HSCARG inhibits activation of NF-kappaB by interacting with IkappaB kinase-beta.

HSCARG is a recently identified human NADPH sensor. Our previous studies have shown that HSCARG can affect NO production and cell viability, but the signal pathway mediated by this protein is unknown. Here, we show that HSCARG is involved in the NF-kappaB signaling pathway and find that HSCARG suppresses TNF- and IL1-induced NF-kappaB activation in a dose-dependent manner. Co-immunoprecipitation and immunofluorescence analyses demonstrate that HSCARG interacts and colocalizes with IKKbeta. HSCARG inhibits the phosphorylation of IKKbeta and further blocks the degradation of IkappaBalpha, the substrate of IKKbeta, which retains NF-kappaB in the cytoplasm and suppresses its activity. In addition, our data indicate that IKKbeta is required for HSCARG-inhibited NF-kappaB activation. Our findings delineate a pathway by which HSCARG negatively regulates NF-kappaB activation.