Although prostate cancer (CaP) is the most frequently diagnosed malignant tumor and the second leading cause of cancer deaths in American men, the mechanisms explaining the development and progression of CaP remain largely unknown. Recent studies have shown that some aberrantly expressed microRNAs (miRNAs) are involved in tumorigenesis. Although aberrant expression of certain miRNAs has been discovered in CaP, their function in this disease has not yet been defined. In this study, we found differential expression of miR-125b in androgen-dependent and independent CaP cells, as well as in benign and malignant prostate tissues. Furthermore, androgen signaling was able to up-regulate the expression of miR-125b. In addition, transfection of synthetic miR-125b stimulated androgen-independent growth of CaP cells and down-regulated the expression of Bak1. Our results suggest that miR-125b acts as an oncogene, contributing to the pathogenesis of CaP.microRNA ͉ miR-125b ͉ ISH ͉ LNCaP

Estrogen receptor ␣ (ER␣)3 is an important marker for prognosis and is predictive of response to endocrine therapy in patients with breast cancer. Although the majority of primary breast cancers are ER␣-positive and respond to antiestrogen therapy, up to one-third of patients with breast cancer lack ER␣ at the time of diagnosis, and a fraction of breast cancers that are initially ER␣-positive lose ER␣ expression during tumor progression (1). These patients fail to respond to antiestrogen therapy and have a poor prognosis. Previous studies have shown that ER␣ absence is a result of hypermethylation of CpG islands in the 5Ј-regulatory regions of ER␣ in a fraction of breast cancers (1). However, the molecular mechanism of the rest of the ER␣-negative cases and the molecule(s) involving ER␣ hypermethylation remain largely unknown (1).MicroRNAs (miRNAs) are a new class of small (ϳ22 nucleotide) noncoding RNAs and negatively regulate protein-coding gene expression by targeting mRNA degradation or translation inhibition (2-5). Frequent deregulation of miRNAs has been detected in breast cancer, and some are associated with breast cancer metastasis and poor prognosis, suggesting an important role of miRNAs in breast oncogenesis and cancer progression (6 -9). In this study, we performed miRNA profiling in ER␣-negative versus ER␣-positive human breast cancer cell lines and primary tumors and identified the deregulation of a panel of miRNAs in ER␣-negative breast cancer. Of the elevated miRNAs, miR-221 and miR-222 were found to directly regulate ER␣ expression by interaction with the 3Ј-untranslated region (3Ј-UTR) of ER␣. Ectopic expression of miR-221 and/or miR-222 reduced ER␣ levels in MCF-7 and T47D cells, whereas knockdown of miR-221 and/or miR-222 restored ER␣ expression and tamoxifen sensitivity in MDA-MB-468 cells. These results indicate that miR-221 and miR-222 could play a pivotal role in the regulation of ER␣ expression in a subset of breast cancers. EXPERIMENTAL PROCEDURESCell Lines, Transfection, and Human Tumor Tissues-Human breast cancer cell lines (T47D, BT474, MDA-MB-361, MCF-7, MDA-MB-453, MDA-MB-157, SKBr3, MDA-MB-468, Hs578T, MDA-MB-231, and MDA-MB-435s) and spontaneously immortalized human breast epithelial cells (MCF-10A) were obtained from American Type Culture Collection. Breast cancer cell lines were grown in either RPMI 1640 medium (Sigma) or Dulbecco's modified Eagle's medium (Sigma) supplemented with 10% fetal bovine serum. MCF-10A cells were cultured in mammary epithelium basal medium plus mammary epithelium growth medium (Clonetics). Transfection of 2Ј-O-MeantamiR oligonucleotides or pcDNA6.2-GW/EmGFP-miR (BLOCK-iT) plasmids was performed using Lipofectamine 2000 (Invitrogen) following the manufacturer's instructions. Stable cell lines were obtained by blasticidin selection. The sequences of 2Ј-O-Me-anta-miR-221 and 2Ј-O-Me-anta-miR-222 are 5Ј-GAAACCCAGCAGACAAUGUAGCU-3Ј and 5Ј-ACCCAGUAGCCAGAUGUAGCU-3Ј. Scrambled 2Ј-O-Me-* This work was supported, in whole or in part, by National Institutes of H...

These miRNAs are the first to be reported for human retinoblastoma and may play significant roles in regulating tumor genesis.