PDF(Pubmed)
Abstract：
Hotspot mutations in the NRAS gene are causative genetic events associated with the development of melanoma. Currently, there are no FDA-approved drugs directly targeting NRAS mutations. Previously, we showed that p38 acts as a tumor suppressor in vitro and in vivo with respect to NRAS-mutant melanoma. We observed that because of p38 activation through treatment with the protein synthesis inhibitor, anisomycin leads to a transient upregulation of several targets of the cAMP pathway, representing a stressed cancer cell state that is often observed by therapeutic doses of MAPK inhibitors in melanoma patients. Meanwhile, genetically induced p38 or its stable transduction leads to a distinct cellular transcriptional state. Contrary to previous work showing an association of invasiveness with high p38 levels in BRAF-mutated melanoma, there was no correlation of p38 expression with NRAS-mutant melanoma invasion, highlighting the difference in BRAF and NRAS-driven melanomas. Although the role of p38 has been reported to be that of both tumor suppressor and oncogene, we show here that p38 specifically plays the role of a tumor suppressor in NRAS-mutant melanoma. Both the transient and stable activation of p38 elicits phosphorylation of mTOR, reported to be a master switch in regulating autophagy. Indeed, we observed a correlation between elevated levels of phosphorylated mTOR and a reduction in LC3 conversion (LCII/LCI), indicative of suppressed autophagy. Furthermore, a reduction in actin intensity in p38-high cells strongly suggests a role of mTOR in regulating actin and a remodeling in the NRAS-mutant melanoma cells. Therefore, p38 plays a tumor suppressive role in NRAS-mutant melanomas at least partially through the mechanism of mTOR upregulation, suppressed autophagy, and reduced actin polymerization. One or more combinations of MEK inhibitors with either anisomycin, rapamycin, chloroquine/bafilomycin, and cytochalasin modulate p38 activation, mTOR phosphorylation, autophagy, and actin polymerization, respectively, and they may provide an alternate route to targeting NRAS-mutant melanoma.
摘要：
NRAS基因中的热点突变是与黑色素瘤发展相关的致病遗传事件。目前,目前尚无FDA批准的直接靶向NRAS突变的药物.以前,我们表明p38在体外和体内对NRAS突变黑色素瘤起肿瘤抑制作用。我们观察到，由于p38通过蛋白质合成抑制剂的处理而激活，茴香霉素导致cAMP途径的几个靶标的瞬时上调，代表黑色素瘤患者中治疗剂量的MAPK抑制剂经常观察到的应激性癌细胞状态。同时,遗传诱导的p38或其稳定的转导导致不同的细胞转录状态。与以前的工作相反，在BRAF突变的黑色素瘤中，侵袭性与高p38水平有关，p38表达与NRAS突变型黑色素瘤侵袭无关，突出BRAF和NRAS驱动的黑色素瘤的差异。虽然p38的作用已被报道为肿瘤抑制和癌基因，我们在此表明p38在NRAS突变黑色素瘤中特异性发挥肿瘤抑制因子的作用.p38的瞬时和稳定激活都会引起mTOR的磷酸化，据报道是调节自噬的总开关。的确,我们观察到磷酸化mTOR水平升高与LC3转化（LCII/LCI）降低之间的相关性，表明抑制自噬。此外，p38-high细胞中肌动蛋白强度的降低强烈提示mTOR在调节NRAS突变黑色素瘤细胞中的肌动蛋白和重塑中的作用.因此,p38在NRAS突变黑色素瘤中发挥肿瘤抑制作用，至少部分通过mTOR上调机制，抑制自噬，和减少肌动蛋白聚合。MEK抑制剂与茴香霉素的一种或多种组合，雷帕霉素,氯喹/巴弗洛霉素，和细胞松弛素调节p38的激活，mTOR磷酸化，自噬,和肌动蛋白聚合，分别,它们可能提供靶向NRAS突变黑色素瘤的替代途径。
