Nandan Mandayam O, McConnell Beth B, Ghaleb Amr M, Bialkowska Agnieszka B, Sheng Hongmiao, Shao Jinyi, Babbin Brian A, Robine Sylvie, Yang Vincent W
Division of Digestive Diseases, Department of Medicine, Emory University, Atlanta, Georgia, USA.
Gastroenterology. 2008 Jan;134(1):120-30. doi: 10.1053/j.gastro.2007.10.023. Epub 2007 Oct 17.
BACKGROUND & AIMS: Krüppel-like factor 5 (KLF5) is a zinc finger-transcription factor that regulates cell proliferation. Oncogenic KRAS mutations are commonly found in colorectal cancers. We aimed to determine whether KLF5 mediates KRAS functions during intestinal tumorigenesis.
The effects of KLF5 on proliferation and transformation were examined in IEC-6 intestinal epithelial cells stably transfected with inducible KRAS(V12G). KLF5 expression was examined in intestinal tumors derived from transgenic mice expressing KRAS(V12G) under villin promoter and in human colorectal cancers with mutated KRAS.
Induction of KRAS(V12G) in IEC-6 cells resulted in increased expression of KLF5, accompanied by increased rates of proliferation and anchorage-independent growth. Inhibition of KLF5 expression by mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK) inhibitors or KLF5-specific small interfering RNA reduced proliferation and anchorage-independent growth despite KRAS(V12G) induction. Human colorectal cancer cell lines with mutated KRAS contained high levels of KLF5 and reduction of KLF5 by MEK inhibitors or KLF5 small interfering RNA also led to reduced proliferation and transformation. In vivo, both intestinal tumors derived from mice transgenic for villin-KRAS(V12G) and human primary colorectal cancers with mutated KRAS contained high levels of KLF5 and increased staining of the proliferative marker Ki67.
Elevated levels of KLF5 protein are strongly correlated with activating KRAS mutations in intestinal tumors in vitro and in vivo. Inhibition of KLF5 expression in tumor cells resulted in significantly reduced rates of proliferation and transforming activities. We conclude that KLF5 is an important mediator of oncogenic KRAS transforming functions during intestinal tumorigenesis.
Krüppel样因子5(KLF5)是一种调节细胞增殖的锌指转录因子。致癌性KRAS突变常见于结直肠癌中。我们旨在确定KLF5在肠道肿瘤发生过程中是否介导KRAS功能。
在稳定转染可诱导型KRAS(V12G)的IEC-6肠上皮细胞中检测KLF5对增殖和转化的影响。在由绒毛蛋白启动子驱动表达KRAS(V12G)的转基因小鼠所产生的肠道肿瘤以及KRAS突变的人类结直肠癌中检测KLF5的表达。
在IEC-6细胞中诱导KRAS(V12G)导致KLF5表达增加,同时增殖率和不依赖贴壁生长增加。丝裂原活化蛋白激酶/细胞外信号调节激酶(MEK)抑制剂或KLF5特异性小干扰RNA抑制KLF5表达,尽管诱导了KRAS(V12G),但仍降低了增殖和不依赖贴壁生长。具有KRAS突变的人类结肠癌细胞系含有高水平的KLF5,MEK抑制剂或KLF5小干扰RNA降低KLF5也导致增殖和转化减少。在体内,源自绒毛蛋白-KRAS(V12G)转基因小鼠的肠道肿瘤和具有KRAS突变的人类原发性结直肠癌均含有高水平的KLF5,且增殖标志物Ki67的染色增加。
在体外和体内,肠道肿瘤中KLF5蛋白水平升高与激活KRAS突变密切相关。抑制肿瘤细胞中KLF5的表达导致增殖率和转化活性显著降低。我们得出结论,KLF5是肠道肿瘤发生过程中致癌性KRAS转化功能的重要介导因子。