Li Y, White R
Howard Hughes Medical Institute, University of Utah, Salt Lake City, Utah 84112, USA.
Cancer Res. 1996 Jun 15;56(12):2872-6.
Human colon carcinoma cell line HCT116 harbors an oncogenic Ki-ras gene. Introduction of an exogenous full-length NF1 gene or its GTPase-activating protein (GAP)-related domain suppressed the tumor-forming ability of this cell line in nude mice. A GAP-related domain peptide carrying a K1423E mutation, which shows greatly diminished GAP activity but a normal binding affinity for p2lras-GTP, was also tested. This construct was able to suppress tumor formation by the HCT116 cell line, thus ruling out the possibility that the observed tumor suppression is due to the GAP activity of NF1. Reduced Raf-1 kinase activity in cells which expressed these NF1 constructs suggested that neurofibromin may interfere with the interaction between Ras and Raf. Introduction of a mutationally activated Raf-1 kinase domain reversed tumor suppression by neurofibromin, implicating Raf-1 as the primary downstream transducer of the oncogenic Ras signal. An increase in apoptotic cell death, which could be delayed by activated Raf-1 kinase, was also seen in cells carrying the exogenous NF1 gene.
人结肠癌细胞系HCT116含有致癌性的Ki-ras基因。导入外源性全长NF1基因或其GTP酶激活蛋白（GAP）相关结构域可抑制该细胞系在裸鼠中的成瘤能力。还测试了携带K1423E突变的GAP相关结构域肽，该肽的GAP活性大大降低，但对p2lras-GTP具有正常的结合亲和力。该构建体能够抑制HCT116细胞系的肿瘤形成，从而排除了观察到的肿瘤抑制是由于NF1的GAP活性所致的可能性。表达这些NF1构建体的细胞中Raf-1激酶活性降低，提示神经纤维瘤蛋白可能干扰Ras与Raf之间的相互作用。导入突变激活的Raf-1激酶结构域可逆转神经纤维瘤蛋白对肿瘤的抑制作用，这表明Raf-1是致癌性Ras信号的主要下游转导分子。在携带外源性NF1基因的细胞中也观察到凋亡细胞死亡增加，而激活的Raf-1激酶可延迟这种增加。
