Transgenic Melanoma Model Research Articles

Paracrine Wnt5a-β-Catenin Signaling Triggers a Metabolic Program that Drives Dendritic Cell Tolerization

Despite recent advances, many cancers remain refractory to available immunotherapeutic strategies. Emerging evidence indicates that the tolerization of local dendritic cells (DCs) within the tumor microenvironment promotes immune evasion. Here, we have described a mechanism by which melanomas establish a site of immune privilege via a paracrine Wnt5a-β-catenin-peroxisome proliferator-activated receptor-γ (PPAR-γ) signaling pathway that drives fatty acid oxidation (FAO) in DCs by upregulating the expression of the carnitine palmitoyltransferase-1A (CPT1A) fatty acid transporter. This FAO shift increased the protoporphyrin IX prosthetic group of indoleamine 2,3-dioxgenase-1 (IDO) while suppressing interleukin(IL)-6 and IL-12 cytokine expression, culminating in enhanced IDO activity and the generation of regulatory Tcells. We demonstrated that blockade of this pathway augmented anti-melanoma immunity, enhanced the activity of anti-PD-1 antibody immunotherapy, and suppressed disease progression in a transgenic melanoma model. This work implicates a role for tumor-mediated metabolic reprogramming of local DCs in immune evasion and immunotherapy resistance.

Comparative analysis of melanoma deregulated miRNAs in the medaka and Xiphophorus pigment cell cancer models

Malignant melanoma is the most aggressive and deadly form of skin cancer, with an almost 100% development of resistance to current therapeutic approaches at progression stages. The incidence of melanoma is steadily increasing worldwide. Although many details leading to the development of malignant melanoma are known, the complex process of melanomagenesis is poorly understood. MicroRNAs (miRNAs) are a class of small noncoding-RNAs of ~22nt length that regulate gene expression at the post-transcriptional level. It is now well established that deregulated miRNA expression is seen in many cancers including melanoma. To further study the miRNA functions in melanoma formation and progression we use a transgenic melanoma model in Japanese ricefish (medaka; Oryzias latipes) and the natural Xiphophorus melanoma model. In these fishes, dependent on the genetic background various histo- and patho-types of tumors appear, comparable to human melanoma types. We have studied expression profiles of ten known human melanoma-associated miRNAs and their respective target gene expression in the fish melanoma models. We show that miRNAs of the miR-17–92 cluster (miR-20a2, miR-92a1, miR-17 and miR-18a), miR-126, miR-182, miR-210 and miR-214 are upregulated and their respective target genes (RUNX1, HIF1A, TGFBR2, THBS1 and JAK2) are down-regulated in melanoma. MicroRNA-125b is down-regulated and the target genes (ERBB3a and ERBB3b) are upregulated in fish melanomas. Results provide clear evidence that the fish melanoma-associated miRNAs and respective target genes are deregulated generally like in human melanoma. Our results confirm the value of fish; such as medaka and Xiphophorus as good model systems to identify and decipher molecular mechanisms associated with malignant melanoma.

Role of the Wnt-β-catenin signaling pathway in melanoma-mediated dendritic cell tolerization

