Apoptotic effect of ethanol is potentiated by caffeine-induced calcium release in rat astrocytes

Cortical astrocytes regulate ethanol consumption and intoxication in mice

Astrocytes are fundamental building blocks of the central nervous system. Their dysfunction has been implicated in many psychiatric disorders, including alcohol use disorder, yet our understanding of their functional role in ethanol intoxication and consumption is very limited. Astrocytes regulate behavior through multiple intracellular signaling pathways, including G-protein coupled-receptor (GPCR)-mediated calcium signals. To test the hypothesis that GPCR-induced calcium signaling is also involved in the behavioral effects of ethanol, we expressed astrocyte-specific excitatory DREADDs in the prefrontal cortex (PFC) of mice. Activating G_q-GPCR signaling in PFC astrocytes increased drinking in ethanol-naïve mice, but not in mice with a history of ethanol drinking. In contrast, reducing calcium signaling with an astrocyte-specific calcium extruder reduced ethanol intake. Cortical astrocyte calcium signaling also altered the acute stimulatory and sedative-hypnotic effects of ethanol. Astrocyte-specific G_q-DREADD activation increased both the locomotor-activating effects of low dose ethanol and the sedative-hypnotic effects of a high dose, while reduced astrocyte calcium signaling diminished sensitivity to the hypnotic effects. In addition, we found that adenosine A1 receptors were required for astrocyte calcium activation to increase ethanol sedation. These results support integral roles for PFC astrocytes in the behavioral actions of ethanol that are due, at least in part, to adenosine receptor activation.

Ethanol-activated CaMKII signaling induces neuronal apoptosis through Drp1-mediated excessive mitochondrial fission and JNK1-dependent NLRP3 inflammasome activation

Background

Neurodegeneration is a representative phenotype of patients with chronic alcoholism. Ethanol-induced calcium overload causes NOD-like receptor protein 3 (NLRP3) inflammasome formation and an imbalance in mitochondrial dynamics, closely associated with the pathogenesis of neurodegeneration. However, how calcium regulates this process in neuronal cells is poorly understood. Therefore, the present study investigated the detailed mechanism of calcium-regulated mitochondrial dynamics and NLRP3 inflammasome formation in neuronal cells by ethanol.

Methods

In this study, we used the SK-N-MC human neuroblastoma cell line. To confirm the expression level of the mRNA and protein, real time quantitative PCR and western blot were performed. Co-immunoprecipitation and Immunofluorescence staining were conducted to confirm the complex formation or interaction of the proteins. Flow cytometry was used to analyze intracellular calcium, mitochondrial dysfunction and neuronal apoptosis.

Results

Ethanol increased cleaved caspase-3 levels and mitochondrial reactive oxygen species (ROS) generation associated with neuronal apoptosis. In addition, ethanol increased protein kinase A (PKA) activation and cAMP-response-element-binding protein (CREB) phosphorylation, which increased N-methyl-D-aspartate receptor (NMDAR) expression. Ethanol-increased NMDAR induced intracellular calcium overload and calmodulin-dependent protein kinase II (CaMKII) activation leading to phosphorylation of dynamin-related protein 1 (Drp1) and c-Jun N-terminal protein kinase 1 (JNK1). Drp1 phosphorylation promoted Drp1 translocation to the mitochondria, resulting in excessive mitochondrial fission, mitochondrial ROS accumulation, and loss of mitochondrial membrane potential, which was recovered by Drp1 inhibitor pretreatment. Ethanol-induced JNK1 phosphorylation activated the NLRP3 inflammasome that induced caspase-1 dependent mitophagy inhibition, thereby exacerbating ROS accumulation and causing cell death. Suppressing caspase-1 induced mitophagy and reversed the ethanol-induced apoptosis in neuronal cells.

Conclusions

Our results demonstrated that ethanol upregulated NMDAR-dependent CaMKII phosphorylation which is essential for Drp1-mediated excessive mitochondrial fission and the JNK1-induced NLRP3 inflammasome activation resulting in neuronal apoptosis.

