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The remodeling of calcium homeostasis contributes to the cancer hallmarks and the molecular mechanisms involved in calcium channel regulation in tumors remain to be characterized. Here, we report that SigmaR1, a stress-activated chaperone, is required to increase calcium influx by triggering the coupling between SK3, a Ca2+-activated K+channel (KCNN3) and the voltage-independent calcium channel Orai1. We show that SigmaR1 physically binds SK3 in BC cells. Inhibition of SigmaR1 activity, either by molecular silencing or by the use of sigma ligand (igmesine), decreased SK3 current and Ca2+entry in breast cancer (BC) and colorectal cancer (CRC) cells. Interestingly, SigmaR1 inhibition diminished SK3 and/or Orai1 levels in lipid nanodomains isolated from BC cells. Analyses of tissue microarray from CRC patients showed higher SigmaR1 expression levels in cancer samples and a correlation with tumor grade. Moreover, the exploration of a cohort of 4937 BC patients indicated that high expression of SigmaR1 and Orai1 channels was significantly correlated to a lower overall survival. As the SK3/Orai1 tandem drives invasive process in CRC and bone metastasis progression in BC, our results may inaugurate innovative therapeutic approaches targeting SigmaR1 to control the remodeling of Ca2+homeostasis in epithelial cancers.

Many studies have reported changes in potassium channel expression in many cancers and the involvement of these channels in various stages of cancer progression. By contrast, data concerning SKCa channels (small conductance calcium-activated potassium channels) have only recently become available. This review aims i) to present the structure and physiology of SKCa channels, ii) to provide an overview of published data concerning the SKCa proteins produced in tumor cells, and, whenever possible, the biological function assigned to them and iii) to review previous and novel modulators of SKCa channels. SKCa channels are activated by low concentrations of intracellular calcium and consist of homo- or heteromeric assemblies of -subunits named SK1, SK2 and SK3. SK2-3 channels are expressed in tumors and have been assigned a biological function in cancer cells: the enhancement of cell proliferation and cell migration by hijacking the functions of SK2 and SK3 channels, respectively. Two major classes of SKCa modulators have been described: toxins (apamin) and small synthetic molecules. Most SKCa blockers are pore blockers, but some modify the calcium sensitivity of SKCa channels without interacting with the apamin binding site. In this review, we present edelfosine and ohmline as atypical anticancer agents and novel SK3 inhibitors. Edelfosine and ohmline are synthetic alkyl-lipids with structures different from all previously described SKCa modulators. They should pave the way for the development of a new class of migration-targeted anticancer agents. We believe that such blockers have potential for use in the prevention or treatment of metastasis.

Edelfosine is an inhibitor of SK3 channel-mediated cell migration. However, this compound bears adverse in vivo side effects. Using cell SK3 dependent cell-migration assay, patch-clamp, 125I-apamin binding, and in vivo experiments we tested the ability of 15 lipid derivatives with chemical structures inspired from edelfosine to inhibit SK3 channels. Using a structure-activity relationship approach we identified an edelfosine analog named Ohmline (1-O-hexadecyl- 2-O-methyl-sn-glycero-3-lactose) with potent inhibitory effects on the SK3 channel. Its potency was greater for SK3 channels than for SK1 channels; it did not affect IKCa channels and only slightly but not significantly affected SK2 channels. This is the first SKCa channel blocker that can be used to discriminate between SK2 and SK1/SK3 channels and represents a useful tool to investigate the functional role of SK3 channels in peripheral tissues (that do not express SK1 channels). This compound, which acts with an IC50 of 300 nM, did not displace apamin from SKCa channels and had no effect on non-specific edelfosine targets such as protein kinase C (PKC), receptors for platelet activating factor (PAF) and lysophosphatidic acid (LPA), as well as non-cancerous cells. This is promising because the pitfalls associated with the use of edelfosine-like compounds have been that their effective and high concentrations are often cytotoxic due to their detergent-like character causing normal cell lysis. Finally, Ohmline reduced metastasis development in a mice model of tumor indicating that this compound could become a lead compound for the first class of lipid-antimetastatic agent.