Recent studies have shown that tumor immune evasion mechanisms significantly contribute to immunotherapy failure. Emerging data is indicating that tumor-associated dendritic cells (DCs) undergo phenotypic tolerization and promote the differentiation and activation of regulatory T cell (Treg) populations to generate local immune subversion. The critical role of DCs in orchestrating anti-tumor immunity suggests that the signaling pathways that regulate DC tolerogenesis may be promising targets for pharmacologically augmenting immunotherapy efficacy. Previous work has shown that the β-catenin signaling pathway plays a potential role in the DC tolerization process. Others have demonstrated that the DC-expressed enzyme, indoleamine 2,3-dioxygenase (IDO), promotes tumor-induced immune tolerance by catalyzing the conversion of the amino acid tryptophan into kynurenine. Other investigators have demonstrated melanomas to upregulate the expression of several Wnt ligands during their malignant transformation. Using a transgenic murine model of melanoma, we have determined that melanoma-associated DCs exhibit elevated levels of expression of IDO and other β-catenin target genes and demonstrate diminished T cell stimulatory capacity in vitro. Further studies have shown that Wnt3a and Wnt5a induce the expression and enzymatic activity of IDO in myeloid DCs (mDCs) in a β-catenin-dependent fashion while IDO reporter assays suggest this process to be mediated by direct promoter activation. This data suggest the Wnt-β-catenin signaling pathway to be a potential target for suppressing melanoma-induced DC tolerization and enhancing anti-tumor immunity. Indeed, both small molecule inhibition and genetic silencing of the PORCN acyl transferase enzyme which is necessary for Wnt secretion, abrogated B16 melanoma paracrine induction of β-catenin signaling and IDO expression by local mDCs. Further studies have shown PORCN-silenced B16 melanomas to exhibit reduced tumorigenecity in vivo and that this effect correlated with decreased mDC IDO expression and reduced levels of local Tregs. We therefore hypothesize that melanoma-expressed Wnt ligands induce DC tolerogenesis and stimulate β-catenin-dependent IDO expression and subsequent Treg generation in the tumor microenvironment, resulting in the development of an immunotolerant state and ultimately allowing for disease progression. Further, we propose that the pharmacological inhibition of this pathway can reverse this mechanism of immune evasion and enhance other immunotherapeutic approaches. Future work will include testing the ability of the small molecule PORCN inhibitor to stimulate the generation of tumor antigen-specific T cell responses in an autochthonous transgenic melanoma model.

Mouse models for melanoma: a personal perspective

Complex biological processes often require in vivo analysis, and many important research advances have been made using mice as a model for the study of various biological systems. Cutaneous melanomas are tumors originating from skin melanocytes, which are present in hair follicles, and interfollicular epidermal and dermal layers. Until recently, mouse melanoma models were largely based on transplantation models, i.e. transplantation of either syngeneic or xenogeneic melanoma cells into wild type or genetically modified animals. More recently, however, the use of novel technologies specifically modifying the genome allows for the generation of mouse strains, which may develop spontaneous melanoma. Nevertheless, it should be kept in mind that animal models provide only an approximation of reality in humans. In this review, we will discuss a representative selection of currently available transplantation and transgenic melanoma models; despite the fact that this selection will be biased by personal experience, we are confident to demonstrate how the use of mouse melanoma models facilitates translational research in several biomedical disciplines.

A Mutated EGFR Is Sufficient to Induce Malignant Melanoma with Genetic Background-Dependent Histopathologies

Melanoma is a tumor with a very low cure rate once metastasized. Although many genes important for melanoma induction, transformation, and metastasis have been identified, the process of melanomagenesis is only partly understood. Melanoma mediators are easiest to investigate in cell culture models, but animal models are required to evaluate their importance in the context of the whole organism. Here, we describe a transgenic melanoma model in medaka. The oncogenic receptor tyrosine kinase, Xmrk, responsible for melanoma formation in Xiphophorus, was stably expressed under the control of a pigment cell-specific promoter. The transgenic fish developed pigment cell tumors with a penetrance of 100%. The model was used for monitoring the in vivo relevance of several apoptosis and differentiation genes, and for induction of melanoma-relevant signal transduction pathways. We found that Stat5 activation, and Mitf and Bcl-2 levels correlated with a more aggressive stage of the malignancy. Interestingly, different types of pigment cell tumors occurred depending on the genetic background, namely invasive melanoma, uveal melanoma, or exophytic and less aggressive pigment cell tumors called xanthoerythrophoroma. Furthermore, on p53 mutant background, the expression of xmrk led to the appearance of giant focal pigment cell tumors, whereas tumor onset was unchanged compared with wild-type medaka.

Cutaneous melanoma in genetically modified animals

Cutaneous melanomas are tumors originating from skin melanocytes which are present in hair follicles, and interfollicular epidermal and dermal layers. Experimental work in model systems involves in silico, in vitro and in vivo analyses. Such models allow to mimick melanocytic aberrations characteristic of melanoma, and to potentially exploit novel therapies. Transgenic technologies can be used to modify specifically the genome of the model organism and thereby generate transgenic strains, and combinations of such strains, which may develop metastasizing melanoma. In such strains, metastasizing melanoma either arises spontaneously after a period of latency or requires additional physical or chemical induction. In this review, we summarize the work of currently available transgenic melanoma models and discuss the most recent progress in creating improved and/or inducible models reflecting the human disease.