Caffeine Potentiates Ethanol-Induced Neurotoxicity Through mTOR/p70S6K/4E-BP1 Inhibition in SH-SY5Y Cells

Caffeine is a popular psychostimulant, which is frequently consumed with ethanol. However, the effects of caffeine on neuronal cells constantly exposed to ethanol have not been investigated. Apoptosis and oxidative stress occurring in ethanol-induced neurotoxicity were previously associated with decreased phosphorylation of the mTOR/p70S6K/4E-BP1 signaling proteins. Evidence also suggested that caffeine inhibits the mTOR pathway. In this study, human SH-SY5Y neuroblastoma cells were exposed to caffeine after pretreatment for 24 hours with ethanol. Results indicated that both ethanol and caffeine caused neuronal cell death in a dose- and time-dependent manner. Exposure to 20-mM caffeine for 24 hours magnified reduced cell viability and enhanced apoptotic cell death induced by 200 mM of ethanol pretreatment. The phosphorylation of mTOR, p70S6K, and 4E-BP1 markedly decreased in cells exposed to caffeine after ethanol pretreatment, associated with a decrease of the mitochondrial membrane potential (ΔΨm). These findings suggested that caffeine treatment after neuronal cells were exposed to ethanol resulted in marked cell damages, mediated through enhanced inhibition of mTOR/p70S6K/4E-BP1 signaling leading to impaired ΔΨm and, eventually, apoptotic cell death.

G protein-coupled estrogen receptor activates cell type-specific signaling pathways in cortical cultures: relevance to the selective loss of astrocytes

Selective activation of the G protein-coupled estrogen receptor has been proposed to avoid some of the side effects elicited by the activation of classical estrogen receptors α and β. Although its contribution to neuroprotection triggered by estradiol in brain disorders has been explored, the results regarding ischemic stroke are contradictory, and currently, there is no consensus on the role that this receptor may play. The present study aimed to investigate the role of GPER in the ischemic insult. For that, primary cortical cultures exposed to oxygen and glucose deprivation (OGD) were used as a model. Our results demonstrate that neuronal survival was strongly affected by the ischemic insult and concurrent GPER activation with G1 had no further impact. In contrast, OGD had a smaller impact on astrocytes survival but G1, alone or combined with OGD, promoted their apoptosis. This effect was prevented by the GPER antagonist G15. The results also show that ischemia did not change the expression levels of GPER in neurons and astrocytes. In this study, we also demonstrate that selective activation of GPER induced astrocyte apoptosis via the phospholipase C pathway and subsequent intracellular calcium rise, whereas in neurons, this effect was not observed. Taken together, this evidence supports a direct impact of GPER activity on the viability of astrocytes, which seems to be associated with the regulation of different signaling pathways in astrocytes and neurons.

Activation of cyclic GMP-dependent protein kinase blocks alcohol-mediated cell death and calcium disruption in cerebellar granule neurons

Alcohol during brain development leads to the widespread neuronal death observed in fetal alcohol spectrum disorders (FASD). In comparison, the mature brain is less vulnerable to alcohol. Studies into maturation-acquired alcohol resistance uncovered a protective mechanism that reduces alcohol-induced neuronal death through nitric oxide-cGMP-cyclic GMP-dependent protein kinase (NO-cGMP-cGK) signaling. However, the downstream processes underlying this neuroprotection remain unclear. Alcohol can disrupt levels of intracellular calcium ([Ca²⁺]_i) in vulnerable neuronal populations to trigger cell death in both in vivo and in vitro models of FASD. Since cGK has been demonstrated to regulate and inhibit intracellular Ca²⁺ release, we examined the hypothesis that cGK confers alcohol resistance by preventing [Ca²⁺]_i disruptions. Alcohol resistance, determined by neuronal survival after 24 h of alcohol exposure, was examined in primary cerebellar granule neuron (CGN) cultures derived from 5 to 7 day-old neonatal mice with an activator, 8-Br-cGMP, and/or an inhibitor, Rp-8-pCPT-cGMPS, of cGK signaling. Intracellular Ca²⁺ responses to alcohol were measured by ratiometric Ca²⁺ imaging in Fura-2-loaded CGN cultures after 8-Br-cGMP treatment. Our results indicate that activating cGK with 8-Br-cGMP before alcohol administration provided neuroprotection, which the cGK inhibitor, Rp-8-pCPT-cGMPS, blocked. Alcohol exposure elevated [Ca²⁺]_i, whereas 8-Br-cGMP pretreatment reduced both the level of the alcohol-induced rise in [Ca²⁺]_i as well as the number of cells that responded to alcohol by increasing [Ca²⁺]_i. These findings associate alcohol resistance, mediated by cGK signaling, to reduction of the persistent and toxic increase in [Ca²⁺]_i from alcohol exposure.

