A novel therapy, using Ghrelin with pegylated G-CSF, inhibits brain hemorrhage from ionizing radiation or combined radiation injury

Medical treatment becomes challenging when complicated injuries arise from secondary reactive metabolic and inflammatory products induced by initial acute ionizing radiation injury (RI) or when combined with subsequent trauma insult(s) (CI). With such detrimental effects on many organs, CI exacerbates the severity of primary injuries and decreases survival. Previously, in a novel study, we reported that ghrelin therapy significantly improved survival after CI. This study aimed to investigate whether brain hemorrhage induced by RI and CI could be inhibited by ghrelin therapy with pegylated G-CSF (i.e., Neulasta®, an FDA-approved drug). B6D2F1 female mice were exposed to 9.5 Gy 60Co-γ-radiation followed by 15% total-skin surface wound. Several endpoints were measured at several days. Brain hemorrhage and platelet depletion were observed in RI and CI mice. Brain hemorrhage severity was significantly higher in CI mice than in RI mice. Ghrelin therapy with pegylated G-CSF reduced the severity in brains of both RI and CI mice. RI and CI did not alter PARP and NF-κB but did significantly reduce PGC-1α and ghrelin receptors; the therapy, however, was able to partially recover ghrelin receptors. RI and CI significantly increased IL-6, KC, Eotaxin, G-CSF, MIP-2, MCP-1, MIP-1α, but significantly decreased IL-2, IL-9, IL-10, MIG, IFN-γ, and PDGF-bb; the therapy inhibited these changes. RI and CI significantly reduced platelet numbers, cellular ATP levels, NRF1/2, and AKT phosphorylation. The therapy significantly mitigated these CI-induced changes and reduced p53-mdm2 mediated caspase-3 activation. Our data are the first to support the view that Ghrelin therapy with pegylated G-CSF is potentially a novel therapy for treating brain hemorrhage after RI and CI.

Response of crypt paneth cells in the small intestine following total-body gamma-irradiation

Ionizing irradiation causes damage and functional failure of irradiation-sensitive systems and tissues such as small intestine. The molecular mechanisms underlying inflammatory and adaptive responses to acute irradiation damage are poorly understood. Using a mouse model of total-body γ-irradiation, we assessed the irradiation response of crypt host-defense Paneth cells by measuring alpha-defensin 4 (AD4) expression and correlated the gathered data with activation of the caspase-1/IL-1β inflammatory signaling cascade. The irradiation injury was produced in CD2F1 mice exposed to 9.25 Gy γ-radiation. This dose resulted in 85-100 percent mortality at the 15(th) day post-irradiation. Small intestine tissue samples were collected at the 7th day post-irradiation. Assessment of irradiation-associated pro-inflammatory alterations in small intestine tissue and expression of AD4 in Paneth cells was conducted using confocal immunofluorescence imaging, transmission electron microscopy (TEM), light microscopy, and immunoblotting techniques. The small intestine analysis revealed an increase in the precursor form of IL-1β, the activated form of IL-1β, and the activated form of caspase-1 (p10 CASP-1) at the 7(th) day post-irradiation. Immunoprecipitation analysis showed increased interaction between IL-1β and p10 CASP-1 after irradiation. This effect was observed in the irradiated small intestine and CD15-positive Paneth cells using confocal imaging techniques. The pro-inflammatory alterations in Paneth cells were accompanied by increases in AD4 mRNA and its 8 kD peptide product. Paneth cell secretory activity was observed at the sites of bacterial translocation in the crypt lumens. These data suggest that Paneth cells can contribute to small intestine inflammatory remodeling during the post-irradiation period.

COX-2 inhibitors are contraindicated for treatment of combined injury

Casualties of radiation dispersal devices, nuclear detonation or major ionizing radiation accidents, in addition to radiation exposure, may sustain physical and/or thermal trauma. Radiation exposure plus additional tissue trauma is known as combined injury. There are no definitive therapeutic agents. Cyclooxygenase-2 (COX-2), an inducible enzyme expressed in pathological disorders and radiation injury, plays an important role in inflammation and the production of cytokines and prostaglandin E(2) (PGE(2)) and could therefore affect the outcome for victims of combined injury. The COX-2 inhibitors celecoxib and meloxicam were evaluated for their therapeutic value against combined injury in mice. In survival studies, the COX-2 inhibitors had no beneficial effect on 30-day survival, wound healing or body weight gain after radiation injury alone or after combined injury. Meloxicam accelerated death in both wounded and combined injury mice. These drugs also induced severe hepatic toxicity, exaggerated inflammatory processes, and did not enhance hematopoietic cell regeneration. This study points to potential contraindications for use of COX-2 inhibitors in patients undergoing therapy for radiation injury and combined injury.

Regulation of heat shock protein 72 kDa and 90 kDa in human breast cancer MDA-MB-231 cells

It has been shown that expression of HSPs can negatively regulate the effectiveness of cytotoxic drugs. In this study, we conducted experiments to study the regulation of expression of heat shock proteins (HSPs) in human breast cancer MDA-MB-231 cells. Using [35S]methionine incorporation and Western immunoblots, we established that heat shock increased production of HSP-72 and -90. Cells exposed to 44 degrees C for 20 min displayed increased expression of HSP-72 and -90, that reached a maximum 3-7 h later and returned to baseline levels within 24 h. The synthesis of both HSP-72 and -90 was attenuated when cells were exposed to heat shock in medium devoid of Ca2+ or pretreated with the calcium chelator BAPTA for 30 min prior to heat shock. Similarly, synthesis of HSP-72 and -90 was inhibited when cells were treated with the protein kinase A inhibitor, H89. These data indicate that Ca2+ and PKA are involved in the regulation of HSP-72 and -90 protein synthesis. Levels of HSP-72 mRNA in cells exposed to heat shock increased, suggesting that the heat-induced increase in HSP-72 occurs at the transcriptional level. Also, heat shock caused phosphorylation and translocation from the cytosol to the nucleus of heat shock factor 1 (HSF 1), a transcription factor for heat shock protein synthesis. Removal of external Ca2+ or treatment with a PKA inhibitor prevented the phosphorylation and the translocation of HSF 1. Cells overexpressing HSP-72 and -90 induced by exposure to a sublethal temperature displayed cytoprotection from thermal injury. Removal of external Ca2+ and treatment with BAPTA or H89 prior to exposure to sublethal heat shock that reduced the amount of HSP-72 and -90 production still protected cells from subsequent thermal injury. The intracellular free calcium concentration ([Ca2+]i) in resting fura-2-loaded MDA-MB-231 cells was 175+/- nM. Heat shock increased [Ca2+]i in a time-and temperature-dependent manner. Exposure of cells to 44 degrees C for 20 min increased [Ca2+]i by 234+/-13%, which subsequently returned to baseline levels within 30 min. Removal of external Ca2+ eliminated the increase, indicating that the increase in [Ca2+]i was due to Ca2+ influx. Pretreatment of the cells with H89 but not GF-109203X for 30 min led to an attenuation of the increase in [Ca2+]i by a subsequent heat shock. The results suggest that HSP-72 and -90 are regulated by [Ca2+]i and PKA activity in MDA-MB-231 cells. Kiang JG, Gist ID, Tsokos GC: Regulation of Heat Shock Protein 72 kDa and 90 kDa in Human Breast Cancer MDA-MB-231 Cells.

Characterization of distinct heat shock- and thapsigargin-induced cytoprotective proteins in FRTL-5 thyroid cells

Heat shock induces the expression of proteins with molecular weights of 70-72 kd and 90 kd, whereas thapsigargin induces the expression of a glucose-regulated protein 78 kd (GRP-78) in certain cells. In this study we examined the induction and cytoprotective effects of heat shock- and thapsigargin-induced proteins in FRTL-5 rat thyroid cells. New protein synthesis was assessed in [35S]methionine-labeled cells and quantitated densitometrically. The expression of specific stress proteins was identified using Western blots, whereas cytoprotection provided by these proteins was evaluated by trypan blue exclusion. Exposure to heat shock (45 degrees C, 15 minutes) induced the expression of proteins with molecular weights at the range of low 70 kD and low 90 kD that peaked between 2-6 hours and returned to baseline within 24 hours. Treatment of cells with thapsigargin (200 nM, 15 minutes) induced the expression of different molecular weight proteins, most likely GRP-78 and -94, that peaked at 4-6 hours and lasted for 24 hours. Neither the removal of growth factors (thyroid-stimulating hormone and insulin) for 5 days nor the elimination of extracellular Ca2+ with EGTA or clamping of the intracellular Ca2+ with BAPTA for 15 minutes affected expression of the heat shock- and the thapsigargin-induced stress proteins. In contrast, protein kinase C inhibitors H7 and GF109203X abolished the expression of all three groups of stress proteins. Both heat shock- and thapsigargin-inuced proteins completely protected cells from subsequent thermal injury (47 degrees C, 35 minutes). The induction of cytoprotective proteins by heat shock and thapsigargin requires the presence of protein kinase C but is Ca(2+)- and growth factor-independent.

N(omega)-nitro-L-arginine decreases resting cytosolic [Ca2+] and enhances heat stress-induced increase in cytosolic [Ca2+] in human colon carcinoma T84 cells

N(omega)-nitro-L-arginine (LNNA) inhibits the synthesis of heat shock proteins in animals and cultured cells exposed to heat stress. Heat shock protein synthesis is known to be Ca2+-dependent. In this study, we have characterized the effect of LNNA on [Ca2+]i before and after heat stress in human colon carcinoma T84 cells. In untreated cells incubated in the presence of external Ca2+, the resting [Ca2+]i was 201+/-3 nM. If these cells were exposed to 45 degrees C for 10 min, [Ca2+]i increased by 50+/-2%. Preincubation with LNNA (100 microM) without subsequent heating led to a decrease in [Ca2+]i in a LNNA concentration-dependent manner. Preincubation with LNNA followed by heating increased [Ca2+]i to levels 88+/-5% greater than cells heated without LNNA pretreatment. Incubating cells in medium without external Ca2+ (no heating, no LNNA treatment) lowered resting [Ca2+]i to 115+/-2 nM and greatly reduced the increase in [Ca2+]i observed if cells were heated in the presence of Ca2+, indicating that external Ca2+ plays an important role in the maintenance of [Ca2+]i in T84 cells. With external Ca2+ absent, LNNA pretreatment further reduced [Ca2+]i in unheated cells, and heating failed to enhance [Ca2+]i. We determined (with external Ca2+ present) that the heat-stress induced increase in [Ca2+]i in T84 cells was blocked by dichlorobenzamil, a Na+/Ca2+ exchanger inhibitor, suggesting that the exchanger mediates Ca2+ entry. The median inhibitory concentration (IC50) in cells not treated with LNNA was 0.970+/-0.028 microM. With LNNA pretreatment, the IC50 was 5.099+/-0.107 microM. Heat stress of T84 cells did not affect the binding affinity of the Na+/Ca2+ exchanger for external Ca2+, but it increased the maximal velocity of the exchanger. In unheated cells, preincubation with LNNA decreased the binding affinity of the exchanger for Ca2+, but after heat treatment, both the binding affinity and maximal velocity of the exchanger increased. Our data are consistent with the idea that LNNA affects the activity of the Na+/Ca2+ exchanger. We also determined there are intracellular Ca2+ pools in T84 cells sensitive to thapsigargin, monensin, and ionomycin. Treatment with TMB-8, a blocker of Ca2+ sequestration and mobilization, or ionomycin inhibited the LNNA-induced decrease in [Ca2+]i observed in the absence of external Ca2+, suggesting that LNNA promotes Ca2+ sequestration.

