INSERM UMR-1037, Toulouse University, Cancer Research Center of Toulouse, Equipe Labellisée Ligue Contre le Cancer and Laboratoire d'Excellence Toulouse Cancer, Toulouse, France.
UMR7286 CNRS-Aix-Marseille University, Neurobiology and Neurophysiology Research Center of Marseille, and Laboratory of Molecular Biology, AP-HM Conception, Marseille, France.
Gastroenterology. 2015 Jun;148(7):1452-65. doi: 10.1053/j.gastro.2015.02.009. Epub 2015 Feb 13.
BACKGROUND & AIMS: The KRAS gene is mutated in most pancreatic ductal adenocarcinomas (PDAC). Expression of this KRAS oncoprotein in mice is sufficient to initiate carcinogenesis but not progression to cancer. Activation of phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) is required for KRAS for induction and maintenance of PDAC in mice. The somatostatin receptor subtype 2 (sst2) inhibits PI3K, but sst2 expression is lost during the development of human PDAC. We investigated the effects of sst2 loss during KRAS-induced PDAC development in mice.
We analyzed tumor growth in mice that expressed the oncogenic form of KRAS (KRAS(G12D)) in pancreatic precursor cells, as well as sst2+/- and sst2-/-, and in crossed KRAS(G12D);sst2+/- and KRAS(G12D);sst2-/- mice. Pancreatic tissues and acini were collected and assessed by histologic, immunoblot, immunohistochemical, and reverse-transcription polymerase chain reaction analyses. We also compared protein levels in paraffin-embedded PDAC samples from patients vs heathy pancreatic tissues from individuals without pancreatic cancer.
In sst2+/- mice, PI3K was activated and signaled via AKT (PKB; protein kinase B); when these mice were crossed with KRAS(G12D) mice, premalignant lesions, tumors, and lymph node metastases developed more rapidly than in KRAS(G12D) mice. In crossed KRAS(G12D);sst2+/- mice, activation of PI3K signaling via AKT resulted in activation of nuclear factor-κB (NF-κB), which increased KRAS activity and its downstream pathways, promoting initiation and progression of neoplastic lesions. We found this activation loop to be mediated by PI3K-induced production of the chemokine CXCL16. Administration of a CXCL16-neutralizing antibody to KRAS(G12D) mice reduced activation of PI3K signaling to AKT and NF-κB, blocking carcinogenesis. Levels of CXCL16 and its receptor CXCR6 were significantly higher in PDAC tissues and surrounding acini than in healthy pancreatic tissues from mice or human beings. In addition, expression of sst2 was progressively lost, involving increased PI3K activity, in mouse lesions that expressed KRAS(G12D) and progressed to PDAC.
Based on analyses of mice, loss of sst2 from pancreatic tissues activates PI3K signaling via AKT, leading to activation of NF-κB, amplification of oncogenic KRAS signaling, increased expression of CXCL16, and pancreatic tumor formation. CXCL16 might be a therapeutic target for PDAC.
KRAS 基因在大多数胰腺导管腺癌（PDAC）中发生突变。KRAS 癌蛋白在小鼠中的表达足以引发癌变，但不足以导致癌症进展。PI3K 磷酸肌醇-4,5-二磷酸 3-激酶的激活对于 KRAS 诱导的小鼠 PDAC 的发生和维持是必需的。生长抑素受体亚型 2（sst2）抑制 PI3K，但在人类 PDAC 的发展过程中 sst2 的表达丢失。我们研究了在 KRAS 诱导的 PDAC 发展过程中 sst2 缺失对小鼠的影响。
我们分析了在胰腺前体细胞中表达致癌形式 KRAS（KRAS(G12D)）的小鼠、sst2+/-和 sst2-/-以及交叉 KRAS(G12D);sst2+/-和 KRAS(G12D);sst2-/-小鼠的肿瘤生长情况。通过组织学、免疫印迹、免疫组织化学和逆转录聚合酶链反应分析收集和评估胰腺组织和腺泡。我们还比较了来自患者的石蜡包埋 PDAC 样本和无胰腺癌个体的健康胰腺组织中的蛋白质水平。
在 sst2+/- 小鼠中，PI3K 通过 AKT（蛋白激酶 B）被激活并发出信号；当这些小鼠与 KRAS(G12D) 小鼠杂交时，癌前病变、肿瘤和淋巴结转移的发展速度比 KRAS(G12D) 小鼠更快。在交叉 KRAS(G12D);sst2+/- 小鼠中，PI3K 信号通过 AKT 激活核因子-κB（NF-κB），从而增加 KRAS 活性及其下游途径，促进肿瘤病变的起始和进展。我们发现这种激活环是由 PI3K 诱导的趋化因子 CXCL16 的产生介导的。向 KRAS(G12D) 小鼠施用 CXCL16 中和抗体可减少 PI3K 信号向 AKT 和 NF-κB 的激活，从而阻断致癌作用。与来自小鼠或人类的健康胰腺组织相比，PDAC 组织及其周围腺泡中 CXCL16 和其受体 CXCR6 的水平明显更高。此外，在表达 KRAS(G12D) 并进展为 PDAC 的小鼠病变中，sst2 的表达逐渐丢失，涉及 PI3K 活性增加，导致 PI3K 信号通过 AKT 激活，从而导致 NF-κB 激活，致癌 KRAS 信号放大，CXCL16 表达增加和胰腺肿瘤形成。CXCL16 可能是 PDAC 的治疗靶点。
