STIM1L is a new actin-binding splice variant involved in fast repetitive Ca2+ release

A newly identified splice variant of STIM1 called STIM1L forms constitutive clusters that interact with actin and Orai1 and allows fast repetitive Ca2+ release

STIM2 contrôle l'influx Ca2+ impliqué dans la différenciation des myoblastes et la signalisation Ca2+ du couplage excitation-contraction des myotubes

STIM2, une protéine activée lors de la déplétion des stocks calciques, contrôle l'amplitude de l'influx Store Operated Calcium Entry (SOCE) dans les myoblastes et les myotubes humains en culture. Le silencing de STIM2 inhibe la différentiation des myoblastes ainsi que les signaux calciques du couplage excitation contraction dans les myotubes. L'interaction endogène de STIM1 et STIM2, mesurée par FRET et co-immunoprécipitation, augmente l'amplitude de l'influx SOCE, cependant, STIM1 et STIM2 sont largement redondantes comme l'expression exogène de STIM2 suffit à rectifier l'effet du silencing de STIM1 et inversément. En conclusion, STIM2 contrôle le développement et la fonction musculaire

Role of the store operated calcium entry in skeletal muscle development and contraction

La myogenèse post-natale est effectuée par les cellules satellites qui sont les cellules souches quiescentes du muscle adulte. Au terme d'un processus prenant plusieurs jours, la cellule satellite génère de nouvelles fibres musculaires. La signalisation calcique intracellulaire joue un rôle clef dans la coordination des principales étapes de la myogenèse post-natale. Nos résultats ont montré que l'influx calcique SOCE est requis lors de l'initiation de la différenciation. En absence de STIM1, Orai1 ou Orai3, l'expression de MEF2 et myogénine ainsi que l'hyperpolarisation membranaire liée au processus de différenciation sont inhibées. Nos travaux ont également permis d'identifier une nouvelle protéine, STIM1L, produite durant la différenciation par un épissage alternatif de STIM1 et dont l'expression est maintenue dans le muscle squelettique adulte. STIM1L permet une activation rapide du SOCE et est nécessaire à la genèse et au maintien de variations répétitives du Ca2+ cytosolique telles que celles observées lors de contractions musculaires

"Frequently Asqued Question" (FAQ) sur l’infection au Papilloma virus humain (HPV)

Les infections à Human Papilloma Virus (HPV) sont les maladies sexuellement transmissibles les plus fréquentes avec une incidence estimée à 1-3% des personnes sexuellement actives et sont un motif de consultation régulier (Steinau et al., 2014). Les connaissances sur le virus et sa pathogénécité ont rapidement progressées ces dernières années et la prise en charge des infections à HPV demeure sou-vent multidisciplinaire et complexe. Nous avons fait le choix d’établir un FAQ sur la base de questions fréquemment posées par nos patients ou collaborateurs lors de notre activité dans le service de dermatologie des Hôpitaux Universitaires de Genève

Epidermal growth factor receptor down-regulation triggers human myoblast differentiation

Initiation of human myoblast differentiation requires a negative shift (hyperpolarization) of the resting potential of myoblasts that depends on the activation of Kir2.1 potassium channels. These channels are regulated by a tyrosine phosphorylation. Using human primary myoblast culture, we investigated a possible role of various receptor tyrosine kinases in the induction of the differentiation process. We found that Epidermal Growth Factor Receptor (EGFR) is a key regulator of myoblast differentiation. EGFR activity is down-regulated during early human myoblast differentiation, and this event is required for normal differentiation to take place. Furthermore, EGFR silencing in proliferation conditions was able to trigger the differentiation program. This occurs through an increase of Kir2.1 channel activity that, via a rise of store-operated Ca(2+) entry, leads to the expression of myogenic transcription factors and muscle specific proteins (Myogenin, Myocyte Enhancer Factor 2 (MEF2), Myosin Heavy Chain (MyHC)). Finally, blocking myoblast cell cycle in proliferation conditions using a cdk4 inhibitor greatly decreased myoblast proliferation but was not able, on its own, to promote myoblast differentiation. Taken together, these results show that EGFR down-regulation is an early event that is required for the induction of myoblast differentiation

