RESUMEN
Studying cancer metabolism gives insight into tumorigenic survival mechanisms and susceptibilities. In melanoma, we identify HEXIM1, a transcription elongation regulator, as a melanoma tumor suppressor that responds to nucleotide stress. HEXIM1 expression is low in melanoma. Its overexpression in a zebrafish melanoma model suppresses cancer formation, while its inactivation accelerates tumor onset in vivo. Knockdown of HEXIM1 rescues zebrafish neural crest defects and human melanoma proliferation defects that arise from nucleotide depletion. Under nucleotide stress, HEXIM1 is induced to form an inhibitory complex with P-TEFb, the kinase that initiates transcription elongation, to inhibit elongation at tumorigenic genes. The resulting alteration in gene expression also causes anti-tumorigenic RNAs to bind to and be stabilized by HEXIM1. HEXIM1 plays an important role in inhibiting cancer cell-specific gene transcription while also facilitating anti-cancer gene expression. Our study reveals an important role for HEXIM1 in coupling nucleotide metabolism with transcriptional regulation in melanoma.
Asunto(s)
Melanoma/metabolismo , Factor B de Elongación Transcripcional Positiva/genética , Pirimidinas/metabolismo , Proteínas de Unión al ARN/genética , Proteínas de Unión al ARN/metabolismo , Animales , Línea Celular Tumoral , Regulación Neoplásica de la Expresión Génica , Humanos , Melanoma/genética , Melanoma/patología , Melanoma Experimental , Proteínas Oncogénicas/genética , Factores de Transcripción , Transcripción Genética , Proteínas Supresoras de Tumor/genética , Pez Cebra/genética , Proteínas de Pez Cebra/genética , Proteínas de Pez Cebra/metabolismoRESUMEN
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.
Asunto(s)
Modelos Animales de Enfermedad , Neoplasias/tratamiento farmacológico , Neoplasias/genética , Animales , Ensayos de Selección de Medicamentos Antitumorales , Neoplasias/patología , Pez CebraRESUMEN
The "cancerized field" concept posits that cancer-prone cells in a given tissue share an oncogenic mutation, but only discreet clones within the field initiate tumors. Most benign nevi carry oncogenic BRAF(V600E) mutations but rarely become melanoma. The zebrafish crestin gene is expressed embryonically in neural crest progenitors (NCPs) and specifically reexpressed in melanoma. Live imaging of transgenic zebrafish crestin reporters shows that within a cancerized field (BRAF(V600E)-mutant; p53-deficient), a single melanocyte reactivates the NCP state, revealing a fate change at melanoma initiation in this model. NCP transcription factors, including sox10, regulate crestin expression. Forced sox10 overexpression in melanocytes accelerated melanoma formation, which is consistent with activation of NCP genes and super-enhancers leading to melanoma. Our work highlights NCP state reemergence as a key event in melanoma initiation.
Asunto(s)
Carcinogénesis/genética , Regulación del Desarrollo de la Expresión Génica , Regulación Neoplásica de la Expresión Génica , Melanoma Experimental/genética , Melanoma/genética , Cresta Neural/metabolismo , Neoplasias Cutáneas/genética , Pez Cebra , Animales , Animales Modificados Genéticamente , Células Madre Embrionarias/metabolismo , Elementos de Facilitación Genéticos , Genes Reporteros , Proteínas Fluorescentes Verdes/genética , Melanocitos/metabolismo , Mutación , Proteínas del Tejido Nervioso/genética , Proteínas Proto-Oncogénicas B-raf/genética , Factores de Transcripción SOXE/genética , Proteína p53 Supresora de Tumor/genética , Proteínas de Pez Cebra/genéticaRESUMEN
In mammalian embryonic stem cells, the acquisition of pluripotency is dependent on Nanog, but the in vivo analysis of Nanog has been hampered by its requirement for early mouse development. In an effort to examine the role of Nanog in vivo, we identified a zebrafish Nanog ortholog and found that its knockdown impaired endoderm formation. Genome-wide transcription analysis revealed that nanog-like morphants fail to develop the extraembryonic yolk syncytial layer (YSL), which produces Nodal, required for endoderm induction. We examined the genes that were regulated by Nanog-like and identified the homeobox gene mxtx2, which is both necessary and sufficient for YSL induction. Chromatin immunoprecipitation assays and genetic studies indicated that Nanog-like directly activates mxtx2, which, in turn, specifies the YSL lineage by directly activating YSL genes. Our study identifies a Nanog-like-Mxtx2-Nodal pathway and establishes a role for Nanog-like in regulating the formation of the extraembryonic tissue required for endoderm induction.