Pro-invasion metastasis drivers in early stage melanoma are oncogenes

Clinical and genomic evidence support the view that the metastatic potential of a primary tumor may be dictated by transforming events acquired early in the tumorigenic process. It has been proposed that the presence of such pro-metastatic events in early-stage tumors reflects their additional capability to function as oncogenes. Here, to test this ‘deterministic’ hypothesis and identify potential pro-metastasis oncogenes, we adopted a comparative oncogenomics-guided functional genetic screening strategy involving (i) global transcriptomic data from two genetically engineered mouse models of melanoma with contrasting metastatic potential, (ii) genomic and transcriptomic profiles of human primary and metastatic melanoma and (iii) an invasion screen in TERT-immortalized human melanocytes and melanoma cells in vitro as well as (iv) evidence of expression selection in human melanoma tissues. This integrated effort led to the identification of 6 genes that are both potently pro-invasive and oncogenic. Further, we show that one such pro-invasion oncogene, ACP5, can confer spontaneous metastasis in vivo, engages a key pathway governing metastasis and is prognostic in human primary melanomas. The tetracycline-inducible MET-driven mouse (iMet) model (Tyr-rtTA;Tet-Met;Ink4a/Arf-/-) was constructed similar to the previously described iHRAS* model (Tyr-rtTA;Tet-HRASV12G;Ink4a/Arf-/-). RNA from cutaneous melanomas derived from iMet (n=6) or iHRAS* (n=6) models were profiled on Affymetrix M430A_2 chips and resultant transcriptomes were compared to generate a phenotype-based (metastatic capable or not) differentially expressed gene list. Cross-species triangulation to human gene expression and copy number aberrations was based on ortholog mapping.