Ql. Zhao et al., Mitochondrial and intracellular free-calcium regulation of radiation-induced apoptosis in human leukemic cells, INT J RAD B, 75(4), 1999, pp. 493-504
Purpose: To investigate the mechanisms and pathways of X-ray apoptosis in M
olt-4 cells, focusing on mitochondrial and cytosolic Ca2+ ([Ca2+](i)) regul
ation.
Materials and methods: X-irradiated Molt-4 cells and cell extract (CE) were
used to analyse: (1) induced apoptosis (Giemsa stain), (2) p53, Bcl-2 and
Bar expressions (immunoblot), (3) mitochondrial potential Delta psi(m) and
(4) [Ca2+](i) (flow cytometry), (5) caspase-3 activity, and (6) roles of [C
a2+]- and caspase-3-mediated pathways by inhibiting either or both pathways
for induced apoptosis.
Results: Molt-4 cells were sensitive to apoptosis since 5 Gy induced 57 and
94% apoptosis at 6 and 24-h. After 5Gy, p53 was accumulated that upregulat
ed Bar but which repressed Bcl-2 with time, resulting in a 7-fold increase
in Bax/Bxl-2 at 6 h. Predominant Bar reduced Delta psi(m), and low-Delta ps
i(m) cells increased 45 min earlier than apoptosis after 5 Gy. Caspase-3 wa
s activated in apoptotic CE. The caspase-3 inhibitor Ac-DEVD-CHO inhibited
apoptosis and DNA-ladder formation by similar to 50%, suggesting a similar
to 50% role of caspase-3-activated DNase (CAD). [Ca2+](i) was increased aft
er 5Gy. [Ca2+](i)-chelating BAPTA-AM (5 mu M) and/or DNase gamma-inhibiting
Zn2+ (0.5 mM) inhibited similar to 50% of induced apoptosis and DNA-ladder
ing, indicating a 50% participation of Ca2+/Mg2+-dependent DNase gamma.
Conclusions: The p53-Bax-mitochondria-caspase-3-CAD pathway and the [Ca2+](
i)-mediated DNase gamma pathway were involved in the regulation of X-ray ap
optosis in sensitive Molt-4 cells.