Ionizing radiation induces neuronal differentiation of Neuro-2a cells via PI3-kinase and p53-dependent pathways.

PURPOSE

The influence of ionizing radiation (IR) on neuronal differentiation is not well defined. In this study, we investigated the effects of IR on the differentiation of Neuro-2a mouse neuroblastoma cells and the involvement of tumor protein 53 (p53) and mitogen-activated protein kinases (MAPK) during this process.

MATERIALS AND METHODS

The mouse neuroblastoma Neuro-2a cells were exposed to (137)Cs γ-rays at 4, 8 or 16 Gy. After incubation for 72 h with or without inhibitors of p53, phosphatidylinositol-4, 5-bisphosphate 3-kinase (PI3K) and other kinases, the neuronal differentiation of irradiated Neuro-2a cells was examined through analyzing neurite outgrowth and neuronal maker expression and the activation of related signaling proteins by western blotting and immunocytochemistry. Mouse primary neural stem cells (NSC) were exposed to IR at 1 Gy. The change of neuronal marker was examined using immunocytochemistry.

RESULTS

The irradiation of Neuro-2a cells significantly increased the neurite outgrowth and the expression of neuronal markers (neuronal nuclei [NeuN], microtubule-associated protein 2 [Map2], growth associated protein-43 [GAP-43], and Ras-related protein 13 [Rab13]). Immunocytochemistry revealed that neuronal class III beta-tubulin (Tuj-1) positive cells were increased and nestin positive cells were decreased by IR in Neuro-2a cells, which supported the IR-induced neuronal differentiation. However, the IR-induced neuronal differentiation was significantly attenuated when p53 was inhibited by pifithrin-α (PFT-α) or p53-small interfering RNA (siRNA). The PI3K inhibitor, LY294002, also suppressed the IR-induced neurite outgrowth, the activation of p53, the expression of GAP-43 and Rab13, and the increase of Tuj-1 positive cells. The increase of neurite outgrowth and Tuj-1 positive cells by IR and its suppression by LY294002 were also observed in mouse primary NSC.

CONCLUSION

These results suggest that IR is able to trigger the neuronal differentiation of Neuro-2a cells and the activation of p53 via PI3K is an important step for the IR-induced differentiation of Neuro-2a cells.