No abstract

Matrix metalloproteinases (MMP) have been identified in vulnerable areas of atherosclerotic plaques and may contribute to plaque instability through extracellular matrix degradation. Human metalloelastase (MMP-12) is a macrophage-specific MMP with broad substrate specificity and is capable of degrading proteins found in the extracellular matrix of atheromas. Despite its potential importance, little is known about the regulation of MMP-12 expression in the context of atherosclerosis. In this study, we report that in human peripheral bloodderived macrophages, MMP-12 mRNA was markedly upregulated by several pro-atherosclerotic cytokines and growth factors including interleukin-1␤, tumor necrosis factor-␣, macrophage colony-stimulating factor, vascular endothelial growth factor, and platelet-derived growth factor-BB. In contrast, the pleiotropic anti-inflammatory growth factor transforming growth factor-␤1 (TGF-␤1) inhibited cytokine-mediated induction of MMP-12 mRNA, protein, and enzymatic activity. Analyses of MMP-12 promoter through transient transfections and electrophoretic mobility shift assays indicated that both its induction by cytokines and its inhibition by TGF-␤1 depended on signaling through an AP-1 site at ؊81 base pairs. Moreover, the inhibitory effect of TGF-␤1 on MMP-12 was dependent on Smad3. Taken together, MMP-12 is induced by several factors implicated in atherosclerosis. The inhibition of MMP-12 expression by TGF-␤1 suggests that TGF-␤1, acting via Smad3, may promote plaque stability.

Expression of allograft inflammatory factor-1 (Aif-1), a 17-kDa protein bearing an EF-hand Ca 2؉ binding motif, increases markedly in monocytes and macrophages participating in allo-and autoimmune reactions, including the perivascular inflammation in transplanted hearts, microglial infiltrates in experimental autoimmune neuritis, and the inflamed pancreas of prediabetic BB rats. To investigate the mechanism of this regulation, we isolated the mouse aif-1 gene and determined its genomic organization. The gene has six exons distributed over 1.6 kilobases, an interferon ␥-inducible DNase I-hypersensitive site near ؊900, and flanking sequences on either side predicted to associate with nuclear matrix. Reporter gene analyses identified sequences between ؊902 and ؊789, including consensus Ets and interferon regulatory factor elements, required for macrophagespecific and interferon ␥-inducible transcriptional activity. Pu.1 bound to the Ets site in electromobility shift assay and forced expression of Pu.1 activated the aif-1 promoter in 3T3 fibroblasts, in which it is normally inactive. However, the transcriptional activity of a concatamer of the Ets site alone did not increase with interferon ␥ treatment. Cooperation between Pu.1 and proteins binding to the interferon regulatory factor element appears to be necessary for both macrophagespecific and interferon ␥-inducible expression of the aif-1 gene.Allograft inflammatory factor-1 (Aif-1) 1 is a 17-kDa protein first described in differential mRNA display analysis of chronically rejecting transplanted rat hearts (1, 2). The Aif-1 protein was identified in infiltrating mononuclear cells in the allografted hearts, and Western blotting indicated its expression in bone marrow-derived macrophages but not T cells. Gene products with a high level of similarity to Aif-1 have been identified in several other model systems and have been reported with the alternative names Iba1 (3), daintain (5), and Mrf-1 (4). Despite the different screening approaches and systems employed in each case, the cells expressing the aif-1 gene product have been derivatives of the monocyte/macrophage lineage; iba1 was reported from differential mRNA display analysis of brain cell cultures, with induction in microglial cells cultured for extended periods of time (3); daintain was identified because of its effects on insulin release and found to localize to microglia in the central nervous system, and macrophages and dendritic cells in other organs (5); and mrf-1, identified in a differential hybridization screen of cerebellar cultures, localized to OX-42-positive microglia in brain sections, with increased expression in activated microglia surrounding injured central motor neurons (4).The cDNA sequences described in these reports are quite similar but show some variability at the 5Ј end. aif-1 and iba1 sequences diverge at the 5Ј end, consistent with alternative transcription start sites from the same gene (4), but are practically identical downstream of aif-1 base 96 (iba1 base 279). The sequence of d...

These data suggest a functional involvement of p53 in starvation-induced G1-block and apoptosis in tumor cells. Altered radiosensitivity after culture in starvation medium seemed to be explained at least in part by the starvation-induced G1-block. The frequency of starvation-induced apoptosis or necrosis was not correlated with radiation sensitivity.

These results suggest that 1. complex formation between the large T antigen and p53 reduces the latter's functionality; 2. in these two strains the G1 arrest is one of the factors determining radiosensitivity.