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(67) Akt REGULATES PGE₂ PRODUCTION THROUGH COX-2 PROTEIN AND mRNA GENE EXPRESSION IN HUMAN ENDOMETRIAL CANCER CELLS.

St-Germain, Marie-Eve¹, Gagnon, Veronique¹, Parent, Sophie¹, Asselin, Eric¹, ¹ Departement de Chimie-Biologie, Trois-Rivieres, CA

ABSTRACT- In human endometrial cancer (HEC), the fourth most common cancer in women, tumor suppressor phosphatase tensin homologue (PTEN) is frequently mutated. PTEN directly blocks PI 3-K/Akt pathway through the dephosphorylation of PIP3 into PIP2. In the presence of a mutated PTEN protein, Akt phosphorylation levels are increased leading to the activation of this survival pathway. Cyclooxygenases (COXs) are the key enzymes involved in prostaglandin synthesis: they catalyze the conversion of arachidonic acid to biologically active prostanoids. COX-1 is a constitutive enzyme while COX-2 is induced in response to various stimuli, including mitogens. Numerous studies indicated that COX-2 is inappropriately induced and up-regulated in a number of malignant cancer cells. COX-2 plays an important role in tumor cell biology, taking part actively in angiogenesis particularly via the production of prostaglandin E₂ (PGE₂). The present study was undertaken to determine the involvement of the PI 3-K/Akt pathway in the regulation of COXs expression and PGE₂ synthesis and to determine the abundance of COXs mRNAs and proteinsin endometrial cells. Four different HEC cells known to have wild type PTEN (HEC1-A and KLE) or a mutated inactive PTEN protein (RL 95-2 and Ishikawa) were used for these studies. Results showed that Akt phosphorylation was high in mutated PTEN cells. COX-2 mRNA expression and protein levels were high in these cells compared to wild type PTEN cells as demonstred by RT-PCR and Western analysis respectively. PGE₂ production was higher in cells expressing high levels of COX-2 compared to wild type PTEN cells. Inhibition of PI 3-K with Wortmannin and LY294002 blocked Akt phosphorylation and inhibited expression of COX-2 in mutated PTEN cells. Inhibition of Akt phosphorylation with specific PI 3-K inhibitors and down-regulation of COX-2 resulted in stimulation of apoptosis in HEC cells. It is concluded that the PI 3-K/Akt survival pathway is directly involved in the regulation of COX-2 and PGE₂ synthesis in HEC cells. Further analysis will be necessary to determine more precisely the downstream targets of Akt involved in this process.

KEY WORDS: Endometrium, Cancer, Apoptosis, Cyclooxygenase/ PGE₂