Signal transduction of thapsigargin-induced apoptosis in osteoblast

The toxicity of thapsigargin, a selective inhibitor of endoplasmic reticula r Ca2+-ATPase, was investigated in osteoblasts. We induced apoptosis in mur ine osteoblastic MC3T3E1 cells by exposure to the thapsigargin. Thapsigargi n transiently increased the phosphotransferase activity of c-Jun N-terminal kinases1 (JNK1), which might in turn activate transcriptional activity of activation protein-1 (AP-1). Wt? then prepared extracts from thapsigargin-t reated MC3T3E1 cells and monitored cleavage of acetyl-YVAD-AMC and acetyl-D EVD-AMC, fluorogenic substrates for caspase 1-like and caspase 3-like prote ases, respectively. Thapsigargin significantly increased the proteolytic ac tivity of caspase 3-like proteases, but not the activity of caspase 1-like proteases. Furthermore, thapsigargin increased the transcriptional activity of nuclear factor-kappa B (NF-kappa B), These data suggest that thapsigarg in-induced apoptosis in osteoblasts may be via activation of JNK1, caspase 3-like family proteases, and transcriptional factors including AP-1 and NF- kappa B. (C) 1999 by Elsevier Science Inc. All rights reserved.