Synergistic effects of Pten loss and WNT/CTNNB1 signaling pathway activation in ovarian granulosa cell tumor development and progression

Either Kras activation or Pten loss similarly enhance the dominant-stable CTNNB1-induced genetic program to promote granulosa cell tumor development in the ovary and testis

WNT, RAS or phosphoinositide 3-kinase signaling pathways control specific stages of ovarian follicular development. To analyze the functional interactions of these pathways in granulosa cells during follicular development in vivo, we generated specific mutant mouse models. Stable activation of the WNT signaling effector β-catenin (CTNNB1) in granulosa cells results in the formation of premalignant lesions that develop into granulosa cell tumors (GCTs) spontaneously later in life or following targeted deletion of the tumor suppressor gene Pten. Conversely, expression of oncogenic KRAS(G12D) dramatically arrests proliferation, differentiation and apoptosis in granulosa cells, and consequently, small abnormal follicle-like structures devoid of oocytes accumulate in the ovary. Because of the potent anti-proliferative effects of KRAS(G12D) in granulosa cells, we sought to determine whether KRAS(G12D) would block precancerous lesion and tumor formation in follicles of the CTNNB1-mutant mice. Unexpectedly, transgenic Ctnnb1;Kras-mutant mice exhibited increased GC proliferation, decreased apoptosis and impaired differentiation and developed early-onset GCTs leading to premature death in a manner similar to the Ctnnb1;Pten-mutant mice. Microarray and reverse transcription-PCR analyses revealed that gene regulatory processes induced by CTNNB1 were mostly enhanced by either KRAS activation or Pten loss in remarkably similar patterns and degree. The concomitant activation of CTNNB1 and KRAS in Sertoli cells also caused testicular granulosa cell tumors that showed gene expression patterns that partially overlapped those observed in GCTs of the ovary. Although the mutations analyzed herein have not yet been linked to adult GCTs in humans, they may be related to juvenile GCTs or to tumors in other tissues where CTNNB1 is mutated. Importantly, the results provide strong evidence that CTNNB1 is the driver in these contexts and that KRAS(G12D) and Pten loss promote the program set in motion by the CTNNB1.

Molecular and functional characteristics of ovarian surface epithelial cells transformed by KrasG12D and loss of Pten in a mouse model in vivo

Ovarian cancer is a complex and deadly disease that remains difficult to detect at an early curable stage. Furthermore, although some oncogenic (Kras, Pten/PI3K and Trp53) pathways that are frequently mutated, deleted or amplified in ovarian cancer are known, how these pathways initiate and drive specific morphological phenotypes and tumor outcomes remain unclear. We recently generated Pten(fl/fl); Kras(G12D); Amhr2-Cre mice to disrupt the Pten gene and express a stable mutant form of Kras(G12D) in ovarian surface epithelial (OSE) cells. On the basis of histopathologic criteria, the mutant mice developed low-grade ovarian serous papillary adenocarcinomas at an early age and with 100% penetrance. This highly reproducible phenotype provides the first mouse model in which to study this ovarian cancer subtype. OSE cells isolated from ovaries of mutant mice at 5 and 10 weeks of age exhibit temporal changes in the expression of specific Mullerian epithelial marker genes, grow in soft agar and develop ectopic invasive tumors in recipient mice, indicating that the cells are transformed. Gene profiling identified specific mRNAs and microRNAs differentially expressed in purified OSE cells derived from tumors of the mutant mice compared with wild-type OSE cells. Mapping of transcripts or genes between the mouse OSE mutant data sets, the Kras signature from human cancer cell lines and the human ovarian tumor array data sets, documented significant overlap, indicating that KRAS is a key driver of OSE transformation in this context. Two key hallmarks of the mutant OSE cells in these mice are the elevated expression of the tumor-suppressor Trp53 (p53) and its microRNA target, miR-34a-c. We propose that elevated TRP53 and miR-34a-c may exert negatively regulatory effects that reduce the proliferative potential of OSE cells leading to the low-grade serous adenocarcinoma phenotype.

