Alterations in cardiac G protein-mediated signaling, most prominently G q/11 signaling, are centrally involved in hypertrophy and heart failure development. Several RGS proteins that can act as negative regulators of G protein signaling are expressed in the heart, but their functional roles are still poorly understood. RGS expression changes have been described in hypertrophic and failing hearts. In this study, we report a marked decrease in RGS2 (but not other major cardiac RGS proteins (RGS3-RGS5)) that occurs prior to hypertrophy development in different models with enhanced G q/11 signaling (transgenic expression of activated G␣ q * and pressure overload due to aortic constriction). To assess functional consequences of selective down-regulation of endogenous RGS2, we identified targeting sequences for effective RGS2 RNA interference and used lipid-based transfection to achieve uptake of fluorescently labeled RGS2 small interfering RNA in >90% of neonatal and adult ventricular myocytes. Endogenous RGS2 expression was dose-dependently suppressed (up to 90%) with no major change in RGS3-RGS5. RGS2 knockdown increased phenylephrine-and endothelin-1-induced phospholipase C stimulation in both cell types and exacerbated the hypertrophic effect (increase in cell size and radiolabeled protein) in neonatal myocytes, with no major change in G q/11 -mediated ERK1/2, p38, or JNK activation. Taken together, this study demonstrates that endogenous RGS2 exerts functionally important inhibitory restraint on G q/11 -mediated phospholipase C activation and hypertrophy in ventricular myocytes. Our findings point toward a potential pathophysiological role of loss of fine tuning due to selective RGS2 down-regulation in G q/11 -mediated remodeling. Furthermore, this study shows the feasibility of effective RNA interference in cardiomyocytes using lipid-based small interfering RNA transfection.
Repeated administration of L-asparaginase leads to the development of specific antibodies and hypersensitivity reactions. The aim of the study was to evaluate a possible cross-reaction of anti-asparaginase antibodies, developed against the native E. coli L-asparaginase (Asparaginase Medac), with other preparations of the enzyme. Sixteen patients with acute lymphoblastic leukemia, in whom in the reinduction phase of treatment hypersensitivity against L-asparaginase was observed and/or the presence of anti-asparaginase antibodies was established were recruited for the present study. Ten out of 16 tested sera showed cross-immunoreactivity to PEG-asparaginase, while no reactivity to L-asparaginase derived from Erwinia chrysantemi was observed. Since cross-reacting antibodies were also found in sera of patients with no overt allergic reaction, L: -asparaginase may undergo silent inactivation during the reinduction phase of therapy. This finding is of clinical importance with regard to appropriate dosage and necessitates careful enzyme activity monitoring in all patients undergoing repeated treatment with various L-asparaginase preparations.
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