Journal
JOURNAL OF IMMUNOLOGY
Volume 169, Issue 9, Pages 5061-5071Publisher
AMER ASSOC IMMUNOLOGISTS
DOI: 10.4049/jimmunol.169.9.5061
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The class II trans-activator (CHTA), which acts as a master regulator for expression of MHC class 11 genes, is expressed constitutively in mature B cells. This constitutive expression of CHTA 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 CHTA-PHI 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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