Ceramide mediates differentiation, growth arrest, apoptosis, proliferation, cytokine biosynthesis and secretion, and a variety of other cellular functions. However, little is known regarding ceramide signaling linked to the cell cycle. In the present study, the effect of ceramide on cell cycle in nasopharyngeal carcinoma cell line CNE2 was investigated. The results showed that ceramide inhibited cell proliferation and induced cell cycle arrest in G1 phase in CNE2 cells. Exposure of CNE2 cells to ceramide resulted in a dose-dependent up-regulation of the cyclin-dependent kinase inhibitor p27 and a decrease of phospho-Akt without reduced expression of total AKT protein. The activation of phosphatidylinositol-3-kinase (PI3K) and the protein expression of PTEN were unaffected following ceramide treatment. We concluded that ceramide induced cell cycle arrest in G1 phase in CNE2 cells and p27 up-regulation was involved in this process. In addition, up-regulation of p27 resulting from ceramide treatment may be due to the interruption of Akt, but decrease of phospho-Akt is independent of PI3K function or PTEN protein expression.

Polysaccharides from aloe are always considered an effective radioprotector on irradiation-induced skin damage. The aim of this study was to determine if aloe polysaccharides (AP) have radioprotective effects on normal human cells in vitro and mouse survival in vivo and to explore the mechanism. Pretreatment with 50 m g/ml AP could improve the surviving fraction at 2 Gy (SF 2) of three normal cell lines 293, ECV304, and C. liver from 41.5%, 46.5%, and 40.9% to 49.4%, 72.1%, and 89.1%, respectively. AP could also reduce the apoptotic rate of C. liver cells from 9.5% and 43.0% to 2.2% and 10.9% 48 h and 72 h after 2 Gy irradiation, respectively. Western blot analysis showed that pretreatment with AP could block the upregulation of pro-apoptotic p53, Bax, and Bad and the downregulation of Bcl-2 by irradiation. AP could lower thymocyte apoptosis of mice in vivo after 6 Gy irradiation and abrogate the cell cycle perturbation. Fifty mg/kg of AP treatment for 30 min before 7.5 Gy irradiation provided the best radioprotective effect and improved the 30-day survival rate of mice to 86.0%, from 10.0%. AP exerted radioprotective effects in vitro and in vivo through an inhibition of apoptosis.