHE1) activation in response to cell acidification. METHODS AND RESULTS: Immunofluorescence microscopy revealed that activated ERM proteins were localized predominantly at the intercalated disc regions in left ventricular (LV) myocytes of both Wistar and GK rats under basal conditions. After acid loading, profound changes in activated ERM distribution were observed in both groups of myocytes, with immunolabelling detected in regions corresponding to the transverse tubules. This correlated with a marked increase in phospho-ERM levels in both groups, which was higher in GK myocytes and blocked by NHE1 inhibitor treatment. Levels of phospho-Akt paralleled those of phospho-ERM under the various experimental conditions used; in particular, the marked acid-induced increase in both phospho-ERM and phospho-Akt in GK myocytes was abolished by an NHE1 inhibitor treatment. Moreover, the pattern of glycogen synthase kinase-3beta (GSK-3beta) phosphorylation in these myocytes was strikingly similar to that observed for Akt activity under the conditions used. CONCLUSION: Activated ERM proteins mediate the effects of acid-induced NHE1 activation in LV myocytes. Akt is a downstream effector in the cascade activated by NHE1-ERM interaction. In addition, GSK-3beta phosphorylation is required for downstream effects of NHE1/ERM-Akt signalling.