Loss of let-7 binding sites resulting from truncations of the 3' untranslated region of HMGA2 mRNA in uterine leiomyomas.
ABSTRACT A subset of uterine leiomyomas (UL) shows chromosomal rearrangements of the region 12q14 approximately q15, leading to an overexpression of the high-mobility group protein A2 gene (HMGA2). Recent studies identified microRNAs of the let-7 family as post-transcriptional regulators of HMGA2. Intragenic chromosomal breakpoints might cause truncated HMGA2 transcripts lacking part of the 3' UTR. The corresponding loss of let-7 complementary sites (LCS) located in the 3' UTR would therefore stabilize HMGA2 mRNA. The aim of this study was to check UL with rearrangements of the chromosomal region 12q14 approximately 15 for truncated HMGA2 transcripts by real-time reverse-transcription polymerase chain reaction. In 8/13 leiomyomas with aberrations of chromosomal region 12q15, the results showed the presence of the complete 3' UTR with all LCS. A differential expression with highly reduced 3' untranslated region levels was found in 5/13 myomas. In two of these, full-length transcripts were almost undetectable. Truncated transcripts were apparently predominant in roughly one-third of UL with chromosomal rearrangements affecting the HMGA2 locus, where they lead to a higher stability of its transcripts and subsequently contribute to the overexpression of the protein. The assay used is also generally suited to detect submicroscopic alterations leading to truncated transcripts of HMGA2.
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ABSTRACT: MicroRNAs are small noncoding RNAs that recognize and bind to partially complementary sites in the 3' untranslated regions of target genes in animals and, by unknown mechanisms, regulate protein production of the target transcript. Different combinations of microRNAs are expressed in different cell types and may coordinately regulate cell-specific target genes. Here, we present PicTar, a computational method for identifying common targets of microRNAs. Statistical tests using genome-wide alignments of eight vertebrate genomes, PicTar's ability to specifically recover published microRNA targets, and experimental validation of seven predicted targets suggest that PicTar has an excellent success rate in predicting targets for single microRNAs and for combinations of microRNAs. We find that vertebrate microRNAs target, on average, roughly 200 transcripts each. Furthermore, our results suggest widespread coordinate control executed by microRNAs. In particular, we experimentally validate common regulation of Mtpn by miR-375, miR-124 and let-7b and thus provide evidence for coordinate microRNA control in mammals.Nature Genetics 06/2005; 37(5):495-500. · 35.21 Impact Factor
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ABSTRACT: HMGA2, a high-mobility group protein, is oncogenic in a variety of tumors, including benign mesenchymal tumors and lung cancers. Knockdown of Dicer in HeLa cells revealed that the HMGA2 gene is transcriptionally active, but its mRNA is destabilized in the cytoplasm through the microRNA (miRNA) pathway. HMGA2 was derepressed upon inhibition of let-7 in cells with high levels of the miRNA. Ectopic expression of let-7 reduced HMGA2 and cell proliferation in a lung cancer cell. The effect of let-7 on HMGA2 was dependent on multiple target sites in the 3' untranslated region (UTR), and the growth-suppressive effect of let-7 on lung cancer cells was rescued by overexpression of the HMGA2 ORF without a 3'UTR. Our results provide a novel example of suppression of an oncogene by a tumor-suppressive miRNA and suggest that some tumors activate the oncogene through chromosomal translocations that eliminate the oncogene's 3'UTR with the let-7 target sites.Genes & Development 06/2007; 21(9):1025-30. · 12.44 Impact Factor
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ABSTRACT: Many benign mesenchymal tumors are characterized by chromosomal abnormalities of the regions 12q15 or 6p21.3 leading to aberrant expression of either HMGA2 (formerly HMGIC) or HMGA1 (formerly HMGIY). The proteins of both genes belong to the HMGA (formerly HMGI(Y)) family of architectural transcription factors. As a rule, aberrant HMGA transcripts found in a variety of benign tumors have intact coding regions at least for the DNA binding domains with a truncation of their 3' untranslated regions. Adding this to the finding that an altered HMGA protein level is not always correlated with an increased amount of corresponding mRNA indicates a posttranscriptional expression control mediated by regulatory elements within the 3'UTR. To check if HMGA expression is under control of such elements we performed luciferase assays with several HMGA2 and HMGA1 3'UTRs of different length. Experiments showed that an up to 12-fold increase in luciferase activity is obtained by the truncation of the 3'UTRs suggesting that the expression of HMGA2 and HMGA1 is controlled by negatively acting regulatory elements within their 3'UTR. Chromosomal aberrations affecting the HMGA genes may therefore influence their expression by an altered stability of the truncated transcripts as a result of the cytogenetic aberrations.Oncogene 08/2001; 20(33):4537-41. · 7.36 Impact Factor