Taxol (Paclitaxel) is an important natural product for the treatment of solid tumors. Despite a well documented tubulin-stabilizing effect, many side effects of taxol therapy cannot be explained by cytoskeletal mechanisms. In the present study submicromolar concentrations of taxol, mimicking concentrations found in patients, induced cytosolic calcium (Ca 2؉ ) oscillations in a human neuronal cell line. These oscillations were independent of extracellular and mitochondrial Ca 2؉ but dependent on intact signaling via the phosphoinositide signaling pathway. We identified a taxol binding protein, neuronal Ca 2؉ sensor 1 (NCS-1), a Ca 2؉ binding protein that interacts with the inositol 1,4,5-trisphosphate receptor from a human brain cDNA phage display library. Taxol increased binding of NCS-1 to the inositol 1,4,5-trisphosphate receptor. Short hairpin RNA-mediated knockdown of NCS-1 in the same cell line abrogated the response to taxol but not to other agonists stimulating the phosphoinositide signaling pathway. These findings are important for studies involving taxol as a research tool in cell biology and may help to devise new strategies for the management of side effects induced by taxol therapy.calcium imaging ͉ calcium release ͉ display cloning ͉ drug-induced side effects ͉ hypersensitivity reactions

Paclitaxel (Taxol) is a well established chemotherapeutic agent for the treatment of solid tumors, but it is limited in its usefulness by the frequent induction of peripheral neuropathy. We found that prolonged exposure of a neuroblastoma cell line and primary rat dorsal root ganglia with therapeutic concentrations of Taxol leads to a reduction in inositol trisphosphate (InsP 3)-mediated Ca 2؉ signaling. We also observed a Taxol-specific reduction in neuronal calcium sensor 1 (NCS-1) protein levels, a known modulator of InsP 3 receptor (InsP3R) activity. This reduction was also found in peripheral neuronal tissue from Taxol treated animals. We further observed that short hairpin RNA-mediated NCS-1 knockdown had a similar effect on phosphoinositide-mediated Ca 2؉ signaling. When NCS-1 protein levels recovered, so did InsP 3-mediated Ca 2؉ signaling. Inhibition of the Ca 2؉ -activated protease -calpain prevented alterations in phosphoinositide-mediated Ca 2؉ signaling and NCS-1 protein levels. We also found that NCS-1 is readily degraded by -calpain in vitro and that -calpain activity is increased in Taxol but not vehicle-treated cells. From these results, we conclude that prolonged exposure to Taxol activates -calpain, which leads to the degradation of NCS-1, which, in turn, attenuates InsP 3-mediated Ca 2؉ signaling. These findings provide a previously undescribed approach to understanding and treating Taxolinduced peripheral neuropathy.calcium imaging ͉ dorsal root ganglia ͉ endoplasmic reticulum ͉ polyneuropathy ͉ inositol 1,4,5-trisphosphate receptor

Regulation and dysregulation of intracellular calcium (Ca 2+ ) signaling via the inositol 1,4,5-trisphosphate receptor (InsP 3 R) has been linked to many cellular processes and pathological conditions. In the present study, addition of neuronal calcium sensor-1 (NCS-1), a high-affinity, low-capacity, calcium-binding protein, to purified InsP 3 R type 1 (InsP 3 R1) increased the channel activity in both a calcium-dependent and -independent manner. In intact cells, enhanced expression of NCS-1 resulted in increased intracellular calcium release upon stimulation of the phosphoinositide signaling pathway. To determine whether InsP 3 R1/NCS-1 interaction could be functionally relevant in bipolar disorders, conditions in which NCS-1 is highly expressed, we tested the effect of lithium, a salt widely used for treatment of bipolar disorders. Lithium inhibited the enhancing effect of NCS-1 on InsP 3 R1 function, suggesting that InsP 3 R1/NCS-1 interaction is an essential component of the pathomechanism of bipolar disorder.

Polyneuropathy is a frequent and potentially severe side effect of clinical tumor chemotherapy. The goal of this study was to characterize paclitaxel-, cisplatin-, vincristine- and bortezomib-induced neuropathy in C57BL/6 mice with a comparative approach. The phenotype of the animals was evaluated at four time points with behavioral and electrophysiological tests, followed by histology. Treatment protocols used in this study were well tolerated and induced a sensory and predominantly axonal polyneuropathy. Behavioral testing revealed normal motor coordination, whereas all mice receiving verum treatment developed mechanical allodynia and distinct gait alterations. Electrophysiological evaluation showed a significant decrease of the caudal sensory nerve action potential amplitude for all cytostatic agents and a moderate reduction of nerve conduction velocity for cisplatin and paclitaxel. This finding was confirmed by histological analysis of the sciatic nerve which showed predominantly axonal damage: Paclitaxel and vincristine affected mostly large myelinated fibers, bortezomib small myelinated fibers and cisplatin damaged all types of myelinated fibers to a similar degree. Neuropathic symptoms developed faster in paclitaxel and vincristine treated animals compared to cisplatin and bortezomib treatment. The animal models in this study can be used to elucidate pathomechanisms underlying chemotherapy-induced polyneuropathy and for the development of novel therapeutic and preventative strategies.

