Uteroglobin (Secretoglobin 1A1, Clara cell secretory protein) is a steroid inducible, multifunctional protein that is secreted by the mucosal epithelia. Uteroglobin has anti-inflammatory, immunomodulatory and anti-cancer activities. Cyclooxygenase-2 (COX-2), which catalyzes the first step in the synthesis of prostanoids, has been shown to be overexpressed in tumors. Recently, we reported tumor supernatant (TSN) induced imbalance of immune response of peripheral blood mononuclear cells (PBMC) or dendritic cells (DC), but uteroglobin reversed this imbalance. The cause was assumed uteroglobin inhibited secretion of prostaglandin E2 (PGE2), COX-2 product in tumor environment. However, the mechanisms of action of uteroglobin still remain largely unknown. This study investigated the effect of uteroglobin on the expression of COX-2 and signaling pathways in immune cells. TSN was prepared from supernatant of A549 cells, lung cancer cell in which uteroglobin is deficient. Uteroglobin was overexpressed by adenovirus in A549 cells. The level of protein expression was analyzed by western blot. And ELISA was followed to check the differences of cytokines secretion. Immune cells, THP1 and K562 were transduced by adenovirus-uteroglobin with liphofectamin. NS398 was used as an inhibitor of COX-2 and PD98059 was utilized as an inhibitor of MAPK. COX-2 expression was increased when THP1 or K562 cells were cultured in TSN but it was suppressed by uteroglobin. Uteroglobin induced Th 1 type cytokines but reduced Th 2 type ones. We screened the signaling proteins associated with COX-2 activation such as NFkB/IkB, PI3K/AKT and RAS/RAF/MAPK pathway. Uteroglobin did not affect NFkB/IkB and PI3K/AKT signaling pathways. However, the level of pMEK, pp38 and pERK was decreased by uteroglobin. Furthermore, STAT-3 which accumulates in the nucleus to drive transcription of COX-2, SOCS and c-Myc was also inactivated by uteroglobin. These results suggest that uteroglobin suppresses cyclooxygenase-2 expression via inactivation of MEK, ERK and STAT3 in immune cells.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]