O-032. the relationship of p85 and the apoptotic signaling of N-(4-hydroxyphenyl)retinamide (4HPR)

Abstract

Aims: The synthetic retinoid, N-(4-Hydroxyphenyl)retinamide (4HPR), is a candidate drug for cancer treatment due to its demonstrated ability to induce apoptosis in many tumor cell lines. To further evaluate its usefulness as a chemopreventive agent, we investigated the basic mechanism of its action by examining the effect on the expression of p85-protein, a regulatory subunit of phosphatidylinositol (PI) 3-kinases known to be a regulator of apoptosis. Methods: The cultured CNE3 epithelial tumor cells established from a poorly differentiated nasopharyngeal carcinoma were used in the present study. The expression of p85 was measured by Western Blotting. Apoptosis was assessed with fluorescence microscopy, DNA fragmentation assay, flow-cytometric analysis and caspase-3 cleavage. Results: Treatment of the CNE3 cells with 4HPR dose-dependently induced apoptosis as well as an elevation in the protein level of p85. The increased expression could be detected after 12 h of incubation with 4HPR at a concentration of 5 μM, and lasted for as long as 4HPR was present. A similar observation was made in another head and neck tumor derived cell line AC3. Inhibition of PI 3-kinases activity by the specific inhibitor LY294002 enhanced 4HPR-induced apoptosis, as detected by flow-cytometry and the increased cleavage of caspase-3. Conclusion: This study demonstrated that the expression of p85 was upregulated in response to 4HPR and suggests that the increased expression of p85 is likely to play a role other than in the activation of PI 3-kinases, which would protect the CNE3 cells against apoptosis.