Detailed delineation of an interferon-gamma-responsive element important in human HLA-DRA gene expression in a glioblastoma multiform line.

Abstract

In this report, we determined that induction of the DR a-chain gene by recombinant human interferon-y (IFN-y) in a human glioblastoma multiform cell line is transcriptionally regulated and showed that protein synthesis is not necessary for this to occur. The regions of the DR a-chain gene that are responsible for basal and recombinant IFN-y-induced gene transcription have been determined by gene transfer of a series of 5' deletion mutants in which the upstream region of the DR a chain was linked to a reporter gene, chloramphenicol acetyltransferase. Chloramphenicol acetyltransferase transcript and protein levels were determined by S1 nuclease protection and chloramphenicol acetyltransferase enzyme assays, respectively. By using these deletion mutants, we were able to draw the following conclusions. Class II major histocompatibility complex (MHC) antigens are crucial to the overall function of the immune system by virtue of their role in antigen presentation and lymphocyte interaction (1, 2). The quality of an immune response is determined in part by the timing and extent of class II antigen expression; therefore, the molecular regulation of these genes is of primary importance.The class II MHC genes are regulated in a complex fashion and provide one of the most interesting systems to study gene regulation. Expression patterns of class II antigens are extremely diverse and tightly regulated (3-8). It is assumed, therefore, that complex mechanisms must be in place that control the tissue-specific, differentiation-dependent, and inducible expression of class II genes.Several laboratories including our own have begun to examine these controlling mechanisms and to identify cisacting DNA sequences responsible for class II MHC gene regulation (9)(10)(11)(12)(13)(14)(15)(16). The present report centers on the detailed delineation of interferon-y (IFN-y)-responsive regions in the DR a-chain (DRa) gene by using a human glioblastoma multiform line as a model system. We have been particularly interested in the basal and inducible expression of these antigens on glioblastomas because class II antigen expression in the brain has been linked to the initiation and propagation of autoimmune-like diseases of the central nervous system.

YB-1 DNA-binding protein represses interferon gamma activation of class II major histocompatibility complex genes.

“…This line was chosen because our previous analysis and delineation of the class II MHC promoter were performed with this line. In addition, IFNy-induced class II MHC gene expression in this line is high (23), better permitting the detection of any suppressive effects of YB-1.…”

High mobility group I/Y protein functions as a specific cofactor for Oct-2A: mapping of interaction domains

“…The expression of human class II MHC genes, which is primarily controlled at the level of transcription [12,13], requires the accurate assembly of transcription factor complexes on a number of distinct conserved cis-elements located in their proximal promoter regions [14,15]. In addition to a TATA motif, these include the X, Y, and Z boxes; elements whose sequences as well as stereospecific relationships to each other are highly conserved [16][17][18][19][20][21][22][23][24][25][26]. Several proteins that interact specifically with these cis-acting elements have been described [27][28][29][30][31][32][33][34][35][36][37][38].…”

The S Box of Major Histocompatibility Complex Class II Promoters Is a Key Determinant for Recruitment of the Transcriptional Co-activator CIITA

“…The W box is a 20-base pair region within which a more tightly conserved 7-base pair subelement, the S box, has been defined (4,6). The presence of the W/S box (43)(44)(45)(46)(47) at a conserved distance from the X box (48 -50) is required for optimal constitutive and inducible MHCII expression. DNA binding activities that show specificity for the W region in gel retardation assays have been detected in nuclear extracts (43,44,51), but neither the identity of these factors nor their functional relevance have been formally established.…”