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MicroRNAs (miRNAs) are a class of small noncoding RNAs that control gene expression by targeting mRNAs and triggering either translation repression or RNA degradation. Their aberrant expression may be involved in human diseases, including cancer. Indeed, miRNA aberrant expression has been previously found in human chronic lymphocytic leukemias, where miRNA signatures were associated with specific clinicobiological features. Here, we show that, compared with normal breast tissue, miRNAs are also aberrantly expressed in human breast cancer. The overall miRNA expression could clearly separate normal versus cancer tissues, with the most significantly deregulated miRNAs being mir-125b, mir-145, mir-21, and mir-155. Results were confirmed by microarray and Northern blot analyses. We could identify miRNAs whose expression was correlated with specific breast cancer biopathologic features, such as estrogen and progesterone receptor expression, tumor stage, vascular invasion, or proliferation index. (Cancer Res 2005; 65(16): 7065-70)

Chronic lymphocytic leukemia (CLL) is the most common human leukemia and is characterized by predominantly nondividing malignant B cells overexpressing the antiapoptotic B cell lymphoma 2 (Bcl2) protein. miR-15a and miR-16-1 are deleted or down-regulated in the majority of CLLs. Here, we demonstrate that miR-15a and miR-16-1 expression is inversely correlated to Bcl2 expression in CLL and that both microRNAs negatively regulate Bcl2 at a posttranscriptional level. BCL2 repression by these microRNAs induces apoptopsis in a leukemic cell line model. Therefore, miR-15 and miR-16 are natural antisense Bcl2 interactors that could be used for therapy of Bcl2-overexpressing tumors.

A unique microRNA signature is associated with prognostic factors and disease progression in CLL. Mutations in microRNA transcripts are common and may have functional importance.

Recent research has identified critical roles for microRNAs in a large number of cellular processes, including tumorigenic transformation. While significant progress has been made towards understanding the mechanisms of gene regulation by microRNAs, much less is known about factors affecting the expression of these noncoding transcripts. Here, we demonstrate for the first time a functional link between hypoxia, a welldocumented tumor microenvironment factor, and microRNA expression. Microarray-based expression profiles revealed that a specific spectrum of microRNAs (including miR-23, -24, -26, -27, -103, -107, -181, -210, and -213) is induced in response to low oxygen, at least some via a hypoxia-inducible-factor-dependent mechanism. Select members of this group (miR-26, -107, and -210) decrease proapoptotic signaling in a hypoxic environment, suggesting an impact of these transcripts on tumor formation. Interestingly, the vast majority of hypoxiainduced microRNAs are also overexpressed in a variety of human tumors.

M icroRNAs (miRNAs) represent a class of small, functional, noncoding RNAs of 19-23 nt cleaved from Ϸ60-to 110-nt hairpin precursors (1, 2). Hundreds of miRNAs have been identified in plants and animals. The miRNAs are involved in various biological processes, including cell proliferation and cell death during development, stress resistance, and fat metabolism, through the regulation of gene expression (3). Some miRNAs, such as miR-15a or miR-16-1 (4, 5), are widely expressed, whereas others, such as miR-1 in mammalian heart (6, 7) or miR-223 in granulocytes and macrophages (5), are expressed in a tissue-specific manner. Little else is known about miRNA expression patterns or function in normal or neoplastic cells.Understanding of the molecular pathogenesis of B cell chronic lymphocytic leukemia (CLL), the most common adult leukemia in the Western world, is incomplete. We have shown previously that miR-15a and miR-16-1 are located at chromosome 13q14.3 within a 30-kb region of loss in CLL cells and that both genes are deleted and͞or down-regulated in the majority of the analyzed CLL cell samples (4). These results provided the indication that deletion of miRNAs might be associated with a human malignancy. We also reported that 98 of the identified 186 miRNAs are located at fragile sites, minimal loss of heterozygosity regions, minimal regions of amplification, or common breakpoint regions in human cancers (8), suggesting that miRNAs might play a large and unanticipated role in the pathogenesis of human cancer. MethodsTissue Samples and CLL Samples. Forty-seven samples were used for this study, including 41 samples from 38 patients with CLL and 6 normal samples, including one lymph node, tonsillar CD5ϩ B cells from two normal donors, and blood mononuclear cells (MNC) from three normal donors. For three cases, two independent samples were collected and processed. CLL samples were obtained after informed consent from patients diagnosed with CLL at the CLL Research Consortium institutions. Briefly, blood was obtained from CLL patients, and MNC were isolated through Ficoll͞Hypaque gradient centrifugation (Amersham Pharmacia Biotech) and processed for RNA extraction according to described protocols (9). For the majority of samples, clinical and biological information, such as age at diagnosis, sex, Rai stage, presence͞absence of treatment, ZAP-70 expression, and IgV H gene mutation status were available (see Table 4, which is published as supporting information on the PNAS web site).Cell Preparation. MNC from peripheral blood of normal donors were separated by Ficoll-Hypaque density gradients. T cells were purified from these MNC by rosetting with neuraminidasetreated sheep erythrocyte and depletion of contaminant monocytes (Cd11bϩ); natural killer cells (CD16ϩ) and B lymphocytes (CD19ϩ) were purified by using magnetic beads (Dynabeads, Unipath, Milan) and specific mAbs (Becton Dickinson). Total B cells and CD5ϩ B cells were prepared from tonsillar lymphocytes as described (10). Briefly, tonsils were obtained from pat...

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Noncoding RNA (ncRNA) transcripts are thought to be involved in human tumorigenesis. We report that a large fraction of genomic ultraconserved regions (UCRs) encode a particular set of ncRNAs whose expression is altered in human cancers. Genome-wide profiling revealed that UCRs have distinct signatures in human leukemias and carcinomas. UCRs are frequently located at fragile sites and genomic regions involved in cancers. We identified certain UCRs whose expression may be regulated by microRNAs abnormally expressed in human chronic lymphocytic leukemia, and we proved that the inhibition of an overexpressed UCR induces apoptosis in colon cancer cells. Our findings argue that ncRNAs and interaction between noncoding genes are involved in tumorigenesis to a greater extent than previously thought.