Molecular and Environmental Toxicology Center, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin.
Department of Dermatology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin.
Mol Cancer Res. 2017 Dec;15(12):1792-1802. doi: 10.1158/1541-7786.MCR-17-0067. Epub 2017 Aug 29.
Cyclic AMP (cAMP) is an important second messenger that regulates a wide range of physiologic processes. In mammalian cutaneous melanocytes, cAMP-mediated signaling pathways activated by G-protein-coupled receptors (GPCR), like melanocortin 1 receptor (MC1R), play critical roles in melanocyte homeostasis including cell survival, proliferation, and pigment synthesis. Impaired cAMP signaling is associated with increased risk of cutaneous melanoma. Although mutations in MAPK pathway components are the most frequent oncogenic drivers of melanoma, the role of cAMP in melanoma is not well understood. Here, using the Braf(V600E)/Pten-null mouse model of melanoma, topical application of an adenylate cyclase agonist, forskolin (a cAMP inducer), accelerated melanoma tumor development and stimulated the proliferation of mouse and human primary melanoma cells, but not human metastatic melanoma cells The differential response of primary and metastatic melanoma cells was also evident upon pharmacologic inhibition of the cAMP effector protein kinase A. Pharmacologic inhibition and siRNA-mediated knockdown of other cAMP signaling pathway components showed that EPAC-RAP1 axis, an alternative cAMP signaling pathway, mediates the switch in response of primary and metastatic melanoma cells to cAMP. Evaluation of pERK levels revealed that this phenotypic switch was not correlated with changes in MAPK pathway activity. Although cAMP elevation did not alter the sensitivity of metastatic melanoma cells to BRAF(V600E) and MEK inhibitors, the EPAC-RAP1 axis appears to contribute to resistance to MAPK pathway inhibition. These data reveal a MAPK pathway-independent switch in response to cAMP signaling during melanoma progression. The prosurvival mechanism involving the cAMP-EPAC-RAP1 signaling pathway suggest the potential for new targeted therapies in melanoma. .
环磷酸腺苷 (cAMP) 是一种重要的第二信使，调节广泛的生理过程。在哺乳动物皮肤黑素细胞中，G 蛋白偶联受体 (GPCR) 激活的 cAMP 介导的信号通路，如黑素皮质素 1 受体 (MC1R)，在黑素细胞稳态中发挥关键作用，包括细胞存活、增殖和色素合成。cAMP 信号转导受损与皮肤黑色素瘤风险增加有关。虽然 MAPK 通路成分的突变是黑色素瘤最常见的致癌驱动因素，但 cAMP 在黑色素瘤中的作用尚未得到很好的理解。在这里，我们使用 Braf(V600E)/Pten-null 黑色素瘤小鼠模型，局部应用腺苷酸环化酶激动剂 forskolin（cAMP 诱导剂），加速了黑色素瘤肿瘤的发展，并刺激了小鼠和人原代黑色素瘤细胞的增殖，但对人转移性黑色素瘤细胞没有作用。原代和转移性黑色素瘤细胞的差异反应也明显表现在 cAMP 效应蛋白激酶 A 的药理学抑制中。药理学抑制和 siRNA 介导的 cAMP 信号通路其他成分的敲低表明，EPAC-RAP1 轴，一种替代的 cAMP 信号通路，介导了原代和转移性黑色素瘤细胞对 cAMP 反应的转变。评估 pERK 水平表明，这种表型转变与 MAPK 通路活性的变化无关。虽然 cAMP 升高不会改变转移性黑色素瘤细胞对 BRAF(V600E)和 MEK 抑制剂的敏感性，但 EPAC-RAP1 轴似乎有助于对 MAPK 通路抑制的耐药性。这些数据揭示了黑色素瘤进展过程中 cAMP 信号转导反应的 MAPK 通路独立转换。涉及 cAMP-EPAC-RAP1 信号通路的促生存机制表明，在黑色素瘤中具有新的靶向治疗潜力。
