Department of Surgery, Vanderbilt University Medical Center, Nashville, TN 37232, USA.
Neoplasia. 2013 Mar;15(3):296-304. doi: 10.1593/neo.122044.
The overexpression of AXL receptor tyrosine kinase is a frequent finding that has been associated with poor prognosis in esophageal adenocarcinoma (EAC). As the majority of EAC are intrinsically resistant to DNA-damaging therapies, an alternative therapeutic approach based on the activation of death receptors may be warranted. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been evaluated in clinical trials and found promising as anticancer agent with mild side effects; unfortunately, resistance to TRAIL remains a major clinical problem. Herein, we explored the role of AXL in TRAIL resistance and elucidated the underlying mechanism. Overexpression of AXL in OE33 and OE19 cells promoted cell survival and attenuated TRAIL-induced cellular and molecular markers of apoptosis. In contrast, knockdown of endogenous AXL sensitized FLO-1 cells to TRAIL. The mechanism by which AXL regulates TRAIL resistance was examined. Protein and mRNA expression of DR4 and DR5 death receptors was not downregulated by AXL. In addition, the possible involvement of FLICE-inhibitory protein (FLIP) in regulating the interaction of caspase-8 with Fas-associated death domain protein (FADD) was excluded, as AXL did not enhance FLIP expression or FLIP/FADD association. Alternatively, protein association of AXL with DR5, independent of TRAIL, was confirmed, suggesting that AXL could regulate DR5 receptor activity. The AXL/DR5 association had no negative effect on TRAIL-induced interaction with FADD. However, the AXL/DR5 interaction blocked the recruitment of caspase-8 to the death-inducing signal complex (DISC). Collectively, our findings uncover a novel mechanism of TRAIL resistance mediated by AXL through regulation of the DISC and provide strong evidence that AXL could be exploited as a therapeutic target to circumvent TRAIL resistance.
AXL 受体酪氨酸激酶的过表达是食管腺癌（EAC）预后不良的常见发现。由于大多数 EAC 对 DNA 损伤疗法具有内在抗性，因此基于激活死亡受体的替代治疗方法可能是合理的。肿瘤坏死因子相关凋亡诱导配体（TRAIL）已在临床试验中进行了评估，并被发现具有作为抗癌剂的潜力，副作用轻微；不幸的是，对 TRAIL 的耐药性仍然是一个主要的临床问题。在此，我们探讨了 AXL 在 TRAIL 耐药中的作用，并阐明了潜在的机制。AXL 在 OE33 和 OE19 细胞中的过表达促进了细胞存活，并减弱了 TRAIL 诱导的细胞和分子凋亡标志物。相比之下，内源性 AXL 的敲低使 FLO-1 细胞对 TRAIL 敏感。检查了 AXL 调节 TRAIL 耐药性的机制。AXL 并未下调 DR4 和 DR5 死亡受体的蛋白和 mRNA 表达。此外，排除了 FLICE 抑制蛋白（FLIP）可能参与调节胱天蛋白酶-8 与 Fas 相关死亡域蛋白（FADD）的相互作用，因为 AXL 不会增强 FLIP 表达或 FLIP/FADD 关联。相反，AXL 与 DR5 的蛋白关联被证实与 TRAIL 无关，这表明 AXL 可以调节 DR5 受体活性。AXL/DR5 关联对 TRAIL 诱导的与 FADD 的相互作用没有负面影响。然而，AXL/DR5 相互作用阻止了胱天蛋白酶-8 募集到致死信号复合物（DISC）。总之，我们的研究结果揭示了 AXL 通过调节 DISC 介导的 TRAIL 耐药的新机制，并提供了强有力的证据表明 AXL 可被用作治疗靶点以规避 TRAIL 耐药性。