Reversal of Murine Epidermal Atrophy by Topical Modulation of Calcium Signaling

Cytosolic Ca2+ signals are performed by Ca2+ releases from the endoplasmic reticulum and Ca2+ influx from the extracellular medium. Releases rely on the refilling of the intracellular Ca2+ stores by the Ca2+ influx “Store-Operated Calcium Entry” (SOCE) via the channel Orai1. Here we show that Orai1 expression, SOCE amplitude, and epidermal proliferation are decreased in the epidermis of patients with skin fragility when compared with aged nonatrophic skin. Epidermal atrophy was induced in mice by the inhibition of Orai1 with small interfering RNA and the topical application of a SOCE blocker BTP2. The inhibition of Orai1 impaired the heparin-binding epidermal growth factor (HB-EGF)-induced Ca2+ influxes and fully prevented the mitogen effect of HB-EGF in primary human keratinocytes. Importantly, epidermal proliferation correlated with Orai1 expression in mice. Conversely, the topical application of an Orai1 activator, the benzohydroquinone (BHQ), increased the epidermal thickness and proliferation, whereas the pro-proliferative effect of BHQ was prevented by the inhibition of Orai1. Finally, the topical application of BHQ reversed the epidermal atrophy induced by corticosteroids in mice. The topical modulation of Ca2+ signals may thus be a promising therapeutic strategy in dermatology

STIM1- and Orai1-dependent store-operated calcium entry regulates human myoblast differentiation

Our previous work on human myoblasts suggested that a hyperpolarization followed by a rise in [Ca(2+)](in) involving store-operated Ca(2+) entry (SOCE) channels induced myoblast differentiation. Advances in the understanding of the SOCE pathway led us to examine more precisely its role in post-natal human myoblast differentiation. We found that SOCE orchestrated by STIM1, the endoplasmic reticulum Ca(2+) sensor activating Orai Ca(2+) channels, is crucial. Silencing STIM1, Orai1, or Orai3 reduced SOCE amplitude and myoblast differentiation, whereas Orai2 knockdown had no effect. Conversely, overexpression of STIM1 with Orai1 increased SOCE and accelerated myoblast differentiation. STIM1 or Orai1 silencing decreased resting [Ca(2+)](in) and intracellular Ca(2+) store content, but correction of these parameters did not rescue myoblast differentiation. Remarkably, SOCE amplitude correlated linearly with the expression of two early markers of myoblast differentiation, MEF2 and myogenin, regardless of the STIM or Orai isoform that was silenced. Unexpectedly, we found that the hyperpolarization also depends on SOCE, placing SOCE upstream of K(+) channel activation in the signaling cascade that controls myoblast differentiation. These findings indicate that STIM1 and Orai1 are key molecules for the induction of human myoblast differentiation

Kir2.1 is activated by EGFR knockdown in myoblasts.

<p>Myoblasts were transfected with either control siRNA or siEGFR. <b>A</b>. Percentages of transfected myoblasts with functional Kir2.1 channels, 48 hours post-transfection. <b>B.</b> Current densities of the total population of myoblasts (including myoblasts with no current, i.e. <5 pA). <b>C.</b> Current-voltage relationships of a myoblast transfected with siEGFR. Voltage-steps were to −40, −60, −80, −100, −120 and −140 mV from a holding potential at −60 mV. The inset shows a control myoblast with no Kir2.1 current, a typical Kir2.1 current recorded from a myoblast, 48 h after transfection with siEGFR. Addition of 500 µM Ba²⁺ inhibited this current. <b>D.</b> Myoblasts were first transfected with control siRNA or siEGFR, and 24 h later with a plasmid coding for GFP-Kir2.1. One day after, immunoprecipitation of GFP was performed. Immunoblots reveal Kir2.1 and phospho-tyrosine (P-Tyr). <b>E</b>. Cytoplasmic Ca²⁺ was assessed with Fura-2-AM on proliferating myoblasts, 2 days after siRNA transfection. Intracellular Ca²⁺ stores were depleted with 10 µM thapsigargin (Tg) in a medium containing 250 nM Ca²⁺. Then 1.8 mM Ca²⁺ was subsequently added to reveal SOCE. The first part of the experiment was performed with a medium containing 30 mM KCl in order to clamp cells at around −40 mV. The second part was performed with a medium containing 5 mM KCl allowing cells to hyperpolarize. <b>F</b>. Quantification of peak SOCE (n = 6; * p<0.05).</p