Mammalian target of rapamycin is a therapeutic target for murine ovarian endometrioid adenocarcinomas with dysregulated Wnt/β-catenin and PTEN

Despite the fact that epithelial ovarian cancers are the leading cause of death from gynecological cancer, very little is known about the pathophysiology of the disease. Mutations in the WNT and PI3K pathways are frequently observed in the human ovarian endometrioid adenocarcinomas (OEAs). However, the role of WNT/β-catenin and PTEN/AKT signaling in the etiology and/or progression of this disease is currently unclear. In this report we show that mice with a gain-of-function mutation in β-catenin that leads to dysregulated nuclear accumulation of β-catenin expression in the ovarian surface epithelium (OSE) cells develop indolent, undifferentiated tumors with both mesenchymal and epithelial characteristics. Combining dysregulated β-catenin with homozygous deletion of PTEN in the OSE resulted in development of significantly more aggressive tumors, which was correlated with inhibition of p53 expression and cellular senescence. Induced expression of both mTOR kinase, a master regulator of proliferation, and phosphorylation of its downstream target, S6Kinase was also observed in both the indolent and aggressive mouse tumors, as well as in human OEA with nuclear β-catenin accumulation. Ectopic allotransplants of the mouse ovarian tumor cells with a gain-of-function mutation in β-catenin and PTEN deletion developed into tumors with OEA histology, the growth of which were significantly inhibited by oral rapamycin treatment. These studies demonstrate that rapamycin might be an effective therapeutic for human ovarian endometrioid patients with dysregulated Wnt/β-catenin and Pten/PI3K signaling.

Decidual PTEN expression is required for trophoblast invasion in the mouse

Trophoblast invasion likely depends on complex cross talk between the fetal and maternal tissues and may involve the modulation of phosphatidylinositol 3-kinase (PI3K)/AKT signaling activity in maternal decidual cells. In this report, we studied implantation in Pten(tm1Hwu/tm1Hwu);Amhr2(tm3(cre)Bhr/+) mice, which lack the PI3K signaling antagonist gene Pten in myometrial and stromal/decidual cells. Primiparous Pten(tm1Hwu/tm1Hwu);Amhr2(tm3(cre)Bhr/+) mice were found to be subfertile because of increased fetal mortality at e11.5. Histopathological analyses revealed a failure of decidual regression in these mice, accompanied by reduced or absent invasion of fetal trophoblast glycogen cells and giant cells, abnormal development of the placental labyrinth, and frequent apparent intrauterine fetal growth restriction. Unexpectedly, the loss of phosphate and tensin homolog deleted on chromosome 10 (PTEN) expression in Pten(tm1Hwu/tm1Hwu);Amhr2(tm3(cre)Bhr/+) decidual cells was not accompanied by a detectable increase in AKT phosphorylation or altered expression or activation of PI3K/AKT downstream effectors such as mammalian target of rapamycin or glycogen synthase kinase-3β. Terminal deoxynucleotidyl transferase-mediated nick end labeling and bromodeoxyuridine incorporation analyses attributed to the lack of decidual regression mainly to decreased apoptosis in Pten(tm1Hwu/tm1Hwu);Amhr2(tm3(cre)Bhr/+) decidual cells, rather than to increased proliferation. Remodeling of the maternal vasculature was delayed in Pten(tm1Hwu/tm1Hwu);Amhr2(tm3(cre)Bhr/+) uteri at e11.5, as evidenced by persistence of vascular smooth muscle and decreased infiltration of uterine natural killer cells. In addition, thickening of the myometrium and disorganization of the muscle fibers were observed before and throughout gestation. Almost all Pten(tm1Hwu/tm1Hwu);Amhr2(tm3(cre)Bhr/+) mice failed to carry a second litter to term, apparently attributable to endometrial hyperplasia and uterine infections. Together, these data demonstrate novel roles of PTEN in the mammalian uterus and its requirement for proper trophoblast invasion and decidual regression.