Caffeine combined with sedative/anesthetic drugs triggers widespread neuroapoptosis in a mouse model of prematurity

OBJECTIVES

Caffeine (CAF) and sedative/anesthetic drugs (SADs) are often coadministered to premature infants in the neonatal intensive care unit (NICU). While SAD neurotoxicity in the developing brain is well established, it is not fully clear whether CAF interacts with SADs and whether this interaction is detrimental. Using a mouse model of prematurity, we hypothesized that CAF would increase apoptotic neurotoxicity when coadministered with SADs.

METHODS

Postnatal day 3 mice were treated with vehicle or 80 mg/kg CAF prior to challenge with 6 mg/kg midazolam, 40 mg/kg ketamine, or 40 μg/kg fentanyl. Six hours later, pups were sacrificed for activated caspase 3 (AC3) immunohistochemistry, and number of AC3 positive cells per mm³ throughout neocortex, hippocampus, caudate, thalamus, and colliculi was analyzed.

RESULTS

CAF caused a statistically significant increase in AC3 positive cells when coadministered with midazolam (p = 0.002), ketamine (p = 0.014), or fentanyl (p < 0.001). Our composite dataset suggests that the addition of CAF to these SADs has a supra-additive effect, causing more neurotoxicity than expected.

CONCLUSIONS

CAF may augment the neurotoxic action of SADs indicated for neonatal sedation/anesthesia in the NICU by triggering widespread apoptosis in the developing brains of premature infants.

Apoptosis of alcohol-exposed human placental cytotrophoblast cells is downstream of intracellular calcium signaling

BACKGROUND

Apoptosis is induced by ethanol (EtOH) in human placental trophoblast cells, possibly disrupting placentation and contributing to intrauterine growth restriction in fetal alcohol spectrum disorder (FASD). EtOH induces programmed cell death in several embryonic tissues by raising intracellular Ca(2+) . Therefore, the role of Ca(2+) signaling in EtOH-induced apoptosis was examined using human first trimester cytotrophoblast cell lines, examining the hypothesis that apoptosis is dependent on intracellular Ca(2+) signaling.

METHODS

Using HTR-8/SVneo and SW.71 cytotrophoblast cell lines, real-time intracellular Ca(2+) concentration was monitored by fluo-4 epifluorescence microscopy and apoptosis was assessed by flow cytometry of cells fluorescently labeled for DNA fragmentation (TUNEL) and annexin V binding.

RESULTS

Intracellular Ca(2+) concentrations increased synchronously in all cells within 10 seconds of exposure to 50 mM EtOH, but not at lower EtOH concentrations (10 to 25 mM) incapable of inducing apoptosis. Trophoblast cells treated with inhibitors of Ca(2+) signaling (BAPTA-AM, U73122, xestospongin D, BAPTA, SKF-96365) produced no intracellular Ca(2+) transients after exposure to 50 mM EtOH and were protected from cell death induced by EtOH.

CONCLUSIONS

EtOH-induced apoptosis in human cytotrophoblast cells, identified by DNA fragmentation and externalized phosphatidylserine, was dependent upon Ca(2+) signaling. Both intracellular Ca(2+) mobilization and extracellular Ca(2+) influx were required, as well as phosphatidylinositol signaling. Inhibition by SKF-96365 suggests that the capacitative Ca(2+) entry mechanism that utilizes TRPC channels was activated by EtOH. Apoptosis occurs downstream of Ca(2+) signaling in trophoblasts and may contribute to placental insufficiency and poor fetal growth associated with FASD.

Intracellular calcium plays a critical role in the alcohol-mediated death of cerebellar granule neurons

Alcohol is a potent neuroteratogen that can trigger neuronal death in the developing brain. However, the mechanism underlying this alcohol-induced neuronal death is not fully understood. Utilizing primary cultures of cerebellar granule neurons (CGN), we tested the hypothesis that the alcohol-induced increase in intracellular calcium [Ca(2+)](i) causes the death of CGN. Alcohol induced a dose-dependent (200-800 mg/dL) neuronal death within 24 h. Ratiometric Ca(2+) imaging with Fura-2 revealed that alcohol causes a rapid (1-2 min), dose-dependent increase in [Ca(2+)](i), which persisted for the duration of the experiment (5 or 7 min). The alcohol-induced increase in [Ca(2+)](i) was observed in Ca(2+) -free media, suggesting intracellular Ca(2+) release. Pre-treatment of CGN cultures with an inhibitor (2-APB) of the inositol-triphosphate receptor (IP(3) R), which regulates Ca(2+) release from the endoplasmic reticulum (ER), blocked both the alcohol-induced rise in [Ca(2+)](i) and the neuronal death caused by alcohol. Similarly, pre-treatment with BAPTA/AM, a Ca(2+) -chelator, also inhibited the alcohol-induced surge in [Ca(2+) ](i) and prevented neuronal death. In conclusion, alcohol disrupts [Ca(2+)](i) homeostasis in CGN by releasing Ca(2+) from intracellular stores, resulting in a sustained increase in [Ca(2+)](i). This sustained increase in [Ca(2+)](i) may be a key determinant in the mechanism underlying alcohol-induced neuronal death.

