Ras Up-Regulation of Cyclooxygenase-2

Oncogenic mutations in Ras (H-Ras, N-Ras, and K-Ras) are found in a wide variety of human malignancies, including adenocarcinomas of the colon, where K-Ras mutations often occur early in tumor development and strongly correlate with the transition to invasive adenocarcinoma. Our laboratory is interested in examining the interaction between Ras signaling and up-regulation of cyclooxygenase-2 (COX-2), a key regulator of prostaglandin biosynthesis. Our studies demonstrate that the Ras oncoprotein can regulate transcriptional activation and stabilization of COX-2 expression by several mechanisms. In this chapter we have outlined protocols and experimental approaches used in our laboratory to measure H-Ras up-regulation of COX-2 expression and to elaborate on more recent techniques that illustrate the importance of activation of Ras by prostaglandin E2 (PGE₂). These methods have facilitated our understanding of the mechanisms by which the COX-2-derived PGE₂ and Ras activation of the mitogen-activated protein kinase (MAPK) signaling promotes oncogenic transformation. In light of the critical roles of both COX-2 and Ras signaling in carcinogenesis, our understanding of the complete signaling nuances between different isoforms of Ras on activation of COX-2, as well as understanding the novel mechanism whereby COX-2-derived PGE₂ constitutively activates Ras, will potentially aid in the identification of new targets for cancer therapy.