Only the HLA class I gene minimal promoter elements are required for transactivation by human cytomegalovirus immediate early genes

The immediate early (IE) genes of human cytomegalovirus (HCMV) are expressed in lymphocytes and are known to transactivate both viral and cellular promoters. The mechanism by which IE gene products of HCMV transactivate expression of the HLA A2 gene promoter in Jurkat cells, a T-lymphocyte cell line, was investigated. Transient expression assays were performed using plasmids containing the HLA A2 promoter-regulatory region linked to the bacterial chloramphenicol acetyltransferase (CAT) gene and a plasmid expressing the CMV IE genes. The upregulation of the HLA A2 promoter by HCVM IE gene products was shown not to be secondary to either interferon-gamma or -alpha. Previously described MHC class I regulatory or enhancer elements such as the interferon-stimulated response element (ISRE), NF-kappa B and H2TF1 binding sequences, and the interferon consensus sequence (ICS) were not required for transactivation of the A2 promoter. Rather, the only known regulatory elements in the HLA A2 promoter necessary for both basal expression and transactivation by HCVM IE gene products are the CCAAT box and TATA box motifs. These results support a model in which HCVM IE gene products act through the minimal HLA A2 promoter elements to increase gene expression.