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

结果表明，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，表明p14（ARF）失活有助于p53-WT胶质瘤的进展。p14（ARF）蛋白结合MDM 2并抑制MDM 2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，我们将体内多西环素（DOX）调节的诱导型p14（ARF）表达系统引入p14（ARF）阴性细胞。本研究使用人胶质母细胞瘤细胞系U87 MG（p14缺失，p53-WT）、U251 MG（p14缺失，p53突变）。我们建立了U87 MG或U251 MG衍生的克隆与体内诱导型p14的表达，并皮下注射到裸鼠的双侧胁下的DOX的存在。当肿瘤体积达到60 mm^3时，我们将小鼠分为两组;一组维持DOX（p14表达-），另一组不维持DOX（p14表达+）。检查肿瘤大小并进行评分。诱导p14表达可显著抑制U87 MG细胞的体内生长。然而，U251 MG细胞生长与p14表达无关。这些发现强烈地表明外源性p14表达抑制p53-WT胶质瘤细胞的增殖。p14的失活在增强胶质瘤的生长中起重要作用，我们发现在大多数间变性或非典型脑膜瘤中p14（ARF）表达缺失。p14（ARF）表达缺失的脑膜瘤不仅表现出p14（ARF）基因的纯合性缺失，而且表现出CDKN 2A基因的纯合性缺失。这两个基因都位于染色体9 p21上。提示p14（ARF）-CDKN 2A基因位点缺失与ARF/p53和CDKN 2A/RB通路有关，导致脑膜瘤细胞恶性转化。

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.