br glucocorticoid receptor have significantly shorter
glucocorticoid receptor have significantly shorter progression-free survival.42
miR-182 targets that may explain its observed association with recurrence were identified from genes that contain predicted miR-182 KPT185 and negatively correlate with miR-182 in benign prostate epithelium. These genes
include CD164, which promotes circulating cancer cell adherence to bone57; ARF4, which contributes to a meta-static increased ER-Golgi trafficking phenotype in breast cancer58; PRKAR1A, which was higher expressed in patients with PCa who developed metastasis41; and NUFIP2, a stress granule protein and member of the metastasis gene set used in the study by Chandran et al.37 Kyoto Encyclopedia of Genes and Genomes pathways enriched in the miR-182 negatively correlated genes have also been linked to
aggressive PCa, including protein degradation, sphingolipid synthesis, and inflammation.59e61 Interestingly, ELL2, one of the most strongly negatively correlated genes with miR-
182, induces a PIN phenotype in murine prostate when conditionally deleted,62 and we observed high expression of miR-182 in PIN. There may be limitations to our miR-182 target-identification method, however, because several pre-
viously reported targets of miR-182 were not strongly negatively correlated with miR-182 in our data set.17,18,20,21
Discrepancies between our target predictions and published targets of miR-182 in prostate cell lines are likely a result of our approach, including using LCM-collected total epithe-lium rather than cell cultures. Our RNA expressionebased associations would not detect targets that are primarily down-regulated by miR-182 by translation blockade rather than mRNA instability. Another limitation is that differ-ences in miR-182 gene targets may also exist between benign prostate and PCa. Although many predicted targets also negatively correlated with miR-182 in TCGA tumor samples, others did not or had positive correlations. This
might support different regulation in tumors; however, because miR-182 in prostate is epithelial, the results are confounded by the varying epithelial/stromal composition of TCGA samples. In future studies, predicted prometastatic targets of miR-182 in LCM-collected prostate epithelium should be tested for correlation to miR-182 in LCM-collected PCa specimens and validated functionally.
Although only a small number of patients with LCM-collected tissue were analyzed in this study, the observa-tion that miR-182 expression was significantly lower in benign prostate epithelium from African American men than European men is of potential interest. African ancestry is considered a risk factor for PCa,43 and both the incidence and mortality of PCa is approximately twice as high in African American men compared with other men.63 Genes that were negatively correlated with miR-182 in our LCM microarray data significantly aligned with gene set signatures of genes highly expressed in PCa from African American patients,38,44 suggesting that miR-182 levels may also be lower in PCa in African American men. Because low miR-182 was associated with recurrence in this study, lower levels of miR-182 may drive a gene expression profile from which aggressive prostate tumors arise in African American men. Importantly, our analysis was limited to benign epithelium, and it remains to be tested if the lower expression of miR-182 observed in African American men persists in cancer. By ISH, the cancer/benign ratio of miR-182 was not significantly different between African American and European men (Supplemental Figure S3), a finding limited by the lack of outcome data available for these men.
In summary, we conclude that the role of miR-182 in PCa is bimodal. Increased expression of miR-182 in PCa may promote early or localized disease, but higher magnitude changes in miR-182 expression in PCa may protect against disease recurrence or not be selected for in aggressive dis-ease. A strength of this study is the use of ISH and LCM, which allowed for precise analysis of an epithelial miR, in
contrast to previous similar studies that use whole or mac-rodissected prostate tissue.21,39,40,47 A limitation to this study is the small sample size of patients with recurrence data analyzed (n Z 56) and that patients with recurrence data lacked data for modern clinical risk estimators. Lower expression of miR-182 in prostate biopsy specimens may be a clinically useful indicator of high-risk PCa in conjunction with existing risk estimators, and future studies in a larger and more ethnically diverse cohort are needed to confirm that miR-182 is associated with recurrence.
We thank Dr. Virgilia Macias for input; UIC urologists Drs. Michael Abern, Simone Crivallaro, and Dan Moriera for consenting patients; and the UIC Biorepository and the patients who donated tissue to this study.