Because of the paucity of available tissue, little information has previously been available regarding the gene expression profiles of primary melanomas. To understand the molecular basis of melanoma progression, we compared the gene expression profiles of a series of nevi, primary melanomas, and melanoma metastases. We found that metastatic melanomas exhibit two dichotomous patterns of gene expression, which unexpectedly reflect gene expression differences already apparent in comparing laser-capture microdissected radial and vertical phases of a large primary melanoma. Unsupervised hierarchical clustering accurately separated nevi and primary melanomas. Multiclass significance analysis of microarrays comparing normal skin, nevi, primary melanomas, and the two types of metastatic melanoma identified 2,602 transcripts that significantly correlated with sample class. These results suggest that melanoma pathogenesis can be understood as a series of distinct molecular events. The gene expression signatures identified here provide the basis for developing new diagnostics and targeting therapies for patients with malignant melanoma.bioinformatics ͉ human ͉ microarray ͉ metastasis ͉ laser capture I n the current staging system for cutaneous melanoma, vertical thickness of the primary tumor is the dominant prognostic factor, belying the fact that a subset of thin tumors metastasize, whereas some thick tumors do not undergo metastasis (1). The original melanoma tumor progression model is characterized by an initial radial growth phase, encompassing in situ and minimally invasive tumors (2). This phase is followed by the development of vertical growth phase, which has been postulated to be the first point at which the tumor gains metastatic capacity. However, metastasis occurs, although with decreased frequency, in patients whose primary melanoma pathology exhibits only a radial growth pattern (3). Previous transcriptome analysis in melanoma defined a cluster of genes expressed in a majority of metastatic melanomas (4); however, this cluster was not related to radial or vertical growth, and precursor nevi (moles) and primary melanomas were not examined. Likewise, mutations in B-RAF occur commonly in both nevi (5) and melanoma (6), and, thus, do not distinguish progressive stages in melanoma progression. In this study, we used cDNA expression array profiling to characterize the global patterns of transcript modulation that underlie the various phases in the known tumor progression pathway of melanoma. MethodsStudy Subjects. Samples from melanoma patients and nevus volunteers presenting to the Melanoma Center were obtained with informed consent under a protocol approved by the UCSF Institutional Review Board. After biopsy, all samples were frozen in OCT freezing medium over dry ice. Subsequently, samples were processed for hematoxylin͞eosin staining and confirmed by pathologic review. Only samples comprised of Ͼ95% tumor cells were analyzed.

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Data on nonspecific mental retardation in two or more sibs ascertained from the British Columbia Health Surveillance Registry are utilized to calculate the frequency of X-linked mental retardation in the population of British Columbia (B.C.). In the 1950-1969 birth cohort there are 107 sibships with only males affected and 35 sibships with only females affected giving an excess of 72 male-affected sibships. Family histories of the sibships with two more more mentally retarded males provide evidence that the mothers of the excess of male-affected sibships are carriers of X-linked mental retardation. Thus, a frequency of 1.83 per 1,000 males for X-linked mental retardation and carrier frequency of 2.44 per 1,000 females are calculated. This frequency can account for all the excess of males in the population who are affected with nonspecific mental retardation. We estimate that seven to 19 X-linked genes exist to cause nonspecific mental retardation, and that the frequency of the marker-X chromosome, associated with X-linked mental retardation in some families, may be 0.92 per 1,000 male births.

BackgroundAlthough p53 is inactivated by point mutations in many tumors, melanomas infrequently harbor mutations in the p53 gene. Here we investigate the biological role of microRNA-18b (miR-18b) in melanoma by targeting the MDM2-p53 pathway.MethodsExpression of miR-18b was examined in nevi (n = 48) and melanoma (n = 92) samples and in melanoma cell lines and normal melanocytes. Immunoblotting was performed to determine the expression of various proteins regulated by miR-18b. The effects of miR-18b overexpression in melanoma cell lines were investigated using assays of colony formation, cell viability, migration, invasion, and cell cycle and in a xenograft model (n = 10 mice per group). Chromatin immunoprecipitation and methylation assays were performed to determine the mechanism of microRNA silencing.ResultsExpression of miR-18b was substantially reduced in melanoma specimens and cell lines by virtue of hypermethylation and was reinduced (by 1.5- to 5.3-fold) in melanoma cell lines after 5-AZA-deoxycytidine treatment. MDM2 was identified as a target of miR-18b action, and overexpression of miR-18b in melanoma cells was accompanied by 75% reduced MDM2 expression and 2.5-fold upregulation of p53, resulting in 70% suppression of melanoma cell colony formation. The effects of miR-18b overexpression on the p53 pathway and on melanoma cell growth were reversed by MDM2 overexpression. Stable overexpression of miR-18b produced potent tumor suppressor activity, as evidenced by suppressed melanoma cell viability, induction of apoptosis, and reduced tumor growth in vivo. miR-18b overexpression suppressed melanoma cell migration and invasiveness and reversed epithelial-to-mesenchymal transition.ConclusionsOur results demonstrate a novel role for miR-18b as a tumor suppressor in melanoma, identify the MDM2-p53 pathway as a target of miR-18b action, and suggest miR-18b overexpression as a novel strategy to reactivate the p53 pathway in human tumors.