Transient receptor potential melastatin-3 (TRPM3) is a broadly expressed Ca(2+)-permeable nonselective cation channel. Previous work has demonstrated robust activation of TRPM3 by the neuroactive steroid pregnenolone sulfate (PS), but its in vivo gating mechanisms and functions remained poorly understood. Here, we provide evidence that TRPM3 functions as a chemo- and thermosensor in the somatosensory system. TRPM3 is molecularly and functionally expressed in a large subset of small-diameter sensory neurons from dorsal root and trigeminal ganglia, and mediates the aversive and nocifensive behavioral responses to PS. Moreover, we demonstrate that TRPM3 is steeply activated by heating and underlies heat sensitivity in a subset of sensory neurons. TRPM3-deficient mice exhibited clear deficits in their avoidance responses to noxious heat and in the development of inflammatory heat hyperalgesia. These experiments reveal an unanticipated role for TRPM3 as a thermosensitive nociceptor channel implicated in the detection of noxious heat.

Summary Despite success with BRAFV600E–inhibitors, therapeutic responses in patients with metastatic melanoma are short-lived because of the acquisition of drug resistance. We identified a mechanism of intrinsic multi-drug resistance based on the survival of a tumor cell subpopulation. Treatment with various drugs, including cisplatin and vemurafenib, uniformly leads to enrichment of slow-cycling, long-term tumor-maintaining melanoma cells expressing the H3K4-demethylase JARID1B/KDM5B/PLU-1. Proteome-profiling revealed an upregulation in enzymes of mitochondrial oxidative-ATP-synthesis (OXPHOS) in this subpopulation. Inhibition of mitochondrial respiration blocked the emergence of the JARID1Bhigh subpopulation and sensitized melanoma cells to therapy, independent of their genotype. Our findings support a two-tiered approach combining anti-cancer agents that eliminate rapidly proliferating melanoma cells with inhibitors of the drug-resistant slow-cycling subpopulation.

Transient receptor potential (TRP) cation channels are renowned for their ability to sense diverse chemical stimuli. Still, for many members of this large and heterogeneous protein family it is unclear how their activity is regulated and whether they are influenced by endogenous substances. On the other hand, steroidal compounds are increasingly recognized to have rapid effects on membrane surface receptors that often have not been identified at the molecular level. We show here that TRPM3, a divalent-permeable cation channel, is rapidly and reversibly activated by extracellular pregnenolone sulphate, a neuroactive steroid. We show that pregnenolone sulphate activates endogenous TRPM3 channels in insulin-producing beta cells. Application of pregnenolone sulphate led to a rapid calcium influx and enhanced insulin secretion from pancreatic islets. Our results establish that TRPM3 is an essential component of an ionotropic steroid receptor enabling unanticipated crosstalk between steroidal and insulin-signalling endocrine systems.

Agonist-induced Ca2+ entry into cells by both store-operated channels and channels activated independently of Ca2+-store depletion has been described in various cell types. The molecular structures of these channels are unknown as is, in most cases, their impact on various cellular functions. Here we describe a store-operated Ca2+ current in vascular endothelium and show that endothelial cells of mice deficient in TRP4 (also known as CCE1) lack this current. As a consequence, agonist-induced Ca2+ entry and vasorelaxation is reduced markedly, showing that TRP4 is an indispensable component of store-operated channels in native endothelial cells and that these channels directly provide an Ca2+-entry pathway essentially contributing to the regulation of blood vessel tone.

TRPM3 is a poorly understood member of the large family of transient receptor potential (TRP) ion channels. Here we describe five novel splice variants of TRPM3, TRPM3␣1-5. These variants are characterized by a previously unknown amino terminus of 61 residues. The differences between the five variants arise through splice events at three different sites. One of these splice sites might be located in the pore region of the channel as indicated by sequence alignment with other, bettercharacterized TRP channels. We selected two splice variants, TRPM3␣1 and TRPM3␣2, that differ only in this presumed pore region and analyzed their biophysical characteristics after heterologous expression in human embryonic kidney 293 cells. TRPM3␣1 as well as TRPM3␣2 induced a novel, outwardly rectifying cationic conductance that was tightly regulated by intracellular Mg 2؉ . However, these two variants are highly different in their ionic selectivity. Whereas TRPM3␣1-encoded channels are poorly permeable for divalent cations, TRPM3␣2-encoded channels are well permeated by Ca 2؉ and Mg 2؉ . Additionally, we found that currents through TRPM3␣2 are blocked by extracellular monovalent cations, whereas currents through TRPM3␣1 are not. These differences unambiguously show that TRPM3 proteins constitute a pore-forming channel subunit and localize the position of the ionconducting pore within the TRPM3 protein. Although the ionic selectivity of ion channels has traditionally been regarded as rather constant for a given channelencoding gene, our results show that alternative splicing can be a mechanism to produce channels with very different selectivity profiles. The transient receptor potential (TRP)1 gene family comprises at least 28 mammalian genes divided into seven subfamilies (1, 2). Most of the encoded proteins exhibit common structural features such as six predicted transmembrane (TM) domains with a putative pore loop between TM5 and TM6 and the so-called TRP box after TM6 (1, 2). Although all members of this group have been reported to form cationic channels, their mechanisms of activation, their regulation, and their biological functions are remarkably diverse. They also display a large variety of different cation selectivities (1, 2). For example, TRPM4 and TRPM5 have been described as impermeable for divalent cations (3-5), whereas TRPV5 and TRPV6 appear to be exclusively permeable for Ca 2ϩ (6, 7). The diversity of TRP channels is further increased by the fact that most members of the TRP gene family can give rise to several different transcripts due to alternative splicing (8).In a few cases, the functional consequences of these alternative splice events are now beginning to emerge. For example, missplicing of TRPM6 transcripts is associated with a hereditary disorder called hypomagnesemia with secondary hypocalcemia (9, 10), and an amino-terminal-truncated variant of TRPM4 appears to modulate Ca 2ϩ oscillations after receptor stimulation in T lymphocytes (11).However, up to now, the largest number of different splice variants ...

