MicroRNAs are small noncoding RNAs that function by regulating target gene expression posttranscriptionally. They play a critical role in developmental and physiologic processes and are implicated in the pathogenesis of several human diseases including cancer. We examined the expression profiles of 241 human microRNAs in normal tissues and the NCI-60 panel of human tumor-derived cell lines. To quantify micro-RNA expression, we employed a highly sensitive technique that uses stem-loop primers for reverse transcription followed by real-time PCR. Most microRNAs were expressed at lower levels in tumor-derived cell lines compared with the corresponding normal tissue. Agglomerative hierarchical clustering analysis of microRNA expression revealed four groups among the NCI-60 cell lines consisting of hematologic, colon, central nervous system, and melanoma tumor-derived cell lines clustered in a manner that reflected their tissue of origin. We identified specific subsets of microRNAs that provide candidate molecular signatures characteristic of the tumor-derived cell lines belonging to these four clusters. We also identified specific microRNA expression patterns that correlated with the proliferation indices of the NCI-60 cell lines, and we developed evidence for the identification of specific microRNAs as candidate oncogenes and tumor suppressor genes in different tumor types. Our results provide evidence that microRNA expression patterns may mark specific biological characteristics of tumors and/or mediate biological activities important for the pathobiology of malignant tumors. These findings call attention to the potential of microRNAs to provide etiologic insights as well as to serve as both diagnostic markers and therapeutic targets for many different tumor types. [Cancer Res 2007;67(6):2456-68]

Glioblastoma multiforme (GBM) is the most common form of malignant glioma, characterized by genetic instability, intratumoral histopathological variability, and unpredictable clinical behavior. We investigated global gene expression in surgical samples of brain tumors. Gene expression profiling revealed large differences between normal brain samples and tumor tissues and between GBMs and lower-grade oligodendroglial tumors. Extensive differences in gene expression were found among GBMs, particularly in genes involved in angiogenesis, immune cell infiltration, and extracellular matrix remodeling. We found that the gene expression patterns in paired specimens from the same GBM invariably were more closely related to each other than to any other tumor, even when the paired specimens had strikingly divergent histologies. Survival analyses revealed a set of Ϸ70 genes more highly expressed in rapidly progressing tumors that stratified GBMs into two groups that differed by >4-fold in median duration of survival. We further investigated one gene from the group, FABP7, and confirmed its association with survival in two unrelated cohorts totaling 105 patients. Expression of FABP7 enhanced the motility of glioma-derived cells in vitro. Our analyses thus identify and validate a prognostic marker of both biologic and clinical significance and provide a series of putative markers for additional evaluation.brain ͉ glioma ͉ tumor ͉ FABP7 ͉ prognosis

Proto-oncogenes may be important in the cellular processes central for the growth and differentiation of normal cells. N-myc is a DNA sequence which shares limited homology to the proto-oncogene c-myc and has been found to be amplified in both primary tissue and cell lines from neuroblastoma, a childhood tumour of neuroectodermal origin. Differentiation of this embryonal tumour is of clinical importance, since occasional tumours have been noted to differentiate in vivo to benign ganglioneuroma. In vitro, many human neuroblastoma cell lines can be induced to differentiate morphologically and biochemically by a variety of agents. Retinoic acid (RA), an analogue of vitamin A, has been shown to inhibit neuroblastoma cell growth and clonability in soft agar, and to induce extensive neurite outgrowth. Therefore we examined the relationship of N-myc expression to the in vitro differentiation of these cells. We report here that in the case of RA-induced differentiation, a decreased level of expression is detected within 6 h of treatment and precedes both cell-cycle changes and morphological differentiation.