Transcriptional activation by a matrix associating region-binding protein. contextual requirements for the function of bright.

Bright (B cell regulator of IgH transcription) is a B cell-specific, matrix associating region-binding protein that transactivates gene expression from the IgH intronic enhancer (E mu). We show here that Bright has multiple contextual requirements to function as a transcriptional activator. Bright cannot transactivate via out of context, concatenated binding sites. Transactivation is maximal on integrated substrates. Two of the three previously identified binding sites in E mu are required for full Bright transactivation. The Bright DNA binding domain defined a new family, which includes SWI1, a component of the SWI.SNF complex shown to have high mobility group-like DNA binding characteristics. Similar to one group of high mobility group box proteins, Bright distorts E mu binding site-containing DNA on binding, supporting the concept that it mediates E mu remodeling. Transfection studies further implicate Bright in facilitating spatially separated promoter-enhancer interactions in both transient and stable assays. Finally, we show that overexpression of Bright leads to enhanced DNase I sensitivity of the endogenous E mu matrix associating regions. These data further suggest that Bright may contribute to increased gene expression by remodeling the immunoglobulin locus during B cell development.

The immunoglobulin heavy-chain matrix-associating regions are bound by Bright: a B cell-specific trans-activator that describes a new DNA-binding protein family.

B lymphocyte-restricted transcription of immunoglobulin heavy-chain (IgH) genes is specified by elements within the variable region (VH) promoter and the intronic enhancer (E mu). The gene encoding a protein that binds a VH promoter proximal site necessary for induced mu-heavy-chain transcription has been cloned. This B-cell specific protein, termed Bright (B cell regulator of IgH transcription), is found in both soluble and matrix insoluble nuclear fractions. Bright binds the minor groove of a restricted ATC sequence that is sufficient for nuclear matrix association. This sequence motif is present in previously described matrix-associating regions (MARs) proximal to the promoter and flanking E mu. Bright can activate E mu-driven transcription by binding these sites, but only when they occur in their natural context and in cell lines permissive for E mu activity. To bind DNA, Bright requires a novel tetramerization domain and a previously undescribed domain that shares identity with several proteins, including SWI1, a component of the SWI/SNF complex.

Endogenous cortisol regulates immunoglobulin E-dependent late phase reactions.

To investigate the impact that physiological variation in serum cortisol has on IgE-mediated events, 10 atopic subjects underwent cutaneous antigen challenge with measurement of the early phase wheal (EPW) at 20 min and the late phase reaction (LPR) at 6 h. All subjects were challenged during control conditions between 8:00 and 9:00 a.m. Repeat challenges were performed in five subjects at 6:00 p.m. and in eight subjects after ingestion of metyrapone, a specific inhibitor of cortisol synthesis. Compared with control values, mean serum cortisol was suppressed in the evening and after metyrapone (P less than 0.05 all time points). No effect was seen on the EPW, but mean LPR diameters at three antigen dilutions were significantly increased by cortisol suppression (P less than 0.05). Replacement doses of hydrocortisone given in the evening and with metyrapone abrogated these increases. Blinded analysis of LPR biopsies from cortisol-suppressed subjects revealed increases in leukocytoclasis (P less than or equal to 0.0001), interstitial leukocytes (P less than or equal to 0.01), and eosinophils (P less than or equal to 0.04). These results indicate that physiological levels of serum cortisol can regulate IgE-dependent cutaneous inflammation by affecting the expression of cellular events at late phase sites.