Quercetin and gossypin inhibit the Plasma Membrane Ca2+-ATPase by different mechanisms

ONTIVEROS M.; GENTILE, L.; RINALDI, D.; MANGIALAVORI, I.; MARDER, M.; ROSSI, JP; FERREIRA-GOMES, M.

San Miguel de Tucumán

Congreso; III Latin American Federation of Biophysical Societies (LAFeBS)-IX IberoAmerican Congress of Biophysics-XLV Reunion Anual SAB 2016; 2016

A large number of flavonoids, mostly O-glycosides, are found in foods of plant origin. These compounds are believed to have cancer chemoprotective properties by triggering apoptosis through an increase of cytosolic concentration of calcium ([Ca2+]c). The increase of [Ca2+]c could be due to the fact that some flavonoids inhibit specific Ca2+ removing systems, as the sarcoplasmic/endoplasmic reticulum Ca2+ ATPase and the plasma membrane calcium ATPase (PMCA) [1, 2].From a screening of Hibiscus flavonoids, quercetin and gossypin emerged as the most active compounds as PMCA inhibitors. The aim of this work was to characterize the effect of these flavonoids on PMCA. We measured the Ca2+-ATPase activity in purified PMCA obtained from human erythrocytes and the [Ca2+]c in HEK293T cells. Results using purified PMCA showed that (1) PMCA activity was inhibited by quercetin and gossypin with a K0.5 of 0.34 ± 0.01 and 5.1 ± 1.0 µM, respectively; (2) the inhibition was noncompetitive with Ca2+; (3) both quercetin as gossypin affected CaM activation, but quercetin produced a decrease in the apparent affinity for CaM while gossypin did not; (4) quercetin led to the increase of phosphoenzyme level (EP) although gossypin induced a decrease. EP formed in the presence of quercetin was dephosphorylated by ADP, suggesting that it could stabilize the E1P intermediate. These results suggest that gossypin could affect the binding of ATP while quercetin could prevent the conformational change E1P → E2P.In HEK293T cells quercetin and gossypin lowered the Ca2+ removal rate by PMCA compared to the control.These results show that quercetin and gossypin inhibit PMCA by different mechanisms, changing the cellular calcium homeostasis possibly due to their different molecular structures.With grants of CONICET, ANPCYT and UBACYT[1] Ogunbayo et al. (2008) IUBMB Life. 60, 853-858[2] Rinaldi et al. Latin American Crosstalk in Biophysics and Physiology. SBF.Uy