Phospholipase C activation by Na+/Ca2+ exchange is essential for monensin-induced Ca2+ influx and arachidonic acid release in FRTL-5 thyroid cells

BACKGROUND

Monensin, a Na+ ionophore, can increase cytosolic Ca2+ ([Ca2+]i) by reversing the Na+/Ca2+ exchange mechanism. This study provided additional insights into the mechanism of this Na+ ionophore-induced increase in [Ca2+]i, and emphasized the critical role of phospholipase C (PLC) in amplifying Na+/Ca2+ exchange-induced Ca2+ influx and subsequent arachidonic acid (AA) release in FRTL-5 thyroid cells. The possible involvement of protein kinase C (PKC), mitogen-activated protein kinase (MAPK), and GTP-binding (G) protein in mediating monensin-induced AA release was also explored.

METHODS

FRTL-5 thyroid cells were maintained in Coon's modified Ham's F-12 medium supplemented with a 6-hormone (6H) mixture. Cytosolic Ca2+ was measured by using indo-1 AM and a dual-wave-length spectrofluorometer. Release of 3H-labeled inositol trisphosphates and arachidonic acid were determined by a scintillation counter.

RESULTS

In Hank's balanced salt solution with Ca2+ (HBSS+), monensin (100 mumol/L) induced a 2.3-fold sustained Ca2+ increase associated with IP3 generation and a 6-fold increase in AA release. Deletion of extracellular Ca2+, or replacement of Na+ by choline chloride in the medium, reduced the [Ca2+]i increase by 77% and completely prevented the monensin-induced rise in AA release. Similar inhibitory effects were observed in cells pretreated with a Na+ channel blocker, or Na+/Ca2+ exchange inhibitors. In HBSS without Ca2+ (HBSS-), monensin induced a 1-fold transient [Ca2+]i increase but did not increase the AA. This Ca2+ increase was not suppressed by U-73122, a PLC inhibitor. In HBSS+, U-73122 did not affect the monensin-induced initial transient peak increase of [Ca2+]i, but reduced the sustained second phase of [Ca2+]i from 400 nmol/L to 250 nmol/L, and completely blocked AA release. A phospholipase A2 (PLA2) inhibitor blocked the monensin-induced AA release without affecting the [Ca2+]i increase. Inhibition of PKC prevented 87% to 94% of the monesin-stimulated AA release. The monensin-induced AA release was also inhibited 94% by pertussis and 51% by a MAP kinase cascade inhibitor.

CONCLUSIONS

The results suggest that monensin initiates an increase in [Ca2+]i via a Na+/Ca2+ exchange mechanism that triggers more pronounced and sustained [Ca2+]i increase via activation of PLC and Ca2+ influx. The PLC activation, followed by sustained Ca2+ influx and PKC activation, is a prerequisite for PLA2-mediated processes in monensin-challenged FRTL-5 thyroid cells.

Biochemical requirements for the expression of heat shock protein 72 kda in human breast cancer MCF-7 cells

Heat shock alters the susceptibility of tumor cells to chemotherapeutic agents. Cultured breast cancer MCF-7 and MDA-MB-231 cells that express high levels of heat shock protein 70 and 27 kDa are resistant to treatment with certain anticancer drugs. These findings indicate that expression of HSPs can negatively regulate the effectiveness of cytotoxic drugs. We conducted experiments to study the regulation of expression of heat shock proteins (HSPs) in human breast cancer MCF-7 cells exposed to heat shock by intracellular free Ca2+ and protein kinase C. Cells exposed to 44 degrees C for 20 min displayed increased expression of HSP-72 and GRP-94, that reached a maximum 4-5 h later and returned to baseline levels within 24 h. Levels of HSP-72 mRNA in cells exposed to heat shock increased, suggesting that the heat-induced increase in HSP-72 occurs at the transcriptional level. The synthesis of HSP-72 but not GRP-94 was inhibited when cells were exposed to heat shock in medium devoid of Ca2+ and attenuated by more than 50% when cells were pretreated with the calcium chelator BAPTA for 30 min prior to heat shock. HSP-72 synthesis was enhanced when cells were treated with the protein kinase C inhibitor, GF-109203X. These data indicate that Ca2+ and PKC are involved in regulation of HSP-72 synthesis. However, removal of external Ca2+ and treatment with BAPTA, GF-109203X, or exposure to sublethal heat shock protected cells from subsequent thermal injury. The intracellular free calcium concentration ([Ca2+]i) in resting fura-2-loaded MCF-7 cells was 156 +/- 16 nM (n = 29). Heat shock increased [Ca2+]i in a time- and temperature-dependent manner. Exposure of cells to 44 degrees C for 20 min increased [Ca2+]i by 234 +/- 13%, which subsequently returned to baseline levels within 120 min. Removal of external Ca2+ eliminated the increase, indicating that the increase in [Ca2+]i was due to Ca2+ influx. Pretreatment of the cells with BAPTA or GF-109203X for 30 min or a sublethal heat shock to allow HSP-72 overexpression led to an attenuation of the increase in [Ca2+]i by a subsequent heat shock. The results suggest that HSP-72 but not GRP-94 is regulated by [Ca2+]i and PKC activity. The cytoprotection produced by chelation of Ca2+, GF-109203X, or HSP-72 overexpression is probably due to their ability to attenuate the [Ca2+]i response to heating.

Corticotropin-releasing factor induces phosphorylation of phospholipase C-gamma at tyrosine residues via its receptor 2beta in human epidermoid A-431 cells

This laboratory previously reported that corticotropin-releasing factor (CRF) increased intracellular free calcium concentrations, cellular cAMP, inositol 1,4,5-trisphosphate, protein kinase C activity, and protein phosphorylation in human A-431 cells. The increase was blocked by CRF receptor antagonist. In this study, we identified the type of CRF receptors present and investigated whether CRF induced tyrosine phosphorylation of phospholipase C-gamma via CRF receptors. Using novel primers in reverse transcriptase-polymerase chain reaction, we determined the CRF receptor type to be that of 2beta. The levels of the CRF receptor type 2beta were not altered in cells treated with activators of protein kinase C, Ca2+ ionophore, or cells overexpressing heat shock protein 70 kDa. Cells treated with CRF displayed increases in protein tyrosine phosphorylation approximately at 150 kDa as detected by immunoblotting using an antibody against phosphotyrosine. Immunoprecipitation with antibodies directed against phospholipase C-beta3, -gamma1, or -gamma2 isoforms (which have molecular weights around 150 kDa) followed by Western blotting using an anti-phosphotyrosine antibody showed that only phospholipase C-gamma1 and -gamma2 were phosphorylated. The increase in phospholipase C-gamma phosphorylation was concentration-dependent with an EC50 of 4.2+/-0.1 pM. The maximal phosphorylation by CRF at 1 nM occurred by 5 min. The CRF-induced phosphorylation was inhibited by the protein tyrosine kinase inhibitors genistein and herbimycin A, suggesting that CRF activates protein tyrosine kinases. Treatment of cells with CRF receptor antagonist, but not pertussis toxin, prior to treatment with CRF inhibited the CRF-induced phosphorylation, suggesting it is mediated by the CRF receptor type 2beta that is not coupled to pertussis toxin-sensitive G-proteins. Treatment with 1,2-bis(2iminophenoxy)ethane-N,N,N',N'-tetraacetic acid attenuated the phospholipase C-gamma phosphorylation. In summary, CRF induces phospholipase C-gamma phosphorylation at tyrosine residues, which depends on Ca2+ and is mediated by activation of protein tyrosine kinases via the CRF receptor type 2beta.

Heat shock protein 70 kDa: molecular biology, biochemistry, and physiology

Heat shock proteins (HSPs) are detected in all cells, prokaryotic and eukaryotic. In vivo and in vitro studies have shown that various stressors transiently increase production of HSPs as protection against harmful insults. Increased levels of HSPs occur after environmental stresses, infection, normal physiological processes, and gene transfer. Although the mechanisms by which HSPs protect cells are not clearly understood, their expression can be modulated by cell signal transducers, such as changes in intracellular pH, cyclic AMP, Ca2+, Na+, inositol trisphosphate, protein kinase C, and protein phosphatases. Most of the HSPs interact with other proteins in cells and alter their function. These and other protein-protein interactions may mediate the little understood effects of HSPs on various cell functions. In this review, we focus on the structure of the HSP-70 family (HSP-70s), regulation of HSP-70 gene expression, their cytoprotective effects, and the possibility of regulating HSP-70 expression through modulation of signal transduction pathways. The clinical importance and therapeutic potential of HSPs are discussed.

Cytoprotection and regulation of heat shock proteins induced by heat shock in human breast cancer T47-D cells: role of [Ca2+]i and protein kinases

Overexpression of heat shock protein 70 kDa alters the susceptibility of tumor cells to chemotherapeutic agents. We conducted experiments to study the regulation of expression of heat shock proteins (HSPs) in heat shock-treated T47-D cells, a human breast cancer cell line that expresses estrogen receptors. Cells exposed to heat shock at 44 degreesC displayed increased expression of heat shock protein 72 kDa (HSP-72), glucose-regulated protein 78 kDa (GRP-78), and GRP-94 in a time-dependent manner, as shown by [35S]methionine incorporation and Western blotting experiments. The maximal rate of synthesis occurred between 2 and 4 h after heat shock. Removal of external Ca2+ inhibited the synthesis of the heat shock-induced GRP-78 but not of HSP-72 and GRP-94, whereas treatment of cells with BAPTA (a Ca2+ chelator) inhibited HSP-72 and GRP-78. Treatment with H89 (a protein kinase A inhibitor) blocked the heat shock-induced GRP-78 synthesis, whereas GF-109203X (a protein kinase C inhibitor) attenuated the heat shock-induced HSP-72 synthesis and completely blocked synthesis of GRP-78 but not of GRP-94. These results indicate that protein kinase C is involved in regulation of the heat shock-induced synthesis of HSP-72, whereas PKA and PKC are involved in the regulation of GRP-78 synthesis. Cells overexpressing HSP-72 and GRPs after heat shock displayed resistance against lethal temperature (47 degreesC for 50 min) -induced death, which was diminished after removal of external Ca2+ and treatment with GF-109203X. Heat shock increased intracellular free Ca2+ concentration ([Ca2+]i) in a temperature- and heating duration-dependent fashion, and the increase was inhibited in the absence of external [Ca2+]i and significantly reduced by pretreatment with H89 and GF-109203X. The results suggest that different pathways are involved in the induction of synthesis of HSP-72, GRP-78, and GRP-94 by heat shock. It is highly likely that only HSP-72 and GRP-78 are involved in the process of cytoprotection from the thermal injury.

