Figure 3

Modulation of cellular calcium homeostasis by LMP-1 protein expression. LMP-1 expression in BJAB-tTA-LMP1 cells was induced by tetracycline withdrawal, and resting cytosolic calcium concentration, as well as thapsigargin-induced calcium release from the endoplasmic reticulum were measured. Panel A: The increase of the resting cytosolic calcium concentration in BJAB-tTA-LMP-1 cells during LMP-1 induction. Panels B and C: Calcium release from thapsigargin-sensitive intracellular pools in the presence (Panel B), and in the absence (Panel C) of inhibition of PMCA and Na⁺/Ca²⁺ exchanger activity. Black curves: non-induced cells, grey curves: cells at day 5 of LMP-1 induction. Panel D: The magnitude of calcium release from non-induced cells (black column) and in cells at day 5 of LMP-1 induction (grey column), expressed as area under curve (AUC) values of measurements presented in Panel B. LMP-1 induction leads to enhanced calcium release from the endoplasmic reticulum by thapsigargin indicating increased calcium sequestration.