Loss of NECTIN1 triggers melanoma dissemination upon local IGF1 depletion.

Cancer genetics has uncovered many tumor-suppressor and oncogenic pathways, but few alterations have revealed mechanisms involved in tumor spreading. Here, we examined the role of the third most significant chromosomal deletion in human melanoma that inactivates the adherens junction gene NECTIN1 in 55% of cases. We found that NECTIN1 loss stimulates melanoma cell migration in vitro and spreading in vivo in both zebrafish and human tumors specifically in response to decreased IGF1 signaling. In human melanoma biopsy specimens, adherens junctions were seen exclusively in areas with low IGF1 levels, but not in NECTIN1-deficient tumors. Our study establishes NECTIN1 as a major determinant of melanoma dissemination and uncovers a genetic control of the response to microenvironmental signals.

SATB2 induction of a neural crest mesenchyme-like program drives melanoma invasion and drug resistance.

Recent genomic and scRNA-seq analyses of melanoma demonstrated a lack of recurrent genetic drivers of metastasis, while identifying common transcriptional states correlating with invasion or drug resistance. To test whether transcriptional adaptation can drive melanoma progression, we made use of a zebrafish mitfa:BRAFV600E;tp53-/- model, in which malignant progression is characterized by minimal genetic evolution. We undertook an overexpression-screen of 80 epigenetic/transcriptional regulators and found neural crest-mesenchyme developmental regulator SATB2 to accelerate aggressive melanoma development. Its overexpression induces invadopodia formation and invasion in zebrafish tumors and human melanoma cell lines. SATB2 binds and activates neural crest-regulators, including pdgfab and snai2. The transcriptional program induced by SATB2 overlaps with known MITFlowAXLhigh and AQP1+NGFR1high drug-resistant states and functionally drives enhanced tumor propagation and resistance to Vemurafenib in vivo. In summary, we show that melanoma transcriptional rewiring by SATB2 to a neural crest mesenchyme-like program can drive invasion and drug resistance in autochthonous tumors.

Neural crest state activation in NRAS driven melanoma, but not in NRAS-driven melanocyte expansion.

NRAS mutations are frequently found in many deadly malignancies and are the second most common oncogene driving malignant melanoma. Here, we generate a rapid transient transgenic zebrafish model of NRASQ61R-mutant melanoma. These fish develop extensive melanocytic proliferation in approximately 4 weeks. The majority of these lesions do not engraft upon transplantation and lack overt histologic features of malignancy. Our previous work demonstrated that activation of a neural crest cell transcriptional program is a key initiating event in zebrafish BRAF/p53-driven melanomas using the fluorescent reporter crestin:EGFP. By 8-12 weeks of age, some lesions progress to malignant melanoma and have cytologic atypia, destructive tissue invasion, and express neural crest progenitor markers, including crestin:EGFP. Our studies demonstrate that NRASQ61R induces extensive melanocyte expansion, which arise during zebrafish development and lack a transformed phenotype. These early lesions are highly predisposed to reactivate a neural crest progenitor fate and form malignant melanomas.

Long-term drug administration in the adult zebrafish using oral gavage for cancer preclinical studies.

Zebrafish are a major model for chemical genetics, and most studies use embryos when investigating small molecules that cause interesting phenotypes or that can rescue disease models. Limited studies have dosed adults with small molecules by means of water-borne exposure or injection techniques. Challenges in the form of drug delivery-related trauma and anesthesia-related toxicity have excluded the adult zebrafish from long-term drug efficacy studies. Here, we introduce a novel anesthetic combination of MS-222 and isoflurane to an oral gavage technique for a non-toxic, non-invasive and long-term drug administration platform. As a proof of principle, we established drug efficacy of the FDA-approved BRAF(V600E) inhibitor, Vemurafenib, in adult zebrafish harboring BRAF(V600E) melanoma tumors. In the model, adult casper zebrafish intraperitoneally transplanted with a zebrafish melanoma cell line (ZMEL1) and exposed to daily sub-lethal dosing at 100 mg/kg of Vemurafenib for 2 weeks via oral gavage resulted in an average 65% decrease in tumor burden and a 15% mortality rate. In contrast, Vemurafenib-resistant ZMEL1 cell lines, generated in culture from low-dose drug exposure for 4 months, did not respond to the oral gavage treatment regimen. Similarly, this drug treatment regimen can be applied for treatment of primary melanoma tumors in the zebrafish. Taken together, we developed an effective long-term drug treatment system that will allow the adult zebrafish to be used to identify more effective anti-melanoma combination therapies and opens up possibilities for treating adult models of other diseases.

Identifying Novel Cancer Therapies Using Chemical Genetics and Zebrafish.

Chemical genetics is the use of small molecules to perturb biological pathways. This technique is a powerful tool for implicating genes and pathways in developmental programs and disease, and simultaneously provides a platform for the discovery of novel therapeutics. The zebrafish is an advantageous model for in vivo high-throughput small molecule screening due to translational appeal, high fecundity, and a unique set of developmental characteristics that support genetic manipulation, chemical treatment, and phenotype detection. Chemical genetic screens in zebrafish can identify hit compounds that target oncogenic processes-including cancer initiation and maintenance, metastasis, and angiogenesis-and may serve as cancer therapies. Notably, by combining drug discovery and animal testing, in vivo screening of small molecules in zebrafish has enabled rapid translation of hit anti-cancer compounds to the clinic, especially through the repurposing of FDA-approved drugs. Future technological advancements in automation and high-powered imaging, as well as the development and characterization of new mutant and transgenic lines, will expand the scope of chemical genetics in zebrafish.

Regulated ADAM17-dependent EGF family ligand release by substrate-selecting signaling pathways.

Ectodomain cleavage of cell-surface proteins by A disintegrin and metalloproteinases (ADAMs) is highly regulated, and its dysregulation has been linked to many diseases. ADAM10 and ADAM17 cleave most disease-relevant substrates. Broad-spectrum metalloprotease inhibitors have failed clinically, and targeting the cleavage of a specific substrate has remained impossible. It is therefore necessary to identify signaling intermediates that determine substrate specificity of cleavage. We show here that phorbol ester or angiotensin II-induced proteolytic release of EGF family members may not require a significant increase in ADAM17 protease activity. Rather, inducers activate a signaling pathway using PKC-α and the PKC-regulated protein phosphatase 1 inhibitor 14D that is required for ADAM17 cleavage of TGF-α, heparin-binding EGF, and amphiregulin. A second pathway involving PKC-δ is required for neuregulin (NRG) cleavage, and, indeed, PKC-δ phosphorylation of serine 286 in the NRG cytosolic domain is essential for induced NRG cleavage. Thus, signaling-mediated substrate selection is clearly distinct from regulation of enzyme activity, an important mechanism that offers itself for application in disease.

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