Overexpression of HSP-70 inhibits the phosphorylation of HSF1 by activating protein phosphatase and inhibiting protein kinase C activity

This laboratory reported previously that overexpressed heat shock protein 70 kDa (HSP-70) inhibited the activation of its transcriptional factor, HSF1. We had conducted experiments to understand the mechanisms whereby HSP-70 down-regulated the activation of HSF1. Genetically overexpressed HSP-70 had no effects on the HSF1 level in cytosol, but significantly inhibited phosphorylation of HSF1 in the nucleus. Transfection of cells with HSF1 cDNA resulted in increases in the unphosphorylated, but not phosphorylated, HSF1 levels in both the cytosol and nucleus. Because serine phosphorylation of various proteins was reduced in HSP-70 cDNA-transfected cells, we measured the activity of enzymes involved in serine phosphorylation. Overexpressed HSP-70 significantly inhibited the enzymatic activities of protein kinase A (PKA by 73 and 62% in the cytosol and membrane-bound fraction, respectively) and protein kinase C (PKC by 61% in membrane-bound fraction), whereas it activated that of protein phosphatase (PP by 33 and 86% in the cytosol and the membrane-bound fraction, respectively). Forskolin (a PKA stimulator), PMA (a PKC stimulator), and okadaic acid (an inhibitor of PP) were used to investigate whether HSP-70-induced changes in PKA, PKC, and PP were responsible for the HSF1 dephosphorylation. Forskolin did not change nuclear HSF1 phosphorylation, suggesting that decreases in PKA activity in HSP-70 overexpressing cells is not associated with HSF1 phosphorylation. PMA and okadaic acid induced an increase in HSF1 phosphorylation in both vector- and HSP-70 cDNA-transfected cells, although levels of phosphorylated HSF1 in HSP-70 cDNA-transfected cells were lower than those in vector-transfected cells. The PMA-induced increase in HSF1 phosphorylation in HSP-70 cDNA-transfected cells was blocked by pretreatment with staurosporine, a PKC inhibitor. These results suggest that overexpression of HSP-70 inhibits phosphorylation of HSF1 at serine residues by activating PP and inhibiting PKC activity.

Overexpression of HSP-70 attenuates increases in [Ca2+]i and protects human epidermoid A-431 cells after chemical hypoxia

This laboratory previously reported that thermotolerance diminishes the NaCN-induced increase in intracellular free calcium concentrations ([Ca2+]i) in human epidermoid A-431 cells and that blocking this increase protects the cells from NaCN toxicity. In this study, we report that cell viability after exposure to NaCN (10 mM, 1 h) is enhanced by the overexpression of HSP-70 resulting from heat shock (45 degrees C, 10 min), treatment with a protein kinase C activator phorbol 12 myristate 13-acetate (PMA; 1 microM, 4 h), or HSP-70 cDNA transfection. Because the toxicity of NaCN is mediated by increases in [Ca2+]i, we sought to determine whether the overexpression of HSP-70 might protect the cells by altering the [Ca2+]i response induced by NaCN. Basal [Ca2+]i in vector-, HSF1 cDNA-, and HSP-70 cDNA-transfected cells was 114 +/- 11 (n = 11), 95 +/- 5 (n = 6), and 151 +/- 11 (n = 15) nM, respectively, suggesting that HSP-70 metabolism is associated with maintenance of resting [Ca2+]i. Removal of external Ca2+ reduced the resting [Ca2+]i in all of these cells. With external Ca2+ reduced the resting [Ca2+]i by 97 +/- 21% in vector-transfected cells and 111 +/- 5% in HSF1 vector-transfected cells but by only 27 +/- 8% in HSP-70 cDNA-transfected cells. Heat shock or PMA treatment of vector- or HSF1 cDNA-transfected cells to induce HSP-70 also attenuated the NaCN-induced increase in [Ca2+]i, perhaps because of a decrease in Vmax for the uptake of external Ca2+. Removal of external Ca2+ or treatment with inhibitors of Na+/Ca2+ exchangers eliminated the NaCN-induced increase in [Ca2+]i in HSP-70 cDNA-transfected cells, but ryanodine treatment did not. HSP-70 cDNA transfection also reduced Ca2+ mobilization stimulated by various Ca(2+)-mobilizing agents. The results suggest that HSP-70 overexpression protects cells from NaCN cytotoxicity, perhaps by attenuating the [Ca2+]i response.

17 beta-estradiol-induced increases in glucose-regulated protein 78kD and 94kD protect human breast cancer T47-D cells from thermal injury

Heat shock alters the susceptibility of tumor cells to chemotherapeutic agents. We conducted experiments to study the regulation of expression of heat shock proteins (HSP) in 17 beta-estradiol-treated T47-D cells, a human breast cancer cell line. Cells exposed to 17 beta-estradiol for 24-48 h displayed increased expression of glucose regulated protein 78kD (GRP-78) and 94kD (GRP-94), as shown by [35S]methionine incorporation and Western blotting experiments. The increase was time (5 h to 48 h)-dependent at 1 nM and 1 microM 17 beta-estradiol. Cells overexpressing GRP-78 and -94 after treatment with 17 beta-estradiol displayed resistance against heat shock (47 degrees C for 50 min)-induced death. Removal of external Ca2+ or treatment of cells with BAPTA (a Ca2+ chelator) did not alter the synthesis of GRP-78 and -94, suggesting that the 17 beta-estradiol effect on the synthesis of GRP-78 and -94 is Ca(2+)-independent. In addition, exposure of cells to 17 beta-estradiol up to 100 microM did not increase [Ca2+]i, which further supports the view that the estrogen-induced GRPs are not regulated by [Ca2+]i. Treatment with H89 (a protein kinase A inhibitor, 1 microM, 30 min) or GF-109203X (a protein kinase C inhibitor, 1 microM, 30 min) also did not change the GRP synthesis, indicating that protein kinase A and C are not involved in regulation of GRP synthesis.

Corticotropin-releasing factor-like peptides increase cytosolic [Ca2+] in human epidermoid A-431 cells

This study investigated whether sauvagine and urotensin I change [Ca2+]i in human epidermoid A-431 cells and whether these changes are correlated with their anti-edema properties in vivo. A-431 cells were used because they possess the corticotropin-releasing factor (CRF) receptor 2. Treatment with either sauvagine or urotensin I led to an immediate increase in [Ca2+]i, the magnitude of which depended on the concentration of the drug. Sauvagine was more effective than urotensin I, with a median effective concentration (EC50) of 1.4 +/- 0.2 fM, compared to an EC50 of 66 +/- 7 fM for urotensin I. Both were more effective at stimulating increases in [Ca2+]i than CRF (EC50 of 6.8 +/- 0.1 pM). There was a correlation between the EC50 for increasing [Ca2+]i and the median effective dose (ED50) for inhibiting edema induced by heating rat paw (r = 0.99). Removal of extracellular Ca2+ or incubation with La3+ eliminated the increase in [Ca2+]i stimulated by either peptide. Pretreatment with a CRF receptor antagonist reduced the increase in [Ca2+]i by these peptides. This occurred in an antagonist concentration-dependent manner, with median inhibitory concentrations (IC50) of 1.99 +/- 0.04 nM and 0.85 +/- 0.04 nM, respectively. Both pertussis toxin (an inhibitor of G proteins) and U-73122 (an inhibitor for inositol trisphosphate (InsP3) production) partially inhibited the increases. InsP3 was measured to determine whether these peptides mobilized Ca2+ from an InsP3-sensitive store. Both sauvagine and urotensin I increased InsP3. The InsP3 increases were inhibited by U-73 122 and CRF antagonist, but not by removal of external Ca2+. Both peptides elevated protein tyrosine phosphorylation. In summary, these peptides increase [Ca2+]i as a result of Ca2+ influx via CRF receptor-operated Ca2+ channels coupled to pertussis toxin-sensitive G proteins and a Ca2+ mobilization from InsP3-sensitive Ca2+ pools. Their in vivo effectiveness at inhibiting edema is related to their respective capacities to stimulate elevations of [Ca2+]i, supporting a role for intracellular Ca2+ in this process.

Overexpression of the heat shock protein 70 enhances the TCR/CD3- and Fas/Apo-1/CD95-mediated apoptotic cell death in Jurkat T cells

To investigate whether the protective effects of the 70-kDa heat shock protein (hsp70) extend to the apoptotic mode of cell death, we transfected Jurkat T cells with the gene for the human hsp70 and challenged the cells with an anti-Fas mAb or with two different murine anti-CD3 mAbs. The anti-Fas mAb-triggered apoptotic cell death and the anti-CD3 mAb-mediated activation-induced cell death were significantly enhanced in the gene-transfected Jurkat cells overexpressing hsp70 compared with the unmanipulated and the vector-transfected cells. On the other hand, the well-established protective effect that this protein offers to the cells was unaffected, as determined by enhanced viability of gene-transfected cells exposed to a lethal heat shock. To investigate the mechanisms that are responsible for the increased susceptibility of the gene-transfected cells to apoptotic death, we studied the TCR/CD3-initiated events that showed a significant down-regulation of the protein tyrosine phosphorylation levels and the cytoplasmic free Ca2+ responses. As for the Fas/Apo-1/CD95-mediated early events, the activity of protein serine/threonine phosphatases was markedly increased in the cells overexpressing hsp70. Our study demonstrates that hsp70 overexpression offers thermoprotection but enhances TCR/CD3- and the Fas-induced apoptotic cell death. This phenomenon is associated with a down-regulation of the Ag receptor-initiated early signal transduction pathways and with an up-regulation of Fas-mediated early metabolic events.

Overexpression of the heat shock protein 70 enhances the TCR/CD3- and Fas/Apo-1/CD95-mediated apoptotic cell death in Jurkat T cells

To investigate whether the protective effects of the 70-kDa heat shock protein (hsp70) extend to the apoptotic mode of cell death, we transfected Jurkat T cells with the gene for the human hsp70 and challenged the cells with an anti-Fas mAb or with two different murine anti-CD3 mAbs. The anti-Fas mAb-triggered apoptotic cell death and the anti-CD3 mAb-mediated activation-induced cell death were significantly enhanced in the gene-transfected Jurkat cells overexpressing hsp70 compared with the unmanipulated and the vector-transfected cells. On the other hand, the well-established protective effect that this protein offers to the cells was unaffected, as determined by enhanced viability of gene-transfected cells exposed to a lethal heat shock. To investigate the mechanisms that are responsible for the increased susceptibility of the gene-transfected cells to apoptotic death, we studied the TCR/CD3-initiated events that showed a significant down-regulation of the protein tyrosine phosphorylation levels and the cytoplasmic free Ca2+ responses. As for the Fas/Apo-1/CD95-mediated early events, the activity of protein serine/threonine phosphatases was markedly increased in the cells overexpressing hsp70. Our study demonstrates that hsp70 overexpression offers thermoprotection but enhances TCR/CD3- and the Fas-induced apoptotic cell death. This phenomenon is associated with a down-regulation of the Ag receptor-initiated early signal transduction pathways and with an up-regulation of Fas-mediated early metabolic events.

