Ras and RhoA suppress whereas RhoB enhances cytokine-induced transcriptionof nitric oxide synthase-2 in human normal liver AKN-1 cells and lung cancer A-549 cells

While both nitric oxide synthase-2 (NOS-2) and low molecular weight GTPases , such as Ras and Rho, have been implicated in malignant transformation, th e cross talk between these important proteins is ill understood. In this st udy we examined the ability of H-Ras, RhoA, RhoB and Rac1 to modulate cytok ine-induced NOS2. In the normal human liver AKN-1 cell line and in the huma n non-small cell lung carcinoma cell line, A-549, the ability of the cytoki nes (INF-gamma, IL-1 beta and TNF-alpha) to activate NOS-2 was blocked by a ctivated L61-H-Ras whereas dominant negative N17-H-Ras enhanced NOS-2 activ ation. Consistent with this dominant negative Erk2 as well as a MEK inhibit or also enhanced cytokine activation of NOS-2. Furthermore, activated L63-R hoA blocked whereas activated V14-RhoB enhanced cytokine NOS-2 activation. Activated I115-Rac1 did not affect NOS-2 activation. These results demonstr ate that the Ras/Erk and the Ras/RhoA pathways negatively regulate whereas RhoB enhances cytokine-induced NOS-2. This is the first demonstration that genes that promote malignant transformation such as Ras and RhoA inhibit, w hereas genes with tumor suppresser activity such as RhoB enhance NOS2 induc tion.