Elsevier

Human Pathology

Volume 46, Issue 7, July 2015, Pages 948-956
Human Pathology

Original contribution
PAX8 expression in ovarian surface epithelial cells

https://doi.org/10.1016/j.humpath.2015.03.017Get rights and content

Summary

High-grade serous ovarian carcinoma (HGSOC) is usually diagnosed at a late stage and is associated with poor prognosis. Understanding early stage disease biology is essential in developing clinical biomarkers to detect HGSOC earlier. While recent studies indicate that HGSOCs arise from fallopian tube secretory epithelial cells, a considerable body of evidence suggests that HGSOC can also arise from ovarian surface epithelial cells (OSECs). PAX8 is overexpressed in HGSOCs and expressed in fallopian tube secretory epithelial cells, but there are conflicting reports about PAX8 expression in OSECs. The purposes of this study were to comprehensively characterize PAX8 expression in a large series of OSECs and to investigate the role of PAX8 in early HGSOC development. PAX8 protein expression was analyzed in the OSECs of 27 normal ovaries and 7 primary OSEC cultures using immunohistochemistry and immunofluorescent cytochemistry. PAX8 messenger RNA expression was quantified in 66 primary OSEC cultures. Cellular transformation was evaluated in OSECs expressing a PAX8 construct. PAX8 was expressed by 44% to 71% of OSECs. Calretinin and E-cadherin were frequently coexpressed with PAX8. Expression of PAX8 in OSECs decreased cellular migration (P = .028), but had no other effects on cellular transformation. In addition, PAX8 expression was significantly increased (P = .003) in an in vitro stepwise model of neoplastic transformation. In conclusion, PAX8 is frequently expressed by OSECs, and endogenous levels of PAX8 expression are non-transforming. These data indicate that in OSECs, PAX8 expression may represent a normal state and that OSECs may represent an origin of HGSOCs.

Introduction

Invasive ovarian carcinoma is a deadly disease characterized by frequent late-stage diagnosis and poor survival rates. It is also a heterogeneous disease encompassing several histological subtypes. High-grade serous ovarian carcinoma (HGSOC) is the most common subtype, accounting for approximately 60% of all ovarian carcinomas. Historically, HGSOCs were thought to arise from ovarian surface epithelial cells (OSECs), the mesothelial-type epithelium covering the ovary, and the epithelial lining of cortical inclusion cysts (CICs), which are derived from invaginations of the ovarian surface. Decades of research have indicated that HGSOCs may arise in these tissues [1], [2], [3], [4]. However, this hypothesis has been criticized because metaplastic ovarian epithelial cells are rarely found on the surface of the ovary, and because ovarian carcinomas exhibited markedly different histological features and marker expression when compared with normal OSECs. More recent evidence indicates that HGSOCs can originate from epithelial cells lining the fallopian tube fimbriae, through a precursor lesion termed serous tubal intraepithelial carcinoma (STIC). STICs are associated with 20% to 60% of sporadic HGSOCs [5], [6], [7], [8], raising the possibility that the remaining 40% to 80% of HGSOCs may arise from an alternative cell of origin.

Several studies have shown that paired box 8 (PAX8) is highly expressed in most HGSOCs [9], [10], [11], [12], [13], [14], suggesting that overexpression of this transcription factor plays a critical role in this tumor type. This is supported by functional evidence showing that PAX8 knockdown in ovarian carcinoma cell lines induces growth arrest and apoptosis, and decreases tumorigenesis [14], [15], [16]. The observation of PAX8 expression in fallopian tube secretory epithelial cells (FTSECs) and in many CICs but not OSECs could suggest that the epithelial lining of CICs is derived from the fallopian tube and that most, if not all HGSOCs, likely originate from FTSECs. Although it is widely considered that OSECs do not express PAX8, there are conflicting reports evaluating PAX8 expression in OSECs [9], [10], [11], [12], [17], [18], [19]. Evidence of PAX8 expression by OSECs has been reported in smaller sample sizes (n > 8 only in 1 study) [4], [10], [12], [17], [19], but this finding has been controversial [20] because it did not agree with the findings of others [9], [11], [18]. The purposes of the current study were to perform a comprehensive analysis of PAX8 protein and messenger RNA (mRNA) expression in both normal ovaries and primary OSECs in culture and to evaluate the functional significance of PAX8 in early stage development of ovarian carcinoma using in vitro models of OSECs.

Section snippets

Tissue culture

Normal OSECs were isolated from histologically normal ovaries of women undergoing surgery for conditions not involving the ovaries (such as endometrial cancer or fibroids). Samples were collected with the approval of the University College London Hospital Ethics Committee and informed patient consent. OSECs were harvested by brushing the surface of the ovary with a cytobrush and cultured in normal OSEC culture media [21]. hTERT (human telomerase reverse transcriptase)–immortalized OSECs

PAX8 protein expression in normal ovaries

PAX8 expression was evaluated in 27 histologically normal ovaries with OSECs present on the surface, 18 of which also contained CICs. From the same patient cohort, 7 fallopian tubes were analyzed as positive controls for PAX8 expression. PAX8 was expressed in the OSECs of 12 ovaries (44%), 9 of which (33% of all ovaries) showed moderate to strong staining (similar to expression levels in FTSECs). OSECs in the remaining 15 ovaries (56%) showed no evidence of PAX8 staining. PAX8 was observed in

Discussion

Ovarian carcinoma is the most lethal gynecological malignancy in Western countries. HGSOC is characterized by frequent late-stage presentation, having no specific symptoms associated with early stage disease. Understanding the molecular mechanisms that underlie cancer initiation and identifying the precursor tissues of the specific subtypes of ovarian carcinoma may lead to the development of novel early stage screening biomarkers for ovarian carcinoma, which would have a substantial impact on

Supplementary data

The following are the supplementary data to this article.

