Girgert R, Hohnecker A, Wittrock J, Schweizer P
Department of Pediatric Surgery, University of Tübingen, Germany.
Anticancer Res. 1999 Jul-Aug;19(4B):2959-62.
Oncogenic Ras is responsible for malignant transformation in a variety of tumors. Farnesylation of Ras by farnesyl-protein-transferase (FPTase) is necessary for membrane localization of Ras-proteins, a prerequisite for its biological activity. Although mutations in ras genes are rare in neuroblastoma inactivation of Ras by inhibition of the FPTase is of interest in neuroblastoma. In this tumor, amplification of N-myc is frequently observed and expression of N-myc is induced via Ras signaling. Farnesyl-protein-transferase of neuroblastoma cells is inhibited by alpha-hydroxyfarnesylphosphonate. In homogenates of the cell line SK-N-AS an ID50 = 6.5 microM is estimated, in SK-N-SH the ID50 is 3.4 microM. The consequences of the inhibition of FPTase on the membrane localization was examined by immunoblots. Western blots of membrane proteins analysed with H-ras and N-ras specific antibodies revealed that H-ras protein is more sensitive to the inhibition of FPTase than N-ras protein. After culturing neuroblastoma cells for 24 hrs in the presence of 20 microM alpha-hydroxyfarnesylphosphonate H-ras protein completely dissappeared from the membrane fraction whereas N-ras protein was only affected by 50%. K-ras was not detectable on Western blots of three neuroblastoma cell lines. The experiments showed that FPTase inhibitors are effective in neuroblastoma cells but for complete inactivation of N-ras stronger conditions are required than for H-ras.
致癌性Ras在多种肿瘤的恶性转化中起作用。法尼基蛋白转移酶（FPTase）对Ras蛋白进行法尼基化是Ras蛋白定位于细胞膜所必需的，而这是其生物学活性的一个先决条件。虽然Ras基因的突变在神经母细胞瘤中很少见，但通过抑制FPTase使Ras失活在神经母细胞瘤中具有重要意义。在这种肿瘤中，经常观察到N-myc的扩增，并且N-myc的表达是通过Ras信号传导诱导的。α-羟基法尼基膦酸盐可抑制神经母细胞瘤细胞的法尼基蛋白转移酶。在细胞系SK-N-AS的匀浆中，估计半数抑制浓度（ID50）为6.5微摩尔，在SK-N-SH中ID50为3.4微摩尔。通过免疫印迹法检测了抑制FPTase对膜定位的影响。用H-ras和N-ras特异性抗体分析膜蛋白的Western印迹显示，H-ras蛋白比N-ras蛋白对FPTase的抑制更敏感。在20微摩尔α-羟基法尼基膦酸盐存在下培养神经母细胞瘤细胞24小时后，H-ras蛋白从膜组分中完全消失，而N-ras蛋白仅受到50%的影响。在三种神经母细胞瘤细胞系的Western印迹上未检测到K-ras。实验表明，FPTase抑制剂在神经母细胞瘤细胞中有效，但要使N-ras完全失活，所需条件比H-ras更严格。
