Although ovarian cancer is the most lethal gynecologic malignancy in women, little is known about how the cancer initiates and metastasizes. In the last decade, new evidence has challenged the dogma that the ovary is the main source of this cancer. The fallopian tube has been proposed instead as the primary origin of high-grade serous ovarian cancer, the subtype causing 70% of ovarian cancer deaths. By conditionally deleting Dicer , an essential gene for microRNA synthesis, and Pten , a key negative regulator of the PI3K pathway, we show that high-grade serous carcinomas arise from the fallopian tube in mice. In these Dicer - Pten double-knockout mice, primary fallopian tube tumors spread to engulf the ovary and then aggressively metastasize throughout the abdominal cavity, causing ascites and killing 100% of the mice by 13 mo. Besides the clinical resemblance to human serous cancers, these fallopian tube cancers highly express genes that are known to be up-regulated in human serous ovarian cancers, also demonstrating molecular similarities. Although ovariectomized mice continue to develop high-grade serous cancers, removal of the fallopian tube at an early age prevents cancer formation—confirming the fallopian tube origin of the cancer. Intriguingly, the primary carcinomas are first observed in the stroma of the fallopian tube, suggesting that these epithelial cancers have a mesenchymal origin. Thus, this mouse model demonstrates a paradigm for the origin and initiation of high-grade serous ovarian carcinomas, the most common and deadliest ovarian cancer.

Endometriosis is a common disease seen by gynecologists. Clinical features involve pelvic pain and unexplained infertility. Although endometriosis is pathologically characterized by endometrial tissue outside the normal uterine location, endometriosis is otherwise not easily explained. Endometriomas, endometriotic cysts of the ovary, typically cause pain and distortion of pelvic anatomy. To begin to understand the pathogenesis of endometriomas, we describe the first transcriptome-microRNAome analysis of endometriomas and eutopic endometrium using next-generation sequencing technology. Using this approach, we generated a total of more than 54 million independent small RNA reads from our 19 clinical samples. At the microRNA level, we found 10 microRNA that were up-regulated (miR-202, 193a-3p, 29c, 708, 509-3-5p, 574-3p, 193a-5p, 485-3p, 100, and 720) and 12 microRNA that were down-regulated (miR-504, 141, 429, 203, 10a, 200b, 873, 200c, 200a, 449b, 375, and 34c-5p) in endometriomas compared with endometrium. Using in silico prediction algorithms, we correlated these microRNA with their corresponding differentially expressed mRNA targets. To validate the functional roles of microRNA, we manipulated levels of miR-29c in an in vitro system of primary cultures of human endometrial stromal fibroblasts. Extracellular matrix genes that were potential targets of miR-29c in silico were significantly down-regulated using this biological in vitro system. In vitro functional studies using luciferase reporter constructs further confirmed that miR-29c directly affects specific extracellular matrix genes that are dysregulated in endometriomas. Thus, miR-29c and other abnormally regulated microRNA appear to play important roles in the pathophysiology of uterine function and dysfunction.

MicroRNAs (miRNAs) are small noncoding RNAs that direct gene regulation through translational repression and degradation of complementary mRNA. Although miRNAs have been implicated as oncogenes and tumor suppressors in a variety of human cancers, functional roles for individual miRNAs have not been described in clear cell ovarian carcinoma, an aggressive and chemoresistant subtype of ovarian cancer. We performed deep sequencing to comprehensively profile miRNA expression in 10 human clear cell ovarian cancer cell lines compared with normal ovarian surface epithelial cultures and discovered 54 miRNAs that were aberrantly expressed. Because of the critical roles of the phosphatidylinositol 3-kinase/v-akt murine thymoma viral oncogene homolog 1/mammalian target of rapamycin (mTOR) pathway in clear cell ovarian cancer, we focused on mir-100, a putative tumor suppressor that was the most down-regulated miRNA in our cancer cell lines, and its up-regulated target, FRAP1/mTOR. Overexpression of mir-100 inhibited mTOR signaling and enhanced sensitivity to the rapamycin analog RAD001 (everolimus), confirming the key relationship between mir-100 and the mTOR pathway. Furthermore, overexpression of the putative tumor suppressor mir-22 repressed the EVI1 oncogene, which is known to suppress apoptosis by stimulating phosphatidylinositol 3-kinase/v-akt murine thymoma viral oncogene homolog 1 signaling. In addition to these specific effects, reversing the expression of mir-22 and the putative oncogene mir-182 had widespread effects on target and nontarget gene populations that ultimately caused a global shift in the cancer gene signature toward a more normal state. Our experiments have revealed strong candidate miRNAs and their target genes that may contribute to the pathogenesis of clear cell ovarian cancer, thereby highlighting alternative therapeutic strategies for the treatment of this deadly cancer.

Significance: MicroRNAs (miRNAs) are small RNAs that regulate genes by selectively silencing their target messenger RNAs. They are often produced as various sequence variants that differ at their 3′ or 5′ ends. While 5′ sequence variations affect which messenger RNAs are targeted by the miRNA, the functional significance of 3′ sequence variants remains largely elusive. Here, we analyze 3′ sequence variants of miR-21, a miRNA well known for its crucial role in cancer and other diseases. We show that tumor suppressor PAPD5 mediates adenosine addition to the 3′ end of miR-21, followed by its 3′-to-5′ trimming by an exoribonuclease. We find that this degradation pathway is disrupted across a wide variety of cancers, highlighting its importance in human disease.