A complex regulatory DNA element associated with a major histocompatibility complex class I gene consists of both a silencer and an enhancer.

Abstract

A novel regulatory element which contributes to the regulation of quantitative, tissue-specific differences in gene expression has been found between -771 and -676 bp upstream of the major histocompatibility complex (MHC) class I gene, PD1. Molecular dissection of this element reveals the presence of two overlapping functional activities: an enhancer and a silencer. Distinct nuclear factors bind to the overlapping enhancer and silencer DNA sequence elements within the regulatory domain. The levels of factors binding the silencer DNA sequence in different cell types are inversely related to levels of class I expression; in contrast, factors binding the enhancer DNA sequence can be detected in all cells. In cultured cell lines, inhibition of protein synthesis leads to the rapid loss of silencer complexes, with a concomitant increase in both enhancer complexes and MHC class I RNA. From these data, we conclude that a labile silencer factor competes with a constitutively expressed, stable enhancer factor for overlapping DNA-binding sites; the relative abundance of the silencer factor contributes to establishing steady-state levels of MHC class I gene expression.The immune responses of all vertebrate species are mediated by molecules encoded within the major histocompatibility complex (MHC) (19). The MHC class I molecules, which serve as the targets of cellular immune responses and allograft rejection, are receptors for peptide antigens (3). These molecules are transmembrane glycoproteins consisting of a polymorphic heavy chain of 42 to 45 kDa and a nonpolymorphic light chain (P2-microglobulin) of 12 kDa.Consistent with their pivotal role in immune surveillance, the class I molecules are expressed on nearly all somatic tissues (28). However, their level of expression varies markedly among the tissues. The highest levels of cell surface expression of class I antigens occur in the lymphoid tissues: lymph node, peripheral blood lymphocytes, and spleen. Markedly lower levels are found on other somatic tissues, such as kidney and liver; there is little detectable cell surface class I antigen expression on germ line tissue or brain (28). In general, these differences reflect tissue-specific regulation of gene expression.Analysis of the 5' flanking regions of a number of class I genes has revealed the presence of a series of DNA elements capable of participating in the regulation of class I gene expression (Fig. 1A). Among these is a major enhancer, enhancer A, located at bp -180 to -170, which overlaps an interferon response element (15,20,27). A functional enhancer A is necessary for optimal expression of the downstream class I gene (13,15,18). A variety of trans-acting factors which bind to enhancer A have been identified, and their genes have been cloned (17, 21). These factors act as inducers of class I expression. Thus, KbF1 and RIIBP, both of which bind enhancer A, are associated with high levels of expression. Factors which bind specifically to the interferon response element and are induced by interferon have also b...

A T Lymphocyte-Specific Transcription Complex Containing RUNX1 Activates MHC Class I Expression

“…Tissue-specific expression is achieved through the combined effects of a promoter distal complex regulatory element and a series of promoter proximal elements. The promoter distal element, located between Ϫ700 and Ϫ800 bp, consists of overlapping enhancer and silencer elements (7). Silencer activity varies inversely with the level of class I expression in a given cell type.…”

Identification and characterization of a silencer regulatory element in the 3′-flanking region of the murine CD46 gene

“…Also the PD1 silencer tends to act in an orientation-dependent manner [40]. Hence, it is not surprising that the CD46 silencer described in this report acts even on the heterologous SV40 promoter position-independently, but orientation-dependently.…”

“…The expression of these two genes are regulated tissue-specifically ; i.e. PD1 is highly expressed in the spleen, but not in the kidney [40], and TNFR2 is expressed primarily on the myeloid and lymphoid cells [41]. Interestingly, these three molecules are also expressed on macrophages and dendritic cells, and have important roles in the innate immune system.…”

“…The silencer element seems to consist of two parts, according to previous reports [40,41]. Two mutated CDPSEs (5hmut CDPSE and 3hmut CDPSE) containing nucleotide substitutions in the 5h and 3h parts were constructed (Figure 7d).…”

“…A motif search revealed the presence of a silencer-binding site 2 (TATTAAAA), which is the 3h-part of the PD1 silencer (silencer sequence of the pig MHC class-I gene) in this 0.2-kb region (Figure 3). The PD1 silencer consists of two relevant sites, one 5h and one 3h [40]. The 3h site is called silencerbinding site 2 and is identical to the putative silencer of murine CD46 (Figure 6a).…”