The p53 tumor suppressor protein is a critical regulator of the cellular response to cancer-initiating insults such as genotoxic stress. In this report, we demonstrate that microRNAs (miRNAs) are important components of the p53 transcriptional network. Global miRNA expression analyses identified a cohort of miRNAs that exhibit p53-dependent upregulation following DNA damage. One such miRNA, miR-34a, is commonly deleted in human cancers and, as shown here, frequently absent in pancreatic cancer cells. Characterization of the miR-34a primary transcript and promoter demonstrates that this miRNA is directly transactivated by p53. Expression of miR-34a causes dramatic reprogramming of gene expression and promotes apoptosis. Much like the known set of p53-regulated genes, miR-34a-responsive genes are highly enriched for those that regulate cell-cycle progression, apoptosis, DNA repair, and angiogenesis. Therefore, it is likely that an important function of miR-34a is the modulation and fine-tuning of the gene expression program initiated by p53.

MicroRNA 34a (miR-34a) is a tumor suppressor gene, but how it regulates cell proliferation is not completely understood. We now show that the microRNA miR-34a regulates silent information regulator 1 (SIRT1) expression. MiR-34a inhibits SIRT1 expression through a miR-34a-binding site within the 3 UTR of SIRT1. MiR-34 inhibition of SIRT1 leads to an increase in acetylated p53 and expression of p21 and PUMA, transcriptional targets of p53 that regulate the cell cycle and apoptosis, respectively. Furthermore, miR-34 suppression of SIRT1 ultimately leads to apoptosis in WT human colon cancer cells but not in human colon cancer cells lacking p53. Finally, miR-34a itself is a transcriptional target of p53, suggesting a positive feedback loop between p53 and miR-34a. Thus, miR-34a functions as a tumor suppressor, in part, through a SIRT1-p53 pathway.microRNA ͉ p53 ͉ cancer

inflammation ͉ nitric oxide ͉ leukocyte ͉ atherosclerosis

Objective. High mobility group box chromosomal protein 1 (HMGB-1), a nuclear DNA binding protein, was recently rediscovered as a new proinflammatory cytokine. The purpose of this study was to demonstrate HMGB-1 expression in vivo and to identify the role of HMGB-1 in the pathogenesis of rheumatoid arthritis (RA).Methods. HMGB-1 concentrations in synovial fluid (SF) and serum from RA and osteoarthritis (OA) patients were measured by immunoblot analysis. The protein's specific receptor, receptor for advanced glycation end products (RAGE), was examined in SF macrophages (SFMs). We measured levels of proinflammatory cytokines released by SFMs treated with HMGB-1 via enzyme-linked immunosorbent assay and used soluble RAGE (sRAGE) to block the release of tumor necrosis factor ␣ (TNF␣). Immunohistochemical analysis and immunofluorescence assay were employed to examine localization of HMGB-1 in RA synovium and its translocation in SFMs after TNF␣ stimulation.Results. HMGB-1 concentrations were significantly higher in SF of RA patients than in that of OA patients. SFMs expressed RAGE and released TNF␣, interleukin-1␤ (IL-1␤), and IL-6 upon stimulation with HMGB-1. HMGB-1 was found in CD68-positive cells of RA synovium, and TNF␣ stimulation translocated HMGB-1 from the nucleus to the cytosol in SFMs. Blockade by sRAGE inhibited the release of TNF␣ from SFMs.Conclusion. HMGB-1 was more strongly expressed in SF of RA patients than in that of OA patients, inducing the release of proinflammatory cytokines from SFMs. HMGB-1 plays a pivotal role in the pathogenesis of RA and may be an original target of therapy as a novel cytokine.High mobility group box chromosomal protein 1 (HMGB-1) has 219 residues in its primary amino acid sequence, and there is Ͼ98% sequence identity between the HMGB-1 of rodents and that of humans (1-6). In most cells, HMGB-1 is located in the nucleus. It is an abundant, highly conserved cellular protein and is widely known as a nuclear DNA binding protein that stabilizes nucleosome formation (7,8), facilitates gene transcription, and regulates the activity of steroid hormone receptors (9,10). However, it has been reported that HMGB-1 might be translocated from the nucleus to the cytosol and then released extracellularly.A previous study demonstrated that extracellular HMGB-1 induces the production of proinflammatory cytokines in macrophages (11). When released by activated monocytes, it participates in the development of lethality and activates downstream cytokine release. Furthermore, like other cytokine mediators of endotoxemia, HMGB-1 activates proinflammatory cytokine re-