Oncogenic KRAS Impairs EGFR Antibodies' Efficiency by C/EBPβ-Dependent Suppression of EGFR Expression
Oncogenic KRAS Impairs EGFR Antibodies' Efficiency by C/EBPβ-Dependent Suppression of EGFR Expression
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DOI：
10.1593/neo.111636
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发表时间：
2012-03-01
期刊：
影响因子：
4.8
通讯作者：
Valerius, Thomas
中科院分区：
文献类型：
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作者：
Derer, Stefanie;Berger, Sven;Valerius, Thomas
结直肠癌（CRC）中的致癌KRAS突变与缺乏表皮生长因子受体（EGFR）导向抗体（Ab）治疗的获益相关。然而，组成性激活的KRAS（KRAS（G12 V））损害EGFR-Ab的效应器机制的机制尚未完全理解。在这里，我们建立了同基因细胞系模型，系统地研究KRAS（G12 V）对小鼠A431异种移植模型中肿瘤生长的影响，以及对体外EGFR-Ab触发的各种作用模式的影响。KRAS（G12 V）通过刺激受体非依赖性下游信号传导而损害EGFR-Ab介导的生长抑制。KRAS（G12 V）还使肿瘤细胞对EGFR-Ab的Fc介导的效应器机制（例如补体依赖性细胞毒性（CDC）和Ab依赖性细胞介导的细胞毒性（ADCC））的反应性降低。受损的CDC和ADCC活性可能与KRAS突变细胞与野生型（wt）细胞相比EGFR表达降低有关，后者可通过小干扰RNA（siRNA）介导的KRAS 4 b敲低恢复。免疫组织化学实验还揭示了KRAS突变与KRAS-wt携带CRC样品相比EGFR表达较低。对KRAS（G12 V）下调EGFR表达的潜在机制的分析表明，6种不同的转录因子的活性显著降低。其他实验表明，CCAAT/增强子结合蛋白（C/EBP）家族通过上调抑制性家族成员C/EBP β-LIP抑制EGFR转录，参与KRAS突变肿瘤细胞中EGFR启动子活性的调节。因此，siRNA介导的C/EBP β敲低导致增强的EGFR表达和Ab介导的针对KRAS突变细胞的细胞毒性。总之，这些结果表明KRAS（G12 V）信号传导诱导EGFR表达的C/EBP β依赖性抑制，从而损害EGFR-Ab的Fc介导的效应器机制，并使KRAS突变的肿瘤细胞对这些治疗剂不太敏感。
Oncogenic KRAS mutations in colorectal cancer (CRC) are associated with lack of benefit from epidermal growth factor receptor (EGFR)-directed antibody (Ab) therapy. However, the mechanisms by which constitutively activated KRAS (KRAS(G12V)) impairs effector mechanisms of EGFR-Abs are incompletely understood. Here, we established isogenic cell line models to systematically investigate the impact of KRAS(G12V) on tumor growth in mouse A431 xenograft models as well as on various modes of action triggered by EGFR-Abs in vitro. KRAS(G12V) impaired EGFR-Ab-mediated growth inhibition by stimulating receptor-independent downstream signaling. KRAS(G12V) also rendered tumor cells less responsive to Fc-mediated effector mechanisms of EGFR-Abs-such as complement-dependent cytotoxicity (CDC) and Ab-dependent cell-mediated cytotoxicity (ADCC). Impaired CDC and ADCC activities could be linked to reduced EGFR expression in KRAS-mutated versus wild-type (wt) cells, which was restored by small interfering RNA (siRNA)-mediated knockdown of KRAS4b. Immunohistochemistry experiments also revealed lower EGFR expression in KRAS-mutated versus KRAS-wt harboring CRC samples. Analyses of potential mechanisms by which KRAS(G12V) downregulated EGFR expression demonstrated significantly decreased activity of six distinct transcription factors. Additional experiments suggested the CCAAT/enhancer-binding protein (C/EBP) family to be implicated in the regulation of EGFR promoter activity in KRAS-mutated tumor cells by suppressing EGFR transcription through up-regulation of the inhibitory family member C/EBP beta-LIP. Thus, siRNA-mediated knockdown of C/EBP beta led to enhanced EGFR expression and Ab-mediated cytotoxicity against KRAS-mutated cells. Together, these results demonstrate that KRAS(G12V) signaling induced C/EBP beta-dependent suppression of EGFR expression, thereby impairing Fc-mediated effector mechanisms of EGFR-Abs and rendering KRAS-mutated tumor cells less sensitive to these therapeutic agents.