Background/objective:Mucosal melanoma (MM) is a poorly responsive, rare and aggressive subtype with few cases having targetable recurrent driver mutations, although Ras/MAPK and PI3K/AKT/mTOR signaling pathway activations are common. Eventual tumor evasion of targeted therapy continues to limit treatment success. Adequate models are necessary to address therapeutic resistance. The relatively greater incidence of naturally occurring MM in dogs, as well as its comparable clinical and pathological characteristics to human MM, represents an opportunity for study as a human MM patient surrogate. Resistance-promoting crosstalk between Ras/MAPK and PI3K/AKT/mTOR signaling under trametinib inhibition of MEK was studied in canine MM. Emphasis was placed on the suppressive effect of trametinib on cell cycle entry and its potential role in drug resistance.Methods: D-type cyclins were investigated following trametinib treatment of five MM cell lines exhibiting differential drug sensitivities. Signaling pathway activation, proliferation, survival, cell death, and cell cycle were analyzed in the context of D-type cyclin expression. Cyclin D2 expression was manipulated using siRNA knockdown or inducible recombinant overexpression.Results: Trametinib diminished cyclin D1 in all cell lines. While relatively trametinib-resistant MM cells exhibited capacity to upregulate cyclin D2, which promoted proliferation, sensitive MM cells lacked similar cyclin D2 compensation. Inhibition of the compensatory cyclin D2 in resistant cells conferred sensitivity. Induced cyclin D2 overexpression in otherwise trametinib-sensitive MM cells promoted survival. Upregulated PI3K/AKT/mTOR signaling under trametinib treatment was suppressed by mTORC1/2 inhibition, which similarly diminished cyclin D2 response.Conclusions: The compensatory switch from preferential reliance on cyclin D1 to D2 plays a role in MM resistance to MEK inhibition.
背景/目的：黏膜黑色素瘤是一种治疗反应差、罕见且侵袭性强的亚型，尽管Ras/MAPK和PI3K/AKT/mTOR信号通路激活较为常见，但具有可靶向性复发性驱动突变的病例极少。靶向治疗最终出现的肿瘤逃逸现象持续限制着治疗成功率。建立合适的模型对于解决治疗耐药性问题至关重要。犬类自然发生的黏膜黑色素瘤发病率相对较高，且其临床与病理特征与人类黏膜黑色素瘤具有可比性，这为将其作为人类黏膜黑色素瘤患者替代模型进行研究提供了契机。本研究在犬黏膜黑色素瘤模型中，探讨了曲美替尼抑制MEK过程中Ras/MAPK与PI3K/AKT/mTOR信号通路间促进耐药的交互作用，重点关注曲美替尼对细胞周期进入的抑制作用及其在耐药性中的潜在作用。 方法：对五种具有不同药物敏感性的黏膜黑色素瘤细胞系进行曲美替尼处理后，研究D型细胞周期蛋白的变化。在D型细胞周期蛋白表达的背景下，分析信号通路激活、增殖、存活、细胞死亡和细胞周期进程。通过siRNA敲低或诱导性重组过表达技术调控细胞周期蛋白D2的表达。 结果：曲美替尼在所有细胞系中均降低了细胞周期蛋白D1水平。相对耐药的黏膜黑色素瘤细胞表现出上调细胞周期蛋白D2的能力，从而促进细胞增殖，而敏感细胞则缺乏类似的细胞周期蛋白D2代偿机制。抑制耐药细胞中的代偿性细胞周期蛋白D2可恢复其药物敏感性。在原本对曲美替尼敏感的黏膜黑色素瘤细胞中诱导细胞周期蛋白D2过表达可促进细胞存活。曲美替尼处理下上调的PI3K/AKT/mTOR信号通路可通过mTORC1/2抑制被阻断，该抑制同样减弱了细胞周期蛋白D2的代偿性反应。 结论：从优先依赖细胞周期蛋白D1向D2的代偿性转换，在黏膜黑色素瘤对MEK抑制剂的耐药机制中发挥着重要作用。
肿瘤(癌症)患者之家