Oncogenic role of the E3 ubiquitin ligase NEDD4-1, a PTEN negative regulator, in non-small-cell lung carcinomas

Loss of the PTEN tumor suppressor gene occurs frequently in non-small-cell lung carcinoma (NSCLC), although neither genetic alterations nor epigenetic silencing are significant predictors of PTEN protein levels. Since recent reports implicated neural precursor cell expressed, developmentally down-regulated 4-1 (NEDD4-1) as the E3 ubiquitin ligase that regulates PTEN stability, we investigated the role of NEDD4-1 in the regulation of PTEN expression in cases of NSCLC. Our findings indicate that NEDD4-1 plays a critical role in the development of NSCLC and provides novel insight on the mechanisms that contribute to inactivate PTEN in lung cancer. Immunohistochemical analysis on tissue microarrays containing 103 NSCLC resections revealed NEDD4-1 overexpression in 80% of tumors, which correlated with the loss of PTEN protein (n=98; P<0.001). Accordingly, adoptive NEDD4-1 expression in NSCLC cells decreased PTEN protein stability, whereas knock-down of NEDD4-1 expression decreased PTEN ubiquitylation and increased PTEN protein levels. In 25% of cases, NEDD4-1 overexpression was due to gene amplification at 15q21. In addition, manipulation of NEDD4-1 expression in different lung cell systems demonstrated that suppression of NEDD4-1 expression significantly reduced proliferation of NSCLC cells in vitro and tumor growth in vivo, whereas NEDD4-1 overexpression facilitated anchorage-dependent and independent growth in vitro of nontransformed lung epithelial cells that lack pRB and TP53 (BEAS-2B). NEDD4-1 overexpression also augmented the tumorigenicity of lung cancer cells that have an intact PTEN gene (NCI-H460 cells).

WNT4 is required for normal ovarian follicle development and female fertility

To study the role of WNT4 in the postnatal ovary, a mouse strain bearing a floxed Wnt4 allele was created and mated to the Amhr2(tm3(cre)Bhr) strain to target deletion of Wnt4 to granulosa cells. Wnt4(flox/-);Amhr2(tm3(cre)Bhr/+) mice had reduced ovary weights and produced smaller litters (P<0.05). Serial follicle counting demonstrated that Wnt4(flox/-);Amhr2(tm3(cre)Bhr/+) mice were born with a normal ovarian reserve and maintained normal numbers of small follicles until puberty but had only 25.2% of the normal number of healthy antral follicles. Some Wnt4(flox/-);Amhr2(tm3(cre)Bhr/+) mice had no antral follicles or corpora lutea and underwent premature follicle depletion. RT-PCR analyses of Wnt4(flox/-);Amhr2(tm3(cre)Bhr/+) granulosa cells and cultured granulosa cells that overexpress WNT4 demonstrated that WNT4 regulates the expression of Star, Cyp11a1, and Cyp19, steroidogenic genes previously identified as downstream targets of the WNT signaling effector CTNNB1. Decreased serum progesterone levels were found in immature, gonadotropin-treated Wnt4(flox/-);Amhr2(tm3(cre)Bhr/+) mice (P<0.05). WNT4- and CTNNB1-overexpressing cultured granulosa cells were analyzed by microarray for alterations in gene expression, which showed that WNT4 regulates additional genes involved in late follicle development via the WNT/CTNNB1 signaling pathway. Together, these data indicate that WNT4 is required for normal antral follicle development and may act by regulating granulosa cell functions including steroidogenesis.

