title: Functional gene expression analysis uncovers phenotypic switch in aggressive uveal melanomas.
abstract: Microarray gene expression profiling is a powerful tool for generating molecular cancer classifications. However, elucidating biological insights from these large data sets has been challenging. Previously, we identified a gene expression-based classification of primary uveal melanomas that accurately predicts metastatic death. Class 1 tumors have a low risk and class 2 tumors a high risk for metastatic death. Here, we used genes that discriminate these tumor classes to identify biological correlates of the aggressive class 2 signature. A search for Gene Ontology categories enriched in our class-discriminating gene list revealed a global down-regulation of neural crest and melanocyte-specific genes and an up-regulation of epithelial genes in class 2 tumors. Correspondingly, class 2 tumors exhibited epithelial features, such as polygonal cell morphology, up-regulation of the epithelial adhesion molecule E-cadherin, colocalization of E-cadherin and beta-catenin to the plasma membrane, and formation of cell-cell adhesions and acinar structures. One of our top class-discriminating genes was the helix-loop-helix inhibitor ID2, which was strongly down-regulated in class 2 tumors. The class 2 phenotype could be recapitulated by eliminating Id2 in cultured class 1 human uveal melanoma cells and in a mouse ocular melanoma model. Id2 seemed to suppress the epithelial-like class 2 phenotype by inhibiting an activator of the E-cadherin promoter. Consequently, Id2 loss triggered up-regulation of E-cadherin, which in turn promoted anchorage-independent cell growth, a likely antecedent to metastasis. These findings reveal new roles for Id2 and E-cadherin in uveal melanoma progression, and they identify potential targets for therapeutic intervention.
authors.affiliation: Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Onken
authors.forename: Justis P
authors.initials: JP
authors.lastname: Ehlers
authors.forename: Lori A
authors.initials: LA
authors.lastname: Worley
authors.forename: Jun
authors.initials: J
authors.lastname: Makita
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Yokota
authors.forename: J William
authors.initials: JW
authors.lastname: Harbour
mesh_terms: D000818:Animals; D015820:Cadherins / Q000096:biosynthesis / Q000235:genetics; D048708:Cell Growth Processes / Q000235:genetics; D045744:Cell Line, Tumor; D020869:Gene Expression Profiling; D006801:Humans; D051797:Inhibitor of Differentiation Protein 2 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D008545:Melanoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008822:Mice, Transgenic; D014162:Transfection; D014604:Uveal Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology
chemical_list: D015820:Cadherins; C497450:ID2 protein, human; D051797:Inhibitor of Differentiation Protein 2