Biological Significance of p16 gene inactivation on glioma progress

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It was shown that the p14 (alternating reading frame : ARF) gene was frequently deleted in the majority of p53 wild-type (WT) glioblastomas, suggesting that p14 (ARF) inactivation plays an important role in p53-WT glioma progression. p14(ARF) protein binds to MDM2 and inhibits MDM2-mediated degradation of p53. These findings suggest that the restoration of p14 (ARF) can suppress the growth of p53-WT glioma cells. Therefore, to clarify the biological significance of p14 (ARF) inactivation in glioma, we introduced a p14 (ARF) cDNA plasmid vector into p14 (ARF)-negative glioma cells. Human glioblastoma cell lines, U87MG and A1207 (p14/p16-deleted, p53-WT), T98G (p14/p16-deleted, p53-mutated), LNZ308 (p14/p16-WT, p53-null), were used in this study. Expression constructs (p14 or p16 cDNA) and green fluorescence protein (GFP) expression vector at a 4:1 ratio were co-introduced into cells using the lipofection method. Transfected cells were indirectly detected by the presence of GFP and analyzed with flow cytometry. Although the transfer of the p14 (ARF) gene induced G2/M arrest but not G1 arrest or apoptosis in U87MG and A1207 cells, cell cycle distributions of T98G and LNZ308 cells were not significantly changed by exogenous p14 (ARF). G1 arrest was observed in three p14/p16-deleted cell lines other than LNZ308 cells by exogenous p16. These results suggest that p14 (ARF) inactivation contributes to further malignant transformation of p53-WT glioma cells by representing cell cycle arrest at G2/M.