Bothrops leucurus venom induces nephrotoxicity in the isolated perfused kidney and cultured renal tubular epithelia

Bites from snake (Bothrops genus) cause local tissue damage and systemic complications, which include alterations such as hemostatic system and acute renal failure (ARF). Recent studies suggest that ARF pathogenesis in snakebite envenomation is multifactorial and involves hemodynamic disturbances, immunologic reactions and direct nephrotoxicity. The aim of the work was to investigate the effects of the Bothrops leucurus venom (BlV) in the renal perfusion system and in cultured renal tubular cells of the type MDCK (Madin-Darby Canine kidney). BlV (10 μg/mL) reduced the perfusion pressure at 90 and 120 min. The renal vascular resistance (RVR) decreased at 120 min of perfusion. The effect on urinary flow (UF) and glomerular filtration rate (GFR) started 30 min after BlV infusion, was transient and returned to normal at 120 min of perfusion. It was also observed a decrease on percentual tubular transport of sodium (%TNa(+)) at 120 min and of chloride (%TCl(-)) at 60 and 90 min. The treatment with BlV caused decrease in cell viability to the lowest concentration tested with an IC(50) of 1.25 μg/mL. Flow cytometry with annexin V and propidium iodide showed that cell death occurred predominantly by necrosis. However, a cell death process may involve apoptosis in lower concentrations. BlV treatment (1.25 μg/mL) led to significant depolarization of the mitochondrial membrane potential and, indeed, we found an increase in the expression of cell death genes in the lower concentrations tested. The venom also evoked an increase in the cytosolic Ca(2+) in a concentration dependent manner, indicating that Ca(2+) may participate in the venom of B. leucurus effect. The characterization of the effects in the isolated kidney and renal tubular cells gives strong evidences that the acute renal failure induced by this venom is a result of the direct nephrotoxicity which may involve the cell death mechanism.

Pathophysiology of astroglial purinergic signalling

Astrocytes are fundamental for central nervous system (CNS) physiology and are the fulcrum of neurological diseases. Astroglial cells control development of the nervous system, regulate synaptogenesis, maturation, maintenance and plasticity of synapses and are central for nervous system homeostasis. Astroglial reactions determine progression and outcome of many neuropathologies and are critical for regeneration and remodelling of neural circuits following trauma, stroke, ischaemia or neurodegenerative disorders. They secrete multiple neurotransmitters and neurohormones to communicate with neurones, microglia and the vascular walls of capillaries. Signalling through release of ATP is the most widespread mean of communication between astrocytes and other types of neural cells. ATP serves as a fast excitatory neurotransmitter and has pronounced long-term (trophic) roles in cell proliferation, growth, and development. During pathology, ATP is released from damaged cells and acts both as a cytotoxic factor and a proinflammatory mediator, being a universal "danger" signal. In this review, we summarise contemporary knowledge on the role of purinergic receptors (P2Rs) in a variety of diseases in relation to changes of astrocytic functions and nucleotide signalling. We have focussed on the role of the ionotropic P2X and metabotropic P2YRs working alone or in concert to modify the release of neurotransmitters, to activate signalling cascades and to change the expression levels of ion channels and protein kinases. All these effects are of great importance for the initiation, progression and maintenance of astrogliosis-the conserved and ubiquitous glial defensive reaction to CNS pathologies. We highlighted specific aspects of reactive astrogliosis, especially with respect to the involvement of the P2X(7) and P2Y(1)R subtypes. Reactive astrogliosis exerts both beneficial and detrimental effects in a context-specific manner determined by distinct molecular signalling cascades. Understanding the role of purinergic signalling in astrocytes is critical to identifying new therapeutic principles to treat acute and chronic neurological diseases.

Maximizing neuroprotection: where do we stand?

