HUMAN DIPEPTIDYL PEPTIDASE-IV GENE PROMOTER - TISSUE-SPECIFIC REGULATION FROM A TATA-LESS GC-RICH SEQUENCE CHARACTERISTIC OF A HOUSEKEEPINGGENE PROMOTER

The dipeptidyl peptidase IV gene encodes a plasma-membrane exopeptidas e that is highly expressed in small intestine, lung and kidney. Ill or der to better understand the mechanisms responsible for this tissue-sp ecific expression we cloned, sequenced and functionally characterized the 5'-flanking region of the human dipeptidyl peptidase IV gene. The first 500 bases of the 5'-flanking sequence constituted an unmethylate d CpG island, contained several Spl-binding sites and lacked a consens us TATA box, all characteristics of gene promoters lacking tissue-spec ific expression. RNase-protection analysis using both small intestinal and Caco2 cell RNA. indicated that the dipeptidyl peptidase IV transc ript was initiated from no fewer than six major and 12 minor start sit es. The 5'-flanking sequence also exhibited functional promoter activi ty in transient transfection experiments. Here, various lengths of the sequence were cloned upstream of a luciferase gene and introduced int o cultured cells using lipofectin. A region located between bases -150 and -109 relative to the start of translation was found to be importa nt for high-level promoter activity in both Caco2 and HepG2 cells, Mor eover, Caco2 cells and HepG2 cells, which express high levels of dipep tidyl peptidase IV activity, exhibited much higher normalized lucifera se activity after transfection than did 3T3, Jurkat or COS-7 cells, wh ich have low enzyme levels. Sodium butyrate was found to increase both enzyme activity and normalized luciferase in HepG2 cells. Thus the di peptidyl peptidase IV promoter possesses the ability to initiate trans cription in a tissue-specific fashion in spite of having the sequence characteristics of a housekeeping gene promoter.