RAW264.7 cells lack prostaglandin-dependent autoregulation of tumor necrosis factor-α secretion

Abstract

Studies of the response of RAW264.7 cells (RAW) to lipopolysaccharide (LPS) were carried out to determine why these cells do not demonstrate the prostaglandin (PG)-dependent autocrine regulation of tumor necrosis factor-α (TNF-α) secretion observed in primary resident peritoneal macrophages (RPMs). The major cyclooxygenase (COX) product of LPS-stimulated RAW was PGD2, with lesser amounts of PGE2. LPS-treated RAW produced PGs more slowly and reached their maximal PG synthetic rate later than did LPS-treated RPMs, as a result of lower constitutive COX-1 expression and a slower rate of COX-2 induction. Cytosolic phospholipase A2 and levels of free arachidonic acid were similar in RAW and RPMs. In contrast to RPMs, LPS-treated RAW produced high quantities of TNF-α, which were not altered in the presence of COX inhibitors. This failure of endogenous PGs to suppress TNF-α secretion was explained by the absence of the prostaglandin D2 receptor and the low levels of PGE2 produced during the first 2 h of the LPS response.These studies demonstrate that autocrine regulation of TNF-α secretion in response to LPS is greatly facilitated by a COX-1-mediated rapid accumulation of PGs as well by a correspondence between the PGs produced and the receptors expressed by the cells.

Keywords

• macrophage
• lipopolysaccharide
• cyclooxygenase-1
• cyclooxygenase-2
• arachidonic acid
• cytosolic phospholipase A2