Biological significance of CDKN2A-ARF inactivation of glioma and meningioma progression.

研究表明，p14（交替阅读框：ARF）基因在大多数p53野生型（WT）胶质母细胞瘤中经常缺失，这表明p14 （ARF）失活有助于p53-WT胶质瘤的进展。p14 （ARF）蛋白结合MDM2并抑制MDM2介导的p53降解。为了评估p14 （ARF）失活在胶质瘤中的生物学意义，我们在p14 （ARF）阴性细胞中引入了多西环素（DOX）调节的体内诱导p14 （ARF）表达系统。本研究使用人胶质母细胞瘤细胞系U87MG (p14缺失，p53-WT), U251MG （p14缺失，p53突变）。我们建立了体内可诱导表达p14的U87MG或u251mg衍生克隆，并在DOX存在下皮下注射到裸鼠双侧。当肿瘤体积达到60 mm^3时，我们将小鼠分为两组；一种是DOX (p14表达-)，另一种是无DOX （p14表达+）。检查肿瘤大小并评分。诱导p14表达可显著抑制U87MG细胞的体内生长。然而，无论p14表达与否，U251MG细胞都能生长。这些发现强烈提示外源性p14表达抑制p53-WT胶质瘤细胞的增殖。p14的失活可能在促进体内不受调节的胶质瘤生长中发挥重要作用。我们发现p14 （ARF）在大多数间变性或非典型脑膜瘤中表达缺失。p14 （ARF）表达缺失的脑膜瘤不仅显示p14 （ARF）基因的纯合缺失，而且显示CDKN2A基因的纯合缺失。这两个基因都位于染色体9p21上。这些结果表明，p14 (ARF) - CDKN2A基因座的缺失与ARF/p53和CDKN2A/RB通路相关，导致脑膜瘤细胞的恶性转化。

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 contributes to p53-WT glioma progression. p14 (ARF) protein binds to MDM2 and inhibits MDM2-mediated degradation of p53. To assess the biological significance of p14 (ARF) inactivation in glioma, we introduced an in vivo Doxycycline (DOX)-regulated inducible p14 (ARF) expression system to p14 (ARF)-negative cells. Human glioblastoma cell lines, U87MG (p14-deleted, p53-WT), U251MG (p14-deleted, p53-mutated) were used in this study. We established U87MG- or U251MG-derived clones with in vivo inducible p14 expression and injected subcutaneously into the bilateral flanks of nude mice in the presence of DOX. When the tumor volume reached to 60 mm^3, we divided mice into two groups; one is maintained with DOX (p14 expression -), and the other without DOX (p14 expression +). The size of tumors were examined and scored. Induction of p14 expression significantly suppressed the in vivo growth of U87MG cells. U251MG cells, however, grew regardless of p14 expression. These findings strongly indicated that exogenous p14 expression inhibits the proliferation of p53-WT glioma cells. Inactivation of p14 would play an important role in the enhancement of unregulated glioma growth in vivo.We found loss of p14 (ARF) expression in majority of anaplastic or atypical meningiomas. Meningiomas with the absence of p14 (ARF) expression exclusively showed homozygous deletion of not only the p14 (ARF) gene but also the CDKN2A gene. Both genes are located on chromosome 9p21. These results suggested that loss of p14 (ARF) - CDKN2A loci was associated with ARF/p53 and CDKN2A/RB pathway, leading to malignant transformation of meningioma cells.