Proteomic signatures in thapsigargin-treated hepatoma cells.

Thapsigargin, an inhibitor of the endoplasmic reticulum (ER) calcium transporters, generates Ca2+-store depletion within ER and simultaneously increases Ca2+ level in the cytosol. Perturbation of Ca2+ homeostasis leads cells to cope with stressful conditions, including ER stress, which affect folding of newly synthesized proteins and induce the accumulation of unfolded polypeptides and eventually apoptosis, via activation of the unfolded protein response pathway. In the present work, we analysed the proteome changes in human hepatoma cells following acute treatment with thapsigargin. We highlighted a peculiar pattern of protein expression, marked by altered expression of calcium-dependent proteins, and of proteins involved in secretory pathways or in cell survival. For specific deregulated proteins, the thapsigargin-induced proteomic signature was compared by western blotting to that resulting from the treatment of hepatoma cells with reducing agents or with proteasome inhibitors, to elicit endoplasmic reticulum stress by additional means, and to reveal novel, potential targets of the unfolded protein response pathway.