title: Gene expression profiling identifies microphthalmia-associated transcription factor (MITF) and Dickkopf-1 (DKK1) as regulators of microenvironment-driven alterations in melanoma phenotype.
abstract: BACKGROUND
  The diversity of functional phenotypes observed within a tumor does not exclusively result from intratumoral genetic heterogeneity but also from the response of cancer cells to the microenvironment. We have previously demonstrated that the morphological and functional phenotypes of melanoma can be dynamically altered upon external stimuli.
  
  
  RESULTS
  In the present study, transcriptome profiles were generated to explore the molecules governing phenotypes of melanospheres grown in the bFGF(+)EGF(+) serum-free cultures and monolayers maintained in the serum-containing medium. Higher expression levels of MITF-dependent genes that are responsible for differentiation, e.g., TYR and MLANA, and stemness-related genes, e.g., ALDH1A1, were detected in melanospheres. These results were supported by the observation that the melanospheres contained more pigmented cells and cells exerting the self-renewal capacity than the monolayers. In addition, the expression of the anti-apoptotic, MITF-dependent genes e.g., BCL2A1 was also higher in the melanospheres. The enhanced activity of MITF in melanospheres, as illustrated by the increased expression of 74 MITF-dependent genes, identified MITF as a central transcriptional regulator in melanospheres. Importantly, several genes including MITF-dependent ones were expressed in melanospheres and original tumors at similar levels. The reduced MITF level in monolayers might be partially explained by suppression of the Wnt/β-catenin pathway, and DKK1, a secreted inhibitor of this pathway, was highly up-regulated in monolayers in comparison to melanospheres and original tumors. Furthermore, the silencing of DKK1 in monolayers increased the percentage of cells with self-renewing capacity.
  
  
  CONCLUSIONS
  Our study indicates that melanospheres can be used to unravel the molecular pathways that sustain intratumoral phenotypic heterogeneity. Melanospheres directly derived from tumor specimens more accurately mirrored the morphology and gene expression profiles of the original tumors compared to monolayers. Therefore, melanospheres represent a relevant preclinical tool to study new anticancer treatment strategies.
authors.affiliation: Department of Molecular Biology of Cancer, Medical University of Lodz, Lodz, Poland.
authors.forename: Mariusz L
authors.initials: ML
authors.lastname: Hartman
authors.affiliation: Department of Molecular Biology of Cancer, Medical University of Lodz, Lodz, Poland.
authors.forename: Beata
authors.initials: B
authors.lastname: Talar
authors.affiliation: Unité INSERM U753, Institut de Cancérologie Gustave Roussy, Villejuif, France.
authors.forename: Muhammad Zaeem
authors.initials: MZ
authors.lastname: Noman
authors.affiliation: Department of Molecular Biology of Cancer, Medical University of Lodz, Lodz, Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Gajos-Michniewicz
authors.affiliation: Unité INSERM U753, Institut de Cancérologie Gustave Roussy, Villejuif, France.
authors.forename: Salem
authors.initials: S
authors.lastname: Chouaib
authors.affiliation: Department of Molecular Biology of Cancer, Medical University of Lodz, Lodz, Poland.
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Czyz
mesh_terms: D002452:Cell Count; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D003470:Culture Media; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D008543:Melanins / Q000096:biosynthesis; D008545:Melanoma / Q000235:genetics* / Q000473:pathology*; D051739:Microphthalmia-Associated Transcription Factor / Q000235:genetics / Q000378:metabolism*; D009361:Neoplasm Invasiveness; D010641:Phenotype; D044967:Serum; D018874:Spheroids, Cellular / Q000378:metabolism / Q000473:pathology; D059016:Tumor Microenvironment / Q000235:genetics*; D015854:Up-Regulation / Q000235:genetics; D060449:Wnt Signaling Pathway / Q000235:genetics; D051176:beta Catenin / Q000378:metabolism
chemical_list: D003470:Culture Media; C501126:DKK1 protein, human; D036341:Intercellular Signaling Peptides and Proteins; D008543:Melanins; D051739:Microphthalmia-Associated Transcription Factor; D051176:beta Catenin
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