B. Van De Water et al., Distinct endoplasmic reticulum signaling pathways regulate apoptotic and necrotic cell death following iodoacetamide treatment, CHEM RES T, 12(10), 1999, pp. 943-951
Environmental stress induces the synthesis of glucose-regulated proteins (G
rps) in the endoplasmic reticulum (ER) and heat shock proteins (Hsps) in th
e cytoplasm. Iodoacetamide (IDAM), a prototypical alkyating agent, induces
both Grp and Hsp synthesis in renal epithelial cells and causes necrosis wh
ich is prevented by prior activation of the ER stress response (pre-ER stre
ss) [Liu, H., et al. (1997) J. Biol. Chem. 272, 21751-21759]. In this study
, we examined the biochemical pathways leading to IDAM-induced apoptosis an
d investigated the role of the ER stress response in apoptotic cell death.
The antioxidant N,N'-diphenyl-p-phenylenediamine (DPPD) prevented necrosis
after IDAM treatment, but the cells went on to die with hallmarks of apopto
sis, i.e., cell detachment, caspase-3 activation, cleavage of poly(ADP-ribo
se)polymerase (PARP), and DNA-ladder formation, all of which were blocked b
y the general caspase inhibitor zVAD. As with IDAM-induced necrosis, dithio
threitol protected against apoptosis, but cell permeable calcium chelators
did not, suggesting that distinct biochemical pathways mediate these two fo
rms of cell death. Pre-ER stress, but not heat shock, prevented IDAM-induce
d apoptosis. pkASgrp78 cells are deficient in Grp78 induction due to expres
sion of a grp78 antisense RNA and are more sensitive to necrosis. However,
these cells were resistant to IDAM-induced apoptosis and had increased basa
l levels of Grp94 and a KDEL-containing protein of about 50 kDa. Thus, the
expression of grp78 antisense perturbs ER functions and activates expressio
n of other ER stress genes accounting for the resistance to apoptosis. Take
n together, the data describe functionally distinct signaling pathways thro
ugh which the ER regulates apoptosis and necrosis caused by chemical toxica
nts.