Repression of major histocompatibility complex IA expression by glucocorticoids: the glucocorticoid receptor inhibits the DNA binding of the X box DNA binding protein

Characterization of a cis-acting regulatory element which silences expression of the class II-A beta gene in epithelium

Class II major histocompatibility complex (MHC) genes encode for alpha/beta chain pairs that are constitutively expressed principally on mature B cells and dendritic cells in mice. These gene products are easily induced on macrophages with cytokines, and may also aberrantly appear on the surface of epithelium during immune injury. The appearance of class II determinants in parenchymal tissue potentially renders these somatic cells capable of antigen presentation to circulating CD4+ T lymphocytes, and their absence may be protective for normal tissues expressing self-antigens. The low surface class II expression observed on parenchymal cells generally correlates with low levels of mRNA, suggesting that transcription rate is a major element in class II regulation. To understand the transcriptional mechanism maintaining low basal surface expression of class II in somatic cells, we transiently transfected mini-gene reporter constructs to study the regulation of the murine A beta promoter in a cultured renal epithelial cell line. We describe here a negative cis-acting regulatory region located between -552 and -489 bp upstream of the A beta cap site that silences the transcriptional activity of the A beta promoter in epithelial cells in an orientation-dependent manner, and is also able to silence a heterologous promoter. This region is not active in class II-expressing B cells (BAL-17) in culture, but is functional in two other murine class II-negative cell lines, fibroblasts and thymoma T cells. Using competition electrophoretic mobility shift assays, we have localized the core protein binding site within this region to an 8-10-bp response element, designated A beta NRE, at -543 to -534 bp. A nuclear extract from BAL-17 cells does not bind to this element. Mutation of this site abrogates the transcriptional silencing activity of the region. We conclude that the transcription of class II-A beta in parenchymal cells, and some lymphocytes, can be actively repressed by an upstream silencing element.

Maternal rescue of transforming growth factor-beta 1 null mice

Maternal sources of transforming growth factor-beta 1 (TGF-beta 1) are shown here to contribute to the normal appearance and perinatal survival of TGF-beta 1 null newborn mice. Labeled TGF-beta 1 crossed the placenta and was recovered intact from various tissues after oral administration to mouse pups. TGF beta-1 protein was also detected in cells recovered from breast milk. In immunohistochemical analyses, TGF-beta 1 null embryos and null newborn pups born to TGF-beta 1 heterozygotes stained positive for TGF-beta 1, whereas those born to a null female were negative and had severe cardiac abnormalities. These results suggest an important role for maternal sources of TGF-beta 1 during development and, more generally, provide evidence for maternal rescue of targeted gene disruption in the fetus.