Lavelle Timothy J, Alver Tine Norman, Heintz Karen-Marie, Wernhoff Patrik, Nygaard Vegard, Nakken Sigve, Øy Geir Frode, Bøe Sigurd Leinæs, Urbanucci Alfonso, Hovig Eivind
Department of Tumor Biology, Institute for Cancer Research, Oslo University Hospital, 0424 Oslo, Norway.
Centre for Cancer Cell Reprogramming, Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, 0424 Oslo, Norway.
Cancers (Basel). 2020 Jun 28;12(7):1719. doi: 10.3390/cancers12071719.
The MC1R/cAMP/MITF pathway is a key determinant for growth, differentiation, and survival of melanocytes and melanoma. MITF-M is the melanocyte-specific isoform of Microphthalmia-associated Transcription Factor (MITF) in human melanoma. Here we use two melanocyte cell lines to show that forced expression of hemagglutinin (HA) -tagged MITF-M through lentiviral transduction represents an oncogenic insult leading to consistent cell transformation of the immortalized melanocyte cell line Hermes 4C, being a melanocortin-1 receptor (MC1R) compound heterozygote, while not causing transformation of the MC1R wild type cell line Hermes 3C. The transformed HA-tagged MITF-M transduced Hermes 4C cells form colonies in soft agar and tumors in mice. Further, Hermes 4C cells display increased MITF chromatin binding, and transcriptional reprogramming consistent with an invasive melanoma phenotype. Mechanistically, forced expression of MITF-M drives the upregulation of the AXL tyrosine receptor kinase (AXL), with concomitant downregulation of phosphatase and tensin homolog (PTEN), leading to increased activation of the PI3K/AKT pathway. Treatment with AXL inhibitors reduces growth of the transformed cells by reverting AKT activation. In conclusion, we present a model system of melanoma development, driven by MITF-M in the context of MC1R loss of function, and independent of UV exposure. This model provides a basis for further studies of critical changes in the melanocyte transformation process.
MC1R/cAMP/MITF信号通路是黑素细胞和黑色素瘤生长、分化及存活的关键决定因素。MITF-M是人类黑色素瘤中小眼相关转录因子（MITF）的黑素细胞特异性异构体。在此，我们利用两种黑素细胞系表明，通过慢病毒转导强制表达血凝素（HA）标记的MITF-M代表一种致癌刺激，导致永生化黑素细胞系Hermes 4C（一种黑皮质素-1受体（MC1R）复合杂合子）持续发生细胞转化，而不会导致MC1R野生型细胞系Hermes 3C发生转化。经转化的HA标记的MITF-M转导的Hermes 4C细胞在软琼脂中形成集落，并在小鼠体内形成肿瘤。此外，Hermes 4C细胞显示MITF染色质结合增加，以及与侵袭性黑色素瘤表型一致的转录重编程。从机制上讲，强制表达MITF-M驱动AXL酪氨酸受体激酶（AXL）上调，同时下调磷酸酶和张力蛋白同源物（PTEN），导致PI3K/AKT信号通路激活增加。用AXL抑制剂处理可通过恢复AKT激活来降低转化细胞的生长。总之，我们提出了一种黑色素瘤发展的模型系统，该系统由MITF-M在MC1R功能丧失的背景下驱动，且独立于紫外线暴露。该模型为进一步研究黑素细胞转化过程中的关键变化提供了基础。
