Zinc deficiency induces apoptosis via mitochondrial p53- and caspase-dependent pathways in human neuronal precursor cells

Previous studies have shown that zinc deficiency leads to apoptosis of
neuronal precursor cells in vivo and in vitro. In addition to the role of
p53 as a nuclear transcription factor in zinc deficient cultured human
neuronal precursors (NT-2), we have now identified the translocation of
phosphorylated p53 to the mitochondria and p53-dependent increases in the
pro-apoptotic mitochondrial protein BAX leading to a loss of mitochondrial
membrane potential as demonstrated by a 25% decrease in JC-1 red:green
fluorescence ratio. Disruption of mitochondrial membrane integrity was
accompanied by efflux of the apoptosis inducing factor (AIF) from the
mitochondria and translocation to the nucleus with a significant increase
in reactive oxygen species (ROS) after 24 h of zinc deficiency.
Measurement of caspase cleavage, mRNA, and treatment with caspase
inhibitors revealed the involvement of caspases 2, 3, 6, and 7 in zinc
deficiency-mediated apoptosis. Down-stream targets of caspase activation,
including the nuclear structure protein lamin and polyADP ribose
polymerase (PARP), which participates in DNA repair, were also cleaved.
Transfection with a dominant-negative p53 construct and use of the p53
inhibitor, pifithrin␮, established that these alterations were largely
dependent on p53. Together these data identify a cascade of events
involving mitochondrial p53 as well as p53-dependent caspase-mediated
mechanisms leading to apoptosis during zinc deficiency.