High tensions of carbon monoxide (CO), relative to oxygen, were used as a tool to investigate the mechanism of chemotransduction. In an in vitrowhole organ, rat carotid body preparation, CO increased sinus nerve chemoafferent discharge in the dark, an effect that was significantly reduced (by ca70 %) by bright white light and by the removal of extracellular Ca2+from the superfusate or by the addition of either Ni2+(2 mM) or methoxyverapamil (100 μM). Addition of the P2purinoceptor antagonist pyridoxalphosphate‐6‐azophenyl‐2′,4′‐disulphonic acid (50 μM) also significantly reduced the neural response to CO. In perforated patch, whole‐cell recordings of isolated rat type I cells, CO induced a depolarisation of ca11 mV and a decrease in the amplitude of an outward current around and above the resting membrane potential. Membrane conductance between ‐50 and ‐60 mV was significantly reduced by ca40 % by CO. These effects were not photolabile and were present also when a ‘blocking solution’ containing TEA, 4‐AP, Ni2+and zero extracellular Ca2+was used. In conventional whole‐cell recordings, CO only decreased current amplitudes above +10 mV and was without effect around the resting membrane potential. These data demonstrate a direct effect of CO upon type I cell K+conductances and strongly suggest an effect upon a background, leak conductance that requires an intracellular mediator. The photolabile effect of CO only upon afferent neural discharge adds further evidence to a dual site of action of CO with a separate action at the afferent nerve terminal that, additionally, requires the permissive action of the neurotransmitter ATP.

1Plasma adenosine concentration increases during hypoxia to a level that excites carotid body chemoreceptors by an undetermined mechanism. We have examined this further by determining the electrophysiological responses to exogenous adenosine of sinus nerve chemoafferents in vitroand of whole‐cell currents in isolated type I cells.2Steady‐state, single‐fibre chemoafferent discharge was increased approximately 5‐fold above basal levels by 100 μM adenosine. This adenosine‐stimulated discharge was reversibly and increasingly reduced by methoxyverapamil (D600, 100 μM), by application of nickel chloride (Ni2+, 2 mM) and by removal of extracellular Ca2+. These effects strongly suggest a presynaptic, excitatory action of adenosine on type I cells of the carotid body.3Adenosine decreased whole‐cell outward currents at membrane potentials above ‐40 mV in isolated type I cells recorded during superfusion with bicarbonate‐buffered saline solution at 34–36 °C. This effect was reversible and concentration dependent with a maximal effect at 10 μM.4The degree of current inhibition induced by 10 μM adenosine was voltage independent (45.39 ± 2.55% (mean ± s.e.m.) between −40 and +30 mV) and largely (∼75%), but not entirely, Ca2+independent. 4‐Aminopyridine (4‐AP, 5 mM) decreased the amplitude of the control outward current by 80.60 ± 3.67% and abolished the effect of adenosine.5Adenosine was without effect upon currents near the resting membrane potential of approximately −55 mV and did not induce depolarization in current‐clamp experiments.6We conclude that adenosine acts to inhibit a 4‐AP‐sensitive current in isolated type I cells of the rat carotid body and suggest that this mechanism contributes to the chemoexcitatory effect of adenosine in the whole carotid body.

Severe hypoxia (< 10 mmHg) induced relaxation of precontracted rings obtained from large diameter (3–4 mm) pulmonary arteries of the rabbit but had no effect upon their basal tone nor upon the length of enzymatically isolated smooth muscle cells. In isolated smooth muscle cells severe hypoxia increased a voltage‐gated K+ current. The magnitude of this response depended upon the degree of intracellular Ca2+ buffering, being abolished by 10 mM EGTA. The hypoxic response of K+ currents demonstrates a direct effect of hypoxia on pulmonary artery smooth muscle cells via a modulation of potassium channel activity.