Background: High grade serous carcinoma (HGSC) represents one of the most aggressive forms of ovarian cancer, accounting for the majority of advanced-staged cases. HGSC often spreads transperitoneally in cell clusters known as spheroids, which detach from the primary tumour and enter the fluid of the abdominal cavity. Overexpression of glycoprotein podocalyxin (PODXL) has been associated with a significant decrease in disease-free survival in HGSC patients (1). This study aimed to examine PODXL expression in HGSC tissues and ovarian cancer cell lines, and to investigate whether PODXL expression is associated with cancer spheroid formation.
Methods: PODXL protein was examined by immunohistochemistry on a tissue array containing 80 patients with epithelial ovarian cancer. Over 37 ovarian cancer cell lines were assessed bioinformatically and the results were confirmed by real-time RT-PCR analysis in SKOV3, Kuramochi, HEY and COV362 lines as representatives. These four lines were then cultured on ultra-low attachment plates to form spheroids and PODXL localisation was determined by immunocytochemistry and confocal imaging.
Results: The tissue array showed positive PODXL staining in 85% of HGSC cases, with 30% being at advanced stages (FIGO stage III and IV). Bioinformatic analysis revealed wide PODXL expression in ovarian cancer cell lines with the highest level detected in Kuramochi, a model HGSC cell line. These data were validated by real-time RT-PCR analysis of four representative lines, confirming Kuramochi expressing the highest level followed by HEY, SKOV3 and COV362. The ability of spheroid formation also followed this order, with COV362 which expressed low levels of PODXL failing to form compact spheroids. PODXL was localised to the surface of the spheroids.
Conclusions: PODXL is widely expressed in HGSC tissues and ovarian cancer cell lines, and positively correlates to the ability of cancer spheroid formation. These data suggest an important role of PODXL in promoting cancer metastasis in HGSC.