Supplementary materials.

Acknowledgments

We would like to thank Lillian Young and the USC IHC Core for immunohistochemistry services, and Lora Barsky and the USC Flow Cytometry Core Facility for flow cytometry services. We thank Dr Peter Kopp and Aigerim Bizhanova for their kind efforts in generating and providing the pEGFP-hPAX8a construct. We also thank Eva Wozniak and Maria Notaridou for technical assistance in the OSEC collection and culture, and Rod Karevan for technical support in qPCR.

References (35)

  • D.A. Bell et al.

    Early de novo ovarian carcinoma. A study of fourteen cases

    Cancer

    (1994)
  • C.G. Przybycin et al.

    Are all pelvic (nonuterine) serous carcinomas of tubal origin?

    Am J Surg Pathol

    (2010)
  • D.W. Kindelberger et al.

    Intraepithelial carcinoma of the fimbria and pelvic serous carcinoma: evidence for a causal relationship

    Am J Surg Pathol

    (2007)
  • S. Tang et al.

    Frequency of serous tubal intraepithelial carcinoma in various gynecologic malignancies: a study of 300 consecutive cases

    Int J Gynecol Pathol

    (2012)
  • A. Ozcan et al.

    PAX2 and PAX8 expression in primary and metastatic mullerian epithelial tumors: a comprehensive comparison

    Am J Surg Pathol

    (2011)
  • D. Tacha et al.

    Expression of PAX8 in normal and neoplastic tissues: a comprehensive immunohistochemical study

    Appl Immunohistochem Mol Morphol

    (2011)
  • TCGAR Network

    Integrated genomic analyses of ovarian carcinoma

    Nature

    (2011)
  • Cited by (31)

    • PAX8 modulates the tumor microenvironment of high grade serous ovarian cancer through changes in the secretome

      2023, Neoplasia (United States)
      Citation Excerpt :

      PAX8 is expressed in ∼90% of HGSC and is a commonly used marker by pathologist to classify ovarian serous tumors [14]. The ovarian surface epithelium (OSE) typically does not express PAX8, however, murine models of HGSC derived from the OSE acquire PAX8, suggesting that it is not only a marker of Müllerian origin, but also essential for cancer progression, potentially from both the OSE and FTE [15]. PAX8 knockdown or deletion causes reduction in tumor cell proliferation, migration and invasion [16–19].

    • Most Commonly Mutated Genes in High-Grade Serous Ovarian Carcinoma Are Nonessential for Ovarian Surface Epithelial Stem Cell Transformation

      2020, Cell Reports
      Citation Excerpt :

      The TE also shares several well-characterized markers of HGSOC that have not been observed in OSE (Perets and Drapkin, 2016). For example, secretory cells in the TE express PAX8, which is present in HGSOC but not in untransformed OSE (Adler et al., 2015; Ozcan et al., 2011; Tacha et al., 2011). Monolayers of PAX8-positive TE cells can also form lesions that express “p53 signatures” that are often associated with mutant TP53 but generally have a low proliferative index and lack cellular atypia (Lee et al., 2007; Leonhardt et al., 2011).

    • A Study of High-Grade Serous Ovarian Cancer Origins Implicates the SOX18 Transcription Factor in Tumor Development

      2019, Cell Reports
      Citation Excerpt :

      Little is known about the key transcription factors (TFs) driving oncogenesis in HGSOC. The most significant TF identified to date is PAX8, which is highly expressed in FTSECs and HGSOCs, moderately expressed in some OSECs, and is functionally involved in disease development (Adler et al., 2015, 2017; Cheung et al., 2011; Elias et al., 2016; Kar et al., 2017). By analyzing epigenomic landscapes annotated from H3K27ac ChIP-seq data, we found that the PAX8 gene locus is marked by a strong SE in both FTSECs and HGSOCs.

    • Comparative transcriptome analysis links distinct peritoneal tumor spread types, miliary and non-miliary, with putative origin, tubes and ovaries, in high grade serous ovarian cancer

      2017, Cancer Letters
      Citation Excerpt :

      Obtained results are shown in Fig. 1B. In Fig. 1C and D the expressions of the single markers paired box 8, PAX8 (a non-exclusive tube marker [38]), and calretinin (an ovarian marker [39]) are shown, respectively. OSE cells on the ovarian surface are largely, but not always PAX8 negative, and OSE-lined inclusion cysts tend to be 100% (weak) PAX8 positive [40–42].

    View all citing articles on Scopus

    Funding/Support: K. L. is funded by a K99/R00 award from the National Cancer Institute (Grant No. 1K99CA184415). The project described was supported, in part, by award number P30CA014089 from the National Cancer Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health.

    1

    Both authors contributed equally to this study.

    View full text