Deregulated glucose metabolism is a critical component of cancer growth and survival, clinically evident via FDG-PET imaging of enhanced glucose uptake in tumor nodules. Tumor cells utilize glucose in a variety of interconnected biochemical pathways to generate energy, anabolic precursors, and other metabolites necessary for growth. Glucagon-stimulated gluconeogenesis opposes glycolysis, potentially representing a pathway-specific strategy for targeting glucose metabolism in tumor cells. Here, we test the hypothesis of whether glucagon signaling can activate gluconeogenesis to reduce tumor proliferation in models of liver cancer. The glucagon receptor, GCGR, was overexpressed in liver cancer cell lines consisting of a range of etiologies and genetic backgrounds. Glucagon signaling transduction was measured by cAMP ELISAs, western blots of phosphorylated PKA substrates, and qPCRs of relative mRNA expression of multiple gluconeogenic enzymes. Lastly, cell proliferation and apoptosis assays were performed to quantify the biological effect of glucagon/GCGR stimulation. Signaling analyses in SNU398 GCGR cells treated with glucagon revealed an increase in cAMP abundance and phosphorylation of downstream PKA substrates, including CREB. qPCR data indicated that none of the three major gluconeogenic genes, G6PC, FBP1, or PCK1, exhibit significantly higher mRNA levels in SNU398 GCGR cells when treated with glucagon; however, this could be partially increased with epigenetic inhibitors. In glucagon-treated SNU398 GCGR cells, flow cytometry analyses of apoptotic markers and growth assays reproducibly measured statistically significant reductions in cell viability. Finally, proliferation experiments employing siCREB inhibition showed no reversal of cell death in SNU398 GCGR cells treated with glucagon, indicating the effects of glucagon in this setting are independent of CREB. For the first time, we report a potential tumor suppressive role for glucagon/GCGR in liver cancer. Specifically, we identified a novel cell line-specific phenotype, whereby glucagon signaling can induce apoptosis via an undetermined mechanism. Future studies should explore the potential effects of glucagon in diabetic liver cancer patients.

中文翻译：

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通过超生理 GCGR 的胰高血糖素信号可以降低细胞活力而不刺激肝癌细胞中的糖异生基因表达

葡萄糖代谢失调是癌症生长和存活的关键组成部分，通过肿瘤结节中葡萄糖摄取增强的 FDG-PET 成像在临床上很明显。肿瘤细胞在各种相互关联的生化途径中利用葡萄糖来产生能量、合成代谢前体和其他生长所需的代谢物。胰高血糖素刺激的糖异生与糖酵解相反，这可能代表了一种针对肿瘤细胞中葡萄糖代谢的途径特异性策略。在这里，我们检验胰高血糖素信号传导是否可以激活糖异生以减少肝癌模型中的肿瘤增殖的假设。胰高血糖素受体 GCGR 在由一系列病因和遗传背景组成的肝癌细胞系中过度表达。通过 cAMP ELISA 测量胰高血糖素信号转导，磷酸化 PKA 底物的蛋白质印迹，以及多种糖异生酶的相对 mRNA 表达的 qPCR。最后，进行细胞增殖和凋亡测定以量化胰高血糖素/GCGR 刺激的生物学效应。用胰高血糖素处理的 SNU398 GCGR 细胞中的信号分析显示 cAMP 丰度和下游 PKA 底物（包括 CREB）的磷酸化增加。qPCR 数据表明，当用胰高血糖素处理时，三种主要的糖异生基因 G6PC、FBP1 或 PCK1 在 SNU398 GCGR 细胞中均未表现出显着更高的 mRNA 水平；然而，这可以通过表观遗传抑制剂部分增加。在胰高血糖素处理的 SNU398 GCGR 细胞中，凋亡标志物的流式细胞术分析和生长测定可重复地测量细胞活力的统计学显着降低。最后，采用 siCREB ​​抑制的增殖实验表明，在用胰高血糖素处理的 SNU398 GCGR 细胞中，细胞死亡没有逆转，表明胰高血糖素在这种情况下的作用与 CREB ​​无关。我们首次报道了胰高血糖素/GCGR 在肝癌中的潜在肿瘤抑制作用。具体来说，我们确定了一种新的细胞系特异性表型，其中胰高血糖素信号传导可以通过未确定的机制诱导细胞凋亡。未来的研究应该探索胰高血糖素对糖尿病肝癌患者的潜在影响。具体来说，我们确定了一种新的细胞系特异性表型，其中胰高血糖素信号传导可以通过未确定的机制诱导细胞凋亡。未来的研究应该探索胰高血糖素对糖尿病肝癌患者的潜在影响。具体来说，我们确定了一种新的细胞系特异性表型，其中胰高血糖素信号传导可以通过未确定的机制诱导细胞凋亡。未来的研究应该探索胰高血糖素对糖尿病肝癌患者的潜在影响。