Changes in c-Jun but not Bcl-2 family proteins in p53-dependent apoptosis of mouse cerebellar granule neurons induced by DNA damaging agent bleomycin.

Tumor suppressor gene p53 is a critical regulator of the cellular response to DNA damage. To examine the function of p53 in postmitotic CNS neurons, we cultured cerebellar granule cells from 15-day-old wild type and p53-deficient mice, and analyzed changes of protein expression in apoptosis elicited by DNA damage. When cerebellar granule cells from wild type mice were treated with bleomycin, a DNA strand-break inducing agent, neuronal death occurred. In contrast, cells from p53-deficient mice were resistant to bleomycin-induced neuronal death. Furthermore, cells from p53 heterozygous mice showed an intermediate resistance between wild type and p53-deficient mice. These results show that p53 is required for the bleomycin-induced cerebellar granule cell death. To examine which proteins are involved in this apoptosis, we examined changes in protein levels of the Bcl-2 family, including Bcl-2, Bcl-X and Bax. The relative amounts of these proteins did not change after bleomycin treatment, suggesting that the changes in the levels of these Bcl-2 family proteins are not necessary for apoptosis in this system. In contrast, the levels of c-Jun protein significantly increased 6 h after treatment with bleomycin in wild type but not in p53-deficient cerebellar granule cells. These results raise the possibility that c-Jun is required for p53-dependent neuronal apoptosis induced by bleomycin.