Department of Otolaryngology - Head & Neck Surgery, University of Virginia School of Medicine, Charlottesville, Virginia.
Center for Applied Proteomics and Molecular Medicine, George Mason University, Manassas, Virginia.
Mol Cancer Res. 2020 Sep;18(9):1392-1401. doi: 10.1158/1541-7786.MCR-19-0592. Epub 2020 May 28.
EGFR inhibitors have shown poor efficacy in head and neck squamous cell carcinoma (HNSCC) with demonstrated involvement of the insulin-like growth factor-1 receptor (IGF1R) in resistance to EGFR inhibition. IGF1R activates the PI3K-Akt pathway, which phosphorylates proline-rich Akt substrate of 40 kDa (PRAS40) to cease mTOR inhibition resulting in increased mTOR signaling. Proliferation assays separated six HNSCC cell lines into two groups: sensitive to EGFR inhibition or resistant; all sensitive cell lines demonstrated reduced sensitivity to EGFR inhibition upon IGF1R activation. Reverse phase protein microarray analysis and immunoblot identified a correlation between increased PRAS40 phosphorylation and IGFR-mediated resistance to EGFR inhibition. In sensitive cell lines, PRAS40 phosphorylation decreased 44%-80% with EGFR inhibition and was restored to 98%-196% of control by IGF1R activation, while phosphorylation was unaffected in resistant cell lines. Possible involvement of mTOR in this resistance mechanism was demonstrated through a similar pattern of p70S6K phosphorylation. However, addition of temsirolimus, an mTORC1 inhibitor, was insufficient to overcome IGF1R-mediated resistance and suggested an alternative mechanism. Forkhead box O3a (FOXO3a), which has been reported to complex with PRAS40 in the cytoplasm, demonstrated a 6-fold increase in nuclear to cytoplasmic ratio upon EGFR inhibition that was eliminated with concurrent IGF1R activation. Transcription of FOXO3a-regulated TRAIL and PTEN-induced putative kinase-1 (PINK1) was increased with EGFR inhibition in sensitive cell lines; this effect was diminished with IGF1R stimulation. IMPLICATIONS: These data suggest PRAS40 may play an important role in IGF1R-based therapeutic resistance to EGFR inhibition, and this likely occurs via inhibition of FOXO3a-mediated proapoptotic gene transcription.
表皮生长因子受体抑制剂在头颈部鳞状细胞癌（HNSCC）中的疗效不佳，已有研究表明胰岛素样生长因子-1 受体（IGF1R）参与了对表皮生长因子受体抑制的抵抗。IGF1R 激活 PI3K-Akt 通路，该通路磷酸化富含脯氨酸的 Akt 底物 40 kDa（PRAS40），从而阻止 mTOR 抑制，导致 mTOR 信号增强。增殖实验将六株 HNSCC 细胞系分为两组：对表皮生长因子受体抑制敏感或耐药；所有对表皮生长因子受体抑制敏感的细胞系在 IGF1R 激活后对表皮生长因子受体抑制的敏感性降低。反相蛋白微阵列分析和免疫印迹鉴定了 PRAS40 磷酸化增加与 IGF1R 介导的表皮生长因子受体抑制耐药之间的相关性。在敏感细胞系中，表皮生长因子受体抑制后 PRAS40 磷酸化降低 44%-80%，IGF1R 激活后恢复至对照的 98%-196%，而耐药细胞系的磷酸化不受影响。通过类似的 p70S6K 磷酸化模式证明 mTOR 可能参与了这种耐药机制。然而，添加 mTORC1 抑制剂替西罗莫司不足以克服 IGF1R 介导的耐药性，这表明存在替代机制。叉头框 O3a（FOXO3a）已被报道在细胞质中与 PRAS40 形成复合物，在表皮生长因子受体抑制后，其核质比增加了 6 倍，而与 IGF1R 同时激活则消除了这种增加。敏感细胞系中，表皮生长因子受体抑制时 FOXO3a 调节的 TRAIL 和 PTEN 诱导的假定激酶-1（PINK1）的转录增加；这种效应在 IGF1R 刺激时减弱。意义：这些数据表明，PRAS40 可能在基于 IGF1R 的表皮生长因子受体抑制耐药中发挥重要作用，这可能是通过抑制 FOXO3a 介导的促凋亡基因转录来实现的。
