Monocytes stimulate COX-2 expression in pancreatic cancer cells

Abstract

COX-2 is an enzyme that modulates human pancreatic cancer (PaCa) cell survival, proliferation, and tumor metastasis. 60–80% of human PaCa express COX-2. However, the regulation of COX-2 expression in PaCa cells is not clear. We hypothesize that inflammatory cell infiltrate—namely monocytes/macrophages found commonly in PaCa—regulates the expression and activity of COX-2. The human histiocytic lymphoma cell line U937 was terminally differentiated with phorbol ester (PMA) and served as a human monocyte/macrophage model. IL-1β levels in the culture medium were measured by ELISA. PaCa cell lines (BxPC-3, Capan-2, HPAF-II) were stimulated with U937 conditioned culture medium (CM). COX-2 protein expression was determined by immunoblotting and prostaglandin E2 (PGE2) production by ELISA. To determine, whether the effect of U937 CM was mediated by IL-1β, we used an IL-1 receptor antagonist (IL-1RA). The effect of recombinant IL-1β on COX-2 expression, PGE2 production, and ERK1/ERK2 phosphorylation in human PaCa cells was analyzed. Since PMA-differentiated U937 cells secreted low levels of IL-1β (15 ± 2 pg/ml), we stimulated differentiated U937 cells with LPS markedly increasing IL-1β secretion (1670 ± 145 pg/ml). CM of U937 cells increased COX-2 protein expression after 24 hours 5.6-fold, 7.7-fold, and 5.3-fold in the BxPC-3, Capan-2, and HPAF-II cells, respectively. Compared to control, U937 CM increased PGE2 production in BxPC-3 (202 ± 8 vs. 516 ± 24 pg/ml, p < 0.01), Capan-2 (19 ± 1 vs. 39 ± 1 pg/ml, p < 0.01), and HPAF-II cells (173 ± 10 vs. 429±33 pg/ml, p<0.01). The effect of U937 CM on COX-2 expression and PGE2 production was only partially inhibited by IL-1RA. Recombinant IL-1β dose- and time dependently increased COX-2 expression, PGE2 production, and ERK1/ERK2 activation in BxPC-3, Capan-2, and HPAF-II cells, an effect which was inhibited by IL-1RA. IL-1β secreted by monocytes stimulates expression of COX-2 in human pancreatic cancer cells. Other cytokines secreted from U937 cells may also activate COX-2 expression. Studies combining immunomodulation with COX-2 inhibition for PaCa treatment may yield significant results.