A novel superoxide-producing NAD(P)H oxidase in kidney

During phagocytosis, gp91(phox), th, catalytic subunit of the phagocyte NAD PH oxidase, becomes activated to produce superoxide, a precursor of microbi cidal oxidants. Currently increasing evidence suggests that nonphagocytic c ells contain similar superoxide-producing oxidases, which are proposed to p lay crucial roles in various events such as cell proliferation and oxygen s ensing for erythropoiesis. Here we describe the cloning of human cDNA that encodes a novel NAD(P)H oxidase, designated NOX4. The NOX4 protein of 578 a mino acids exhibits 39% identity to gp91(Phox) with special conservation in membrane-spanning regions and binding sites for heme, FAD, and NAD(P)H, in dicative of its function as a superoxide-producing NAD(P)H oxidase. The mem brane fraction of kidney derived human embryonic kidney (HEK) 293 cells, ex pressing NOX4, exhibits NADH-and NADPH-dependent superoxide-producing activ ities, both of which are inhibited by diphenylene iodonium, an agent known to block oxygen sensing, and decreased in cells expressing antisense NOX4 m RNA. The human NOX4 gene, comprising 18 exons, is located on chromosome 11q 14.2-q21, and its expression is almost exclusively restricted to adult and fetal kidneys. in human renal cortex, high amounts of the NOX4 protein are present in distal tubular cells, which reside near erythropoietin-producing cells. In addition, overexpression of NOX4 in cultured cells leads to incr eased superoxide production and decreased rate of growth. The present findi ngs thus suggest that the novel NAD(P)H oxidase NOX4 may serve as an oxygen sensor and/or a regulator of cell growth in kidney.