ROLE OF EGR-1 IN THAPSIGARGIN-INDUCIBLE APOPTOSIS IN THE MELANOMA CELL-LINE A375-C6

Induction of apoptosis by diverse exogenous signals is dependent on el evation of intracellular Ca2+. This process of cell death can be block ed by actinomycin D, indicating that it requires gene transcription ev ents. To identify genes that are required for apoptosis, we used thaps igargin (TG), which inhibits endoplasmic reticulum-dependent Ca2+-ATPa se and thereby increases cytosolic Ca2+. Exposure to TG led to inducti on of the zinc finger transcription factor, EGR-1, and apoptosis in hu man melanoma cells, A375-C6. To determine the functional relevance of EGR-1 expression in TG-inducible apoptosis, we employed a dominant neg ative mutant which functionally competes with EGR-1 in these cells. In terestingly, the dominant negative mutant inhibited TG-inducible apopt osis. Consistent with this observation, an antisense oligomer directed against Egr-1 also led to a diminution of the number of cells that un dergo TG-inducible apoptosis. These results suggest a novel regulatory role for EGR-1 in mediating apoptosis that is induced by intracellula r Ca2+ elevation. We have previously shown that in these melanoma cell s, EGR-1 acts to inhibit the growth arresting action of interleukin-1. Together, these results imply that EGR-1 plays inducer-specific roles in growth control.