Negative Regulation of NF-B Signaling by

The NF-B family of transcription factors is activated by a wide variety of signals to regulate a spectrum of cellular processes. The proper regulation of NF-B activity is critical, since abnormal NF-B signaling is asso-ciated with a number of human illnesses, such as chronic inflammatory diseases and cancer. We report here that PIAS1 (protein inhibitor of activated STAT1) is an important negative regulator of NF-B. Upon cytokine stimulation, the p65 subunit of NF-B translocates into the nucleus, where it interacts with PIAS1. The binding of PIAS1 to p65 inhibits cytokine-induced NF-B-dependent gene activation. PIAS1 blocks the DNA binding activity of p65 both in vitro and in vivo. Consistently, chromatin immunoprecipitation assays indicate that the binding of p65 to the promoters of NF-B-regulated genes is significantly enhanced in Pias1/ cells. Micro-array analysis indicates that the removal of PIAS1 results in an increased expression of a subset of NF-B-mediat-ed genes in response to tumor necrosis factor alpha and lipopolysaccharide. Consistently, Pias1 null mice showed elevated proinflammatory cytokines. Our results identify PIAS1 as a novel negative regulator of NF-B. A large variety of signals, such as proinflammatory cytokines (tumor necrosis factor alpha [TNF-] and interleukin-1 [IL-1]) and bacterial lipopolysaccharide (LPS), activate the NF-B signaling pathway. NF-B is a family of dimeric transcriptio