Abstract 3384: Down-regulation of 5’-nucleotidase (CD73)-generated adenosine: A novel mechanism for regulating endometrial cancer metastasis
Authors: Bowser Jessica L. , Blackburn Michael R. , Shipley Gregory L. , Xie Susu , Broaddus Russell R. 
Published: February 2011

Metastasis remains a significant concern for women with advanced or recurrent endometrial cancer (EC), as adjuvant chemotherapy and hormonal therapy have little effect. Therefore, more attention recently has been focused on the development of targeted therapies. The purinergic pathway, a metabolic cascade responsible for adenosine biosynthesis and regulation, has been clinically targeted in chronic lung and neurodegenerative diseases. Of interest is the association of adenosine dysregulation with epithelial-to-mesenchymal transition (EMT) in chronic lung diseases, as EMT is an essential hallmark of tumor metastasis. Adenosine and the purinergic pathway's involvement in cancer EMT are unknown. In this study, we evaluated the expression of purinergic pathway components (adenosine receptor subtypes, A1R, A2AR, A2BR, and A3R; adenosine biosynthesis enzyme, 5′-nucleotidase (CD73); nucleoside transporter, equilibrative nucleoside transporter 1 (ENT1); and adenosine metabolizing enzyme, adenosine deaminase (ADA)), by quantitative real-time RT-PCR in 12 normal endometrial tissues and 46 endometrial carcinomas of varying histotypes. CD73 was the single component significantly altered in EC. Specifically, CD73 was down-regulated in poorly-differentiated, invasive and metastatic ECs. Similar correlations were observed by immunoassays. CD73 was also evaluated in EC cell lines representative of various EMT stages (HEC-1A, well- and KLE, poorly-differentiated, primary tumor; AN3CA, poorly-differentiated, metastatic lesion). CD73 transcript levels were highest in HEC-1A, low in KLE, and undetectable in AN3CA. Immunoanalyses confirmed these findings and revealed CD73 to be primarily localized to extracellular membranes in direct contact with neighboring cells. Using reverse phase HPLC, we demonstrated CD73's potential to function catalytically, and in addition, confirmed a direct correlation between transcript expression and production of adenosine in endometrial tissues and cell lines (p&lt;0.05, R2=0.9388; p&lt;0.05, R2=0.9816, respectfully). Moreover, as seen by enzyme histochemistry and electron microscopy, CD73 activity occurred exclusively at established intercellular adhesions. Our results suggest a novel function for CD73-generated adenosine in maintaining endometrial epithelial adhesions, with its down-regulation being an essential event of EC EMT. For a variety of different cancer types, clinical correlations have been previously established between tumor cells retaining intercellular adhesions and therapeutic responsiveness, but factors regulating these adhesions have not yet been successfully directly targeted. The drugable nature of adenosine and the purinergic pathway and its likely role in mediating endometrial epithelial intercellular adhesions represents a potential therapeutic strategy for metastatic EC.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3384.