Heat shock gene-expression in HSP-70 and HSF1 gene-transfected human epidermoid A-431 cells

Thermotolerant cells display attenuated heat shock protein 70 kD (HSP-70) gene expression and signal transduction such as intracellular Ca2+ concentration and inositol trisphosphate in response to sublethal heat. To further investigate the regulation of heat shock gene expression, we developed constructs containing human HSP-70 and HSF1 genes and transfected human epidermoid A-431 cells. These cells were chosen because skin cells are especially vulnerable to heat shock and other environmental stressors. We report that A431 cells can be successfully transfected with HSP-70 and HSF1 genes as shown by the elevated levels of respective message and protein. Overexpression of HSP-70 in cells transfected with HSP-70 gene led to a down-regulation of the HSF1 gene expression. Interestingly, transfection of cells with the HSF1 gene was not associated with increased expression of HSP-70. Exposure of HSF1 gene-transfected cells to heat resulted in a transient but significant increase in HSP-70 gene expression as compared to that found in vector-transfected cells, which was completely inhibited by treatment with staurosporine. In conclusion, we have demonstrated successful transfection of human A-431 cells with HSF1 and HSP-70 genes, where the regulation of their expression can be studied.

Heat shock factor-1 protein in heat shock factor-1 gene-transfected human epidermoid A431 cells requires phosphorylation before inducing heat shock protein-70 production

Heat shock factor-1 (HSF1) is a transcriptional factor that binds to heat shock elements located on the promoter region of heat shock protein genes. The purpose of this study was to further investigate the regulation of the expression of the heat shock protein-70 (HSP-70) gene. The HSF1 gene was inserted into pCDNA3 plasmid and then transfected into human epidermoid A431 cells using the CaOP3 method. Control cells were transfected with vector alone. Expression of HSP-70, HSF1, and HSF2 genes and protein were determined. We found a significant increase in the expression of the HSF1 gene, but not HSP-70 and HSF2 genes, in the HSF1 gene-transfected cells. The amount of HSF1-heat shock element complex was significantly increased in both the nucleus and cytosol in HSF1 gene-transfected cells, indicating increased synthesis of HSF1. The amount of HSP-72 in these cells did not change. Therefore, overexpression of HSF1 protein failed to initiate transcription of the HSP-70 gene. Subsequently, we treated the cells with 1 microM PMA (a protein kinase C stimulator), and HSP-70 mRNA and protein were measured at 1 or 4 h of the treatment, respectively. The levels of both HSP-70 mRNA and HSP-72 protein were significantly increased in nontransfected and transfected cells; the levels of HSP-72 in HSF1 gene-transfected cells were greater than that found in the vector-transfected cells. The PMA-induced increase in HSP-72 protein peaked 8 h after treatment with PMA and returned to baseline levels at 72 h. This increase was blocked by a PKC inhibitor, staurosporine. After treatment with PMA, HSF1 translocated quickly from cytosol to nucleus. The results suggest that phosphorylation of newly synthesized HSF1 and possibly of other factors are necessary for the induction of HSP-72. Activation of PKC can cause phosphorylation of HSF1, which leads to an enhanced but transient increase in HSP-70 production.

Evidence for the involvement of protein kinase C isoforms in alpha-1 adrenergic activation of phospholipase A2 in FRTL-5 thyroid cells

BACKGROUND

FRTL-5 thyroid cells are a cell line extensively used for the investigation of thyroid functions. Activation of alpha-1 adrenergic receptors stimulates both arachidonic acid (AA) release and cytosolic Ca2+ increase in this cell line. Cytosolic Ca2+ and arachidonic acid are known to be important second messengers regulating a variety of thyroid functions. The generation of these messengers is regulated primarily by two different types of phospholipases, phospholipase C (PLC) and phospholipase A2 (PLA2).

METHODS

Norepinephrine (NE, 10 mumol/L) was used as an alpha-1 adrenergic activator, and cytosolic-free Ca2+ concentration ([Ca2+]i) was determined using the fluorescent dye indo-1. Arachidonic acid release was measured as an indicator of PLA2 activation, and protein kinase C (PKC) activity determination and isoforms identification were performed using commercial kits.

RESULTS

Norepinephrine increased [Ca2+]i and AA release. Prevention of NE-induced cytosolic Ca2+ influx, either by removal of extracellular Ca2+ or by use of Ca2+ channel blockers, NiCl2 or CoCl2, inhibited AA generation entirely. Inhibition of NE-induced increase in [Ca2+]i by the Ca2+ chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), also significantly suppressed NE-induced AA release. Inhibition of PKC activity by PKC inhibitors (H-7 or staurosporine) or downregulation induced by prolonged treatment with phorbol 12-myristate 13-acetate (PMA) or thyleametoxin (TX) significantly blocked the NE-induced AA release, which indicates PKC is involved in mediating NE-induced AA release. Protein kinase C activity measurement indicated that NE induced an activation of PKC in 5 minutes. To further characterize the role of PKC or Ca2+ in regulation of AA release, we identified PKC isoforms by immunoblotting with specific antibodies against 8 different Protein kinase C isoforms. PKC-alpha, -beta I, -beta II, -gamma, delta, -epsilon, -zeta, and -eta isoforms were identified. Norepinephrine induced translocation of PKC-alpha, -beta I, -beta II, -gamma, -delta, and -epsilon isoforms but not -zeta and -eta from cytosol to membrane. Chelation of intracellular Ca2+, prevention of Ca2+ influx, or prolonged treatment with thymeleatoxin (TX) completely blocked the NE-induced translocation of PKC-alpha.

CONCLUSIONS

These results, taken together with data obtained from AA experiments, suggest that PKC plays a critical role in alpha-1 adrenergic receptor mediated PLA2 activation and subsequent AA release. Extracellular Ca2+ influx is a prerequisite for both PKC-alpha translocation and AA release. Whether Ca2+ acts directly upon the PLA2, or via PKC-alpha, to regulate AA generation is an intriguing question that remains to be clarified.

Heat shock inhibits the hypoxia-induced effects on iodide uptake and signal transduction and enhances cell survival in rat thyroid FRTL-5 cells

Chronic hypoxia inhibits rat thyroid function in vivo. To determine possible mechanisms, we studied the effect of hypoxia on iodide uptake, the involvement of second messengers, and cell membrane permeability in rat thyroid FRTL-5 cells. Since sublethal heat stress protects tissues from ischemia, we also determined effects of heat stress. The initial rate of iodide uptake in untreated cells was between 12.98 and 15.28 pmol/micrograms DNA/min. Hypoxia (5% O2) increased the rate of uptake in a time-dependent manner. Heating cells at 45 degrees C for 15 min (heat shock) prior to exposure to hypoxia for 3 days inhibited the increase in the initial rate of I-uptake. Using fura-2, we found that the resting [Ca2+]i in suspended FRTL-5 cells was 65 +/- 7 nM (n = 16). [Ca2+]i was not increased in cells exposed to hypoxia for 1 day, while a 3-day exposure increased [Ca2+]i by 43 +/- 4% (p < 0.05); no additional increase occurred after 7 days of exposure. When cells were heated prior to hypoxia exposure for 3 days, the hypoxia-induced increase in [Ca2+]i did not occur. Similar observations were found with inositol trisphosphates (InsP3). Exposure of cells to hypoxia for 3 days increased InsP3 from 0.08 +/- 0.02 (n = 5) to 0.32 +/- 0.04% total cpm (n = 5, p < 0.05), but sublethal heating of cells prior to hypoxia exposure prevented the increase. Three-day hypoxia increased PKC activity in the membrane fraction (from 67 +/- 7 to 86 +/- 4% of total activity, p < 0.05), and heat shock inhibited these changes also. Immunoblots showed that hypoxia treatment alone and heat shock plus hypoxia resulted in the translocation of PKC-alpha, -delta, -epsilon, and -zeta isoforms, whereas heat shock alone translocated only PKC-beta I, -beta II, and -zeta. Cell membrane integrity was assayed by trypan blue exclusion. Hypoxia alone for 3 days did not affect membrane permeability, but only 49 +/- 3% of cells excluded trypan blue when a 3-day hypoxia exposure was followed by a 6 h reoxygenation. Heat shock prior to hypoxia and reoxygenation protected cell membrane function. Heat shock also induced heat shock protein 70 kDa (HSP-70) synthesis at the transcriptional level. Results suggest that heat shock protects FRTL-5 cells from hypoxic injury, perhaps by inhibiting the initial rate of iodide uptake and second messengers. It is likely that HSP-70 plays an essential role in the process of protection.

Characterization of intracellular calcium pools and their desensitization in thermotolerant human A-431 cells

BACKGROUND

This study characterizes the intracellular Ca2+ pools in nonthermotolerant and thermotolerant human A-431 cells and the reduced cytotoxicity using the inhibitors of Ca2+ mobilizations.

METHODS

Nonthermotolerant and thermotolerant cells were treated with different Ca2+ mobilizers in the absence of external Ca2+. The cytosolic Ca2+ concentration using fura-2 fluorescence probe was measured to identify the presence of intracellular Ca2+ pools. The cytotoxicity of the increase in [Ca2+]i was studied using the colony forming efficiency assay.

RESULTS

The resting intracellular Ca2+ concentration ([Ca2+]i) in the absence of extracellular Ca2+ was 42 +/- 9 nm, determined by fura-2. Bradykinin (10 mumol/L), monensin (200 mumol/L), and ionomycin (1 mumol/L) sequentially treated to cells mobilized Ca2+ and increased [Ca2+]i by 64 +/- 23, 40 +/- 6, and 59 +/- 21 nm, respectively. The bradykinin effect was blocked by 5 mumol/L U-73122 (an inhibitor of inositol trisphosphate production); the ionomycin effect was inhibited by increasing intracellular pH (pHi) or treatment with 100 mumol/L ryanodine while the monensin effect was enhanced by increasing pHi, but was not inhibited by ryanodine. Cells that were made tolerant to lethal temperatures also responded to bradykinin, monensin, and ionomycin, but the magnitude of the response was diminished. Subsequent treatments with bradykinin, monensin, and ionomycin increased [Ca2+]i in thermotolerant cells to levels 68 +/- 8, 44 +/- 5, and 45 +/- 5%, respectively, of values found in nonthermotolerant cells. Higher concentrations of these agents did not further increase [Ca2+]i. The bradykinin-induced increase in inositol trisphosphates in thermotolerant cells was also reduced, which perhaps accounts for the attenuation in Ca2+ mobilization. Unlike nonthermotolerant cells, the monensin effect was not enhanced when pHi was increased. However, the ionomycin effect was still dependent on pHi and was blocked by ryanodine at a higher concentration.

CONCLUSIONS

These results show that there are bradykinin-, monensin-, and ryanodine-sensitive pools and that thermotolerance attenuates Ca2+ mobilization stimulated by these three agents. Ionomycin at 10 mumol/L or NaCN at 10 mM for 1 hour demonstrated cytotoxicity. Pretreatment with 100 mumol/L ryanodine and/or 5 mumol/L U-73122 reduced cytotoxicity produced by either NaCN or ionomycin. These results suggest that an attenuation of [Ca2+]i increases can diminish cytotoxicity.

Rapid assay of HSF1 and HSF2 gene expression by RT-PCR

Primers were developed to allow the rapid and reliable assay of heat shock transcriptional factors 1 and 2 in human epidermoid A431 cells by following the protocol described in this study. Using the primers, the heat-induced increase in heat shock transcriptional factor 1 but not 2 was observed. This is the first report to show that heat shock increases the mRNA amount of HSF1 with no changes in HSF2 mRNA.

