Evidence for involvement of Bax and p53, but not caspases, in radiation-induced cell death of cultured postnatal hippocampal neurons
✍ Scribed by Mark D. Johnson; Hong Xiang; Susan London; Yoshito Kinoshita; Michael Knudson; Marc Mayberg; Stanley J. Korsmeyer; Richard S. Morrison
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 652 KB
- Volume
- 54
- Category
- Article
- ISSN
- 0360-4012
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✦ Synopsis
Bax (a death-promoting member of the bcl-2 gene family), the tumor suppressor gene product p53, and the ICE/ced-3-related proteases (caspases) have all been implicated in programmed cell death in a wide variety of cell types. However, their roles in radiation-induced neuronal cell death are poorly understood. In order to further elucidate the molecular mechanisms underlying radiation-induced neuronal cell death, we have examined the ability of ionizing radiation to induce cell death in primary cultured hippocampal neurons obtained from wild-type, p53deficient and Bax-deficient newborn mice. Survival in neuronal cultures derived from wild-type mice decreased in a dose-dependent manner 24 hr after a single 10 Gy to 30 Gy dose of ionizing radiation. In contrast, neuronal survival in irradiated cultures derived from p53-deficient or Bax-deficient mice was equivalent to that observed in control, nonirradiated cultures. Western blot analyses indicated that neuronal p53 protein levels increased after irradiation in wild-type cells. However, Bax protein levels did not change, indicating that other mechanisms exist for regulating Bax activity. Adenovirus-mediated overexpression of p53 also caused neuronal cell death without increasing Bax protein levels. Irradiation resulted in a significant induction in caspase activity, as measured by increased cleavage of fluorogenic caspase substrates. However, specific inhibitors of caspase activity (zVAD-fmk, zDEVD-fmk and BAF) failed to protect postnatal hippocampal neurons from radiationinduced cell death. Staurosporine (a potent inducer of apoptosis in many cell types) effectively induced neuronal cell death in wild-type, p53-deficient and Bax-deficient hippocampal neurons, indicating that all were competent to undergo programmed cell death. These results demonstrate that both p53 and Bax are necessary for radiation-induced cell death in postnatal cultured hippocampal neurons. The fact that cell death occurred despite caspase inhibition suggests that radiation-induced neuronal cell death may occur in a caspase-independent manner.