Redox regulation of lipopolysaccharide-mediated sulfiredoxin induction, which depends on both AP-1 and Nrf2.

Sulfiredoxin (Srx) is an enzyme that catalyzes the reduction of cysteine sulfinic acid of hyperoxidized peroxiredoxins and exerts a protective antioxidant role. Here we investigated the regulatory mechanism of Srx induction by lipopolysaccharide (LPS) in mouse macrophages. LPS up-regulated Srx expression on the transcriptional level. The promoter region of the Srx gene contained putative NF-κB and AP-1 (activator protein-1) sites, and the proximal site of three AP-1 sites was embedded within the antioxidant response element (ARE), a cis-acting element for Nrf2 (nuclear factor erythroid 2-related factor). Mutational analysis of the Srx promoter revealed that Srx induction is dependent on AP-1 sites and ARE but not on NF-κB sites. Consistently, both transcription factors, AP-1 and Nrf2, were required for LPS-mediated Srx induction, as revealed by chromatin immunoprecipitation using antibodies specific for c-Jun and c-Fos and little Srx induction in Nrf2-null bone marrow-derived macrophages. Among mitogen-activated protein kinases that mediate the signal transduction by LPS, JNK played a major role in Srx induction. Moreover, chemical antioxidants, such as N-acetylcysteine and butylated hydroxyanisole, and the NADPH oxidase inhibitor diphenyleneiodonium inhibited Srx induction as well as generation of reactive oxygen species, both of which were also suppressed in Nox2 (NADPH oxidase 2)-deficient bone marrow-derived macrophages. These results suggest that LPS-mediated Srx induction is dependent on both AP-1 and Nrf2, which is regulated by Nox2-derived reactive oxygen species.

Circadian regulation of rice (Oryza sativa L.) CONSTANS-like gene transcripts.

We identified three rice cDNA clones showing amino acid similarity to the Arabidopsis CONSTANS-like proteins from a database search (S12569, S3574, and C60910), to examine if their transcript abundances were under circadian control. Unlike the other two proteins, the protein encoded by the S12569 cDNA contains only one CONSTANS-like zinc finger B box, and a CCT region. We found that the transcript levels of these rice CONSTANS-like (COL) genes were under circadian control. The oscillation phase of the S12569 gene transcript was more or less opposite to those of OsGI (rice GIGANTEA homolog) and Hd1 (rice COSTANS homolog), whereas the phases of the other two gene transcripts were similar to that of the Hd1 transcript. S12569 mRNA started to increase about 3 h after the onset of the dark period, with a peak about 3 h after its end. The S3574 and C60910 genes were expressed to similar extents during the vegetative and reproductive phases, like OsGI. Higher levels of S12569 transcripts, however, like those of Hd1, were detected in the earlier stages of panicle development. Unlike Hd1 transcripts, S12569, S3574, and C60910 transcripts were present at similar levels in the aerial parts of plants and in their roots during the vegetative phase. In conclusion, the rice COL genes showed distinctive expression patterns from the CO and COL genes, as well as Hd1, a rice CO homolog.