Increases in HSF1 translocation and synthesis in human epidermoid A-431 cells: role of protein kinase C and [Ca2+]i

BACKGROUND

It is known that heat shock increases both heat shock protein 70 kd (HSP-70) mRNA synthesis, and intracellular cytosolic free calcium concentration ([Ca2+]i). The latter enhances the heat inducible form of HSP-70 production by increasing the complex formation between heat shock transcriptional factor (HSF) and heat shock elements (HSE). In this study, we investigated the effect of agonists (PMA; ionomycin) and antagonists (BAPTA; staurosporine) of protein kinase C (PKC), and calcium channel on translocation and synthesis of HSF1, and activation of HSP-70 gene in human epidermoid A-431 cells.

METHODS

Cells were incubated with poly 12-myristate 13-acetate (PMA) or ionomycin at different concentrations for various periods of time. Messenger RNAs of HSF and HSP-70 were measured with RT-PCR. The HSP-70 protein was determined with Western blots, and HSF protein was measured by gel mobility retardation assay.

RESULTS

Significant increases in HSF binding to [32P]labeled HSE were found at 30 minutes in nuclear extract and at 4 hours in both nuclear and cytosol extracts. The PMA- and ionomycin-induced increases in HSF were in a concentration-dependent manner with a maximal increase at 10(-6) mol/L of each drug. Meanwhile, the mRNAs encoded for HSF1 and HSP-70, but not HSF2, were significantly increased and reached the maximum at 1 hour after the treatment. The PMA increased [Ca2+]i by 92% because of Ca2+ influx. The increases in mRNA of HSF1 and HSP-70 induced by treatment with 1 mumol/L PMA were completely blocked by preincubating cells with either 2 mumol/L staurosporine in the presence of extracellular Ca2+ or 100 mumol/L BAPTA-am in absence of extracellular Ca2+. Like PMA, the increases induced by ionomycin were also inhibited by 100 mumol/L BAPTA-am in absence of extracellular Ca2+. Furthermore, Western blots show that 1 mumol/L PMA or ionomycin induced maximal increase in HSP-70 after 7 hours of continuous incubation with either agent. When cells were simultaneously treated with 1 mumol/L PMA and ionomycin together for 1 hour, the increase in HSP-70 and HSF1 mRNAs reached a greater level than the level stimulated by either drug alone.

CONCLUSIONS

These results indicate that both PMA and ionomycin stimulate HSF1, but not HSF2, translocation and synthesis leading to the HSP-70 expression and that their effects are Ca(2+)-dependent.

Thermotolerance attenuates heat-induced increases in [Ca2+]i and HSP-72 synthesis but not heat-induced intracellular acidification in human A-431 cells

BACKGROUND

Thermotolerance affects cell viability, retards translation of heat shock proteins, and protects RNA slicing mechanisms. We reported previously that heat shocking nonthermotolerant cells causes an intracellular acidification and an increase in cytosolic free Ca2+ ([Ca2+]i) in addition to an induction of heat shock protein 72kDa (HSP-72) production. This study characterized heat-induced changes in cytosolic Ca2+, H+, and HSP-72 synthesis in thermotolerant A-431 cells.

METHODS

We studied heat-induced changes in pH(i), [Ca2+]i, and HSP-72 using thermotolerant A-431 cell monolayers. pH(i) and [Ca2+]i were determined using fluorescence probes, and HSP-72 was measured by SDS-PAGE. The mRNA encoding HSP-72 was measured by Northern blots probed with a [32P]-labeled 2.3 kb fragment of an HSP-70 cDNA insert.

RESULTS

Heat shocking thermotolerant cells induced the same degree of intracellular acidification as that induced in nonthermotolerant cells, but the heat-induced increase in [Ca2+]i was less in thermotolerant cells. This diminished response was characterized by an increase in Km for external Ca2+ and was blocked by pretreatment with cycloheximide, indicating a newly synthesized protein is involved. Similar to what was seen in nonthermotolerant cells, the heat-induced increase in [Ca2+]i in thermotolerant cells depended on external Na+ concentration and was blocked by dichlorobenzamil, though thermotolerant cells were more sensitive to the inhibitor (IC50 = 0.21 mumol/L for nonthermotolerant, 0.025 mumol/Lm for thermotolerant). Thermotolerant cells contained high resting levels of HSP-72. Heat shocking these cells attenuated the HSF translocation from cytosol to nucleus and did not induce a further synthesis of HSP-72 mRNA and protein.

CONCLUSIONS

The results suggest that thermotolerance desensitizes the machinery required for Ca2+ entry. Low [Ca2+]i levels probably result in diminished HSP-72 mRNA production and less HSP-72 synthesis.

Mystixin-7 and mystixin-11 increase cytosolic free Ca2+ and inositol trisphosphates in human A-431 cells

Mystixin-7 and mystixin-11, small peptides structurally related to corticotropin-releasing factor (CRF), have been shown to attenuate vascular leakage in injured skin. The goal of this study was to characterize changes in cytosolic Ca2+ concentration ([Ca2+]i) in human epidermoid A-431 cells treated with these two peptides and to investigate the mechanisms by which these changes occurred. The resting [Ca2+]i in A-431 cells at 37 degrees C was 76 +/- 2 nM (n = 373). When cells were treated with either peptide, [Ca2+]i increased immediately. The increase depended on the peptide concentration, with a median effective concentration of 299 +/- 9 pM for mystixin-7 and 2.23 +/- 0.04 pM for mystixin-11. The increases also depended on extracellular Ca2+ and were blocked by Cd2+, Co2+, verapamil, and nifedipine. alpha-Helical CRF-(9-41), a synthetic CRF receptor antagonist, and pertussis toxin also blocked the increase in [Ca2+]i induced by the two peptides. Taken together, these results suggest that mystixin-7 and mystixin-11 interact with CRF receptors to activate pertussis-sensitive G proteins coupled to L-type Ca2+ channels that allow an uptake of extracellular Ca2+. Because U-73122, an inhibitor of 1,4,5-inositol trisphosphate production, partially inhibited the increase in [Ca2+]i, we measured inositol trisphosphates in cells stimulated by the two peptides. Both increased inositol trisphosphate levels within 1 min. The increase was inhibited by the removal of extracellular Ca2+ or treatment with U-73122. The results suggest that the Ca2+ influx stimulated by mystixin-7 and mystixin-11 induces an increase in inositol trisphosphates, resulting in a mobilization of Ca2+ from 1,4,5-inositol trisphosphate-sensitive Ca2+ pools.

Opioid-induced increase in [Ca2+]i in ND8-47 neuroblastoma x dorsal root ganglion hybrid cells is mediated through G protein-coupled delta-opioid receptors and desensitized by chronic exposure to opioid

delta-Receptor agonists induce a concentration-dependent increase in intracellular calcium concentration ([Ca2+]i) in ND8-47 cells by activating dihydropyridine-sensitive Ca2+ channels. The role of G proteins in transducing the opioid effect has been studied. Pretreatment of cells with pertussis toxin (100 ng/ml, 24 h) almost completely blocked [D-Ser2,Leu5]enkephalin-Thr (DSLET)-induced increase in [Ca2+]i. Cholera toxin (10 nM, 24 h) had no effect on DSLET-induced response. Pretreatment of the cells with 1 microM DSLET for 1 h resulted in a 30% inhibition of DSLET-induced increase in [Ca2+]i and a 78% inhibition after exposure for 24 h. After 1 h of exposure to DSLET, there was a decrease in agonist affinity with no significant changes in receptor density. Cells exposed to 1 microM DSLET for 24 h demonstrate a nearly 90% decrease in [3H]diprenorphine binding, with a decrease in affinity for agonist at the remaining binding sites. G protein subunits alpha i2, alpha i3, alpha s, and alpha q were detected in ND8-47 cell membranes by western blot; alpha o and alpha i1 were not present. Chronic DSLET treatment had no significant effect on the quantity of each of the alpha-subunits. These results suggest that the DSLET-induced increase in [Ca2+]i mediated through pertussis toxin-sensitive G proteins (probably Gi2 or Gi3) and the attenuation of this response in chronically treated cells is associated with a relatively rapid reduction in receptor affinity to DSLET and a slow reduction in receptor density.

Antisense oligodeoxynucleotide to the Gi2 protein alpha subunit sequence inhibits an opioid-induced increase in the intracellular free calcium concentration in ND8-47 neuroblastoma x dorsal root ganglion hybrid cells

In ND8-47 cells, a neuroblastoma x dorsal root ganglion hybrid cell line, activation of delta-opioid receptors induced an increase in the intracellular free calcium concentration ([Ca2+]i) through dihydropyridine-sensitive calcium channels. This effect was mediated by pertussis toxin-sensitive G proteins. The G protein alpha subunits alpha i2, alpha i3, alpha q, and alpha s were detected using Western blots, whereas alpha o and alpha i1 were not found in ND8-47 cell membranes. To identify the specific G protein alpha subunit(s) responsible for the increase in [Ca2+]i, we treated ND8-47 cells with antisense oligodeoxynucleotides (AS) complementary to the mRNA for each G protein alpha subunit (alpha i2, alpha i3, or alpha s), at a concentration of 10 microM, for up to 6 days and examined their effects on opioid-induced increases in [Ca2+]i and on the levels of G protein alpha subunits. [Ca2+]i was measured in adherent cells using the fluorescent dye fura-2. Treatment of cells with alpha i2-AS (10 microM, for 6 days) resulted in a 73% inhibition of the [D-Ser2,Leu5]-enkephalin-Thr-induced increase in [Ca2+]i. In contrast, pretreatment of cells with alpha i3-AS (10 microM, for 6 days) or alpha s-AS (10 microM, for 6 days) had no effect on the [D-Ser2,Leu5]-enkephalin-Thr-induced responses. Western blots indicated that the levels of alpha i2 were decreased when cells were exposed to alpha i2-AS (10 microM) for 6 days, whereas the levels of alpha i3, alpha s, and alpha q were not affected by this treatment. Treatment of the cells with alpha i3-AS or alpha s-AS for 6 days significantly reduced alpha i3 or alpha s levels, respectively. These results indicate that the opioid-induced increase in [Ca2+]i in ND8-47 cells is mediated by G alpha i2.

Identification of protein kinase C and its multiple isoforms in FRTL-5 thyroid cells

Protein kinase C (PKC) has been implicated as an important regulator of signal transduction in the FRTL-5 thyroid cell line, but little is known about its isoforms in this cell line. In the present investigation, we characterized the activation of PKC by measuring the enzyme activity and identifying its isoforms in both cytosol and membrane fractions. Phorbol 12-myristate 13-acetate (PMA) was used as a PKC activator in this study. PKC activity assay revealed that PMA (300 nM) induced a rapid translocation from cytosol to membrane within 1 min and led to an almost complete translocation within 15 min. Multiple PKC isoforms were examined by Western blot analysis with specific antibodies against alpha, beta, gamma, delta, epsilon, and zeta isoforms. PKC alpha, delta, epsilon, and zeta were identified in this cell line, but PKC beta and gamma were not. Exposure of the cells to PMA (300 nM) for 5 to 30 min led to the translocation of PKC alpha, delta, and epsilon from the cytosol to the membrane fraction, while PKC zeta was not affected. Treatment with PMA (300 nM) for 24 h resulted in the down-regulation of PKC alpha, delta, and epsilon, but not PKC zeta. This study demonstrates for the first time direct evidence for the activation of PKC, and expression and distribution of its isoforms in FRTL-5 thyroid cells.

