Melanoma systems biology for therapeutic discovery

This project utilized a systems biology approach to identify novel potential therapeutic targets in malignant melanoma. The project contained two published papers and one submitted manuscript. The PhD thesis based on this project has been successfully defended by the candidate and was accepted for the degree of PhD by the The Faculty of Medicine, University of Oslo, June 29th 2020. Project 1: The transcription factor MITF (Microphthalmia-Associated Transcription Factor) has been shown to play a role in the development of acquired vemurafenib drug resistance. In this subproject study, we discovered that under normal conditions (in melanoma cell lines), MITF inhibits growth factor receptor ERBB3 and its ligand NRG1. However, during vemurafenib treatment, MITF levels began to decrease, leading to an increase in ERBB3 and NRG1 expression. An up-regulation of ERBB3 and NRG1 expression contributed to sustained proliferation and survival of melanoma cell lines under vemurafenib treatment. This study was published in Oncotarget in 2016 doi: 10.18632/oncotarget.10422 Project 2: The role of MITF in melanoma development remains poorly understood. In a second subproject study, we attempted to gain insight into MITF regulation in wild type MC1R vs. MC1R mutants. MC1R mutants give rise to red hair, with a consequence for melanoma risk. To achieve insight, we analyzed the regulatory landscape of immortalized human melanocytes and gene modified variants by genome-wide MITF binding (Chip-Seq) and transcriptome (RNA-Seq). These data sets and corresponding histone modification sets were integrated by in silico regulatory landscape analysis to map regulatory variation between the two genotypes. We have here identified candidate factors involved in oncogenesis as potential targets of therapy. This paper was published in Cancers in 2020. https://doi.org/10.3390/cancers12071719 Project 3: The roles of AXL/GAS6 and ERBB3/NRG1 expression and signalling in melanoma have been associated with tumor growth, invasion and drug resistance. In this subproject, we show that these pathways are mainly controlled by the SOX10/MITF axis and that they interplay to sustain tumor growth. Melanoma cell lines can be divided into subgroups according to their expression levels of AXL and ERBB3. Our results show that all of these sub-groups utilize either the AXL/GAS6, ERBB3/NRG1 or both pathways for activation of the PI3K/AKT pathway. We demonstrate that evaluation of MITF/SOX10 and ERBB3/AXL levels in tumors is essential for finding the appropriate drug combination, and that AXL or ERBB3 inhibitors are useful in combination with MAPK inhibitors for overcoming MAPK resistance. A manuscript describing these findings has been submitted. Altogether, we have demonstrated potential therapeutic targets, and demonstrated that important pathways may be manipulated to modify signalling in these targets. We have developed a model system for induction of spontaneous transformation of melanocytes to cell able to form tumors in mice. We aim to develop this model further to derive insights into the epigenetic regulation of melanoma. This work has primarily been to build further underpinning for melanoma management, through better understanding of signalling mechanisms that are at play, and how the interconnect and may be manipulated.