THD EME ARTICLE y Gynecologic Cancer Review For reprint orders, please contact [email protected] Role of canonical Wnt signaling in endometrial carcinogenesis Expert Rev. Anticancer Ther. 12(1), 51–62 (2012) Thanh H Dellinger*1, While the role of Wnt signaling is well established in colorectal carcinogenesis, its function in Kestutis Planutis2, gynecologic cancers has not been elucidated. Here, we describe the current state of knowledge Krishnansu S Tewari1 of canonical Wnt signaling in endometrial cancer (EC), and its implications for future therapeutic b and Randall F targets. Deregulation of the Wnt/ -catenin signaling pathway in EC occurs by inactivating 2 b-catenin mutations in approximately 10–45% of ECs, and via downregulation of Wnt antagonists Holcombe by epigenetic silencing. The Wnt pathway is intimately involved with estrogen and progesterone, 1Divison of Gynecologic Oncology, and emerging data implicate it in other important signaling pathways, such as mTOR and Department of Obstetrics and Gynecology, University of California, Hedgehog. While no therapeutic agents targeting the Wnt signaling pathway are currently in Irvine,Medical Center, 101 The City clinical trials, the preclinical data presented suggest a role for Wnt signaling in uterine Drive, Building 56, Room 260, Orange, carcinogenesis, with further research warranted to elucidate the mechanism of action and to CA 92868, USA proceed towards targeted cancer drug development. 2Department of Medicine, Division of Hematology and Oncology, The Tisch Cancer Institute of Mount Sinai School KEYWORDS: b-catenin • canonical Wnt signaling • carcinogenesis • endometrial cancer • novel therapeutic targets of Medicine, New York, NY 10029, • Wnt antagonists USA *Author for correspondence: Endometrial cancer (EC) is the most common predict prognosis based on a surgical pathology Tel.: +1 714 456 8020 Fax: +1 714 456 7754 gynecologic malignancy in the USA, with an study carried out by the Gynecologic Oncology [email protected] estimated 46,470 cases diagnosed in 2011 [1]. Group (GOG) in the 1970s (GOG 33) [7], little It is a heterogeneous disease that can be largely is known of the molecular characteristics to pre- classified into two major types: type I ECs, the dict who will recur, and who should receive what most common type, which are usually of endo- type of treatment (e.g., adjuvant radiation and metrioid histology, and are often associated with chemotherapy). Moreover, the response to radia- obesity; versus type II ECs, which are of non- tion, cytotoxic or hormonal therapy is difficult to endometrioid histology (e.g., papillary serous predict. Therefore, identifying novel molecular or clear cell), are not a result of unopposed biomarkers and therapeutic targets is imperative. estrogen, and usually carry a worse prognosis The Wingless-type (Wnt) signaling pathways [2]. Despite a good survival rate for early-stage play key roles in embryonic development and and Type I ECs, the prognosis for advanced- maintenance of tissue homeostasis, but addition- stage EC has been poor, with survival rates of ally regulates diverse developmental processes, just 12 months for patients with metastatic EC such as proliferation, differentiation, motility, enrolled in chemotherapy trials [3]. Few effec- and survival and/or apoptosis. Dysregulation tive treatment options are currently available for of the Wnt pathway has been implicated in a advanced stage EC, with a limited number of variety of human malignancies, most notably novel biologics showing promise, such as mTOR in colorectal cancer (CRC). Greater than 90% inhibitors and bevacizumab, both with approxi- of all CRCs carry an activating mutation of the mately 14% clinical response rates in Phase II canonical Wnt signaling pathway, most fre- trials [4–6]. There is thus a dire need for a search quently in the form of a mutational inactiva- for further treatment options in advanced EC. tion of adenomatous polyposis coli (APC) [8]. Importantly, the molecular pathogenesis of EC This ultimately leads to the stabilization of the is understudied, and research in this field has cytoplasmic pool of b-catenin, resulting in its lagged far behind breast, ovarian, and cervical accumulation and translocation to the nucleus, cancer in terms of grant money allocation and where b-catenin associates with T-cell factor progress. Despite a clinicopathologic model to (TCF)/lymphoid enhancer factor-1 (LEF1) and www.expert-reviews.com 10.1586/ERA.11.194 © 2012 Expert Reviews Ltd ISSN 1473-7140 51 Review Dellinger, Planutis, Tewari & Holcombe promotes transcription of target genes. Some CRCs exhibit con- of this gene inhibiting tumor proliferation in vitro [25,45]. The stitutive b-catenin/TCF transcriptional activity despite the lack