Toulany Mahmoud, Baumann Michael, Rodemann H Peter
Division of Radiobiology and Molecular Environmental Research, Department of Radiation Oncology, Eberhard-Karls University Tuebingen, Roentgenweg 11, 72076 Tuebingen, Germany.
Mol Cancer Res. 2007 Aug;5(8):863-72. doi: 10.1158/1541-7786.MCR-06-0297.
Previous results showed an inducible radiation sensitivity selectively observable for K-RAS-mutated cell lines as a function of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor blockade of phosphatidylinositol 3-kinase (PI3K)-AKT signaling. Therefore, the role of K-Ras activity for a direct (i.e., through activation of PI3K by K-Ras) or an indirect stimulation of PI3K-AKT signaling (through K-Ras activity-dependent EGFR ligand production) was investigated by means of small interfering RNA and inhibitor approaches as well as ELISA measurements of EGFR ligand production. K-RASmt tumor cells presented a constitutively activated extracellular signal-regulated kinase-1/2 signaling, resulting in enhanced production and secretion of the EGFR ligand amphiregulin (AREG). Medium supernatants conditioned by K-RASmt tumor cells equally efficiently stimulated EGFR signaling into the PI3K-AKT and mitogen-activated protein kinase pathways. Knocking down K-Ras expression by specific small interfering RNA markedly affected autocrine production of AREG, but not PI3K-AKT signaling, after treatment of K-RAS-mutated or wild-type cells with EGFR ligands or exposure to ionizing radiation. These results indicate that PI3K-mediated activation of AKT in K-RASmt human tumor cells as a function of EGFR ligand or radiation stimulus is independent of a direct function of K-Ras enzyme activity but depends on a K-Ras-mediated enhanced production of EGFR ligands (i.e., most likely AREG) through up-regulated extracellular signal-regulated kinase-1/2 signaling. The data provide new differential insight into the importance of K-RAS mutation in the context of PI3K-AKT-mediated radioresistance of EGFR-overexpressing or EGFR-mutated tumors.
先前的结果表明，作为表皮生长因子受体（EGFR）酪氨酸激酶抑制剂对磷脂酰肌醇3激酶（PI3K）-AKT信号传导阻断作用的函数，K-RAS突变细胞系具有可诱导的辐射敏感性，这是可选择性观察到的。因此，通过小干扰RNA和抑制剂方法以及EGFR配体产生的ELISA测量，研究了K-Ras活性对PI3K的直接刺激作用（即，通过K-Ras激活PI3K）或间接刺激PI3K-AKT信号传导（通过K-Ras活性依赖性EGFR配体产生）。K-RASmt肿瘤细胞呈现组成性激活的细胞外信号调节激酶-1/2信号传导，导致EGFR配体双调蛋白（AREG）的产生和分泌增加。由K-RASmt肿瘤细胞条件培养的培养基上清液同样有效地刺激EGFR信号传导进入PI3K-AKT和丝裂原活化蛋白激酶途径。在用EGFR配体处理K-RAS突变或野生型细胞或暴露于电离辐射后，通过特异性小干扰RNA敲低K-Ras表达显著影响AREG的自分泌产生，但不影响PI3K-AKT信号传导。这些结果表明，在K-RASmt人肿瘤细胞中，PI3K介导的AKT激活作为EGFR配体或辐射刺激的函数，独立于K-Ras酶活性的直接作用，但依赖于通过上调的细胞外信号调节激酶-1/2信号传导由K-Ras介导的EGFR配体（即，最可能是AREG）的产生增加。这些数据为K-RAS突变在EGFR过表达或EGFR突变肿瘤的PI3K-AKT介导的放射抗性背景下的重要性提供了新的差异见解。
