Inhibition of TRAIL-induced apoptosis by IL-8 is mediated by the p38-MAPK pathway in OVCAR3 cells

Abstract

TRAIL (TNF-Related Apoptosis Inducing Ligand) is a member of the TNF superfamily of cell death inducing ligands. Interestingly, while malignant cells are responsive to TRAIL-induced cell death when used alone or in combination with other agents, normal cells do not appear to be sensitive to this ligand, making it a desirable therapeutic compound against many cancers, including many ovarian carcinomas. Interleukin-8 (IL-8), a member of the C-X-C chemokine family, has been found to be at significantly higher level in the ascites from patients with ovarian cancer. We have previously demonstrated a role for IL-8 in blocking TRAIL's ability to induce apoptosis in the ovarian cancer cell line, OVCAR3, possibly by repressing the DR4 TRAIL receptor expression and blocking caspase-8 cleavage. In addition, we showed a member of the mitogen-activated protein kinase (MAPK) superfamily, p38gamma, is among the genes regulated in OVCAR3 cells by TRAIL and IL-8. The present study further investigates involvement of the p38 MAPK pathway in IL-8's ability to block TRAIL-induced apoptosis in the ovarian surface epithelial cancer cell line, OVCAR3. In this study we demonstrate that p38gamma as well as p38alpha play a significant role in IL-8's ability to block TRAIL-induced apoptosis. Through array analysis, as well as confirmation with other methods, we detected regulation of p38gamma and p38alpha following treatment of the cancer cell line with IL-8 or TRAIL. We also tested two other isoforms of p38 MAPK, p38beta and p38delta, but did not find significant regulation by IL-8 or TRAIL. We also examined activation of the p38 MAPK pathway, up-stream as well as down-stream, and noticed activation of the pathway following treatment with TRAIL and decreased activity when IL-8 was introduced. With the use of specific inhibitors, we were able to further confirm the role of this pathway in TRAIL-induced apoptosis, and IL-8's ability to block this apoptosis, in ovarian cancer cell lines. Taken together, these results further solidify the role of IL-8 in blocking the TRAIL-induced apoptosis in these ovarian carcinoma cells and provide new molecular insight into this potentially important therapeutic target.