Beta-catenin (CTNNB1) promotes preovulatory follicular development but represses LH-mediated ovulation and luteinization

Wingless-type mouse mammary tumor virus integration site family (WNT)/beta-catenin (CTNNB1) pathway components are expressed in ovarian granulosa cells, direct female gonad development, and are regulated by the pituitary gonadotropins. However, the in vivo functions of CTNNB1 during preovulatory follicular development, ovulation, and luteinization remain unclear. Using a mouse model Ctnnb1((Ex3)fl/fl);Cyp19-Cre (Ctnnb1((Ex3)gc-/-)), expressing dominant stable CTNNB1 in granulosa cells of small antral and preovulatory follicles, we show that CTNNB1 facilitates FSH-induced follicular growth and decreases the follicle atresia (granulosa cell apoptosis). At the molecular level, WNT signaling and FSH synergistically promote the expression of genes required for cell proliferation and estrogen biosynthesis, but decrease FOXO1, which negatively regulates proliferation and steroidogenesis. Conversely, dominant stable CTNNB1 represses LH-induced oocyte maturation, ovulation, luteinization, and progesterone biosynthesis. Specifically, granulosa cells in the Ctnnb1((Ex3)gc)(-/-) mice showed compromised responses to the LH surge and decreased levels of the epidermal growth factor-like factors (Areg and Ereg) that in vivo and in vitro mediate LH action. One underlying mechanism by which CTNNB1 prevents LH responses is by reducing phosphorylation of cAMP-responsive element-binding protein, which is essential for the expression of Areg and Ereg. By contrast, depletion of Ctnnb1 using the Ctnnb1(fl/fl);Cyp19-Cre mice did not alter FSH regulation of preovulatory follicular development or female fertility but dramatically enhanced LH induction of genes in granulosa cells in culture. Thus, CTNNB1 can enhance FSH and LH actions in antral follicles but overactivation of CTNNB1 negatively effects LH-induced ovulation and luteinization, highlighting the cell context-dependent and developmental stage-specific interactions of WNT/CTNNB1 pathway and G protein-coupled gonadotropin receptors in female fertility.

The ovary: basic biology and clinical implications

The classical view of ovarian follicle development is that it is regulated by the hypothalamic-pituitary-ovarian axis, in which gonadotropin-releasing hormone (GnRH) controls the release of the gonadotropic hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH), and that ovarian steroids exert both negative and positive regulatory effects on GnRH secretion. More recent studies in mice and humans indicate that many other intra-ovarian signaling cascades affect follicular development and gonadotropin action in a stage- and context-specific manner. As we discuss here, mutant mouse models and clinical evidence indicate that some of the most powerful intra-ovarian regulators of follicular development include the TGF-beta/SMAD, WNT/FZD/beta-catenin, and RAS/ERK1/2 signaling pathways and the FOXO/FOXL2 transcription factors.

Wide-field four-channel fluorescence imager for biological applications

A wide-field four-channel fluorescence imager has been developed. The instrument uses four expanded laser beams to image a large section (6 mm x 9 mm). An object can be sequentially illuminated with any combination of 408-, 532-, 658-, and 784-nm lasers for arbitrary (down to 1 ms) exposure times for each laser. Just two notch filters block scattered light from all four lasers. The design approach described here offers great flexibility in treatment of objects, very good sensitivity, and a wide field of view at low cost. There appears to be no commercial instrument capable of simultaneous fluorescence imaging of a wide field of view with four-laser excitation. Some possible applications are following events such as flow and mixing in microchannel systems, the transmission of biological signals across a culture, and following simulations of biological membrane diffusion. It can also be used in DNA sequencing by synthesis to follow the progress of the photolytic removal of dye and terminator. Without utilizing its time resolution, it can be used to obtain four independent images of a single tissue section stained with four targeting agents, with each coupled to a different dye matching one of the lasers.

