The oncogenic receptor tyrosine kinase AXL is overexpressed in cancer and plays an important role in carcinomas of multiple organs. However, the mechanisms of AXL overexpression in cancer remain unclear. In this study, using HEK293T, Panc-1, and Panc-28 cells and samples of human pancreatic intraepithelial neoplasia (PanIN), along with several biochemical approaches and immunofluorescence microscopy analyses, we sought to investigate the mechanisms that regulate AXL over-expression in pancreatic ductal adenocarcinoma (PDAC). We found that AXL interacts with hematopoietic progenitor kinase 1 (HPK1) and demonstrate that HPK1 down-regulates AXL and decreases its half-life. The HPK1-mediated AXL degradation was inhibited by the endocytic pathway inhibitors leupeptin, bafilomycin A1, and monensin. HPK1 accelerated the movement of AXL from the plasma membrane to endosomes in pancreatic cancer cells treated with the AXL ligand growth arrest-specific 6 (GAS6). Moreover, HPK1 increased the binding of AXL to the Cbl proto-oncogene (c-Cbl); promoted AXL ubiquitination; decreased AXL-mediated signaling, including phospho-AKT and phospho-ERK signaling; and decreased the invasion capability of PDAC cells. Importantly, we show that AXL expression inversely correlates with HPK1 expression in human PanINs and that patients whose tumors have low HPK1 and high AXL expression levels have shorter survival than those with low AXL or high HPK1 expression (p < 0.001). Our results suggest that HPK1 is a tumor suppressor that targets AXL for degradation via the endocytic pathway. HPK1 loss of function may contribute to AXL overexpression and thereby enhance AXL-dependent downstream signaling and tumor invasion in PDAC.

中文翻译：

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造血祖细胞激酶 1 下调胰腺癌中的致癌受体酪氨酸激酶 AXL。


致癌受体酪氨酸激酶AXL在癌症中过度表达，并在多个器官的癌中发挥重要作用。然而，AXL 在癌症中过度表达的机制仍不清楚。在这项研究中，我们使用 HEK293T、Panc-1 和 Panc-28 细胞以及人胰腺上皮内瘤变 (PanIN) 样本，结合多种生化方法和免疫荧光显微镜分析，试图研究调节 AXL 过表达的机制。胰腺导管腺癌（PDAC）。我们发现 AXL 与造血祖细胞激酶 1 (HPK1) 相互作用，并证明 HPK1 下调 AXL 并缩短其半衰期。 HPK1 介导的 AXL 降解受到内吞途径抑制剂亮肽素、巴弗洛霉素 A1 和莫能菌素的抑制。在用 AXL 配体生长抑制特异性 6 (GAS6) 处理的胰腺癌细胞中，HPK1 加速了 AXL 从质膜到内体的运动。此外，HPK1 增加了 AXL 与 Cbl 原癌基因 (c-Cbl) 的结合；促进AXL泛素化；减少 AXL 介导的信号传导，包括磷酸化 AKT 和磷酸化 ERK 信号传导；并降低PDAC细胞的侵袭能力。重要的是，我们发现 AXL 表达与人 PanIN 中的 HPK1 表达呈负相关，并且肿瘤具有低 HPK1 和高 AXL 表达水平的患者比具有低 AXL 或高 HPK1 表达水平的患者生存期更短 (p < 0.001)。我们的结果表明 HPK1 是一种肿瘤抑制因子，通过内吞途径靶向 AXL 进行降解。 HPK1 功能丧失可能导致 AXL 过度表达，从而增强 PDAC 中 AXL 依赖性下游信号传导和肿瘤侵袭。