Brain and spinal cord traumas include blunt and penetrating trauma, disease, and required surgery. Such traumas trigger events such as inflammation, infiltration of inflammatory and other cells, oxidative stress, acidification, excitotoxicity, ischemia, and the loss of calcium homeostasis, all of which cause neurotoxicity and neuron death. To prevent trauma-induced neurological deficits and death, each of the many neurotoxic events that occur in parallel or sequentially must be minimized or prevented. Although neuroprotective techniques have been developed that block single neurotoxic events, most provide only limited neuroprotection and are only applied singly. However, because many neurotoxicity triggers arise from common events, an approach for invoking more effective neuroprotection is to apply multiple neuroprotective methods simultaneously before the many neurotoxic triggers and cascades are initiated and become irreversible. This paper first discusses some triggers of neurotoxicity and neuroprotective mechanisms that block them, including hypothermia, alkalinization, and the administration of adenosine. It then examines how the simultaneous application of these techniques provides significantly greater neuroprotection than is provided by any technique alone. The paper also stresses the importance of determining whether the neuroprotection provided by these techniques can be further enhanced by combining them with additional techniques, such as the systemic administration of glucocorticoids. Finally, the paper stresses the absolute critical importance of applying these techniques within the "golden hour" following trauma, before the many neurotoxic events and cascades are manifest and before the neurotoxic cascades become irreversible.

Possible involvement of calcium channels and plasma membrane receptors on Staurosporine-induced neurite outgrowth

Staurosporine as a protein kinases inhibitor induced cell death or neurite outgrowth in PC12 cells. We investigated the involvement of calcium channel and plasma membrane receptors on staurosporine inducing neurite outgrowth in PC12 cells. PC12 cells were preincubated with NMDA receptor inhibitors (1.8 mM ketamine and 1µM MK801, treatment 1) or L-Type Calcium channels (100 μM nifedipine and 100 µM flavoxate hydrochloride, treatment 2) or calcium-calmoduline kinasses (10 μM trifluoprazine, treatment 3) and nifedipine, MK801, flavoxate hydrochloride and ketamine (treatment4) or without pretreatments (control). Then, the cells were cultured in RPMI culture medium containing 214nM staurosporine for induction of neurite outgrowth. The percentage of Cell cytotoxicity and apoptotic index was assessed. Total neurite length (TNL) and fraction of cell differentiation were assessed. After 24h, the percentage of cell cytotoxicity were increased in treatments 1, 2 and 4 compared with control (p<0.05). After 6h, apoptotic index was similar between all treatments. After 12h, apoptotic index were increased in treatment 4 compared with control (p<0.05). After 24h, apoptotic index were increased in treatments 1, 2 and 4 compared with control (p<0.05). TNL were decreased in treatments 1, 2 and 4 compared with control in different times of assessment (6, 12 and 24 h) (p<0.05). The fraction of cell differentiation were decreased in treatments 1, 2 and 4 compared with control (p<0.05). It can be concluded that the possible involvement of L-type calcium channel and the N-methyl D-aspartate receptor on staurosporine-induced neurite outgrowth process in PC12 cells.

The retinoid, 6-[3-adamantyl-4-hydroxyphenyl]-2-napthalene carboxylic acid, controls proliferative, morphological, and inflammatory responses involved in microglial activation without cytotoxic effects

Activation of microglia is regulated by controlling both its population size (through modulation of proliferation/death) and the production of inflammatory mediators. Retinoids control cellular proliferation, differentiation, and death. Natural retinoids have been shown to exhibit anti-inflammatory actions against activated microglia. However, the synthetic forms, which are regarded to be more stable in their actions, have not been explored for their capacity to modulate microglial activation, proliferation, and/or trigger cell death. The aim of the current study was to address these issues by using a model, lipopolysaccharide (LPS)-activated primary cultures of rat microglia, and the stable synthetic retinoid, 6-[3-adamantyl-4-hydroxyphenyl]-2-napthalene carboxylic acid (AHPN). Morphological observations of cluster of differentiation (CD) 11b (CD11b)-positive cells suggested that low concentration of AHPN (i.e. 5 μM) reduced LPS (1 μg/ml, 24 h)-activated morphology of microglia possibly toward a lower activated state, while attenuating nitrite production and the level of its synthesizing enzyme, inducible nitric oxide synthase (iNOS), as well as the chemokine, monocyte chemotactic protein-1 (MCP-1). The mechanisms behind these anti-inflammatory actions likely involved decreased activation of nuclear factor kappa B (NF-κB) as shown by the attenuated phosphorylation of its p65 subunit. In addition, fluorescence-activated cell sorting revealed that AHPN reduced the immunophenotypic marker of activation, CD68. LPS-mediated increase in cell number was reduced by low concentration AHPN, which resulted from inhibition of proliferation, based on decreased labeling for Ki-67 and reduced protein expression of cyclin D1, and not cell death. Higher concentrations of AHPN (50-100 μM) attenuated activation and cell number; however, the release of lactate dehydrogenase and appearance of annexin V and propidium iodide-positive cells suggested that cell death was its primary cause for reduced microglial activity. Overall, the current study shows that synthetic retinoids, such as AHPN, at low concentration attenuate microglial activation-associated responses, possibly via the inhibition of their cell proliferation without triggering cell death.