The estrogen-inducible transferrin receptor-like membrane glycoprotein is related to stress-regulated proteins

It was previously shown that estrogen induces a membrane glycoprotein (molecular mass, 95 kDa) in the chicken oviducts, which exhibits several properties similar to transferrin receptors (Poola, I., and Lucas, J. J. (1988) J. Biol. Chem. 263, 19137-19146). In the present study, we have further investigated its molecular and transferrin binding properties. We have sequenced several internal peptides isolated from the purified protein by endopeptidase Lys-C. We have found that it has a high degree of sequence homologies with those of chicken heat-shock protein (cHsp108), mouse endoplasmic reticulum protein (mERp99), hamster glucose-regulated protein (hagrp94), and human tumor rejection antigen (hTRAgp96), all of which are shown to be highly homologous to each other and to yeast hsp90. We demonstrate here that the [35S]methionine-labeled immunoaffinity-purified estrogen-inducible membrane glycoprotein binds to the transferrin affinity columns similar to iron-modulated transferrin receptors. Indirect immunofluorescence microscopic studies indicate that it is an intracellular glycoprotein unlike transferrin receptors. We have isolated two molecular forms of the protein, with molecular masses of 116 and 104 kDa, by immunoaffinity column purification, immunoprecipitation, Western blotting, and pulse-chase labeling analyses. Both 116-and 104-kDa species bind transferrin. This protein can be induced by heat-shocking the oviduct cells at 45 degrees C for 3h and recovering at 37 degrees C for 2-3 h. It is also expressed in the human breast cancer cell lines, MCF-7 and T-47D. All these properties taken together strongly suggest that the estrogen-inducible membrane glycoprotein is a novel transferrin-binding protein, structurally related to the stress-regulated proteins.

A phospholipase C inhibitor, U-73122, blocks TSH-induced inositol trisphosphate production, Ca2+ increase and arachidonic acid release in FRTL-5 thyroid cells

To characterize the role of phospholipase C (PLC)-mediated intrathyroid signal transduction by thyrotropin, we studied the effect of U-73122, an aminosteroid inhibitor of PLC-dependent activity, on TSH-activated PLC-Ca2+ and arachidonic acid (AA) signalling systems in cultured FRTL-5 rat thyroid cells. In the presence of extracellular Ca2+, TSH (0.1 microM) increased intracellular free calcium concentration ([Ca2+]i) by 63 +/- 6% with a sustained plateau phase, and AA release by 160 +/- 16%. By deletion of extracellular Ca2+, TSH induced a similar maximal [Ca2+]i increase, but the plateau phase and AA release were entirely suppressed. U-73122 (5 microM) inhibited TSH stimulation of 3H-labelled inositol trisphosphates (IP3) production by 73 +/- 3% (P < 0.01) in one study, and completely in another. U-73122 concentration-dependently blocked the TSH-induced Ca2+ increase in either the presence or absence of external Ca2+. U-73122 also showed a similar concentration-response inhibition of TSH-induced AA release. These results provide direct evidence of PLC mediation of TSH-stimulated signal transduction in FRTL-5 thyroid cells. TSH-induced external Ca2+ entry, as well as intracellular Ca2+ mobilization, is probably a PLC-mediated process. From an IP3-sensitive intracellular pool, TSH induces intracellular Ca2+ mobilization. External Ca2+ entry seems to be a prerequisite for TSH-induced AA release. U-73122 inhibition of both cytosolic Ca2+ increase and AA release further confirms [Ca2+]i dependence for TSH stimulation of AA release.

Sodium cyanide increases cytosolic free calcium: evidence for activation of the reversed mode of the Na+/Ca2+ exchanger and Ca2+ mobilization from inositol trisphosphate-insensitive pools

This study characterized the cytosolic free Ca2+ concentration ([Ca2+]i) in NaCN-treated human A-431 cells. The resting [Ca2+]i was 85 +/- 8 nM (n = 141) in untreated cells at 37 degrees C, determined with the fura-2 fluorescence probe. When cells were treated with NaCN, [Ca2+]i increased in a time- and NaCN concentration-dependent manner. When cells were exposed to 10 mM NaCN for 10 min, [Ca2+]i increased 278 +/- 28% (n = 5) but returned to normal within 45 min after treatment. The [Ca2+]i increase depended on the presence of external Ca2+. La3+ and Cd2+, but not verapamil or nifedipine, inhibited the NaCN-induced [Ca2+]i increase. The NaCN-induced [Ca2+]i increase also depended on external Na+ (K1/2 = 85 mM). The intracellular Na+ concentration, measured with the fluorescence probe SBFI, increased 267 +/- 16% after NaCN treatment. The NaCN-induced [Ca2+]i increase was modulated by treatment with ouabain or veratridine and was completely blocked by tetrodotoxin, amiloride (K1/2 = 5.4 microM), and dichlorobenzamil (K1/2 = 0.28 microM). These results suggest NaCN activates the Na+/Ca2+ exchange system. TMB-8 and ryanodine both partially blocked the increase in [Ca2+]i in the presence of external Ca2+, indicating that Ca2+ release from intracellular pools also occurred after the initial Ca2+ influx. NaCN decreased inositol trisphosphates production. U-73122, bradykinin, or monensin did not prevent the NaCN-induced increase in [Ca2+]i. However, the magnitude of the [Ca2+]i increase caused by NaCN was abolished in ionomycin-treated the [Ca2+]i increase caused by NaCN was abolished in ionomycin-treated cells, indicating that intracellular Ca2+ release induced by NaCN is derived from an ionomycin-sensitive Ca2+ pool. The results suggest that NaCN initially increased Na+ influx, which activated the reverse mode of a Na+/Ca2+ exchanger, leading to an increase in Ca2+ influx. The Ca2+ influx induced a Ca2+ mobilization from only an ionomycin-sensitive intracellular Ca2+ pool containing ryanodine receptors.

Opioids acting through delta receptors elicit a transient increase in the intracellular free calcium concentration in dorsal root ganglion-neuroblastoma hybrid ND8-47 cells

The neuronal cell line ND8-47 (neuroblastoma x dorsal root ganglion neuron hybrid) expressed opioid delta-type receptors. We report opioid-induced changes in cytosolic intracellular free calcium ([Ca++]i) in differentiated ND8-47 cells. Delta-opioid receptor agonists induced a transient (< 2 min) increase in [Ca++]i in a concentration-dependent fashion with the potency order: [D-Ser2,Leu5]enkephalin-Thr (DSLET) > or = deltorphin II > [D-Pen2,5] enkephalin. Their effects were blocked by naloxone (IC50 = 20 nM) and naltrindole (IC50 = 2.5 nM). Selective mu and kappa receptor agonists had no effect on [Ca++]i. The subtype specific delta receptor antagonists, 7-benzylidene naltrexone (delta-1) and naltriben (delta-2), were used to characterize further the subtype of delta receptors mediated by this response. Naltriben was more potent than 7-benzylidene naltrexone in antagonizing the DSLET-induced increase in [Ca++]i. The increase in [Ca++]i induced by DSLET was blocked by nifedipine (1 microM) or verapamil (1 microM), and was not observed in the absence of external calcium. Changes in [Ca++]i also were measured in single ND8-47 cells. The percentage of cells responding to DSLET (1 microM), deltorphin-II (1 microM) and [D-Pen2,5]enkephalin (1 microM) were 86, 84 and 37%, respectively. The results suggest that an increase in [Ca++]i induced by opioids is mediated through opioid delta receptors which can activate dihydropyridine-sensitive Ca++ channels.

HSP-72 synthesis is promoted by increase in [Ca2+]i or activation of G proteins but not pHi or cAMP

The family of 70-kDa heat-shock proteins (HSP-70) is evolutionarily highly conserved and has been shown to enhance cell survival from thermal injury. This study characterized HSP-72 induction in human epidermoid A-431 cells exposed to 45 degrees C for 10 min and determined the relationship between HSP-72, intracellular pH (pHi), adenosine 3',5'-cyclic monophosphate (cAMP), G proteins, and intracellular cytosolic free Ca2+ concentration ([Ca2+]i). Heat shock induced HSP-72 production, which was dependent on both temperature and the duration of heating. This HSP-72 induction was confirmed by Western blot analysis. HSP-72 levels in cells that had been heated then returned to 37 degrees C were elevated at 2 h (1.5 +/- 0.1 x control), reached a maximum at 8 h (2.7 +/- 0.1 x control), and remained above baseline for up to 4 days. Levels of HSP-72 mRNA, determined by dot-blot analysis, reached a maximum at 2 h and returned to baseline within 8 h. Both actinomycin D and cycloheximide blocked HSP-72 induction. Because heating causes intracellular acidification and increases in cAMP and [Ca2+]i, we studied the effect of pHi, cellular cAMP, and [Ca2+]i on HSP-72 induction. The reduction of pHi to 6.9 by acid loading did not affect the basal level of HSP-72 in unheated cells. Treatment with pertussis toxin, cholera toxin, or forskolin, but not 8-bromo-cAMP, 3-isobutyl-1-methylxanthine, or N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide potentiated heat-induced HSP-72 production. Inhibition of the heat-induced increase in [Ca2+]i attenuated, but failed to completely block, heat-induced HSP-72 production, mRNA synthesis, and the heat-shock transcriptional factor-heat-shock element binding complex formation, which suggests there are Ca(2+)-dependent and -independent processes involved in HSP-72 synthesis. Our results show that an increase in [Ca2+]i or activation of G proteins, but not pHi and cAMP, enhances HSP-72 induction.

Corticotropin-releasing factor increases [Ca2+]i via receptor-mediated Ca2+ channels in human epidermoid A-431 cells

Corticotropin-releasing factor (CRF) has been shown to attenuate vascular leakage in injured skin, mucous membrane, muscle, and brain. Calcium is thought to play an important role in many of the physiological responses to CRF, but there has been little characterization of how calcium is involved in process by which CRF protects damaged tissues. The goal of this study was to characterize changes in cytosolic free calcium concentrations ([Ca2+]i) in human epidermoid A-431 cells exposed to human/rat-CRF and to investigate the mechanisms by which these changes occur. The resting [Ca2+]i in normal cells at 37 degrees C was 66 +/- 4 nM (n = 32). When cells were treated with CRF, [Ca2+]i increased immediately. The increase depended on CRF concentration, with a median effective concentration of 11 pM. This increase in [Ca2+]i depended on external Ca2+ but not Na+, Mg2+, or K+. La3+ (10 microM) and Co2+ (10 microM) inhibited the CRF-induced [Ca2+]i increase, whereas verapamil and nifedipine tested at concentrations up to 1 mM did not. alpha-Helical CRF-(9-41), a synthetic CRF receptor antagonist, and pertussis toxin blocked the increase in [Ca2+]i induced by CRF, which suggests that the entry of extracellular Ca2+ is mediated by receptor-operated Ca2+ channels coupled with pertussis toxin-sensitive G proteins. Although 420 pM CRF stimulated an immediate increase in [Ca2+]i, inositol trisphosphate and cellular cAMP levels did not change within 1 min either in the presence or absence of external Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Purinergic (P2) receptor-operated calcium entry into rat thyroid cells

In the epithelial cell line FRT, derived from rat thyroid, extracellular ATP, at a concentration as low as 1 x 10(-7) M, specifically increases cytosolic Ca++ two fold over the basal level of 255 +/- 45 nM. A maximum increase of 5 fold over basal is seen at 1 x 10(-5) M ATP. The effect occurs in the absence of any measurable phosphatidyl inositol metabolism and requires the presence of extracellular Ca++, but is independent of extracellular Na+; it is duplicated by ATP gamma S but not by adenosine, AMP, ADP, AMP-PNP, AMP-CPP, or AMP-PCP. In the presence of the P2-receptor antagonist suramin, the ATP induced Ca++ influx is completely inhibited, whereas Mg++, La , and verapamil are ineffective. It appears that the most likely (and unique) mechanism of ATP induced increase of cytosolic Ca++ in FRT cells in an increased influx through the activation of a P2 receptor operated Ca++ channel.

