The oncogenic BRAFV600E mutation has been associated with almost half of diagnosed human melanoma cases. Its importance in progression is underscored by the ability of a phase III BRAF inhibitor to enhance treatment in the majority of melanoma patients. However, the eventual recurrence of the disease remains prominent in a substantial subset of patients treated with BRAF inhibitors, indicating a high propensity for tumor drug resistance to this therapy.
Melanoma tumors have been found to exhibit both high intertumoral heterogeneity and contain a higher levels of somatic mutations when compared with other solid tumors. Due to this heterogeneity, researchers at the Houston Methodist Research Institute believe that synergistically targeting genes and pathways cooperating with BRAFV600E to drive tumor formation may provide a more durable melanoma therapy.
Dr. Michael Mann and fellow Houston Methodist researchers used Sleeping Beauty (SB) transposon-mediated mutagenesis to identify such candidate genes and pathways. Interestingly, the research team was able to initiate melanoma-like disease in mice (expressingBRAFV600E ) using SB mutagenesis, observing that the derived mutations were cooperative with BRAFV600E.
By analyzing 77 melanomas obtained from these mice, the researchers used whole-exome sequencing to identify the spectrum of mutations found as a result of SB mutagenesis. Mutations in tumor suppressor genes were most common, an unsurprising fact considering these mutations lead to tumor evolution. Interestingly, common transposon insertion sites (CIS) genes were often found to have one or more functional connection to another CIS gene, suggesting coordination.
Moreover, there was an enrichment for transcription factors and their cognate DNA binding sites in promoters of other CIS genes. Furthermore, CIS genes were enriched for signaling pathways and biological processes, both of which seemed to be regulated at several levels, including epigenetically. Lastly, 46 CIS genes were found to be associated with patient survival and impact patient outcomes.
The key finding of this study was the identification of CEP350 as a novel tumor suppressor gene that may drive the progression of melanoma. Abrogation of CEP350 expression augmented the progression of tumor formation, highlighting its importance. Notably, the researchers state that the tumor suppressive ability of CEP350 is likely to be a dependent on the BRAFV600E oncogene.
Using SB mutagenesis, the researchers employ a systems biology stance as a means to project promising therapeutic outcomes for the future. They predict that targeting signaling pathways and nodes, identified using SB mutagenesis, will be crucial in the development of future melanoma therapies. They state that CIS genes identified using this approach should be considered as candidate genes for more durable drug therapy aimed at targeting human melanoma.