The purpose of this study was to evaluate the extent of constitutive activity among orphan class-A G protein coupled receptors within the cAMP signaling pathway. Constitutive signaling was revealed by changes in gene expression under control of the cAMP response element. Gene expression was measured in Chinese hamster ovary cells transiently co-transfected with plasmids containing a luciferase reporter and orphan receptor. Criteria adopted for defining constitutive activation were: 1) 200% elevation over baseline reporter gene expression; 2) 40% inhibition of baseline expression; and 3) 40% inhibition of expression stimulated by 3 μM forskolin. Five patterns of activity were noted: 1) inhibition under both baseline and forskolin stimulated expression (GPR15, GPR17, GPR18, GPR20, GPR25, GPR27, GPR31, GPR32, GPR45, GPR57, GPR68, GPR83, GPR84, GPR132, GPR150, GPR176); 2) no effect on baseline expression, but inhibition of forskolin stimulated expression (GPR4, GPR26, GPR61, GPR62, GPR78, GPR101, GPR119); 3) elevation of baseline signaling coupled with inhibition of forskolin stimulated expression (GPR6, GPR12); 4) elevation of baseline signaling without inhibition of forskolin stimulated expression (GPR3, GPR21, GPR52, GPR65); and 5) no effect on expression (GPR1, GPR19, GPR22, GPR34, GPR35, GPR39, GPR63, GPR82, GPR85, GPR87). Constitutive activity was observed in 75% of the orphan class-A receptors examined (30 of 40). This constitutive signaling cannot be explained by simple overexpression of the receptor. Inhibition of cAMP mediated expression was far more common (65%) than stimulation of expression (15%). Orphan receptors that were closely related based on amino acid homology tended to have similar effects on gene expression. These results suggest that identification of inverse agonists may be a fruitful approach for categorizing these orphan receptors and targeting them for pharmacological intervention.

Lysyl oxidase (LOX) and LOX-like (LOXL) proteins are copperdependent metalloenzymes with well-documented roles in tumor metastasis and fibrotic diseases. The mechanism by which copper is delivered to these enzymes is poorly understood. In this study, we demonstrate that the copper transporter ATP7A is necessary for the activity of LOX and LOXL enzymes. Silencing of ATP7A inhibited LOX activity in the 4T1 mammary carcinoma cell line, resulting in a loss of LOX-dependent mechanisms of metastasis, including the phosphorylation of focal adhesion kinase and myeloid cell recruitment to the lungs, in an orthotopic mouse model of breast cancer. ATP7A silencing was also found to attenuate LOX activity and metastasis of Lewis lung carcinoma cells in mice. Metaanalysis of breast cancer patients found that high ATP7A expression was significantly correlated with reduced survival. Taken together, these results identify ATP7A as a therapeutic target for blocking LOX-and LOXL-dependent malignancies.breast cancer | lung cancer | copper | lysyl oxidase | metastasis

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Background: While doxorubicin (DOX) is widely used in cancer chemotherapy, long-term severe cardiotoxicity limits its use. This is the first report of the chemoprotective efficacy of a relatively new thiol antioxidant, N-acetylcysteine amide (NACA), on DOX-induced cell death in cardiomyocytes. We hypothesized that NACA would protect H9c2 cardiomyocytes from DOXinduced toxicity by reducing oxidative stress. Accordingly, we determined the ability of NACA to mitigate the cytotoxicity of DOX in H9c2 cells and correlated these effects with the production of indicators of oxidative stress.

BackgroundOxidative stress increases the cytosolic content of calcium in the cytoplasm through a combination of effects on calcium pumps, exchangers, channels and binding proteins. In this study, oxidative stress was produced by exposure to tert-butyl hydroperoxide (tBHP); cell viability was assessed using a dye reduction assay; receptor binding was characterized using [3H]N-methylscopolamine ([3H]MS); and cytosolic and luminal endoplasmic reticulum (ER) calcium concentrations ([Ca2+]i and [Ca2+]L, respectively) were measured by fluorescent imaging.ResultsActivation of M3 muscarinic receptors induced a biphasic increase in [Ca2+]i: an initial, inositol trisphosphate (IP3)-mediated release of Ca2+ from endoplasmic reticulum (ER) stores followed by a sustained phase of Ca2+ entry (i.e., store-operated calcium entry; SOCE). Under non-cytotoxic conditions, tBHP increased resting [Ca2+]i; a 90 minute exposure to tBHP (0.5-10 mM ) increased [Ca2+]i from 26 to up to 127 nM and decreased [Ca2+]L by 55%. The initial response to 10 μM carbamylcholine was depressed by tBHP in the absence, but not the presence, of extracellular calcium. SOCE, however, was depressed in both the presence and absence of extracellular calcium. Acute exposure to tBHP did not block calcium influx through open SOCE channels. Activation of SOCE following thapsigargin-induced depletion of ER calcium was depressed by tBHP exposure. In calcium-free media, tBHP depressed both SOCE and the extent of thapsigargin-induced release of Ca2+ from the ER. M3 receptor binding parameters (ligand affinity, guanine nucleotide sensitivity, allosteric modulation) were not affected by exposure to tBHP.ConclusionsOxidative stress induced by tBHP affected several aspects of M3 receptor signaling pathway in CHO cells, including resting [Ca2+]i, [Ca2+]L, IP3 receptor mediated release of calcium from the ER, and calcium entry through the SOCE. tBHP had little effect on M3 receptor binding or G protein coupling. Thus, oxidative stress affects multiple aspects of calcium homeostasis and calcium dependent signaling.