New insights into ovarian function

Infertility adversely affects many couples worldwide. Conversely, the exponential increase in world population threatens our planet and its resources. Therefore, a greater understanding of the fundamental cellular and molecular events that control the size of the primordial follicle pool and follicular development is of utmost importance to develop improved in vitro fertilization as well as to design novel approaches to regulate fertility. In this review we attempt to highlight some new advances in basic research of the mammalian ovary that have occurred in recent years focusing primarily on mouse models that have contributed to our understanding of ovarian follicle formation, development, and ovulation. We hope that these new insights into ovarian function will trigger more research and translation to clinically relevant problems.

WNT signaling in ovarian follicle biology and tumorigenesis

The WNTS are an expansive family of glycoprotein signaling molecules known mostly for the roles they play in embryonic development. WNT signaling first caught the attention of ovarian biologists when it was reported that the inactivation of Wnt4 in mice results in partial female-to-male sex reversal and oocyte depletion. More recently, studies using loss- and gain-of-function transgenic mouse models demonstrated the requirement for Wnt4, Fzd4 and Ctnnb1, components of the WNT pathway, for normal folliculogenesis, luteogenesis and steroidogenesis, and showed that dysregulated WNT signaling can cause granulosa cell tumor development. This review covers our current knowledge of WNT signaling in ovarian follicles, highlighting both the great promise and the many unresolved questions of this emerging field of research.

A mouse surgical model for metastatic ovarian granulosa cell tumor

We recently described a genetically engineered mouse model that develops ovarian granulosa cell tumors (GCTs) that mimic many aspects of the advanced human disease, including distant dissemination. However, because the primary tumors killed their hosts before metastases were able to form, the use of these mice to study metastatic disease required the development of a simple, reliable, and humane surgical protocol for the excision of large GCTs from debilitated mice. Here we describe a protocol involving multimodal anesthesia, tumor removal through ventral midline celiotomy and perioperative fluid therapy, and analgesia that led to the postoperative survival of more than 90% of mice, despite the removal of tumors representing as much as 10% of the animal's body weight. Intraabdominal recurrence of the GCT did not occur in surviving animals, but most developed pulmonary or adrenal metastases (or both) by 12 wk after surgery. We propose that this mouse model of metastatic GCT will serve as a useful preclinical model for the development of novel treatment modalities and diagnostic techniques. Furthermore, our results delineate anesthetic and surgical principles for the removal of large abdominal tumors from mice that will be applicable to other models of human cancers.

Convergence of 3',5'-cyclic adenosine 5'-monophosphate/protein kinase A and glycogen synthase kinase-3beta/beta-catenin signaling in corpus luteum progesterone synthesis

Progesterone secretion by the steroidogenic cells of the corpus luteum (CL) is essential for reproduction. Progesterone synthesis is under the control of LH, but the exact mechanism of this regulation is unknown. It is established that LH stimulates the LH receptor/choriogonadotropin receptor, a G-protein coupled receptor, to increase cAMP and activate cAMP-dependent protein kinase A (PKA). In the present study, we tested the hypothesis that cAMP/PKA-dependent regulation of the Wnt pathway components glycogen synthase kinase (GSK)-3beta and beta-catenin contributes to LH-dependent steroidogenesis in luteal cells. We observed that LH via a cAMP/PKA-dependent mechanism stimulated the phosphorylation of GSK3beta at N-terminal Ser9 causing its inactivation and resulted in the accumulation of beta-catenin. Overexpression of N-terminal truncated beta-catenin (Delta90 beta-catenin), which lacks the phosphorylation sites responsible for its destruction, significantly augmented LH-stimulated progesterone secretion. In contrast, overexpression of a constitutively active mutant of GSK3beta (GSK-S9A) reduced beta-catenin levels and inhibited LH-stimulated steroidogenesis. Chromatin immunoprecipitation assays demonstrated the association of beta-catenin with the proximal promoter of the StAR gene, a gene that expresses the steroidogenic acute regulatory protein, which is a cholesterol transport protein that controls a rate-limiting step in steroidogenesis. Collectively these data suggest that cAMP/PKA regulation of GSK3beta/beta-catenin signaling may contribute to the acute increase in progesterone production in response to LH.

