Human　immunodeficiency　virus　(HIV)　regulatory　protein　Tat　has　pro-oxidant　property,　which　might　contribute　to　Tat-induced　long　terminal　repeat　region　(LTR)　transactivation.　However,　the　intracellular　mechanisms　whereby　Tat　triggers　ROS　production,　and　the　relationship　between　Tat-induced　ROS　production　and　LTR　transactivation,　are　still　subject　to　debate.　The　present　study　was　undertaken　to　evaluate　the　specific　effects　of　Tat　on　nicotinamide　adenine　denucleotide　phosphate　(NADPH)　oxidase　in　MAGI　cells,　and　to　determine　the　specific　role　of　NADPH　oxidase　in　Tat-induced　LTR　transactivation.　Application　of　Tat　to　MAGI　cells　caused　increases　in　ROS　formation　that　were　prevented　by　both　pharmacologic　NADPH　oxidase　inhibitors　and　by　siRNA　Nox2,　but　not　by　other　inhibitors　of　pro-oxidant　enzymes　or　siRNA　Nox4.　Furthermore,　inhibition　of　NADPH　oxidase　by　both　pharmacologic　NADPH　oxidase　inhibitors　and　by　siRNA　Nox2　attenuated　Tat-induced　p65　phosphorylation　and　IKK　phosphorylation.　Phosphatidylinositol　3-kinase/Akt　signaling　pathway　was　involved　in　Tat-induced　NADPH　oxidase　stimulation.　Finally,　NADPH　oxidase　inhibitors　or　Nox2　siRNA,　but　not　control　siRNA,　inhibited　Tat-induced　LTR　transactivation.　Tat-induced　HIV-1　LTR　transactivation　was　inhibited　in　wortmannin　or　LY294002　treated　cells　compared　to　control　cells.　Together,　these　data　describe　a　specific　and　biologically　significant　signaling　component　of　the　MAGI　cells　response　to　Tat,　and　suggest　the　PI3K/Akt　signaling　pathway　might　originate　in　part　with　Tat-induced　activation　of　NADPH　oxidase　and　LTR　transactivation.　(C)　2010　Elsevier　Inc.　All　rights　reserved.