Effect of epigallocatechin-3-gallate on calcium homeostasis through inhibition of the plasma membrane Ca2+-ATPase

RINALDI, D. E.; ONTIVEROS, M. Q.; MANGIALAVORI, I. C.; ROSSI, R. C.; ROSSI, J. P. F. C.; FERREIRA GOMES, M. S.

Congreso; Reunión Conjunta de Sociedades de Biociencias; 2017

Catechins are polyphenols that exhibit beneficial properties for health, such as, antioxidant, anticancer, cardioprotective, neuroprotective and vasorelaxant properties. Epigallocatechin-3-gallate (EGCG), which is the major polyphenol component of green tea, is believed to be the main responsible for many of such properties. Different studies have shown that EGCG produces alterations in intracellular Ca2+ homeostasis, which could be linked to alterations in the function of the mitochondria, different types of Ca2+ channels and calcium pumps, including the Plasma Membrane Ca2+-ATPase (PMCA). PMCA transports Ca2+ actively to the extracellular medium coupled to the ATP hydrolysis maintaining a very low concentration of intracellular Ca2+. The purpose of this work is to investigate the effect of EGCG on the PMCA and its relationship with the calcium homeostasis. We evaluated the effect of EGCG on the ATPase activity of PMCA purified from human red blood cells. EGCG showed a strong inhibition with an apparent affinity of 30 nM by increasing the phosphorylated intermediate which was found to be ADP sensitive. This suggests that EGCG stabilizes the E1P intermediate on the reaction cycle of hydrolysis of ATP by PMCA. In addition, while EGCG did not modify significantly the value of K0.5 for Ca2+, it increased the apparent affinity for Mg2+. In order to assess whether this inhibition may be of physiological relevance, we characterized this effect in the context of a living cell by monitoring in real time the changes in the cytosolic calcium levels. We tested the influence of EGCG on the activity of the PMCA transiently expressed in human embryonic kidney (HEK293) cells. We found that EGCG produced an increase of the cytoplasmic basal Ca2+ concentration and decreased the rate of removal of Ca2+ suggesting that PMCA activity was inhibited. These results suggest that inhibition of the PMCA by EGCG can explain the observed effects on intracellular Ca2+ levels.