Minireview: physiological and pathological actions of RAS in the ovary

The small G proteins of the RAS superfamily act as molecular switches in the transduction of cellular signals critical for a wide range of normal developmental events as well as pathological processes. However, the functions of Ras genes in ovarian cells have only started to be unveiled. RAS, most likely KRAS that is highly expressed in granulosa cells of growing follicles, appears crucial for mediating the gonadotropin-induced events associated with the unique physiological process of ovulation. By contrast, conditional expression of a constitutively active Kras(G12D) mutant in granulosa cells results in ovulation defects due to the complete disruption of normal follicular growth, cessation of granulosa cell proliferation, and blockage of granulosa cell apoptosis and differentiation. When the tumor suppressor Pten is disrupted conditionally in the Kras(G12D)-expressing granulosa cells, granulosa cell tumors fail to develop. However, ovarian surface epithelial cells expressing the same Pten;Kras(G12D) mutations rapidly become ovarian surface epithelial serous cystadenocarcinomas. In this minireview, we summarize some of the physiological as well as pathological functions of RAS in the rodent ovary, discuss the implications of the Kras(G12D) mutant mouse models for understanding human diseases such as premature ovarian failure and ovarian cancers, and highlight new questions raised by the results of recent studies.

The mammalian ovary from genesis to revelation

Two major functions of the mammalian ovary are the production of germ cells (oocytes), which allow continuation of the species, and the generation of bioactive molecules, primarily steroids (mainly estrogens and progestins) and peptide growth factors, which are critical for ovarian function, regulation of the hypothalamic-pituitary-ovarian axis, and development of secondary sex characteristics. The female germline is created during embryogenesis when the precursors of primordial germ cells differentiate from somatic lineages of the embryo and take a unique route to reach the urogenital ridge. This undifferentiated gonad will differentiate along a female pathway, and the newly formed oocytes will proliferate and subsequently enter meiosis. At this point, the oocyte has two alternative fates: die, a common destiny of millions of oocytes, or be fertilized, a fate of at most approximately 100 oocytes, depending on the species. At every step from germline development and ovary formation to oogenesis and ovarian development and differentiation, there are coordinated interactions of hundreds of proteins and small RNAs. These studies have helped reproductive biologists to understand not only the normal functioning of the ovary but also the pathophysiology and genetics of diseases such as infertility and ovarian cancer. Over the last two decades, parallel progress has been made in the assisted reproductive technology clinic including better hormonal preparations, prenatal genetic testing, and optimal oocyte and embryo analysis and cryopreservation. Clearly, we have learned much about the mammalian ovary and manipulating its most important cargo, the oocyte, since the birth of Louise Brown over 30 yr ago.

Ovarian cancer mouse models: a summary of current models and their limitations

Development of mouse models representing human spontaneous ovarian cancer has been hampered by the lack of understanding of the etiology of this very complex disease. Mouse models representing the different types of ovarian cancer are needed to understand how epithelial ovarian cancer differs from granulosa cell tumors. Many different methods have been used to generate a viable genetic model with limited success. This review focuses on the methods of various investigators and the limitations of each model in establishing a reproducible and inheritable line to study this disease.

Cell type-specific targeted mutations of Kras and Pten document proliferation arrest in granulosa cells versus oncogenic insult to ovarian surface epithelial cells

