ABSTRACT
Treatment options for metastatic renal cell carcinoma (RCC) are limited. In this study, we investigated impact of prostaglandin E2 (PGE2) receptor 4 (EP4) on RCC metastasis. We found that knockdown of EP4 in two RCC cell lines, ACHN and SN12C, does not affect xenograft tumor take or growth rate in mice, but reduces metastasis by decreasing tumor intravasation. Using chick chorioallantoic membrane (CAM) assay, we confirmed that blockade of EP4 signaling inhibits tumor intravasation. In vitro studies associated EP4 expression and activity with RCC cell transendothelial migration (TEM). Gene expression analysis and validation assays showed that EP4 knockdown decreases expression of CD24, a ligand to the adhesion molecule P-selectin. Forced expression of CD24 in EP4 knockdown RCC rescues TEM capacity of the cells. Pharmacologic inhibition or knockdown of endothelial P-selectin blocks EP4-mediated cancer cell TEM, and inhibition of P-selectin prevents RCC tumor intravasation in CAM assay. Our results demonstrate that inhibition of EP4 attenuates the RCC intravasation and metastasis by downregulating CD24 and that P-selectin participates in tumor intravasation, implying a potential for these molecules as therapeutic targets for advanced RCC treatment.
