Molecular structure and function of rat CCAAT-enhancer binding protein-delta gene promoter

CCAAT-enhancer binding protein-delta (C/EBP delta) is a transcriptional nuclear factor, and belongs to basic region-leucine zipper class DNA binding proteins. One genomic clone containing a 12-kb sequence of the C/EBP delta gene was isolated from a rat genomic library, and a 2,056-bp fragment containing the 5'-flanking region was characterized. Sequence analysis of this fragment revealed that there were a TATA-like sequence (TAGAAAA) and many transcriptional regulatory elements. The transcription start site of the gene was determined by both primer extension analysis and riboprobe mapping. Both analyses indicated that the transcription start site was located at 31-bp downstream of the TATA-like sequence. Transient transfection experiments showed that the fragment cloned in this study was able to act as a functional promoter in rat vascular smooth muscle cells. The 5'-deletion analysis of this fragment revealed that the sequence spanning -235 through -82, which was designated as an upstream control element (UCE), remarkably increased a basal promoter activity of the C/EBP delta gene, and was also able to act as a promoter by itself. In addition, we also studied effects of the UCE on the heterologous gene promoter including rat alpha-actin gene promoter or SV40 virus promoter. Interestingly, the UCE specifically increased the promoter activity of the rat alpha-actin gene suggesting that the C/EBP delta gene may be positively controlled by the UCE via a cell-type or promoter-type specific manner.