The small G-protein KRAS is crucial for mediating gonadotropin-induced events associated with ovulation. However, constitutive expression of KrasG12D in granulosa cells disrupted normal follicle development leading to the persistence of abnormal follicle-like structures containing nonmitotic cells. To determine what factors mediate this potent effect of KrasG12D, gene profiling analyses were done. We also analyzed KrasG12D;Cyp19-Cre and KrasG12;Pgr-Cre mutant mouse models that express Cre prior to or after the initiation of granulosa cell differentiation, respectively. KrasG12D induced cell cycle arrest in granulosa cells of the KrasG12D;Cyp19-Cre mice but not in the KrasG12D;Pgr-Cre mice, documenting the cell context-specific effect of KrasG12D. Expression of KrasG12D silenced the Kras gene, reduced cell cycle activator genes, and impaired the expression of granulosa cell and oocyte-specific genes. Conversely, levels of PTEN and phosphorylated p38 mitogen-activated protein kinase (MAPK) increased markedly in the mutant granulosa cells. Because disrupting Pten in granulosa cells leads to increased proliferation and survival, Pten was disrupted in the KrasG12D mutant mice. The Pten/Kras mutant mice were infertile but lacked granulosa cell tumors. By contrast, the Ptenfl/fl;KrasG12D;Amhr2-Cre mice developed aggressive ovarian surface epithelial cell tumors that did not occur in the Ptenfl/fl;KrasG12D;Cyp19-Cre or Ptenfl/fl;KrasG12D;Pgr-Cre mouse strains. These data document unequivocally that Amhr2-Cre is expressed in and mediates allelic recombination of oncogenic genes in ovarian surface epithelial cells. That KrasG12D/Pten mutant granulosa cells do not transform but rather undergo cell cycle arrest indicates that they resist the oncogenic insults of Kras/Pten by robust self-protecting mechanisms that silence the Kras gene and elevate PTEN and phosphorylated p38 MAPK.

Dysregulation of WNT/CTNNB1 and PI3K/AKT signaling in testicular stromal cells causes granulosa cell tumor of the testis

Synergistic effects of dysregulation of the WNT/CTNNB1 and phosphatidylinositol 3-kinase (PI3K)/AKT pathways are thought to be important for the development and progression of many forms of cancer, including the granulosa cell tumor of the ovary. Sustained WNT/CTNNB1 signaling in Sertoli cells causes testicular degeneration and the formation of foci of poorly differentiated stromal cells in the seminiferous tubules in mice. To test if concomitant dysregulation of the WNT/CTNNB1 and PI3K/AKT pathways could synergize to cause testicular cancer, Pten(tm1Hwu/tm1Hwu);Ctnnb1(tm1Mmt/+);Amhr2(tm3(cre)Bhr/+) mice that express a dominant, stable CTNNB1 mutant and lack the expression of phosphatase and tensin homolog (PTEN) in their Sertoli cells were generated. These mice developed aggressive testicular cancer with 100% penetrance by 5 weeks of age, and 44% of animals developed pulmonary metastases by 4 months, whereas Pten(tm1Hwu/tm1Hwu);Amhr2(tm3(cre)Bhr/+) controls were phenotypically normal. Surprisingly, the tumors could not be classified as Sertoli cell tumors, but rather bore histologic and ultrastructural characteristics of granulosa cell tumors of the testis (GCTT). Pten(tm1Hwu/tm1Hwu);Ctnnb1(tm1Mmt/+);Amhr2(tm3(cre)Bhr/+) testicular tumors did not express CYP17, CYP19, germ cell nuclear antigen, estrogen receptor 1 or progesterone receptor, but expressed the early granulosa cell markers WNT4 and FOXL2, confirming the diagnosis of GCTT. Immunohistochemical analyses of Pten(tm1Hwu/tm1Hwu);Ctnnb1(tm1Mmt/+);Amhr2(tm3(cre)Bhr/+) GCTT demonstrated a tumor marker profile similar to that reported in human GCTT. Immunoblotting analyses revealed high levels of phosphorylation of AKT and the PI3K/AKT signaling effector FOXO1A in Pten(tm1Hwu/tm1Hwu);Ctnnb1(tm1Mmt/+);Amhr2(tm3(cre)Bhr/+) GCTT, suggesting the involvement of FOXO1A in the mechanism of GCTT development. Together, these data provide the first insights into the molecular etiology of GCTT and the first animal model for the study of GCTT biology.