Effect of heat shock, [Ca2+]i, and cAMP on inositol trisphosphate in human epidermoid A-431 cells

The basal levels of inositol monophosphate, inositol bisphosphate, and inositol trisphosphate (InsP3) in A-431 cells incubated in Na(+)-Hanks' solution were, respectively, 1.23 +/- 0.18, 0.17 +/- 0.03, and 0.69 +/- 0.07% of the total radioactivity in the cell. When cells were heated, InsP3 increased in a temperature-dependent manner related to the duration of heating. The active form of InsP3, inositol 1,4,5-trisphosphate, increased 237 +/- 17% after heating (45 degrees C, 20 min) then returned to baseline within 15 min after the return to 37 degrees C. The heat-induced increase in InsP3 was not observed in the absence of extracellular Ca2+ or with amiloride treatment. Treatment with the nonhydrolyzable GTP analogue 5'-guanylylimidodiphosphate stimulated that component of the InsP3 increase due to G proteins. U-73122, an inhibitor of phospholipase C-mediated processes, blocked the increase in InsP3 resulting from heat exposure. Both pertussis toxin (30 ng/ml, 24 h), an inhibitor of G inhibitory protein, and cholera toxin (1 microgram/ml, 1 h), a stimulator of G stimulatory protein, increased InsP3 in unheated cells, and heating failed to induce a further increase, suggesting that heat activates G proteins. Likewise, 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP), 3-isobutyl-1-methylxanthine, Ro 20-1724, or forskolin increased InsP3 in unheated cells, and heat did not cause an additional increase. The InsP3 increase induced by 8-BrcAMP was inhibited by removal of extracellular Ca2+ or treatment with verapamil, suggesting that an influx of extracellular Ca2+ stimulates InsP3 production.(ABSTRACT TRUNCATED AT 250 WORDS)

U-73122, an aminosteroid phospholipase C antagonist, noncompetitively inhibits thyrotropin-releasing hormone effects in GH3 rat pituitary cells

TRH increases cytosolic-free calcium ([Ca2+]i) by activating phospholipase C(PL-C), which induces phosphoinositol hydrolysis, leading to Ca2+ mobilization from inositol trisphosphate (IP3) sensitive stores, and by increasing Ca2+ influx. Increases in [Ca2+]i stimulate PRL secretion. We investigated the effects of U-73122, an aminosteroid inhibitor of PL-C dependent processes, on TRH-stimulated second messenger pathways and on PRL secretion in GH3 rat pituitary cells. [Ca2+]i was monitored by Indo-1 fluorescence, and IP3 and metabolites separated on ion exchange columns. In Ca(2+)-free buffer, [Ca2+]i was 96 +/- 6 nM and increased to 323 +/- 23 nM (P less than 0.001) after TRH (100 nM). U-73122 dose dependently inhibited the TRH effect (IC50 = 967 nM; complete inhibition at 3-5 microM). Subsequent addition of monensin (100 microM) increased [Ca2+]i from 107 +/- 4 to 142 +/- 4 nM (P < 0.001), confirming our previous findings of a non-TRH regulated Ca2+ pool in GH3 cells. Pretreatment (15 sec) with U-73122 partly inhibited the TRH effect on [Ca2+]i; complete suppression occurred with 70 sec of pretreatment. An inactive analog (U-73343) had no inhibitory effect at 5 microM. U-73122 acted noncompetitively, as the mean maximum velocity (expressed as percent increase in [Ca2+]i after TRH) was reduced from 225 to 91 while the Michaelis-Menten constant for TRH was unchanged (15.4 vs. 13.8 nM, n = 3). Of note, U-73122, at 3-5 microM, increased basal [Ca2+]i from 109 +/- 5 to 120 +/- 5 nM (P less than 0.001). In 1.3 mM Ca2+ buffer containing nifedipine (1 microM) and verapamil (50 microM), similar effects of U-73122 (5 microM) were observed on basal and TRH-stimulated [Ca2+]i. IP3, IP2, and IP1 increased to 241 +/- 12%, 148 +/- 23%, and 167 +/- 39% of control, 30 sec after TRH (100 nM); these responses were prevented by 1 microM U-73122. At 5 microM, U-73122 also significantly increased IP3 levels. TRH (100 nM) increased 4-h PRL secretion from 16.3 +/- 1.4 to 27.6 +/- 3.2 ng/well (P less than 0.05). U-73122 (5 microM) increased basal PRL secretion to 35.9 +/- 3.2 ng/well (P less than 0.05), but abolished the TRH effect. In contrast, U-73343 (with Ca2+ channel blockers) did not inhibit the TRH effect on PRL (control: 24.3 +/- 2.1; TRH: 51.0 +/- 6.3 ng/well).(ABSTRACT TRUNCATED AT 400 WORDS)

Heat shock increases cytosolic free Ca2+ concentration via Na(+)-Ca2+ exchange in human epidermoid A 431 cells

This study characterized cytosolic free Ca2+ concentration ([Ca2+]i) in normal and thermally injured human epidermoid A 431 cells. The resting [Ca2+]i in normal cells at 37 degrees C was 87 +/- 5 nM (n = 105). When cells were subjected to hyperthermia (40-50 degrees C), [Ca2+]i increased in a temperature- and time-dependent manner. The maximal increase in cells exposed to 45 degrees C was observed at 20 min; [Ca2+]i returned to normal within 1 h. The heat-induced [Ca2+]i increase depended on the presence of external Ca2+. La3+ and Cd2+ but not Co2+, verapamil, or nifedipine attenuated the heat-induced [Ca2+]i increase. TMB-8 partially blocked the increase in [Ca2+]i but pertussis toxin and cholera toxin pretreatment did not. The magnitude of the heat-induced [Ca2+]i increase or 45Ca2+ uptake depended on the presence of extracellular Na+. Heat treatment reduced the apparent Michaelis constant for external Ca2+ from 490 +/- 91 to 210 +/- 60 microM, whereas the maximal velocity remained the same. The intracellular Na+ concentration decreased 62.5% after heating. The heat-induced [Ca2+]i increase was completely blocked by amiloride (5 microM) and 5'-(N,N-dimethyl)-amiloride (1 microM). These results suggest heat activates the Na(+)-Ca2+ exchange system so as to increase [Ca2+]i and reduce [Na+]i.

Na+-H+ antiport and monensin effects on cytosolic pH and iodide transport in FRTL-5 rat thyroid cells

Na+-H+ exchange may proceed via an endogenous antiporter or by exposure to the Na+ ionophore monensin. We investigated the characteristics of Na+-H+ exchange induced by antiporter stimulation and by monensin in FRTL-5 rat thyroid cells. We also examined the effects of intracellular pH (pHi) changes on iodide uptake and efflux. pHi was determined using 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. The resting pHi was 7.33 +/- 0.02 units; this level correlated directly with extracellular pH. In acid-loaded cells, Km for external Na+ activation of the antiporter was 7.1 mM and maximum velocity was 0.3801 delta pH units/min. Dimethylamiloride was 42 times more potent than amiloride in inhibiting sodium-dependent recovery in acidified cells. Metabolic inhibition reduced the initial alkalinization rate. Monensin increased pHi, and this response was dependent on extracellular Na+ and HCO3- but not on antiporter function. Low-dose monensin (1 microM) and 1 mM NH4Cl enhanced 125I uptake. High-dose monensin (100 microM), but not NH4Cl, reduced iodide uptake. Neither NH4Cl nor monensin altered 125I efflux. Thus FRTL-5 cells possess an amiloride-sensitive Na+-H+ exchanger, which is not essential for maintaining basal pHi but is affected by ATP depletion. Monensin also alkalinizes these cells but independently of the antiporter. Iodide uptake, but not efflux, is affected by changes in intracellular Na+ and H+ levels.

Pharmacological characterization of endothelin-stimulated phosphoinositide breakdown and cytosolic free Ca2+ rise in rat C6 glioma cells

Because increasing evidence indicates that glial cells are a target of endothelin, we have characterized endothelin-induced phosphoinositide (PI) turnover and Ca2+ homeostasis in C6 glioma cells. Endothelin-1 (ET) increased formation of 3H-inositol phosphate (IP) from PI and elicited an increase in cytosolic free Ca2+ ([Ca2+]i) in rat C6 glioma. In the presence of Li+, the increase in 3H-inositol trisphosphate formation was rapid, reaching its peak at 5 min after stimulation. ET also elicited a rapid and sustained increase in [Ca2+]i in a dose-dependent manner (1-100 nM). The rank orders of efficacy for ET-related peptides in increasing [Ca2+]i were ET = ET-2 greater than sarafotoxin greater than ET-3. Both ET-mediated stimulation of IP formation and [Ca2+]i increase were largely inhibited in the absence of external Ca2+ but unaffected by the depletion of external Na+ and the presence of dihydropyridine derivatives or verapamil. Inorganic Ca2+ channel blockers Cd2+, La3+, and Mn2+ at 1 mM inhibited both responses induced by ET. Cross-desensitization and nonadditivity were observed for both events among ET-related peptides tested, but not between ET and ATP. Pretreatment of cells with pertussis toxin (PTX) attenuated the PI response to ET, but had no effect on ET-elicited [Ca2+]i increase. ET-induced Ca2+ mobilization (measured in Ca(2+)-free medium) was only transient and was inhibited by 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate. Moreover, the intracellular Ca2+ pools mobilized by ET and ATP appeared to overlap, as indicated by their partial heterologous desensitization.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of intracellular pH on cytosolic free [Ca2+] in human epidermoid A-431 cells

