On the mechanism of inhibition of plasma membrane calcium pump by aurintricarboxylic acid

CECILIA SOUTO GUEVARA; CAMILA BRUNO; .ROSSI, JUAN PABLO F.C.; MANGIALAVORI IRENE

Congreso; Primeras Jornadas Virtuales SAB 2020; 2020

SAB

Plasma membrane calcium ATPases (PMCAs) are high-affinity calcium pumps that extrude calcium from the cytosol to the extracellular medium. In humans, PMCAs are encoded by 4 independent genes termed PMCA1 to 4. PMCA1 and 4 are expressed ubiquitously, whereas the expression of PMCA2 and 3 is restricted to specific cells and tissues. PMCA4 regulates calcium concentration within its vicinity and modulates the activity of its interacting partners. PMCA4 is the isoform more abundant in hematopoietic tissue. PMCA4 has emerged as an important negative regulator of several pathophysiological processes that involve angiogenesis, increasing the interest on its pharmacological blockade to potentiate the efficiency of therapeutic strategies. Mohamed et al (2013)1 showed that low concentrations of aurintricarboxylic acid (ATA) strongly inhibit the calcium extrusion activity of PMCA4 in HEK cells without affecting the activity of PMCA1 or other major pumps. Recently, Kurasamy et al (2017)2 have showed that ATA inhibits PMCA4 in endothelial cells triggering a marked increase in cell motility and blood vessel formation. However, the PMCA inhibition mechanism by ATA remains unknown. The aim of this study was to characterize the effect of ATA on PMCA from human erythrocytes (ePMCA), where about 80% is PMCA4 and 20% PMCA1. Our current results show that: (1) ATA inhibited Ca2+-ATPase activity of purified ePMCA with an apparent Ki = 100 nM; (2) The value of Ki depended on Mg2+ concentration; (3) The value of Ki did not modify by ATP concentration; (4) When ePMCA is in its native membrane environment, the value of Ki increased more than twenty times. Our results suggest that ATA does not bind to the ATP binding site of ePMCA and Mg2+ is necessary to the total inhibition of Ca2+-ATPase activity.