Intracellular Ca2+ signalling evoked by Ca2+ mobilizing agonists, like angiotensin II in the adrenal gland, involves the activation of inositol(1,4,5)trisphosphate(InsP3)‐mediated Ca2+ release from internal stores followed by activation of a Ca2+ influx termed capacitative calcium entry. Here we report the amino acid sequence of a functional capacitative Ca2+ entry (CCE) channel that supports inward Ca2+ currents in the range of the cell resting potential. The expressed CCE channel opens upon depletion of Ca2+ stores by InsP3 or thapsigargin, suggesting that the newly identified channel supports the CCE coupled to InsP3 signalling.

Mast cells are key effector cells in allergic reactions. Aggregation of the receptor FceRI in mast cells triggers the influx of calcium (Ca 2+ ) and the release of inflammatory mediators. Here we show that transient receptor potential TRPM4 proteins acted as calcium-activated nonselective cation channels and critically determined the driving force for Ca 2+ influx in mast cells. Trpm4 -/-bone marrow-derived mast cells had more Ca 2+ entry than did TRPM4 +/+ cells after FceRI stimulation. Consequently, Trpm4 -/-bone marrow-derived mast cells had augmented degranulation and released more histamine, leukotrienes and tumor necrosis factor. Trpm4 -/-mice had a more severe IgE-mediated acute passive cutaneous anaphylactic response, whereas late-phase passive cutaneous anaphylaxis was not affected. Our results establish the physiological function of TRPM4 channels as critical regulators of Ca 2+ entry in mast cells.Mast cells are bone marrow-derived hematopoietic cells localized near surfaces exposed to the environment, such as the skin, the airway epithelia and the intestine, where pathogens, allergens and other environmental agents are frequently encountered 1 . Activation and degranulation of mast cells is a key step in the pathogenesis of allergic diseases such as bronchial asthma and systemic anaphylaxis 2 . An allergic reaction develops when allergens encountered by antigen-presenting cells are processed and presented to T cells. Ensuing T helper type 2 responses cause B cells to produce allergen-specific immunoglobulin E (IgE). The IgE molecules bind to the receptor FceRI on the surfaces of mast cells. After re-exposure to the allergen, FceRI-associated IgE molecules bind allergen and aggregate, thereby activating mast cells. Activated mast cells secrete preformed mediators, including proteases and vasoactive amines, such as histamine, that are stored in cytoplasmic granules. In addition, mast cell activation results in the de novo synthesis of proinflammatory lipid mediators, cytokines and chemokines. The instant release of histamine is crucial for the development of immediate-type allergic reactions that result in vasodilatation, increased vascular permeability and smooth muscle contraction 1,2 . In addition, IgE-dependent mast cell activation may be complemented by signaling cascades triggered by several endogenous ligands, such as adenosine, resulting in the amplification and maintenance of FceRI-mediated degranulation 3,4 .FceRI crosslinking activates many signaling molecules 5,6 . A chief 'downstream' target is phospholipase C-g1, which catalyzes the hydrolysis of phosphatidylinositol-4,5-bisphosphate to diacylglycerol and inositol-1,4,5-trisphosphate 5 . In contrast, adenosine stimulation involves the activation of G ai protein-coupled A 3 adenosine receptors in mouse mast cells, which leads to the activation of phospholipase C and phospholipase D through G bg protein and phosphatidylinositol-3-OH kinase-g 7,8 . Inositol-1,4,5-trisphosphate and diacylglycerol promote the activation of protein kinase C an...

In addition to voltage-gated calcium influx, capacitative calcium entry (CCE) represents a major pathway for calcium entry into the cell. Here we report the structure, expression and functional properties of a novel CCE channel, TRP5. This channel is a member of a new subfamily of mammalian homologues of the Drosophila transient receptor potential (TRP) protein, now comprising TRP5 (also CCE2) and the structurally related CCE1 (also TRP4). Like TRP4, TRP5 forms ion channels mainly permeable for Ca 2⍣ which are not active under resting conditions but can be activated by manoeuvres known to deplete intracellular calcium stores. Accordingly, dialysis of TRP5-expressing cells with inositol-(1,4,5)-trisphosphate evokes inward rectifying currents which reversed polarity at potentials more positive than ⍣30 mV. Ca 2⍣ store depletion with thapsigargin induced TRP5-mediated calcium entry dependent on the concentration of extracellular calcium, as seen by dual wavelength fura-2 fluorescence ratio measurements. TRP5 transcripts are expressed almost exclusively in brain, where they are present in mitral cells of the olfactory bulb, in lateral cerebellar nuclei and, together with TRP4 transcripts, in CA1 pyramidal neurons of the hippocampus, indicating the presence of CCE channels in excitable cells and their participation in neuronal calcium homeostasis.