Endogenously produced nitric oxide increases tumor necrosis factor-α production in transfected human U937 cells

Abstract

Various functions of human phagocytes are modulated by nitric oxide (NO). We transfected the human U937 monoblastold cell line with an expression vector containing human endothelial NO synthase (eNOS) or murine inducible NOS (iNOS) cDNA to study the regulatory role of NO without the nonspecific effects associated with exogenous NO sources. Western blot confirmed expression of eNOS or iNOS in respectively transfected cells, but not in naive or empty-vector transfected cells. Transfectants expressing iNOS, a calcium-independent enzyme, but not eNOS, a calcium-dependent enzyme, spontaneously produced NO (P < .001). The NO release from iNOS-transfected cells, as measured by nitrite and nitrate accumulation and by cyclic guanosine monophosphate (cGMP) increases in rat reporter cells, was inhibitable (P