Abstract 4032: Elevated level of let-7a and mir-30c microRNAs in human prostate cancer

MicroRNAs (miRNAs) are endogenously expressed non-coding RNAs that negatively regulate the expression of protein coding genes at the translational level. Evidence from recent studies suggests that cancer development is associated with deregulation of specific set of miRNAs that determines the cancer characteristics. Recently, miRNA profiling has been shown to identify cancer specific miRNA signatures that are specific to different cellular origin. However, the functional significance of specific miRNAs in prostate cancer developmental stages remains to be investigated. Further, identification and characterization of tumor derived miRNAs using advanced and reliable techniques may benefit early detection and prevention strategies. In this study, to identify potential miRNAs in human prostate cancer tissue specimens, we used 15 human prostate cancer tissue microarrays (TMAs) with 36 cores in each representing different stages of the cancer. We detected the expression of miRNA let-7a and mir-30c by performing locked nucleic acid-in-situ hybridization (LNA-ISH) (EXIQON, Vedbaek, Denmark). To obtain maximal sensitivity of miRNA expression signal, we used double (3′ and 5″) digoxigenin-labeled LNA probes (MiRCURY LNA) of 20uM each after optimizing with lower and higher dilutions. Oversaturation was avoided by reducing the temperature (30-35°C) and the time of exposure (24h). As a negative control the tissues were hybridized either with mismatch or no probe. We determined the expression level of the miRNAs in (a) precancerous single acinus or small group of acini and (b) in the regions of prostatic adenocarcinoma or high grade PIN. Our findings indicated abundant expression of both let-7a and mir-30c localized only in the nucleus of the cells in HGPIN, in contrary to that in the early PIN lesions, where let-7 and mir-30c miRNAs were localized both in the cytoplasm, as well as in the nucleus. Interestingly, not all the acini showed a positive staining for let-7, suggesting the possibility of down regulation of let-7 in the non-neoplastic regions. Finally, the difference in the expression of let-7a and mir-30c in the stroma vs. tumor acini were compared and quantified to predict their functional significance related to tumor proliferation. Although the findings on the expression of let-7a and mir-30c were consistent in more than 20% of the TMAs examined, we observed weak or no signal in several of the tumor acini (5%) suggesting a heterogeneous expression pattern. Overall, our findings suggest that examining the expression level of miRNAs in the nucleus vs. cytoplasm of tumor cells at different stages of prostate cancer is critical to determine the functional status of let-7a and mir30c. Most importantly, monitoring a shift in their expression pattern will provide significant opportunities to define diagnostically useful miRNA as biomarkers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4032.