Inhibition of Sarcoplasmic/Endoplasmic Reticulum Calcium ATPases (SERCA) by Polycyclic Aromatic Hydrocarbons in HPB-All Human T Cells and Other Tissues

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are immunosuppressive chemicals found in the environment that have been shown to disrupt intracellular Ca2+ homeostasis and Ca(2+)-dependent signaling in human and murine lymphocytes. Many PAHs produce a rapid and sustained increase in intracellular free Ca2+ in lymphocytes. The mechanism of persistent Ca2+ perturbation remains undefined. In the present studies, ATP-dependent 44Ca2+ uptake into vesicles prepared from a 15,000g supernatant of HPB-ALL human T cell lysates was significantly inhibited by 0.1, 1, and 10 microM concentrations of the immunotoxic PAHs 7,12-dimethylbenz[a]anthracene (DMBA), benzo[a]pyrene (BAP), benz[a]anthracene, and 9,10-dimethylanthracene, but not by the less immunotoxic compounds anthracene (ANT) and benzo[e]pyrene (BEP). Ca(2+)-ATPase catalytic activity was determined by quantitating hydrolysis of ATP in the presence or absence of PAHs, with known ATPase inhibitors included as controls. Formation of inorganic phosphate was significantly decreased (> 65% of control at 10 microM) by DMBA and BAP, whereas ANT and BEP caused only a slight reduction in activity (10% of control at 10 microM). Anthracene partially reversed the inhibitory effect of DMBA and BAP on ATP hydrolysis when agents were coincubated. Both DMBA and BAP, but not ANT and BEP, inhibited the activity of all known SERCA-type Ca(2+)-ATPases, while not affecting either Na+, K(+)-ATPase activity or plasma membrane Ca(2+)-ATPase activities. These results demonstrate that immunotoxic and carcinogenic polycyclic aromatic hydrocarbons have a thapsigargin-like effect in human lymphocytes and SERCA-containing tissues from various species. Inhibition of SERCA activity may play an important role in altered Ca2+ homeostasis in lymphocytes and other tissues.