Targeted Smad2-Dominant Negative Expression Induces Oviductal-Like Ovarian Cysts and Tumors Irrespective of p53 Deletion in the Ovarian Surface or Oviductal Epithelium.

Abstract

Epithelial ovarian cancer is the most lethal gynecological malignancy and fifth leading cause of cancer death among US women due to the lack of early detection methods and an incomplete understanding of the disease etiology including the cell type of origin. The progenitor cell may either be the ovarian surface epithelium (OSE) or the distal epithelium of the fallopian tube fimbriae (TEC). Regardless of origin, two recent meta-analyses of human microarray data concluded that p53 and the Transforming Growth Factor Beta (TGFβ) pathway are frequently disrupted in high-grade serous ovarian cancer. The tumor suppressor p53 is implicated in many cellular processes including DNA repair and cell cycle arrest and is mutated in over 96% of high-grade serous ovarian cancers. Smads and p53 can physically interact and due to the high rate of transcriptional changes in both pathways in tumor samples, we investigated p53 deletion and abrogation of Smad signaling in a mouse model. A Smad2 dominant negative (DN) transgenic mouse model was developed to target tissues of the reproductive tract. The Smad2DN docks the receptor but lacks the C-terminal serine residues that are normally phosphorylated thus attenuating signaling. Mice with heterozygous expression of the transgene developed endosalpingiosis characterized by epithelial-lined inclusion cysts, a potential precursor lesion, which morphologically resemble the TEC, but lack the tubal markers oviductal glycoprotein and Pax8. In contrast, mice with homozygous expression of the transgene developed large, mixed-cell ovarian tumors that did not metastasize into the peritoneal space and also lacked OVGP1 and Pax8, but acquired acetylated tubulin, a marker of cilia typically seen in the oviduct. In order to evaluate if inclusion cysts would develop into tumors when p53 was deleted, tissue specific deletion of p53 in the ovary and oviducts was investigated. Due to the lack of tissue specific promoters, conditional deletion of p53 in the OSE or TEC was achieved through intrabursal or intratubal injection of cre-recombinase expressing adenovirus into mice harboring p53floxed/floxed. Tumors were detected in mice 6 months after p53 inactivation in the OSE, while no pathologies were detected in mice with p53 deletion in the TEC. The absence of tumors could be due to decreased infectivity of adenovirus into the TEC as compared to the OSE or bursa. Bitransgenic mice were then generated expressing both the Smad2DN transgene and p53floxed/floxed. These mice developed a phenotype similar to the Smad2DN transgenic mice suggesting that loss of p53 is not sufficient to convert benign cysts to malignant tumors. Future studies will investigate the role of gain-of-function, mutant p53 as a critical factor in serous ovarian cancer. This research was supported by RO3 CA139492 and the UIC Graduate College Medical Research Fellowship.