Ca(+) mishandling due to impaired activity of cardiac sarco(endo)plasmic reticulum Ca(2+) ATPase (SERCA2a) has been associated with the development of left ventricular diastolic dysfunction in insulin-resistant cardiomyopathy. However, the molecular causes underlying SERCA2a alterations induced by insulin resistance and related metabolic disorders, such as metabolic syndrome (MetS), are not completely understood. In this study, we used a sucrose-fed rat model of MetS to test the hypothesis that decreased SERCA2a activity is mediated by elevated oxidative stress produced in the MetS heart. Production of ROS and cytosolic Ca(2+) concentration were recorded in left ventricular myocytes using confocal imaging. The level of SERCA2a oxidation was determined in left ventricular homogenates by biotinylated iodoacetamide labeling. Compared with control rats, sucrose-fed rats exhibited several characteristics of MetS, including central obesity, insulin resistance, hyperinsulinemia, and hypertriglyceridemia. Moreover, relative to myocytes from control rats, myocytes from MetS rats exhibited elevated basal production of ROS accompanied by slowed cytosolic Ca(2+) removal, reflected by prolonged Ca(2+) transients. The slowed cytosolic Ca(2+) removal was associated with a significant decrease in SERCA2a-mediated Ca(2+) reuptake and increased SERCA2a oxidation. Importantly, myocytes from MetS rats treated with the antioxidant N-acetylcysteine showed normal ROS levels and SERCA2a-mediated Ca(2+) reuptake as well as accelerated cytosolic Ca(2+) removal. These data suggest that elevated oxidative stress may induce oxidative modifications on SERCA2a leading to abnormal function of this protein in the MetS heart.

Breast cancer is the most frequent malignancy affecting women worldwide. It has been suggested that infection by Epstein Barr Virus (EBV), Mouse Mammary Tumor Virus or a similar virus, MMTV-like virus (MMTV-LV), play a role in the etiology of the disease. However, studies looking at the presence of these viruses in breast cancer have produced conflicting results, and this possible association remains controversial. Here, we used polymerase chain reaction assay to screen specific sequences of EBV and MMTV-LV in 86 tumor and 65 adjacent tissues from Mexican women with breast cancer. Neither tumor samples nor adjacent tissue were positive for either virus in a first round PCR and only 4 tumor samples were EBV positive by a more sensitive nested PCR. Considering the study's statistical power, these results do not support the involvement of EBV and MMTV-LV in the etiology of breast cancer.

IGF-I induces alpha(1B)-adrenoceptor (alpha(1B)-AR) phosphorylation. The effect of IGF-I was rapid and transient, reaching near-maximal values at 10 min and decreasing after 30 min; it was observed at low IGF-I concentrations (EC(50) approximately 10 ng/ml) and was associated to receptor desensitization as evidenced by a decreased alpha(1B)-adrenergic effect on intracellular calcium and production of inositol phosphates. The effect of IGF-I was markedly decreased in cells treated with pertussis toxin suggesting involvement of pertussis toxin-sensitive G proteins. Transfection of the carboxyl terminus of the beta-adrenergic receptor kinase or the Deltap85 mutant of phosphoinositide 3-kinase (PI3K) markedly decreased the alpha(1B)-AR phosphorylation induced by IGF-I without decreasing the receptor phosphorylation induced by noradrenaline. Inhibitors of PI3K and protein kinase C blocked IGF-I-induced alpha(1B)-AR phosphorylation. In addition, it was observed that AG1478, an inhibitor of the epidermal growth factor (EGF) receptor kinase, and BB-94, a metalloproteinase inhibitor, also diminished IGF-I-induced adrenoceptor phosphorylation. The data clearly show that IGF-I triggers a complex signaling pathway, which leads to the phosphorylation and desensitization of a serpentine G protein-coupled receptor, suggesting the following hypothetical model: 1) stimulation of IGF-I receptors activate pertussis toxin-sensitive G proteins; 2) the growth factor action activates metalloproteinases, which catalyze heparin binding-EGF shedding, and transactivation of EGF receptors, and 3) dissociated Gbetagamma subunits and phosphotyrosine residues seem to trigger PI3K activity, which leads to activation of protein kinase C, resulting in alpha(1B)-AR phosphorylation and desensitization.

No abstract

No abstract

No abstract

Sphingosine-1-phosphate-induced α1B-adrenergic receptor desensitization and phosphorylation was studied in rat-1 fibroblasts stably expressing enhanced green fluorescent protein-tagged adrenoceptors. Sphingosine-1-phosphate induced adrenoceptor desensitization and phosphorylation through a signaling cascade that involved phosphoinositide 3-kinase and protein kinase C activities. The autocrine/paracrine role of sphingosine-1-phosphate was also studied. It was observed that activation of receptor tyrosine kinases, such as insulin growth factor-1 (IGF-I) and epidermal growth factor (EGF) receptors increased sphingosine kinase activity. Such activation and consequent production of sphingosine-1-phosphate appears to be functionally relevant in IGF-I- and EGF-induced α1B-adrenoceptor phosphorylation and desensitization as evidenced by the following facts: a) expression of a catalytically inactive (dominant-negative) mutant of sphingosine kinase 1 or b) S1P1 receptor knockdown markedly reduced this growth factor action. This action of sphingosine-1-phosphate involves EGF receptor transactivation. In addition, taking advantage of the presence of the eGFP tag in the receptor construction, we showed that S1P was capable of inducing α1B-adrenergic receptor internalization and that its autocrine/paracrine generation was relevant for internalization induced by IGF-I. Four distinct hormone receptors and two autocrine/paracrine mediators participate in IGF-I receptor- α1B-adrenergic receptor crosstalk.

No abstract