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外文期刊>The journal of immunology
>Transcriptional Regulation of the MHC Class II Trans-Activator (CIITA) Promoter III: Identification of a Novel Regulatory Region in the 5′-Untranslated Region and an Important Role for cAMP-Responsive Element Binding Protein 1 and Activating Transcription Factor-1 in CIITA-Promoter III Transcriptional Activation in B Lymphocytes
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Transcriptional Regulation of the MHC Class II Trans-Activator (CIITA) Promoter III: Identification of a Novel Regulatory Region in the 5′-Untranslated Region and an Important Role for cAMP-Responsive Element Binding Protein 1 and Activating Transcription Factor-1 in CIITA-Promoter III Transcriptional Activation in B Lymphocytes
The class II trans -activator (CIITA), which acts as a master regulator for expression of MHC class II genes, is expressed constitutively in mature B cells. This constitutive expression of CIITA is driven by CIITA promoter III (CIITA-PIII). However, little is known about the factors that control the B cell-mediated trans -activation of CIITA-PIII. In this study using B cells we have identified several cAMP-responsive elements (CREs) in the proximal promoter and in the 5′-untranslated region (5′-UTR) that are involved in the activation of CIITA-PIII. We show that activating transcription factor (ATF)/CRE binding protein (CREB) factors bind to the CREs in vitro and in vivo. Notably, our results also reveal that the 5′-UTR of CIITA-PIII functions as an important regulatory region in B lymphocytes. Furthermore, transient cotransfections of a CIITA-PIII luciferase reporter construct with either CREB-1 or ATF-1 boost CIITA-PIII trans -activation in a dose-dependent manner, which was further enhanced by addition of general coactivator CREB-binding protein. Transient transfections using mutant CIITA-PIII luciferase reporter constructs that either lack the (5′-UTR) or abolish binding of CREB-1 and ATF-1 to the CRE located in activation response element-2, displayed severely reduced promoter activity in B cells. A similar successive deletion of the CREs resulted in a subsequent reduction of CREB-1-induced activity of CIITA-PIII in B cells. Together our results argue for an important role of ATF/CREB factors and the 5′-UTR of CIITA-PIII in the trans -activation of CIITA-PIII in B cells.
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