This study characterizes the correlation between intracellular pH (pHi) and the cytosolic free Ca2+ concentration ([Ca2+]i) in suspended and adherent human epidermoid A-431 cells. Using the fluorescent dyes 2,7-bis(carboxyethyl)carboxyfluorescein acetoxymethyl ester (BCECF) and fura-2, the resting pHi and [Ca2+]i in suspended cells were 7.23 +/- 0.03 and 209 +/- 30 nM; those in adherent cells were 7.28 +/- 0.02 and 87 +/- 5 nM. Removal of external Ca2+ did not change the resting pHi but reduced the resting [Ca2+]i, indicating the resting level of [Ca2+]i is in part maintained by an influx of Ca2+ from the external medium. When both suspended and adherent cells were acidified or alkalinized, resting [Ca2+]i was altered. An intracellular acidification induced a fall in [Ca2+]i, and a rise in pHi induced a rise in [Ca2+]i. These changes in [Ca2+]i were correlated with an uptake of 45Ca2+ from the external medium, whereas no Ca2+ efflux occurred. The alteration in [Ca2+]i induced by modification of pHi was abolished in the absence of external Ca2+ or by adding 2 mM CoCl2, LaCl3, and attenuated by the addition of 2 mM MnCl2 to the bathing medium. It was insensitive to the voltage-gated Ca2+ channel blockers nifedipine or verapamil (1 mM). CoCl2, LaCl3, and MnCl2 each induced changes in pHi and [Ca2+]i but verapamil and nifedipine did not. Because CoCl2, LaCl3, and MnCl2 are also known to block Na+/Ca2+ exchange, intracellular Na+ ([Na+]i) was measured by flame photometry in acidified or alkalinized cells. In either case no change in [Na+]i was observed. Furthermore, treatment with amiloride (100 microM), a blocker of the Na+/Ca2+ exchanger, did not inhibit the pH-induced changes in [Ca2+]i. 1,2-bis(o-Aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) (100 microM), a Ca2+ chelator, induced a decrease in pHi as well as a reduction of [Ca2+]i, also supporting the direct relation between pHi and [Ca2+]i. 3,4,5-Trimethoxybenzoic acid 8-(diethylamino)ocytl ester HCl (TMB-8) (100 microM), a known blocker of intracellular Ca2+ mobilization, did not change the resting pHi and [Ca2+]i in normal cells or cells acidified or alkalinized. This observation, taken together with data from cells incubated in the absence of external Ca2+, suggests intracellular Ca2+ pools are not involved in changes in [Ca2+]i that result from a modification of pHi. Resting pHi and [Ca2+]i in cells treated with either 8-bromo-dibutyryl cAMP (1 mM) or forskolin (150 microM) are not changed.(ABSTRACT TRUNCATED AT 400 WORDS)

Heat treatment induces an increase in intracellular cyclic AMP content in human epidermoid A-431 cells

The basal level of intracellular cyclic AMP (cAMPi) in A-431 cells incubated at 37 degrees C in Na(+)-containing Hanks solution is 2086 +/- 139 fmol/10(6) cells. When cells are exposed to 45 degrees C for 10 min, cAMPi increases by 40 +/- 4%, and then returns to basal levels within 30 min. Incubating cells in Ca(2+)-free or Mg(2+)-free Hanks solution has no effect on the heat-induced increase in cAMPi, but the increase is inhibited by acid-loading cells to intracellular pH 7.0 or 6.8. In unheated cells, cAMPi increases by 16 +/- 8%, 53 +/- 7%, or 39 +/- 8%, when incubated with isobutyl-1-methylxanthine (1 mM), Ro 20-1724 (0.5 mM), or theophylline (1 mM) respectively. However, heat treatment further elevates cAMPi in cells treated with phosphodiesterase inhibitors, indicating that heat treatment and phosphodiesterase inhibitors elevate cAMPi by a different pathway(s). Heat treatment increases adenylate cyclase activity 2.5-fold. When forskolin (150 microM), an adenylate cyclase stimulator, is applied to cells, the basal cAMPi increases 28 +/- 6-fold compared with controls. Subsequent heating of these cells lowers cAMPi levels to 7.0 +/- 0.5 times that in control cells. This decrease is prevented by pretreatment with pertussis toxin (30 ng/ml, 24 h), suggesting that G-proteins are involved in the process of heat-induced cAMPi increase. 2-Deoxy-D-glucose (10 mM), NaN3 (10 mM) and 2,4-dinitrophenol (1 mM) also increase cAMPi in A-431 cells. However, application of these metabolic inhibitors to cells before heat treatment does not result in cAMPi levels greater than that observed in cells with heat alone. Similar observations are obtained in heat-treated cells previously exposed to adenosine, but not to AMP or ADP. These data are the first to suggest that thermally induced increase in cAMPi is due to a combination of activation of adenylate cyclase and G-proteins, and an increase in adenosine owing to ATP breakdown caused by hyperthermia.

Heat induces intracellular acidification in human A-431 cells: role of Na(+)-H+ exchange and metabolism

The resting intracellular pH (pHi) of A-431 cells at 37 degrees C in Na+ Hanks' solution is 7.23 +/- 0.02. In the presence of amiloride (100 microM) pHi decreases to 7.08 +/- 0.03. Hyperthermia induces a temperature- and time-dependent intracellular acidification of 0.2 pH units in either bicarbonate-free or bicarbonate-buffered solutions. After heat treatment (45 degrees C, 10 min) pHi returns to normal 1 h after incubation at 37 degrees C. The activity of the Na(+)-H+ exchanger was examined in heated and unheated cells in the absence of bicarbonate. Unheated cells recover from an acid load in a [Na+]o-dependent and amiloride-sensitive manner. The apparent Michaelis constant for extracellular Na+ is 38 +/- 9 mM, and the apparent mean affinity constant for amiloride is 11 +/- 3 microM. In heated cells the apparent affinity of the Na(+)-H+ exchanger for extracellular Na+ is not changed, but the maximal recovery rate is approximately 40% slower than that of unheated cells. The rate of recovery from acid loading returns to normal 2 h after heat treatment. [Na+]i and intrinsic buffering power in heated cells are the same as those in unheated cells. Decreases in both intracellular ATP and lactic acid are observed in heated cells. 2-Deoxy-D-glucose and sodium azide induce an intracellular acidification but prevent most of the acidification induced by heat. Heat treatment causes no further acidification in cells that are acidified by both amiloride and 2-deoxy-D-glucose together. These data are the first to suggest that thermally induced intracellular acidification is due to both an inhibition of Na(+)-H+ exchange and an inhibition of metabolic pathways.

Decreased inflammatory responsiveness of hypophysectomized rats to heat is reversed by a corticotropin-releasing factor (CRF) antagonist

Hypophysectomy, but not adrenalectomy, decreased (relative to sham-operated controls) the swelling and Evans blue dye extravasation responses of the anesthetized rat's pawskin to thermal injury. alpha-Helical CRF (9-41), a synthetic competitive antagonist of corticotropin-releasing factor (CRF) on isolated pituitary cells, did not affect in sham-operated rats the swelling response after immersion of the paw in 58 degrees C water for 30 s. Swelling was measured over a 1 h period using the fluid displacement method for quantifying paw volume. But, when alpha-helical CRF (9-41) was injected 92 micrograms/kg i.v. 10 min before or immediately after heat exposure, it both attenuated and reversed the insensitive state produced by hypophysectomy: that is, the swelling response reappeared. Under the same test conditions, naloxone hydrochloride, an opioid antagonist, was ineffective. The results suggest that hypophysectomy may induce a condition whereby endogenous CRF or CRF-like peptides may act as an anti-inflammatory agent.

Peptides of the corticoliberin superfamily attenuate thermal and neurogenic inflammation in rat pawskin

The paws of pentobarbital-anesthetized rats were immersed in 48 or 58 degree C water for 5 min and the thermal inflammatory response to heat was measured by Evans blue dye leakage into the pawskin. Sauvagine, sucker fish urotensin I and human/rat corticotropin-releasing factor (CRF), homologous peptides belonging to the corticoliberin superfamily, injected i.v. 10 min before heat exposure, inhibited dye leakage with ED50 (nmol/kg) of 0.44, 1.5 and 5.9, respectively. The same rank order of potency was observed when the peptides were tested against the protein extravasation evoked by antidromic stimulation of the rat saphenous nerve. The alpha-helical CRF-(-9-41) antagonist, administered alone at 24 nmol/kg i.v., did not affect the heat-induced dye leakage into skin; but it attenuated the effects of h/rCRF, urotensin I and sauvagine. h/r[Tyr0]CRF, ovine[Nle21,Tyr32]CRF and h/r[Met(O)21,38]CRF, administered 24 nmol/kg i.v., did not affect the dye leakage response to heat. Peptides of the corticoliberin superfamily may have the unusual property of making small blood vessels less permeable when responding to injurious stimuli.

Corticotropin-releasing factor inhibits thermal injury

Thermal injury to the skin increases transfer of plasma fluids and proteins into the interstitium. Here, protein extravasation and edema were produced by immersion of the anesthetized rat's paw in 48 degrees C or 58 degrees C water for 5 min. Protein extravasation was measured by Evans blue dye leakage into the skin and edema by increases in skin weights. Corticotropin-releasing factor (CRF), having the human/rat 41-amino acid sequence, was efficacious in reducing these indices of thermal injury. Injected i.v. at microgram doses or intradermally at nanogram doses, it inhibited the protein extravasation and edema produced by heat. The intradermal median inhibitory dose (ED50) of CRF against protein extravasation elicited by 48 degrees C water was 21.8 times lower than the i.v. ED50, indicating that CRF's actions occurred locally in the paw skin. Ovine-CRF and dynorphin A(1-13) injected i.v. inhibited the protein extravasation and edema induced by 58 degrees C water, but morphine, ethylketocyclazocine and FK 33,824 (a stabilized enkephalin analog) were not active at this temperature. CRF may be a powerful inhibitor of the acute inflammatory response of the skin to thermal irritation.

Inhibition of protein exudation from the trachea by corticotropin-releasing factor

Increased vascular permeability in the trachea, as measured by Evans blue dye leakage, was produced in the anesthetized rat by antidromic stimulation of the right vagus or by exposure to dilute formalin vapors. Corticotropin-releasing factor (CRF) inhibited tracheal protein extravasation at dosages of 6-24 nmol (29-114 micrograms)/kg i.v. injected 10 min before nerve stimulation or formaldehyde exposure. The decrease in respiration rate and blood pressure produced by formaldehyde was also attenuated by CRF.

Corticotropin-releasing factor inhibits neurogenic plasma extravasation in the rat paw

Increased exudation of plasma proteins, as measured by Evans blue leakage into the innervated paw, was produced by antidromic stimulation of the saphenous nerve in the pentobarbital-anesthetized rat. This condition, termed neurogenic plasma extravasation (NPE), was inhibited by morphine, FK 33,824 (a stabilized enkephalin analog), dynorphin (1-13), dynorphin(1-10)amide and corticotropin-releasing factor (CRF) at median effective doses of 2700, 0.45, 1180, 4050 and 5.6 nmol/kg i.v., respectively. The inhibitory effect of CRF was present when injected up to 60 min before electrical stimulation of the nerve. By contrast, the effects of morphine and FK 33,824 were shorter in duration, lasting for only 20 to 30 min before nerve stimulation. Inhibition of NPE by morphine, FK 33,824 dynorphin (1-13) and dynorphin (1-10)amide was blocked by naloxone, 1 mg/kg i.v., but the CRF inhibition was not affected. CRF inhibited NPE in both hypophysectomized and adrenalectomized rats, indicating that its effects were not due to secondary release of endogenous opioid peptides. The inhibitory effect of CRF on NPE was also separable from its hypotensive properties and could be obtained at intradermal doses of CRF into the paw skin which were approximately 11 times lower than the i.v. doses. Intracerebroventricular injection of CRF did not affect the tail-flick latency of rats to warm water. CRF administered i.v. in mice did, however, inhibit writhing responses to phenylbenzoquinone (PBQ), suggesting possible peripheral antinociceptive properties.