Salinomycin is a polyether antibiotic with properties of an ionophore, which is commonly used as cocciodiostatic drug and has been shown to be highly effective in the elimination of cancer stem cells (CSCs) both in vitro and in vivo. One important caveat for the potential clinical application of salinomycin is its marked neural and muscular toxicity. In the present study we show that salinomycin in concentrations effective against CSCs exerts profound toxicity towards both dorsal root ganglia as well as Schwann cells. This toxic effect is mediated by elevated cytosolic Na+ concentrations, which in turn cause an increase of cytosolic Ca2+ by means of Na+/Ca2+ exchangers (NCXs) in the plasma membrane as well as the mitochondria. Elevated Ca2+ then leads to calpain activation, which triggers caspase-dependent apoptosis involving caspases 12, 9 and 3. In addition, cytochrome c released from depolarized mitochondria directly activates caspase 9. Combined inhibition of calpain and the mitochondrial NCXs resulted in significantly decreased cytotoxicity and was comparable to caspase 3 inhibition. These findings improve our understanding of mechanisms involved in the pathogenesis of peripheral neuropathy and are important to devise strategies for the prevention of neurotoxic side effects induced by salinomycin.

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Polycystin-2 (PC2), the gene product of one of two genes mutated in dominant polycystic kidney disease, is a member of the transient receptor potential cation channel family and can function as intracellular calcium (Ca 2؉ ) release channel. We performed a yeast two-hybrid screen by using the NH 2 terminus of PC2 and identified syntaxin-5 (Stx5) as a putative interacting partner. Coimmunoprecipitation studies in cell lines and kidney tissues confirmed interaction of PC2 with Stx5 in vivo. In vitro binding assays showed that the interaction between Stx5 and PC2 is direct and defined the respective interaction domains as the t-SNARE region of Stx5 and amino acids 5 to 72 of PC2. Single channel studies showed that interaction with Stx5 specifically reduces PC2 channel activity. Epithelial cells overexpressing mutant PC2 that does not bind Stx5 had increased baseline cytosolic Ca 2؉ levels, decreased endoplasmic reticulum (ER) Ca 2؉ stores, and reduced Ca 2؉ release from ER stores in response to vasopressin stimulation. Cells lacking PC2 altogether had reduced cytosolic Ca 2؉ levels. Our data suggest that PC2 in the ER plays a role in cellular Ca 2؉ homeostasis and that Stx5 functions to inactivate PC2 and prevent leaking of Ca 2؉ from ER stores. Modulation of the PC2/Stx5 interaction may be a useful target for impacting dysregulated intracellular Ca 2؉ signaling associated with polycystic kidney disease.Ca 2ϩ channel ͉ polycystic kidney disease ͉ t-SNARE ͉ TRP channel A utosomal dominant polycystic kidney disease (ADPKD) is characterized by the growth of cysts, occurring over decades, in previously normal appearing kidney tubules (1). A functional hallmark of ADPKD is the loss of a calcium (Ca 2ϩ ) signal that serves to inhibit dysregulated kidney tubule cell proliferation, polarization, and secretory function. Either of two causative genes, PKD1 or PKD2, can initiate cyst formation after homozygous loss-of-function mutations, typically resulting from a combination of germline mutation on one allele followed by somatic second step mutation occurring at the level of individual cells. The respective protein products, polycystin-1 (PC1) and polycystin-2 (PC2), form a receptor-channel complex in the membrane of the apical primary cilia in renal tubular cells (2, 3), as well as in bile and pancreatic duct cells. PC2 (TRPP2), a member of the transient receptor potential (TRP) cation channel family, is abundantly expressed in the endoplasmic reticulum (ER) membrane (4) and has been shown to function as a Ca 2ϩ release channel from intracellular stores (5, 6). Indirect evidence has led to the proposal that PC2 channel activity is required for the rise in cellular Ca 2ϩ in ciliated monolayers of cultured epithelial cells under conditions of laminar shear stress because of fluid flow (7,8). This response to flow requires Ca 2ϩ from both extracellular and ER stores (9).Although variations in the reported channel properties of PC2 exist, it is generally accepted that PC2 is a high conductance cation channel (40-177 pS) whose a...

Chemotherapy-induced central nervous system (CNS) neurotoxicity presents an unmet medical need. Patients often report a cognitive decline in temporal correlation to chemotherapy, particularly for hippocampus-dependent verbal and visuo-spatial abilities. We treated adult C57Bl/6 mice with 12 × 20 mg kg−1 paclitaxel (PTX), mimicking clinical conditions of dose-dense chemotherapy, followed by a pulse of bromodesoxyuridine (BrdU) to label dividing cells. In this model, mice developed visuo-spatial memory impairments, and we measured peak PTX concentrations in the hippocampus of 230 nm l−1, which was sevenfold higher compared with the neocortex. Histologic analysis revealed a reduced hippocampal cell proliferation. In vitro, we observed severe toxicity in slowly proliferating neural stem cells (NSC) as well as human neuronal progenitor cells after 2 h exposure to low nanomolar concentrations of PTX. In comparison, mature post-mitotic hippocampal neurons and cell lines of malignant cells were less vulnerable. In PTX-treated NSC, we observed an increase of intracellular calcium levels, as well as an increased activity of calpain- and caspase 3/7, suggesting a calcium-dependent mechanism. This cell death pathway could be specifically inhibited with lithium, but not glycogen synthase kinase 3 inhibitors, which protected NSC in vitro. In vivo, preemptive treatment of mice with lithium prevented PTX-induced memory deficits and abnormal adult hippocampal neurogenesis. In summary, we identified a molecular pathomechanism, which invokes PTX-induced cytotoxicity in NSC independent of cell cycle status. This pathway could be pharmacologically inhibited with lithium without impairing paclitaxel’s tubulin-dependent cytostatic mode of action, enabling a potential translational clinical approach.