THAPSIGARGIN INDUCES 78K GRP IN HUMAN TE671/RD CELLS

The effects of thapsigargin (TG) on the homeostasis of cytosolic Ca2+ and on the protein synthesis were investigated in TE671/RD (human rabdomyosarcoma) cells. TE671/RD cells exhibited a long lasting rise of cytosolic free Ca2+ concentration [Ca2+](i) after TG (100 nM) bath application. TG was more efficient as compared to acetylcholine (ACh, 10 mu M) in rising [Ca2+](i) . The overall protein synthetic activity was inhibited by TG: H-3-leucine incorporation was reduced to about 60% of control level in cells treated for 20 min with 100 nM TG, while following I hr exposure to 1 mu M TG the amount of leucine incorporated into proteins was only 28% of control. Anyway, even after a very strong treatment (1 mu M TG for 1 hr) the protein synthetic activity partially resumed when cells were allowed to recover in drug-free medium. Furthermore, TG treatment selectively induced the expression of a 78 Icd protein, identified with the 78 kd glucose - regulated protein (78K GRP). The level of induction was dose and time-dependent and maximal 78K GRP expression was obtained at TG concentration of 100 nM for 10 min.