expression pattern of SFRPs in nonsarcomatous uterine cancers of an inactivating APC mutation. This has been shown to result has only been explored in the setting of microsatellite instability, from activating b-catenin gene mutations [9]. Thus, an inactivat- where SFRP1 expression was compared between non-matched ing APC gene mutation approximates an activating b-catenin gene normal endometrial tissues and microsatellite unstable (MSI) and mutation: both lesions finally lead to the initiation of constitutive microsatellite stable (MSS) EC tissues [46]. b-catenin/TCF-mediated transcription and CRC progression. Unlike in colon cancer, the mechanism of Wnt pathway involve- Since these key findings in CRC, the role of Wnt signaling in ment in EC has not been well elucidated, and does not appear carcinogenesis in many other solid tumors has been explored, to be as simple as that involving APC and b-catenin mutations. including melanoma, osteosarcoma, other gastrointestinal can- Instead, the evidence suggests that Wnt signaling is probably cers, prostrate, breast, liver, lung and ovarian cancer [10]. In the involved via multiple, diverse mechanisms. In this review, we late 1990s, investigations into the role of Wnt signaling in uterine present a brief overview of the Wnt signaling pathway, the current cancers have primarily focused on findings of b-catenin gene literature implicating the Wnt/b-catenin pathway in uterine can- mutations. While activating b-catenin mutations are detected cer development and progression, and its potential as a prognostic in 50% of CRCs that contain wild-type APC [9], b-catenin marker and therapeutic target in EC. gene mutations in EC are less common. Early studies report a b-catenin mutation frequency of 10–45% in ECs [11–21], with The canonical Wnt signaling pathway frequent associated b-catenin nuclear accumulations in tumors Brief overview with gene mutations. These findings were more common in endo- Nuclear b-catenin is the hallmark of an active canonical Wnt metrioid (type I) ECs than in nonendometrioid ECs. By contrast, pathway. In the absence of Wnt signal, unstimulated cells regulate APC mutations are less common, with a mutation frequency of b-catenin levels through its phosphorylation by a multiprotein 10% or less [22]. More recently, there has been increasing evidence complex consisting of APC, axin, and GSK-3b, thus marking it to suggest that altered expression of Wnt antagonists, including for subsequent ubiquitination and degradation [47]. Upon bind- members of both the SFRP family [23–27] and Dickkopf family ing of the Wnt ligand to its frizzled receptor (FZD), a signaling [27–37], may be associated with human cancer development and cascade ensues to destabilize this degradation complex, and allows progression. The Dickkopf proteins are secreted Wnt inhibitors unphosphorylated b-catenin to accumulate and translocate to the which induce removal of the Wnt coreceptor low-density lipo- nucleus, where it functions as a cofactor for transcription factors protein receptor-related protein (LRP), and thus prevent Wnt of the TCF/LEF family (FIGURE 1). The result of this process is the signaling. Dkk3 is a member of the Dickkopf family, and has transcription of specific genes designed to determine cell fate and been suggested as a tumor suppressor [31]. Its overexpression regulate proliferation. suppresses tumor growth in vitro in osteosarcoma [27], although Dkk-3 knock-out mice have shown no enhanced tumor forma- Extracellular & cell membrane components tion [29]. The SFRP family members are putative extracellular The term ‘Wnt’ (pronounced ‘wint’) was introduced in 1982 modulators of the Wnt pathway, which can directly bind Wnt by Harold and Varmus Roeland Nusse, and fused the names ligands and inhibit Wnt signaling. Several reports have surfaced of two orthologous genes: wingless (Wg), a Drosophila segment regarding the downregulation or inactivation of SFRPs in human polarity gene, and Int-1, a mouse proto-oncogene [48,49]. Wnts are cancers, suggesting a role for SFRPs as tumor suppressors [26,38]. secreted glycoprotein-signaling molecules which act as ligands for In prostate cancer, SFRP3 suppresses tumor growth and invasion a transmembrane receptor complex, the FZD, forming a trimeric in prostate cancer cells in vitro [26], while in hepatocellular carci- complex with an additional single-pass transmembrane protein, noma (HCC), SFRP1 is significantly downregulated in human the LRP. A total of 19 Wnt ligands and ten FZD receptors have HCC specimens, as compared with their adjacent noncancerous been identified in the human genome[201] . Wnts exert their effect tissues; additionally overexpression of SFRP1 in vitro significantly either via the ‘canonical’ Wnt/b-catenin signaling,