Ethanol alters the physiology of neuron-glia communication

In the central nervous system (CNS), both neurones and astrocytes play crucial roles. On a cellular level, brain activity involves continuous interactions within complex cellular circuits established between neural cells and glia. Although it was initially considered that neurones were the major cell type in cerebral function, nowadays astrocytes are considered to contribute to cerebral function too. Astrocytes support normal neuronal activity, including synaptic function, by regulating the extracellular environment with respect to ions and neurotransmitters. There is a plethora of noxious agents which can lead to the development of alterations in organs and functional systems, and that will end in a chronic prognosis. Among the potentially harmful external agents we can find ethanol consumption, whose consequences have been recognized as a major public health concern. Deregulation of cell cycle has devastating effects on the integrity of cells, and has been closely associated with the development of pathologies which can lead to dysfunction and cell death. An alteration of normal neuronal-glial physiology could represent the basis of neurodegenerative processes. In this review we will pay attention on to the recent findings in astrocyte function and their role toward neurons under ethanol consumption.

Inhibition of ethanol-induced toxicity by tanshinone IIA in PC12 cells

AIM

To observe the effects of tanshinone IIA (Tan IIA) on the neurotoxicity induced by ethanol in PC12 cells and to explore its protective role.

METHODS

PC12 cell survival was measured by MTT assay. The formation of reactive oxygen species (ROS) and lactate dehydrogenase (LDH) release were detected by 2',7'-dichlorofluorescin (DCF) fluorescence and calorimetric method, respectively. The percentage of cell apoptosis was monitored by flow cytometry. The expression of p53 was detected by immuno-fluorescence and flow cytometry.

RESULTS

Ethanol significantly impaired the survival of PC12 cells as demonstrated by MTT assay. Ethanol also induced significant ROS formation and increased LDH release. Pre-incubation with Tan IIA in the culture medium significantly reversed these changes. Ethanol caused cell apoptosis and the upregulation of p53 protein. The anti-apoptosis effects of Tan IIA on ethanol-induced toxicity were accompanied by the downregulation of pro-apoptotic p53 protein expression.

CONCLUSION

Tan IIA can protect neurons from apoptosis and might serve as a potential therapeutic drug for neurological disorders induced by ethanol.

The calcium-binding domain of the stress protein SEP53 is required for survival in response to deoxycholic acid-mediated injury

Stress protein responses have evolved in part as a mechanism to protect cells from the toxic effects of environmental damaging agents. Oesophageal squamous epithelial cells have evolved an atypical stress response that results in the synthesis of a 53 kDa protein of undefined function named squamous epithelial-induced stress protein of 53 kDa (SEP53). Given the role of deoxycholic acid (DCA) as a potential damaging agent in squamous epithelium, we developed assays measuring the effects of DCA on SEP53-mediated responses to damage. To achieve this, we cloned the human SEP53 gene, developed a panel of monoclonal antibodies to the protein, and showed that SEP53 expression is predominantly confined to squamous epithelium. Clonogenic assays were used to show that SEP53 can function as a survival factor in mammalian cell lines, can attenuate DCA-induced apoptotic cell death, and can attenuate DCA-mediated increases in intracellular free calcium. Deletion of the highly conserved EF-hand calcium-binding domain in SEP53 neutralizes the colony survival activity of the protein, neutralizes the protective effects of SEP53 after DCA exposure, and permits calcium elevation in response to DCA challenge. These data indicate that the squamous cell-stress protein SEP53 can function as a modifier of the DCA-mediated calcium influx and identify a novel survival pathway whose study may shed light on mechanisms relating to squamous cell injury and associated cancer development.