PROSTAGLANDIN-E(2) REGULATION OF TUMOR-NECROSIS-FACTOR RECEPTOR RELEASE IN HUMAN MONOCYTIC THP-1 CELLS

Recent in vitro studies indicate that tumor necrosis factor (TNF) prod uction in human monocytic THP-1 cells is suppressed by action of arach idonic acid metabolite prostaglandin-E(2) (PGE(2)). PGE(2) stimulation of human monocytic cell line THP-1 demonstrates that PGE(2) not only regulates TNF activity at production levels, but does so through the r elease of two soluble TNF receptors (BP-55, BP-75) as well. PGE(2) can thus exert a regulatory effect on TNF biologic activity by interferin g with its ability to reach cell membrane receptors. THP-1 cells were activated with PGE(2) for either 2- or 6-hr time periods, and the supe rnatants subsequently tested by ELISA to quantitate the levels of solu ble receptor released. In addition, we examined mechanisms of receptor shedding by investigating the rate of membrane internalization and th e role of serine proteases. PGE(2)-stimulated THP-1 cells showed solub le 55- and 75-kDa TNF receptor release levels which exceeded that of s pontaneous release at both 2- and 6-hr activation periods. The numbers of both membrane TNF receptors were significantly upregulated as well in PGE(2)-activated cells, whereas the levels of 55- and 75-kDa TNF r eceptor mRNA levels remained unchanged. Thus, PGE(2) induces TNF recep tor release primarily at posttranscriptional levels. Inhibition of ser ine proteases with Pefabloc, a phenylmethylsulfonyl fluoride analog, r esulted in the inhibition of both spontaneous and PGE(2)-stimulated re lease. Treatment of THP-1 cells with N-ethylmaleimide and low-temperat ure incubation, both known to block membrane internalization, also blo cked spontaneous and PGE(2)-induced release. Internalization and cleav age by protease are therefore critical factors in PGE(2)-induced relea se of soluble TNF receptor shedding. (C) 1996 Academic Press, Inc.