The EMT Transcription Factor ZEB2 Promotes Proliferation of Primary and Metastatic Melanoma While Suppressing an Invasive, Mesenchymal-Like Phenotype.

Epithelial-to-mesenchymal transition (EMT)-inducing transcription factors (TF) are well known for their ability to induce mesenchymal states associated with increased migratory and invasive properties. Unexpectedly, nuclear expression of the EMT-TF ZEB2 in human primary melanoma has been shown to correlate with reduced invasion. We report here that ZEB2 is required for outgrowth for primary melanomas and metastases at secondary sites. Ablation of Zeb2 hampered outgrowth of primary melanomas in vivo, whereas ectopic expression enhanced proliferation and growth at both primary and secondary sites. Gain of Zeb2 expression in pulmonary-residing melanoma cells promoted the development of macroscopic lesions. In vivo fate mapping made clear that melanoma cells undergo a conversion in state where ZEB2 expression is replaced by ZEB1 expression associated with gain of an invasive phenotype. These findings suggest that reversible switching of the ZEB2/ZEB1 ratio enhances melanoma metastatic dissemination. SIGNIFICANCE: ZEB2 function exerts opposing behaviors in melanoma by promoting proliferation and expansion and conversely inhibiting invasiveness, which could be of future clinical relevance. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/14/2983/F1.large.jpg.

Mouse Cutaneous Melanoma Induced by Mutant BRaf Arises from Expansion and Dedifferentiation of Mature Pigmented Melanocytes.

To identify the cells at the origin of melanoma, we combined single-cell lineage-tracing and transcriptomics approaches with time-lapse imaging. A mouse model that recapitulates key histopathological features of human melanomagenesis was created by inducing a BRafV600E-driven melanomagenic program in tail interfollicular melanocytes. Most targeted mature, melanin-producing melanocytes expanded clonally within the epidermis before losing their differentiated features through transcriptional reprogramming and eventually invading the dermis. Tumors did not form within interscales, which contain both mature and dormant amelanotic melanocytes. The hair follicle bulge, which contains melanocyte stem cells, was also refractory to melanomagenesis. These studies identify varying tumor susceptibilities within the melanocytic lineage, highlighting pigment-producing cells as the melanoma cell of origin, and indicate that regional variation in tumor predisposition is dictated by microenvironmental cues rather than intrinsic differences in cellular origin. Critically, this work provides in vivo evidence that differentiated somatic cells can be reprogrammed into cancer initiating cells.

Comparative oncogenomics identifies tyrosine kinase FES as a tumor suppressor in melanoma.

Identification and functional validation of oncogenic drivers are essential steps toward advancing cancer precision medicine. Here, we have presented a comprehensive analysis of the somatic genomic landscape of the widely used BRAFV600E- and NRASQ61K-driven mouse models of melanoma. By integrating the data with publically available genomic, epigenomic, and transcriptomic information from human clinical samples, we confirmed the importance of several genes and pathways previously implicated in human melanoma, including the tumor-suppressor genes phosphatase and tensin homolog (PTEN), cyclin dependent kinase inhibitor 2A (CDKN2A), LKB1, and others. Importantly, this approach also identified additional putative melanoma drivers with prognostic and therapeutic relevance. Surprisingly, one of these genes encodes the tyrosine kinase FES. Whereas FES is highly expressed in normal human melanocytes, FES expression is strongly decreased in over 30% of human melanomas. This downregulation correlates with poor overall survival. Correspondingly, engineered deletion of Fes accelerated tumor progression in a BRAFV600E-driven mouse model of melanoma. Together, these data implicate FES as a driver of melanoma progression and demonstrate the potential of cross-species oncogenomic approaches combined with mouse modeling to uncover impactful mutations and oncogenic driver alleles with clinical importance in the treatment of human cancer.

Synthetic lethality between Rb, p53 and Dicer or miR-17-92 in retinal progenitors suppresses retinoblastoma formation.

Synthetic lethality is a promising strategy for specific targeting of cancer cells that carry mutations that are absent in normal cells. This approach may help overcome the challenge associated with targeting dysfunctional tumour suppressors, such as p53 and Rb (refs 1, 2). Here we show that Dicer1 targeting prevents retinoblastoma formation in mice by synthetic lethality with combined inactivation of p53 and Rb. Although Dicer1 functions as a haploinsufficient tumour suppressor, its complete loss of function is selected against during tumorigenesis(3-5). We show that Dicer1 deficiency is tolerated in Rb-deficient retinal progenitor cells harbouring an intact p53 pathway, but not in the absence of p53. This synthetic lethality is mediated by the oncogenic miR-17-92 cluster because its deletion phenocopies Dicer1 loss in this context. miR-17-92 inactivation suppresses retinoblastoma formation in mice and co-silencing of miR-17/20a and p53 cooperatively decreases the viability of human retinoblastoma cells. These data provide an explanation for the selective pressure against loss of Dicer1 during tumorigenesis and a proof-of-concept that targeting miRNAs may potentially represent a general approach for synthetic lethal targeting of cancer cells that harbour specific cancer-inducing genotypes.